Generally plant disease is quite common for gardeners to have to deal with.

It is very heart breaking to watch plants fail to thrive yet they have been tended to and a lot of time invested on them.

Failure of plants to do well may be as a result of them being infected with common plant diseases of various kinds.

However, other times the plants might not be suffering from a disease but could just be requiring a little attention and actions such as water addition to them or even shifting them to a sunnier spot.

Therefore, farmers should pay attention as they observe their plants in order to determine whether the plant failure is due to common plant disease or a correctable factor.

Plant diseases are caused by several factors and occur in various forms such as;


This common plant disease is brought about by warm environments and high contents of nitrogen in the soil.

It is identified by bugs that appear to be small, green or yellow in color.


It is treated by wiping infected plants using soapy water or rather using rubbing alcohol. Neem oil is another organic option.

⦁ Bacterial spot

This Plant disease is brought about by a warm and wet environment

Table of Contents


Leaf Disease identification:

Many farmers may be wondering why some plants in their gardens may be having leaves appearing as though they have dark patches.

There is an easy way of identifying this kind of common plant disease by looking for small and dark spots that are raised occurring on leaves of plants.

By so doing, the farmer is able to take the correct action in order to ensure that the plant is well catered for.


The farmer is supposed to destroy the infected plants. Besides, the farmer should also apply a fungicide on the plant.

This will help in doing away with the small and black spots occurring on the leaves and hence ensuring that healthy plants are the result.

Bacterial wilt Plant Disease

This kind of common plant disease is caused by cool and wet weather.

Leaf Disease Identification
Farmers should look up for large, yellow spots on leaves. Those yellow spots often change to a brown color.

The appropriate corrective action that should be taken is removal of infected plants. On the other hand, farmers should ensure that they space plants correctly to prevent crowding.

Cucumber mosaic virus

The cucumber mosaic virus is a disease caused by organisms called aphids.

Leaf Disease Identification:

Often, farmers might find yellow spotting on leaves of plants such as coffee plants. Also, leaves could appear streaking.

This is a clear sign of this kind of ailment.

Cucumber Mosiac Virus on leaves

One corrective measure that should be taken is discarding the virus infected plant. In addition, farmers should maintain a strict aphid control practice.

Black root rot

This kind of Common Plant disease is also referred to as thielaviopsis.

It caused by damp soil with temperatures ranging between fifty five to sixty degrees Fahrenheit. This temperature is a bit not conducive for plant roots to do well.

Root Disease Identification:

The combination of high temperatures and the dampness of the soil, roots begin to rot.

They appear to have blackened areas. Also, foliage of these plants may appear stunted.

By checking on the foliage of plants for this kind of signs will be a sure way to discover this disease.

Leaf Disease Identification:

This disease usually occurs on ornamental s and soft fruits such as raspberries, blackberries as well as strawberries.

In addition, cabbages are also not left behind as they too may be found to suffer from this condition.

This condition is corrected by ensuring improvement of the ventilation if growing plants under glass.

Also, farmers should ensure that they remove the affected areas the soonest the symptoms are detected so to ensure that the entire plant does not get infected.

⦁ Cylindrocladium
This kind of common plant disease is caused by humid environment as well as overhead irrigation.

Leaf Disease Identification:
It is commonly identified by dark brown spots occurring on leaves of plants.

This disease is managed by removal of infected plants to ensure that the disease does not spread to other plant sections.

⦁ Rhizoctonia
This disease is caused by warm and soil that appears to be overly moist.

It is identified by the stem rotting at the soil line associated with brown to red lesions.

It is best to ensure that the infected plant is removed and the application of fungicides.

Common plant diseases Angular leaf spot

This disease is caused by seed and plant debris.

Leaf Disease Identification:
It is identified by holes occurring in leaves.

Treatment The disease is managed by growing plants in arid climates. In addition, growing plants that are resistant to harsh conditions will help control the disease.

This Plant disease is attracted by over watering of plants as well as soil with excess levels of nitrogen.

Leaf Disease Identification:
It is identified by small, white insects that have a white coating that appears fluffy.

Treatment The disease is managed by removal of affected plants manually using rubbing alcohol or using of insecticide.

To avoid spreading of disease try to avoid spreading of disease try to avoid working in the garden when plants are wet.

It is not recommended to compost infected leaves. To prevent overwintering of fungal spores.

Anthracnose : Cause
This disease is caused by seed and plant debris.

Leaf Disease Identification:
This disease is identified by leaf tips turning yellow and eventually turning to brown.


It is managed by removal of infected leaves as well as avoiding over watering of plants.

To avoid spreading of disease try to avoid working on the garden when plants are wet.

It is not recommended to compost infected leaves. To prevent over wintering of fungal spores.

Spider mites

It is brought about by warm heated temperatures. It is identified by fine webbing on the undersides of leaves.

. Treatment

This disease is managed by isolation of plants and pruning of the damaged leaves.

Also, cleaning of infected plants using soapy water may help. Application of insecticides does wonder when it comes to fighting this disease.

⦁ Downy mildew
This common plant disease is brought about by prolonged wetness on plants. It is clearly identified by white mildew on the underside sections of the leaves.

This disease is managed by removal of infected plants to ensure that it does not spread to other sections of the plant.

The correct spacing should be done in between the plants to ensure that proper air circulation occurs between the plants.

Prune or Stake Plants for better air circulation.

Tip: Water in early hours of the morning to allow them to dry during the day.


Blight is a common plant disease that is responsible for most sudden deaths of leaves, flowers and stems of plants. There are various kinds of blight including

Fire blight

This is a bacterial disease that mostly affects fruits such as apples, pears, fruit trees and small fruits. Often, affected shoots are usually a bit blackened. Also, farmers may tend to notice lesions on branches as well as limbs oozing an orangish-brown fluid during extremely warm days.


Fire blight should be treated the soonest to ensure that it does not spread to the entire fruit tree as it may kill it.

The farmer should put on some protective gloves and add four cups of water to a bowl. Pour in a cup of bleach to the large bowl containing water slowly to ensure that it does not splash out.

Stir the mixture using a spoon. Go ahead and prune all the branches that are affected by fire blight using a pair of shears.

Immerse the shears in the bleach solution created after each cut so as to ensure that the infection is not spread.

Carefully cut off all the branches at least twelve inches below the last branch which appears wilted as well as discolored.

Gather all the branches that have been cut off and make sure to dispose them at least one hundred feet away from that particular tree being worked on.

Afterwards, put six cups of water into a one-gallon garden sprayer and to them, add about four cups of white vinegar.

Make sure to close the lid of the sprayer then shake vigorously to ensure that the contents mix well. Proceed to putting on protective glasses to ensure that eyes are not contaminated.

Pump the handle that is at the sprayer to exert pressure on the solution. Direct the nozzle towards the tree and it starting from the bottom to the top.

Spray on the leaves as well as under them. Take a step back, and spray the tree again beginning from the top the bottom.

Ensure that the tree is sprayed until the leaves are left saturated and start dripping off the solution. Spray thoroughly on the trunk of the tree that is affected.

Repeat this whole procedure after two weeks to ensure that the fire blight is completely eliminated.

⦁ Early blight

Fungal blight is a disease that occurs on vegetables, shade trees as well as fruit trees. When fungal blight affects tomatoes, peppers or potatoes, it is referred to as early blight.

Farmers might be wondering why there could be brown or black colored spots on leaves which develop concentric rings.

When the blight is just too much, the leaves may dry up and eventually die as the spots grow close together.

First symptoms are usually on the lower leaves. For potato tubers, they tend to develop dark spots that seem sunken.

Early blight often occurs at any given time during the growing season with relatively high temperatures accompanied by wet humid conditions.

This causes it to spread rapidly.


The best thing to do is to prevent plants from suffering early blight. This is achieved by ensuring that disposing off of infected plants.

On the other hand, the farmer is required to space out plants in a way that they are able to breathe as air is able to circulate freely between the plants.

Also, seeds ought to be purchased from trusted sources to ensure that they are of high quality and healthy as well.

Plants should be checked frequently especially during wet climates to ensure that in case a sign of blight is detected then the corrective action is taken without allowing it more time to spread.

If a sign is detected then, the farmer should use an organic copper spray as it is considered relatively safe.

To avoid causing harm to bees, spraying should be carried out early in the morning before they start roaming around.

However, excessive quantities of copper may build up in the soil if sprayed in large amounts and result to toxicity. In case the farmer adds more copper, then they should consider shifting to another section and plant their crops there.

⦁ Late blight

This common plant disease is known to infect flowers such as holly, lilacs, azaleas and rhododendrons. It causes dieback of shoots and stem cankers of these flowers.

On the other, late blight can also affect potatoes, tomatoes and peppers. The very first symptoms are occurrence of water-soaked spots on leaves that are on the lower sections.

This spots later grow bigger and are mirrored with a white downy growth on the under surface of the leaf.

In the case of potatoes, the black colored blotches often penetrate the flesh and may appear as though they are sunken lesions.

Occasionally, during the wet seasons, the affected plant will often rot and eventually die.


As prevention remains of key importance, treatment measures are also a necessity to prevent infected plants from dying.

The disease can be prevented by ensuring that during the wet seasons, branches of plants are kept off the ground by use of trellis and plant supports.

Use of mulch in plenty can also help to keep this disease away from plants.

It is also very healthy to spray plants from below and not above like most people do.

Also, watering should be done in the early morning hours to ensure that by night fall, the plants are already dry.

In the event of occurrence of blight, then the farmer is obliged to get rid of the affected plants and place them in a trash bag.

It is necessary that the farmer avoids composting the affected plants as this would only result to this contagious disease spreading quickly. And may even affect the plants in the neighboring gardens.

⦁ Cankers

This disease is often identified by dead sections that are a bit discolored on the stems of plants.

Occasionally, they form on woody plants and appear to be cracks, sunken areas or raised areas of dead tissue or abnormal tissues.

These sections often ooze or result to girdle trunks or shoots that may at times cause total death of plants.

There are several types of cankers or forms in which cankers occur.

⦁ Cytospora cankers

This kind of cankers is as a result of fungal infections. It is known to affect spruces, stone fruits and popular. They are identified by circular discolored areas occurring on barks of plant.

⦁ Nectria cankers

This disease may attack hardwoods, shrubs as well as vines of some plants. However, it is known to cause much damage on maple trees. It is identified by areas that appear as sunken areas around the bark next to wounds.

Also, small and pink structures that produce spores may be seen indicating presence of this disease. Branches and twigs may die in the process while the disease may girdle trees of a tender age.

This disease can be controlled by removal of diseased branches and ensuring limitation of pruning cuts.

⦁ Rusts
This is a common plant disease that is caused by fungal infections and requires two different species of plants to use as hosts in order to complete their life cycle.

They are identified by light tan to rust-hued coating. They often appear on small twigs and needles and needles at first.


It is best to control this common plant disease by allowing plants free space that is adequate to allow free circulation of air. Besides, application of neem oil can be very helpful at preventing this disease because it is responsible for killing the spores on leaves.

In case the plant disease develops, the infected plants should be removed and eventually burnt when autumn season comes.

On the other hand, some types of rusts can be controlled by removing the alternate hosts as it would help to ensure that an outbreak does not occur.

These kinds of rust include white pine blister, wheat as well as cedar apple rust.

Wheat rust needs a barberry plant as an alternate host for the disease to thrive.

On the other hand, white pine blister needs a member of the family of currants while cedar apple requires a combination of both the apple and a relative of the juniper.

Elimination of the mentioned alternate hosts will therefore help to do away with this disease in case of infection of the mentioned plants.

⦁ Wilts

Often, wilting is usually brought about by plants failing to get adequately watered.

However, permanent wilting may be brought about by cases where fungi or bacteria infect plants that are in the wilting process.

Permanent wilting will eventually lead to death of infected plants. There are different types of wilt including;

⦁ Verticillium wilting

This refers to a fungal disease that is known to attack a variety of fruits, vegetables, ornamentals as well as flowers. This disease causes plants to wilt and the end result is usually causing them to turn yellow.

Occasionally, the infection enters plants via their roots and usually spreads through the vascular system of the plant. It causes the entire vascular system and the plant at large to die.


Treatment of this disease is impossible as it is incurable the moment it enters the plant. The only option is to ensure the removal of the affected plant and destroying them completely.

In cases where it’s the branch of a plant that is affected, then cutting off the infected region preferably the area below the symptoms would greatly help to slow down or rather reduce the spread of the disease.

However, it is important to note that the disease might remain in the soil even after complete removal of the infected plants.

It is therefore necessary that another area is used for planting other plants lest they also get to suffer from the same disease.

⦁ Stewart’s wilting

This is a bacterial caused disease that is usually widespread on sweet corn often grown in the eastern regions of the United States of America as well as Canada.

It is usually identified by decaying of the crown, bleached or yellow streaks on the leaf as well as the internal vascular discoloration.

Often, bacterial slime usually oozes out of the stalks or leaves once they are cut.

The end result is usually death of the plant.

If the plant survives death then, it might end up being sufficiently stunted to an extent that no ears are produced.

Club root

This is a common plant disease that often affects vegetables that are in the family of cabbages. It is usually caused by fungi.

Often, plants usually wilt during the day and become revived again during the night while yellow leaves that are older will drop off.

Occasionally, roots usually appear swollen or even distorted. This disease causes the plants to lower their yields or eventually die.

Prevention of this disease can be done by ensuring that the garden is clean as well as rotating of crops. Also, controlling of weeds like shepherd’s purse and mustard will help to prevent the club root infection

. In the cases where the plants are infected, then they should be removed with so much caution.

The garden tools used to remove them should be sterilized using a solution of four cups of water and a cup of bleach both combined.

In addition, if club root has been encountered before, the best solution is to adjust the soil pH to a more alkaline level of about 7.2 or at least to a level of at least 6.8 prior planting of plants newly.

However, the spores of this particular disease can persist in the soil for a period of up to twenty years.

In such a case then, the farmer is advised to solarize his or her farm soil in order to get rid of this disease.

⦁ Leaf curl

This is a fungal disease that causes leaves of many trees to appear distorted. There are different types of this kind of plant disease such as the peach leaf curl.

Often, it attacks almonds as well as peaches and is identified by pale new leaves and failure of the midrib to grow along with the leaves thus causing them to curl and pucker as they expand.

The fruit may also get damaged and unfortunately the tree may eventually die as a result of leaf curl disease.

⦁ Leaf blister

Oak leaf blister can kill oak trees. It is identified by yellow bumps on the upper surface of the leaves as well as gray depressions around the lower surfaces of the leaves.


Leaf curl and leaf blisters can be prevented by using a dormant oil spray that is usually safe for the tree, pets, humans and the environment.

Also, there is a great dormant oil formula to manage the disease. This oil formula contains two table spoons of canola oil and one table spoon of baking soda which is mixed into a gallon of water.

In order for it to be effective, it is necessary to treat the tree during stages when the tree is dormant. The dormant stages are usually between November and early spring but before breakage of the bud.

The farmer is supposed to fill up the spray bottle with the homemade spray and coat the tree or rather the trees thoroughly.

The stems as well as both sides of the leaves should also be sprayed with the oil. Application should be done only when the fruit tree is dry and not during times when the temperatures are below freezing.

⦁ Black spot

This is a common plant disease that usually affects roses. This spots appear on the leaves of the rose plant up to a half inch across with margins that are of yellow color.

In occasions where they are left unchecked then, an entire rose bush may end up totally defoliating.

Often, when a rose bush is attacked by black spot fungus, then its markings are present until the leaves that are marked fall off and a new leaf is finally generated.

However, the fungus that is responsible for causing the disease can be killed in order to prevent further damage to the foliage and causing death to the entire plant. The marks will remain for a particular amount of time.

Prevention remains the key but this disease can be treated in various ways. It can be prevented by ensuring an adequate planting site that is at a position to receive plenty of sunlight as well as circulation.

In addition, frequent pruning as well as using of resistant cultivars. Besides, mulching can also help to prevent dirt and spores from being splash upwards and falling on the plant.

Some people also prefer to use a baking powder spray. This helps to change the level of pH of the leaf surfaces. As a result, this will cause it to be more difficult for the black spot to infect the plants.

An organic solution can be made by mixing a number of tablespoons of baking soda with a particular amount of water. The farmer should proceed to spraying on both sides of the foliage

. This application process should be repeated after every week or after it happens to rain. Neem oil can also be used as it is known to help manage many other rose pests also.

If black spot happens to develop, the farmer should destroy all the dropped leaves.

Pruning should also be applied to plants to control them from contracting these diseases.

Coral spot

This condition occurs commonly on woody branches of shrubs as well as trees. During periods of high rainfall or even watering the plants, a fungus known as coral spot that lives on dead wood might be spread in the course. It appears as pink pustules occurring on the branches of woody shrubs and trees.


It is necessary to ensure that corrective action is partaken the soonest the condition is detected.

Often, the controller should heavily prune the shrub of the tree and ensure that they cut out all the regions that are affected and proceed to burning the parts that have been chopped off so as to prevent the disease from spreading.

In conclusion, it is clear that plants are affected by diseases that are many in numbers. However, treatment is possible to save plants from dying down if carried out effectively basing on the above discussion.

Signs and symptoms of plant disease: Is it fungal, viral or bacterial?

Most plant diseases – around 85 percent – are caused by fungal or fungal-like organisms. However, other serious diseases of food and feed crops are caused by viral and bacterial organisms. Certain nematodes also cause plant disease. Some plant diseases are classified as “abiotic,” or diseases that are non-infectious and include damage from air pollution, nutritional deficiencies or toxicities, and grow under less than optimal conditions. For now, we’ll look at diseases caused by the three main pathogenic microbes: fungus, bacteria and virus. If plant disease is suspected, careful attention to plant appearance can give a good clue regarding the type of pathogen involved.

A sign of plant disease is physical evidence of the pathogen. For example, fungal fruiting bodies are a sign of disease. When you look at powdery mildew on a lilac leaf, you’re actually looking at the parasitic fungal disease organism itself (Microsphaera alni). Bacterial canker of stone fruits causes gummosis, a bacterial exudate emerging from the cankers. The thick, liquid exudate is primarily composed of bacteria and is a sign of the disease, although the canker itself is composed of plant tissue and is a symptom.

A symptom of plant disease is a visible effect of disease on the plant. Symptoms may include a detectable change in color, shape or function of the plant as it responds to the pathogen. Leaf wilting is a typical symptom of verticilium wilt, caused by the fungal plant pathogens Verticillium albo-atrum and V. dahliae. Common bacterial blight symptoms include brown, necrotic lesions surrounded by a bright yellow halo at the leaf margin or interior of the leaf on bean plants. You are not actually seeing the disease pathogen, but rather a symptom that is being caused by the pathogen.

Here are a few examples of common signs and symptoms of fungal, bacterial and viral plant diseases:

Fungal disease signs:

  • Leaf rust (common leaf rust in corn)
  • Stem rust (wheat stem rust)
  • Sclerotinia (white mold)
  • Powdery mildew

Fungal disease symptoms:

  • Birds-eye spot on berries (anthracnose)
  • Damping off of seedlings (phytophthora)
  • Leaf spot (septoria brown spot)
  • Chlorosis (yellowing of leaves)

Stripe rust pustules on a winter wheat leaf is a symptom.
Photo credit: Fred Springborn, MSUE

Bacterial disease signs (difficult to observe, but can include):

  • Bacterial ooze
  • Water-soaked lesions
  • Bacterial streaming in water from a cut stem

Bacterial disease symptoms:

  • Leaf spot with yellow halo
  • Fruit spot
  • Canker
  • Crown gall
  • Sheperd’s crook stem ends on woody plants

Dark red kidney bean leaf showing bacterial leaf spot symptom (brown leaf spot with yellow halo).
Photo credit: Fred Springborn, MSUE

Viral disease signs:

  • None – the viruses themselves can’t be seen

Viral disease symptoms:

  • Mosaic leaf pattern
  • Crinkled leaves
  • Yellowed leaves
  • Plant stunting

You can see that there is a lot of overlap between fungal, bacterial and viral disease symptoms. Also, abiotic diseases, herbicide injury and nematode problems must be considered possibilities when an unknown plant problem appears. These lists are not complete or exhaustive, only examples.

Michigan State University Extension offers publications and online information to assist producers in identifying and controlling serious plant diseases. In addition, MSU Diagnostic Services offers online factsheets covering many common plant diseases in Michigan, and can diagnose diseased plant samples at an affordable cost. The lab website has submittal forms and details on sample submission and costs.

For more basic information on plant disease, visit Ohio State University’s Introduction to Plant Disease Series webpage.

How to identify and control tomato plant disease

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Tomato growers are a passionate bunch. Some of us spend long hours combing over seed catalogs and nursery benches full of plants to select the perfect tomato varieties for our garden. We plant, tend, prune, fertilize, stake, and otherwise care for our tomato plants with a dedication rivaled only by our dedication to our human family. But, even with all that care and attention, sometimes a tomato plant disease strikes our garden. Today, let’s review some of the most common tomato plant diseases and discuss ways to prevent and manage them, without resorting to synthetic chemicals for control.

Types of tomato diseases

Unfortunately, there are several pathogens that can cause tomato plant disease. I’m going to introduce you to several specific tomato diseases later in this article, but before I get to that, it’s important to talk briefly about the different types of pathogens and how to prevent them from striking your garden in the first place.

Some tomato disease pathogens are fungal organisms while others are bacterial or even viral. Different regions of North America are affected by different tomato pathogens, and rates of infection are dependant on many factors, including wind patterns, temperature, humidity, varietal resistance, and plant health, to name just a few. It’s important to remember that tomato plants that are healthy and properly cared for will often show more resistance to tomato plant disease, so ensuring your tomato crop has ample moisture and healthy, fertile soil is a must.

Preventing tomato diseases is a must, if you want to have productive plants.

Preventing tomato plant disease

Other than making sure your tomato plants are happy and healthy, there are a few other things you can do to help prevent tomato plant diseases. Here are nine tips to get you started on the road to disease-free, productive tomato plants:

  1. Rotate your crops. Since many tomato pathogens live in the soil, plant tomatoes in a different spot in the garden each year.
  2. Pinch off leaves with any signs of disease immediate and dispose of them in the trash to keep a possible infection from spreading.
  3. Don’t work in the garden when tomato foliage is wet or you may inadvertently spread pathogens from plant to plant.
  4. Choose disease-resistant varieties when selecting which types of tomatoes to grow.
  5. Remove all diseased tomato plant debris at the end of the growing season and burn it or toss it in the trash. Do not put diseased foliage in the compost pile.
  6. Provide adequate air circulation around each plant. Here’s our guide to spacing tomatoes properly.
  7. Mulch your tomato plants well at the start of the season. Two or three inches of compost, leaf mold, straw, or hay serves to keep soil-dwelling fungal spores from splashing up onto the lower leaves when it rains.
  8. Try to keep the foliage dry whenever possible. Hand irrigation or soaker hoses allow you to target the water on the root zone. The splash from overhead sprinklers can spread disease and wet foliage promotes fungal issues.
  9. Disinfect the empty pots if you grow your tomatoes in containers, using a 10% bleach solution at the end of the growing season and replace the spent potting soil with a new mix every spring.

    Follow every prevention tip you can to keep your tomato plants from being ravaged by diseases like this one.

6 Common tomato plant diseases

Despite your best efforts at preventing tomato diseases, they may still get a foothold in your garden from time to time. Here’s the low-down on six of the most common tomato plant diseases with information on identifying, preventing, and managing each of them.

Early blight

Identify: This common tomato plant disease appears as bulls-eye-shaped brown spots on the lower leaves of a plant. Often the tissue around the spots will turn yellow. Eventually, infected leaves will fall off the plant. In most cases, the tomatoes will continue to ripen, even as the disease symptoms progress up the plant.

Prevent: The early blight pathogen (Alternaria solani) lives in the soil and once a garden has shown signs of the early blight fungus, it’s there to stay because the organism easily overwinters in the soil, even in very cold climates. Fortunately, most tomatoes will continue to produce even with moderately severe cases of early blight. To prevent this tomato fungal disease, mulch plants with a layer of newspaper topped with untreated grass clippings, straw, leaf mold, or finished compost immediately after they are planted. This mulch forms a protective barrier, preventing the soil-dwelling spores from splashing up out of the soil and onto the plant.

Manage: Once the fungus strikes, organic fungicides based on Bacillus subtilis or copper can help prevent or stop the spread of this tomato plant disease. Bicarbonate fungicides are also effective (including BiCarb, GreenCure, etc).

Early blight often begins as irregularly shaped, bulls-eyed brown spots on the lower leaves of a tomato plant.

Fusarium wilt

Identify: The pathogen that causes Fusarium wilt (Fusarium oxysporum) is generally more common in warm, southern regions where this tomato plant disease can wipe out entire fields. Symptoms include drooping leaf stems. Sometimes an entire branch may wilt, often starting with the lower portion of the plant and then progressing upwards until the whole plant collapses. To confirm an infection, cut the main stem of the plant open and look for dark streaks running lengthwise through the stem. Sometimes there are also dark cankers at the base of the plant

Prevent: The spores of this tomato plant disease live in the soil and can survive for many years. They’re spread by equipment, water, plant debris, and even people and animals. The best method of prevention is to plant resistant varieties if you’ve had trouble with Fusarium wilt in the past. Also disinfect tomato cages and stakes with a 10% bleach solution at the end of every season.

Manage: Once this tomato plant disease strikes, there’s little you can do to control it. Instead, focus on preventing it for future years. Soil solarization can help kill fungal spores in the top few inches of soil, and crop rotation is key. There are also several biological fungicidal drenches that can be applied to soil (look for one based on the bacteria Streptomyces griseoviridis called MycoStop® or a granular one based on the fungus Trichoderma virens called Soil Guard®). These products may help prevent the infection from colonizing the roots of future crops.

Late blight

Identify: Late blight (Phytophthora infestans) is among the most destructive tomato plant diseases. Thankfully, it’s not very common, especially in the north where it doesn’t survive winter’s freezing temperatures without a host plant. Late blight is caused by a fungus, and it creates irregularly shaped splotches that are slimy and water-soaked. Often, the splotches occur on the top-most leaves and stems first. Eventually, entire stems “rot” on the vine, turning black and slimy. There may also be patches of white spores on the leaf undersides. In the north, the pathogen overwinters in buried potato tubers. In the south, it easily survives the winter.

Prevent: The spores of this disease are fast-spreading, moving on the wind for miles. If you live in the northern half of the continent, do not purchase potatoes and tomatoes that were grown in the south as you may inadvertently introduce late blight spores to your garden. This is not a common pathogen, but if late blight is reported in your area, there is little you can do to prevent the disease because the spores spread so rapidly. Plant only locally grown plants to help keep the pathogen out of your area.

Manage: Once late blight strikes, there is little you can do. Tear out the plants, put them in a garbage bag, and throw them out to keep the disease from spreading. Organic fungicides based on Bacillus subtilis are somewhat effective in preventing this tomato plant disease when it’s first discovered in your area.

Late blight is an extremely difficult tomato disease. It’s not common, but it is troublesome.

Septoria leaf spot

Identifiy: Appearing as tiny, round splotches on the leaves, this tomato disease (Septoria lycopersici) typically starts on the lowest leaves first. The spots have dark brown edges and lighter centers, and there are usually many spots on each leaf. Infected leaves eventually turn yellow and then brown, and fall off.

Prevent: Remove diseased tomato plants at the end of the season to prevent the spores from overwintering in the garden. Cut off and destroy infected leaves as soon as you spot them and disinfect pruning equipment before moving from one plant to another.

Manage: Organic fungicides based on copper or Bacillus subtilis are effective against septoria leaf spot, especially when used as a preventative measure.

Septoria leaf spot is a tomato disease that produces splotches and spots on the foliage and can reduce yields.

Southern bacterial wilt

Identify: Unfortunately, once present, Southern bacterial wilt (Ralstonia solanacearum) is a tomato plant disease that spreads like wildfire. It’s soil-borne, but the bacteria that cause this tomato disease can travel by soil, water, plant debris, and even on clothes, tools, and skin. It’s naturally found in tropical regions and greenhouses, but it can arrive in the garden via infected plants that were purchased from other areas. Initial symptoms include the wilting of just a few leaves on a plant, while the rest of the foliage appears healthy. Over time, more and more leaves wilt and turn yellow until all the leaves succumb, though the stem remains upright. Slimy ooze threads out of the cut stems, and when they’re placed in water, milky streams of bacteria stream out of the cut.

Prevent: Southern bacterial wilt is soil borne and can survive for long periods in the soil on roots and plant debris. Like many other tomato diseases, it favors high temperatures and high humidity. The best way to prevent this disease is to purchase and plant only locally grown plants, or grow your own plants from seed. Southern bacterial wilt is more common in warmer regions, but has been found in Massachusetts and other northern regions as well.

Manage: There is no cure for this disease. Once confirmed, immediately remove infected plants and discard them in the trash.

Verticillium wilt

Identify: This fungal disease is caused by several soil-borne pathogens (Verticillium spp.). When present in a tomato plant, they block the vascular tissue in the plant and cause the leaves and stems to wilt. Symptoms progress slowly, often one stem at a time. Eventually, the entire plant yellows and withers. To confirm diagnosis, cut through the main stem of the plant and look for dark brown discoloration inside. Verticillum wilt is most problematic in late summer.

Prevent: Verticillium fungi can survive for many years in the soil and on plants. They thrive in slightly cooler summer temperatures (between 70 and 80 degrees F). Plant only resistant varieties.

Manage: Once verticillium wilt occurs, there’s little you can do to control the current year’s infection. Instead, focus on preventing this tomato plant disease in future years. Soil solarization will help kill the fungal spores in the top few inches of soil. Practice crop rotation: do not plant other members of the same plant family in that same planting area for at least four years after the infection.

Many soil-borne tomato diseases aren’t as problematic when the plants are grown in containers. Check out this video introducing 5 of the best varieties of tomatoes for growing in containers.

With an eye toward prevention and employing early management practices as soon as a disease is spotted, you’ll be able to grow a terrific crop of tomatoes each and every season.

For more on growing great tomatoes, check out the following posts:
Our favorite cherry tomato varieties
The best heirloom tomato varieties
5 Tips for growing tomatoes in raised beds
How to grow tomatoes from seeds
Top tomato varieties from the experts

Do you have a favorite tomato variety you grow every year? We’d love to hear about it in the comment section below!

Plant diseases

Diseases of apple

  • Apple scab of apples and crabapples
  • Black rot of apple
  • Cedar-apple rust and related rust diseases
  • Fire blight
  • Sooty blotch and flyspeck

Diseases of blueberry

  • Armillaria root rot
  • Blueberry witches’ broom
  • Viruses of backyard fruit

Diseases of raspberry

  • Gray mold of strawberry and raspberry
  • Late leaf rust on raspberry
  • Orange rust on raspberry
  • Raspberry cane diseases
  • Raspberry leaf spot
  • Viruses of backyard fruit

Diseases of stone fruit

  • Black knot
  • Brown rot of stone fruit
  • Cherry leaf spot
  • Plum pockets

Diseases of strawberry

  • Angular leaf spot of strawberry
  • Anthracnose fruit rot of strawberry
  • Black root rot of strawberry
  • Gray mold of strawberry and raspberry
  • Leaf blight of strawberry
  • Leaf scorch of strawberry
  • Leaf spot of strawberry
  • Leather rot of strawberry

These integrated pest management guides for home gardeners recommend disease and insect control strategies for home fruit growing. They are multi-page, downloadable PDFs.

  • Pest management for the home apple orchard
  • Pest management for home blueberry plants
  • Pest management for the home raspberry patch
  • Pest management for the home stone fruit orchard
  • Pest management for the home strawberry patch

Identification and Treatment for Houseplant Diseases

Indoor Plant Disease Prevention

Healthy indoor plants will be able to resist and fight off pests and diseases much better than weak plants. In order to keep your houseplants strong you need to meet their cultural requirements, which involves using proper soil, avoiding drafts, not crowding plants and then keeping a good balance of temperature, humidity, light, water and drainage.

All plants have different requirements and if you aren’t sure what these are, be sure to check out our Plant Hub to find out what balance and care your particular plant needs to thrive.

Chances are though you are on this page because prevention is too late and you have been afflicted with something nasty and want a treatment and you want it now! Trust us when we say, we feel your frustration. All is not lost however and the rest of this article offers some solutions.

The eight most common diseases that afflict houseplants are listed below along with the identifying symptoms and a suggested treatment. If you’re having problems with something different let us know in the comments and we’ll try and help you out.

Sometimes your plant will have a pest problem rather than a disease in which case you will need to head on over to our pest guide .

Crown and Stem Rot (Basal Stem Rot)

This is caused by fungal mycelia which lives in most soils. It normally lives peacefully with the houseplant, however when conditions become very damp through overwatering, cool conditions or poor ventilation it rapidly multiplies and infects the plant.


Black or discolored rotten patches at the base of the plant. It normally effects the base because this is the closest part to the soil and therefore the fungus, although it’s possible other parts will be infected instead. Succulents and cacti are most at risk.


The only treatment is to cut out the rot and dust with an anti fungicide such as sulphur. If the base has been very badly effected there is very little you can do because obviously if you’re having to cut out whole lower sections of the plant you will kill it. It’s therefore worth taking cuttings from the healthy parts and trying to propagate replacements.

Grey mold (Botrytis)

Gray Mold or Grey Mould is caused by airborne fungal that lands on damaged or dying tissue. Small wounds are normal on plants, if it’s healthy and the conditions are reasonably dry it shouldn’t be a problem. The issue arises when the plant is weak anyway and the surrounding atmosphere is humid and cool.


Soft rotting patches which are soon covered in a grey fungus. There will more than likely be dead brown patches on the leaves or stems, white or pale brown spots on flower petals or rotting on bulbs etc.

Remove the infected parts of the plant. Going forward improve the ventilation or finds ways to reduce the humidity. If the Mold has got out of hand you may have to throw it away completely.

Nutrient deficiency

If you’ve never fed or repotted your plant then a nutrient deficiency is quite probable. The majority of plants make their own food through photosynthesis, however small levels of nutrients are needed to sustain that new growth and to ensure a healthy look.

The nutrients are found in the soil but once they’re gone they’re gone and therefore it’s important nutrients are replaced either by a fertiliser or by changing the soil occasionally.

There are many symptoms of nutrient deficiency in houseplants, although as a general rule you’ll be experiencing unusual or poor growth. The leaves may be very small with odd shapes, the colour of the plant may be dull or transparent in places. No flowers or flowers which are discolored or aborted before they can open can all be symptoms.

The immediate treatment for your plant is to either fertilise using an all purpose mixture or to repot using fresh compost. Choose only one to start with, rather than both at the same time as this could result in too much fertiliser which can damage the plant further. The rule of thumb is to wait at least 8 weeks before you start fertilising newly repotted plants.

Powdery mildew

Fortunately powdery mildew is often disfiguring rather than fatal. Nor is it overly common on indoor houseplants because it’s caused by fungi spores that travel through the wind.

Obviously if you’ve been summering your houseplants outdoors then you increase your risk. Warm, damp locations and plants which are situated very close together all increase your chances of the fungi taking hold and spreading.

A white film which looks like a light dusting of flour coats the leaves, over time the white look may dull and become darker. If left unchecked it will spread over the entire plant, including the stems and flowers.

Remove the badly infected mildewed leaves with care (you don’t want to be acting like an artificial wind by blowing the spores around other plants). Then spray with a product containing Myclobutanil, Penconazole, Flutriafol or lightly dust the leaves with Sulphur to give control.


Rust is a common disease on Roses outdoors but inside, it’s rather rare.

If you grow Roses, Chrysanthemums, Pelargoniums or Fuchsias as houseplants you will need to watch out for infection as eradication is very difficult. Therefore if Rust is suspected you must isolate it from other houseplants to prevent it spreading.

Brown rings or spots on the leaves. They usually start on the underside although in more advanced stages they can appear on either side. Leaves may fall prematurely without any yellowing before hand and often when you gently brush past.


Normally complete eradication of Rust is difficult and you may only be able to control it. In any event you should carefully remove the infected leaves and try not to shake or knock the Rust spores from the discs as this will just spread the infection to other parts of the same plant or close neighbors. If this doesn’t work, any chemical product containing Mancozeb, Penconazole or Flutriafol should help.

Sooty Mold (or Mould)

This is a disease which has a very visible presence. It’s not actually a direct attack on the plant but rather on the honeydew that is produced as a waste product by several pests, such as Scale.

The honeydew is a clear substance but at certain visual angles you can see it as a sticky looking residual. As soon as the room becomes humid and less ventilated, perhaps as Winter approaches and we close our windows and switch on the central heating, the fungus takes hold and all the previously clear residual turns greeny black and moldy.

Black or dark green soot like spots. In extreme cases it will coat entire leaves as in the photo above.

Sooty Mold does not directly harm the plant however it’s horrible and unpleasant to look at. You can remove it by wiping over the leaves with a damp cloth. Afterwards rinse the leaves with clean water. Ensure you eradicate the pest problem at the same time to prevent future attacks.


Viruses are a broad topic, the symptoms are varied and most types of plant are effected from time to time. They’re typically spread by long term pests such as Aphids or by the plant being in close proximity to one that has already been effected with a virus.

There are many symptoms of a plant virus and they can appear differently depending what type of houseplant has been infected. Growth may be stunted, twisted or distorted. Leaves may be yellowed or mottled in spots, mosaics or streaks. Any flowers may become streaked or not develop correctly i.e. they may mature and open but still be a green colour when they should be something else.

There is no cure. If the symptoms can’t be tolerated then you will need to throw it away. Don’t try to propagate any part of the plant because there is a high possibility the virus will remain and prosper in the new plants.

White Mold (or Mould)

“What’s the white mold growing in my houseplant’s soil”? Is one of our frequently asked questions. It’s another fungus that quickly colonise the soil surface when conditions are moist, humid and over watered.

Ventilation is also typically poor therefore it tends to appear more in cooler months of the year when everything in the home is shut up tight. Don’t worry though, as white mold is easily dealt with and basically harmless to plants and people.

The surface of the soil is coated in a white fluffy substance that looks like cotton wool.

No need to reach for the sprays here. All you need do is gently rake up the effected soil using something like the end of a pencil or pen. You don’t need to pick it out or anything like that so it’s a very easy job. The raking could free up the fungal spores into the air though so do be careful not to inhale them as they may potentially trigger allergies and aggravate asthma.

After delivering the treatment think about moving your plant to a more ventilated space or try and free the growing medium by making it more “open”.

Tom Knight

Over the last 20 years Tom has successfully owned hundreds of houseplants and is always happy to share knowledge and lend his horticulture skills to those in need. He is the main content writer for the Ourhouseplants Team.

Also on

Photo credit of the first diseased plant Anna
Photo credit of Botrytis on a strawberry Rasbak
Photo credit of Sooty mold Amnon Shavit

It can be pretty heartbreaking when your plants look less than stellar. Sometimes an easy remedy to restore plant health is adding more water or moving to a sunnier spot. If that doesn’t work and you’ve tried many options, it could be a sign of a larger problem. Your plant could have a disease.

To help you quickly diagnose and keep your plants looking fresh, we’ve compiled a handy guide below of most common plant diseases you can encounter. So the next time you see a weird substance forming on the soil or strange discoloration of leaves, you’ll be an expert.

What About Fungicide?

Fungicide can be a useful preventative measure for gardeners with plants that are especially prone to rot and disease. If you’re concerned about adding chemicals to your garden, depending on the condition and the disease, there are some natural alternatives:

  • Milk is known as an effective treatment for powdery mildew. Mix a 50:50 milk to water solution in a spray bottle and apply to leaves of plants.
  • Sulfur in dust form can keep disease at bay. Be sure to apply while wearing a mask so the dust doesn’t irritate your eyes and mouth.
  • The “Cornell Formula” is a well known natural fungicide, which includes mixing 1 tablespoon baking soda, 1 tablespoon horticultural oil and 1 to 2 drops dishwashing liquid.

How to Dispose of a Diseased Plant

Many plant diseases can quickly return if the dead plant matter isn’t properly disposed of. In fact, most fungal, bacterial and viral plant diseases are spread naturally by wind currents, rain, soil seeds, insects and other animals. Others can survive on nearby dead plants or infected gardening tools. When you think you’ve collected all of the dead plant, follow these disposal tips:

  • Compost: For less persistent diseases like powdery mildew, simply removing from live plants and allow to die off in compost. If you don’t have a compost at home, check with your local government for a nearby green waster center.
  • Burial: For leaves or fruits with rot, burying the decay in a 1 foot deep hole will work.
  • Bonfires: Dry, woody material like branches can be disposed of by setting a small bonfire. Be sure to handle on a non-windy day to reduce the risk of the fire spreading.
  • Household trash: Infected bulbs, small wooden pruning and collapsed seedling can be tossed into your home garbage can.

How to Keep Your Home Vibrant

While you await the first sign of spring, browse our bright blooms to bring some sunshine inside.

Images used in graphic are courtesy of Scot Nelson and Virens.

Houseplants have been growing in popularity as a way to relieve stress, purify air and bring a bit of nature indoors. They can brighten up an office, living room or kitchen with their vibrant colors or sooth the space with their earthy scents.

Obviously, you want to choose a houseplant that fits your needs, but you want to make a healthy selection to ease long-term maintenance. This is why it’s important to purchase your houseplants at a reputable garden center and fully examine your plant for signs of insects, disease and malnourishment.

It’s also important to consider where you’re planning to put your plant and choose a variety that’s well suited to the location’s light intensity, temperature and humidity level. However, even under similar conditions your new houseplant will take time to adjust after being raised in an ideal greenhouse environment.

More than likely, your new houseplant will become established and bounce back in a couple of weeks. Don’t be too concerned if you notice droopy leaves with brown edges or a slightly different color. Once your plant has adjusted it will start to look healthier.

If it looks like a zombie plant over a longer period of time, you might need to start ruling out common houseplant problems.

Environmental problems

Some of the most common houseplant problems are a result of poor regulation of water, temperature, humidity and light. While it’s easy to give a plant too much or too little of one or more of those factors, it’s also easy to correct them. The tricky part is when one problem is a combination of several factors.

Here is a list of common environmental problems and their causes.

    • Spindly plants: Poor lighting conditions.
    • Weak growth: Too much or too little light, root system is damaged from poor soil drainage or over-watering.
    • Wilting: Over-watering, under-watering, root rot, salt build up, too much fertilizer, needs a larger pot.
    • Defoliation: Over-watering, under-watering, needs a larger pot, poor lighting conditions, injured by extreme hot or cold temperatures, low humidity, insects and diseases.
    • Yellowing plant: Poor lighting conditions, not enough fertilizer, insects or mites, over-watering.
    • Spotty leaves: Watering with cold water or splashing water on leaves can cause white or pale yellow colored spots or patches on the leaves of some plants.
    • Yellowing leaves: Over-watering, poor lighting conditions, low humidity, poor soil drainage, injured by low temperatures from a draft.
    • Yellowing, browning and death of lower leaves: Nitrogen or iron deficiency.
    • Scorched or faded leaves: Too much direct sunlight.
    • Reddened leaves: Temperature is too low, phosphorous or potassium deficiency.
    • Brown leaf tips: Chemical burn from over applying pesticides or fertilizer, soft water, long stretches of dry soil, temperature is too low, low humidity.
    • Small leaves: Soil is either too wet or too dry.
    • Small pale leaves: Poor lighting, not enough fertilizer.
    • Oedema (rough corky swellings on the undersides of leaves and stems): Over-watering, poor lighting, low temperatures.
    • Few flowers: Poor lighting conditions.
    • Few flowers and excessive growth: Too much nitrogen fertilizer.
    • Bud drop: Not enough fertilizer, too much nitrogen, under-watering, over-watering, spraying with cold water.
    • White crust on soil: Salt buildup.
    • White or yellow mold like growth: Soil fungus.

Pest Problems

If you’ve ruled out environmental causes as to why your plant isn’t thriving, it may be time to consider some common pests that affect houseplants.

Here is a quick list of the most common insects to watch for:

Aphids: These tiny insects live on the undersides of leaves. They can be green, brown or black in appearance. Look for them if you notice stunted plant growth and curled or distorted foliage.

Mealybugs: They are a scale insect that live on the stems, undersides of leaves and on the nodes of houseplants. They appear white and cottony. Mealybugs cause stunted plant growth.

Mites: Mites are actually tiny, pale spiders. They produce webbing on leaves and stems and can cause distorted yellow leaves.

Scale: These are oval or round, brown insects that live on the leaves and stems of house plants. They suck the plant’s juices and cause stunted plant growth.

Thrips: These very tiny insects are white before maturity and range from tan to dark brown as adults. They feed on flowers and leaves, causing them to become distorted or discolored.

Whitefly: These small, gnat-like insects feed on the leaves of houseplants, which causes them to turn pale shades of yellow or white.

Fungus gnats: As adults they resemble fruit flies and do not cause damage to plants. However, their larvae can sometimes be a problem for plant roots. Certain species of the tiny white and black-headed maggots will feed on the root hairs of plants, causing reduced plant growth.

The best way to get rid of any pest is through non-chemical management, removing insects by hand and wiping off the affected areas.

Diseases are probably the least common issue houseplants face as proper environmental conditions promote healthy growth. However, weak plants are more susceptible to infection.

Here are some common diseases and their symptoms:

Anthracnose: Leaf tips turn yellow and then brown with the potential for the entire leaf to die.

Solution: Remove the infected leaves and avoid misting the plant.

Leaf spots: There are two types of leaf spots. Fungal spots appear brown with a yellow halo and will kill either portions or the entire leaf. Bacterial leaf spots appear water soaked and can also have a yellow halo.

Solution: Remove the infected leaves, increase the air circulation around your plant and avoid getting water on the unaffected leaves.

Powdery mildew: A white, powdery fungal growth will start to take over foliage, causing leaf distortion and potentially leaf drop.

Solution: Increase air circulation, ensure the soil is draining properly and remove the severely infected leaves.

Root and stem rots: Rotting will cause stems and roots to appear brown or black and feel very soft. It causes plants to initially wilt and eventually die.

Solution: Rot is primarily caused by over-watering, so you want to avoid this and make sure your soil is draining properly as a preventative measure. In the event of rot where symptoms are affecting some, but not all of the roots you can try to cut out the infected roots and repot the plant.


  • PennState Extension
  • Clemson Cooperative Extension
  • North Dakota State University


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Plant Disease Library

Learning about the major diseases that can affect your plants and how to treat those diseases can help to make your harvest healthy, fruitful and enjoyable.

Black Spot

Roses, especially hybrid tea roses, are highly susceptible to this infectious fungal disease. Black spots, as the name implies, will appear on the leaves, followed by a yellowing surrounding the spots.

learn about Black Spot”

Botrytis Blight

This fungal disease affects flowering plants, ornamentals, and fruits & vegetables. Also known as gray mold, it can cause dying tissue and buds as well as fruit or bulb rot.

Images courtesy of Clemson University – USDA Cooperative Extension Slide Series,

learn about Botrytis Blight”

Leaf Spot

Leaf Spot affects many different types of plants, but most commonly attacks trees and shrubs. In large clusters or rows, it may also be referred to as anthracnose.

learn about Leaf Spot”

Numerous strains of fungi are commonly referred to as Powdery Mildew. Since this disease removes essential nutrients from the plant, leaves may become yellow, stunted or drop off prematurely.

learn about Powdery Mildew”

This isn’t the same as rust on metal! Rust spores travel through the air and land on plants, spreading the fungal disease. Although plants do not die from rust, it can contribute to the plant’s decline.

learn about Rust”

Common Plant Diseases & Organic Control Options

We’ve posted several in-depth articles on disease control and prevention here on our Seed Hopper blog before, and you can find them all archived in the “Plant Diseases” category in the left-hand navigation column. They include coverage of Late Blight, Downy Mildew and Disease Prevention in High Tunnel Production. Our “What’s Wrong with My Garden?” series goes over the basics of disease prevention and details control measures for many common diseases including: Powdery Mildew, Angular Leaf Spot, Downy Mildew, Bacterial Wilt, Early Blight, Late Blight, Septoria Leaf Spot, Scab, Black Rot, Fusarium Yellows, Club Root, Damping Off and Stewart’s Wilt. Also in our blog archive is a guide to diagnosing abiotic plant disorders, which may look like diseases but are in fact caused by environmental or cultural sources.

This post will go into some detail on diseases the following diseases – to jump to a certain section, click on the name of the disease you’re looking to learn about: Alternaria (Early Blight) · Black Rot · Botrytis (Gray Mold) · Cucumber Mosaic Virus · Rhizoctonia

Alternaria on carrot foliage.


Type: Fungal, various species

Crops: Potato, tomato, Brussels sprouts, broccoli, cabbage, cauliflower, kohlrabi, carrot, parsnip, parsley

How it spreads: Crop residues, weed hosts, pests, soil, seeds, machines/workers

Diagnosis: Symptoms include the appearance of dark brown or black lesions on foliage and/or stems (and eventually fruit), defoliation, yellowing and “bullseye” leaf spots.

Prevention: The best way to prevent alternaria, colloquially called “early blight,” is to start with disease-free soil and seeds. This fungal disease requires adequate moisture to activate spores, so adequate airflow and appropriate watering techniques are key for reducing risk. Good sanitation practices, crop rotation, and appropriate spacing and pruning of plants will help reduce the risk of spreading spores. Resistant cultivars (like Iron Lady F1) can also help fend off infections.

Mitigation: Once a crop has been infected it is very difficult to stem the flood of further infection. Some organically approved copper sulfate sprays can slow the spread of the disease. The most critical action to take once a field has been infected is to ensure that the disease does not have any favorable hosts to overwinter and appear again the following season. Good sanitation techniques and crop rotation will help prevent spores from over wintering.


Type: Bacterial (not to be confused with the fungal black rots that attack apples, grapes, citrus and sweet potatoes)

Crops: Broccoli, Brussels sprouts, cabbage, cauliflower, kale, kohlrabi, radish, rutabaga, turnip and mustard greens

How it spreads: Seeds, host weeds, machines/workers, occasionally pests

Diagnosis: Symptoms include yellowing, shedding of lower leaves, dark spots and blackened veins.

Prevention: Starting with disease-free seed is the best prevention method. Selecting resistant varieties (like Capture F1 cabbage) can also reduce the risk of infection. High Mowing tests all of our seed in the brassica family for black rot and black leg. No infected lots will ever be sold. Read more about our commitment to disease-free seed here. Other prevention techniques include hot water treatment of seeds (if purchasing from an uncertified source), crop rotation, and appropriate watering techniques to avoid unnecessary moisture among plants (bacteria can spread by splashing water).

Mitigation: Similar to Alternaria, once a crop has been infected it is very difficult to stem the flood of further infection. Some organically approved sprays can slow the spread of the disease. The most critical action to take once a field has been infected is to ensure that the disease does not have any favorable hosts to overwinter and appear again the following season. Good sanitation techniques and crop rotation will help prevent overwintering.

Botrytis on a lettuce.


Type: Fungal

Crops: Can affect a wide range of species (over 200 hosts have been reported) and is especially problematic in greenhouse tomato culture. Other important affected crops include cabbage, snap and lima beans, lettuce, muskmelon, peas, peppers and potatoes.

How it spreads: Crop residues, soil, seeds, host weeds

Diagnosis: Symptoms include lesions on stems and foliage (especially near a damaged area), and the appearance of a gray, velvety covering on flowers or fruit. White circular spots (“ghost spots”) can appear on fruit; plants will often abort infected fruit, leading to lots of fruit discard around infected plants. Pollen and flower parts that have fallen onto leaves are a common starting point for leaflet colonization.

Prevention: There is no known resistance to botrytis in tomatoes. Because the fungus spreads through moisture and splashing water, the best prevention techniques include controlling and carefully monitoring humidity and temperature. Adequate spacing, airflow, pruning and crop rotation can help reduce the risk of outbreaks.

Mitigation: There are limited options for organic controls once botrytis fungal spores have started to spread. The best mitigation is good prevention practices. If an area is infected, after the crop is removed for the season diligent sanitation techniques and crop rotation will help prevent an outbreak the following season.

Cucumber mosaic virus on watermelon.


Type: Viral

Crops: Spinach and lettuces

How it spreads: Pests (most commonly winged aphids) and infected weeds (i.e., chickweed, milkweed, purslane, dayflower, etc.). Can be seed-borne, though it is a very unstable virus and therefore not commonly transmitted by seed.

Diagnosis: Symptoms include veinal browning, stunted growth, yellowing, mottling of older leaves and malformation of younger leaves.

Prevention: Resistant varieties such as Winter Bloomsdale have proven effective for production success. Good sanitation practices and holistic management practices like crop rotation, cover cropping and aggressive weed management can help break pest and disease cycles and prevent initiation and spread.

Mitigation: Reducing primary inoculum is critical to delaying virus epidemics, but if an infection is identified some mineral oil sprays have been known to reduce spread. Spraying border areas with mineral oil is also beneficial. The technique used is sophisticated; consult with your local extension service before applying any sprays.

Rhizoctonia (bottom rot) on lettuce.


Type: Fungal

Crops: Potatoes and lettuce

How it spreads: Soil, plant debris, potato tubers

Diagnosis: Commonly called “black scurf” when seen on potatoes and “bottom rot” when seen on lettuce. Symptoms for potatoes include irregular brown and black hard masses on the surface of potato tubers; although the masses are superficial and do not cause damage to the quality of the tubers, even in storage, they can be considered unmarketable due to the aesthetic damage they cause. If Rhizoctonia is present at planting, the most severe damage occurs under the soil and often goes unnoticed: the fungus attacks underground sprouts before they emerge from the soil and can either prevent emergence or stunt growth. Symptoms for lettuce include brown, sunken lesions on the lettuce midribs that are in contact with the soil. As the fungus progresses, the bottom of the plant will continue to rot through to the interior leaves and can result in the collapse of the head.

Prevention: Starting with disease-free seed and utilizing a rigorous crop rotation can help prevent the presence of rhizoctonia in fields. Using resistant varieties (like Red Tide, New Red Fire, Optima and Pirat lettuces) can reduce the risk of infection. Because potato plants are more susceptible to rhizoctonia damage before emergence, getting potato plants to emerge quickly in the spring is key to minimizing damage. Greensprouting can help with this in areas that experience damp springs.

Mitigation: If you suspect rhizoctonia is present in a potato field, harvesting tubers as early as possible after skin set can reduce black scurf significantly. Never use infected tubers as seed potatoes for planting the next season, as it will increase the risk of damage to emerging potato sprouts.

Do you have advice on how to prevent or control these or other diseases? Share your insights in the comments below!

6 Common Plant Diseases & Pests

In the landscape industry, plant diseases and pests are a common occurrence. An experienced commercial contractor should be prepared with the expertise and knowledge needed to combat these diseases and pests, to ensure a property’s landscape thrives throughout the year. Here are some of the plant diseases and pests we commonly see and how you can prevent and treat them.

1. Sooty Mold

Sooty mold is caused by insects excreting honeydew onto plant leaves and other surfaces, such as outdoor furniture, and can be identified by its dark, soot-like appearance. It’s especially common in warm climates and during drought. Although sooty mold doesn’t directly infect plants, it can inhibit the plant’s sunlight exposure which can inhibit plant growth. To control sooty mold growth, your commercial contractor should utilize an effective pest management program to reduce insect populations.

2. Fusarium Wilt

Fusarium wilt is one of the most devastating and costly plant diseases, most often affecting Canary Island palms here in Southern California. When infected with Fusarium, a type of fungus, a canary palm’s leaves turn yellow and then brown, and it can die within a few months depending on the surrounding climate. It’s important to dispose of these palms properly, so as not to increase risk of spreading Fusarium to other palms, and avoid planting another palm in the same location since the soil most likely contains remnants of the fungus.

3. Fire Blight

Fire blight is a disease that commonly affects Ornamental Pear trees as well as Camphors, which can cause the branches can cause the fruit or tree leaves to turn black when infected. To control fire blight, your commercial contractor should monitor the fruit trees regularly (if tree maintenance is included in your contract) to identify and remove infected areas, use treatments that control the disease, and the proper maintenance techniques needed.

4. Aphids

Aphids, plant-damaging pests, are a common issue for landscape professionals in Southern California. If untreated, they can destroy entire affected plants and surrounding plants, and lead to sooty mold growth. Implementing proper pest management techniques and constant monitoring are essential to prevent and/or control current aphid infestations.

5. Thrips

Thrips are plant-feeding insects which cause discoloration of plant leaves. While thrips may not threaten the life of a plant, the damage is often unsightly. If your commercial contractor encounters thrips within your landscape and significant damage is caused, it may be a good time to consider landscape renovations that are more sustainable. If damage is not that substantial, there are integrated pest management programs that can be effective in controlling thrips.

6. Oleander Leaf Scorch

Oleander Leaf Scorch is a disease that causes Oleander shrubs to decline and die within 3 to 5 years of being infected. It’s a common plant disease in Southern California, and one that landscapers are encountering more frequently in recent years. Symptoms of Oleander Leaf Scorch develop year round but are more noticeable in late Spring and early Summer when weather is warm, and include yellowing and wilting of leaves. As the disease progresses, other branches will be affected, and the plant will eventually die.

How do you know if your leaves are dying?

They could be dying at faster than normal rates, changing color in strange ways, withering, or curling under or over. Generally speaking, leaf death is the result of one of three things: the pH level being off, your watering being too much or too little, or the wrong amount of nutrients (either toxicity or deficiency).

Different problems in your marijuana plant will be evident in a variety of ways on your plant’s leaves, so it’s important to understand how these two things correlate. It takes a bit of detective work to figure it out, but usually, you can safely begin with checking the pH levels and then if that doesn’t work, going from there. Let’s look at the various aspects of unexplained leaf death on your marijuana plants.

Dying Marijuana leaves

It’s pretty clear when your leaves begin to die off. They first start with discoloration, which can range in color from red to brown to gray to yellow. They may be curling over or under, or simply falling off the plant after discoloring a bit. Once they fall off the plant, they have officially died.

How do you heal sick leaves?

Once marijuana leaves have begun to discolor, there is nothing you can do to save that leaf. Besides, it’s not the leaves you should be the most worried about. Always remember that leaf symptoms are just a sign of a deeper problem. To prevent further leaf death, you will need to solve whatever is at the root of the problem.

Underwatered Marijuana plants

Remember, the three possible reasons for the death of your leaves are a pH imbalance, a nutrient toxicity or deficiency, or overwatering or underwatering your plants. Think about whether it’s possible that you caused one of those things to be off before doing anything else.

Download my free Marijuana Grow Bible and learn how to recognize all marijuana plant problems

pH imbalance

The first thing you should always check when you see unhealthy leaves is the pH level because this is the most common reason for leaf death. The pH level at the roots of your plants needs to be balanced for your marijuana plants to be able to take in the nutrients.

ph imbalance

Sometimes symptoms that look like nutrient deficiencies are actually because the pH level is wrong, therefore “blocking” the nutrients from being absorbed, even when the grower is feeding their plants enough of the right nutrients. For that reason, fixing the pH level will also fix the nutrient deficiency (if that is indeed the problem).

What do you need to know about the pH level and marijuana leaf issues?

Basically, the pH level is the measure the alkaline and the acidity of a solution. The range starts at 0 and goes up through 14. Numbers lower than 7 mean the solution is acidic, while numbers greater than 7 mean the solution is alkaline.

A pH level of 7 indicates that the solution is exactly neutral. Remember, it is just the pH level in the soil near the roots that matters since the roots are what absorb the nutrients and water that you feed your marijuana plants. The pH level doesn’t always need to be exactly perfect, but it should be around the right level to ensure healthy soil pH.

nutrient burn

In fact, some pH level fluctuation helps maintain your plant’s ability to absorb different types of nutrients at different rates, improving the overall health of your marijuana plant and helping to avoid marijuana leaf issues. The key is to always maintain and manage the pH level of the soil at your plants’ roots. Do this by testing the solution of nutrients and water before feeding it to your plants. This is quite easy to maintain with pH Up/Down. Keep adjusting and testing until the pH level is right.

Some people prefer to use more natural means of adjusting the pH level. You can lower the pH level by using vinegar, and you can raise the pH level by whisking the water (and therefore adding oxygen). You can also mix dolomite lime into the soil to bring up the pH level (and also add magnesium and calcium).

Remember, a healthy pH level is between 6 and 7. Problems arise if the pH level leaves these bounds. Also, a range between 5.5 and 6.5 is better if you are growing your marijuana plants hydroponically. More about pH in my free marijuana grow bible .

ph problems

Adjusting the solution that you are about to feed to your marijuana plants’ roots is not the only way to get the pH level fixed at the root level. You can also test the water that comes out from the bottom of the pots (if your plants are potted) — that will help you know what the pH level is down at your roots. If the pH level changes significantly from when you feed it to your plants to when it comes out the bottom, you know there is some pH-related thing going on.

Flushing the system is a good way to balance out the pH level and avoid this these types of marijuana leaf issues. Simply water the plant with pH-balanced water three times (or all at once with three times the normal amount of water), and then resume normal feeding. Keep an eye on the pH levels immediately after that as well, so you know whether it worked or not. Some growers flush their plants on a regular basis to ensure that there is no buildup.

Overwatering or Underwatering

If you’ve already addressed the pH level issue and know that’s not what is causing the problems in your marijuana plant’s leaves, then the next thing you need to do is consider the possibility of overwatering or underwatering. The growing medium plays a big part in whether you are overwatering or underwatering. For example, coco coir or other soilless media could cause a drainage issue rather than it being the fault of your watering routine.

It’s a good rule of thumb to have a fifth of the water you put in come out from the bottom of the pots your plants are growing in. Once this has been done, you should wait until the top inch or so is dry before you water again. Poking your finger into the soil until the first knuckle is a good way to check if the top layer is dry enough.

Underwatered Marijuana Plants

Hydroponics systems don’t have an issue with actual overwater or underwatering, of course, but they could be experiencing an oxygen deficiency, causing them to drown (which is more or less the same as overwatering in terms of how it affects your plant). Adding in an air stone is a good way to combat this problem.

More watering tips in my free Marijuana Grow Bible at

Plants with root rot often develop it because of overwatering. You can identify root rot by the color and smell: they will be brown, smelly, and mushy. This can also be from poor drainage or temperatures that are too high. Use Aquashield, Great White, or Subculture B to fight root rot.

Nutrient problems

Nutrient deficiencies are are a tougher type of marijuana leaf issues. Before you consider that, be sure to check that it isn’t a pH imbalance or an improper watering problem. Once you have crossed both of those off your list, you can know that a nutrient toxicity or deficiency is the problem.

nutrient problems

Each nutrient has its own symptoms, so it’s important to do the proper amount of research to establish which nutrient is causing marijuana leaf issues. Then you can solve the problem without too much trouble, as long as it’s not too late.

Want to know more about growing and marijuana leaf issues? Get my free grow guide . The best marijuana seeds are available in the ILGM webshop.

Happy growing,

Robert Bergman

Diagnosing Cannabis Nutrient Deficiencies in Sick Plants

Leafly StaffSeptember 23, 2016 Share Print

The secret to growing great cannabis isn’t really a secret at all; provide your plants with adequate light, a suitable climate, the right amount of water, and proper nutrients, and you will have healthy plants capable of fighting off most pests and diseases.

When plants do not receive the correct level of nutrients, they become stressed and more susceptible to bugs, mold, and other pathogens. Their growth may also be stunted, resulting in reduced yields. Knowing the signs of nutrient deficiency is a vital skill for budding cannabis growers, so let’s take a look at all the essential nutrients, the symptoms associated with their absence, as well as other factors in potential deficiencies.

Getting the Right pH for Your Cannabis Plants

Plants can only absorb nutrients through their roots if the growth medium or hydroponic solution is at the correct pH. If conditions are too acidic or too alkaline, certain nutrients become unavailable to the root system. Over-fertilizing your plants can quickly lead to pH problems and nutrient lockout, showing symptoms that are easily mistaken for a nutrient deficiency to the untrained eye.

Before attempting to diagnose any nutrient deficiency, be sure that the pH of your soil, medium, or hydroponic solution is within the acceptable range. For soil and soil-like media, the range is 5.8 to 6.8, with 6.3 considered optimum. The proper range for hydroponic solutions is 5.5 to 6.5, and most brands of hydroponic nutrients will indicate an ideal level for their product. Testing the pH of your water is also recommended, as it can vary widely depending on the source.

“Mobile” and “Immobile” Nutrients

Nutrients are classified as mobile or immobile depending on whether they can be translocated once they have been fully assimilated by the plant. A mobile nutrient stored in the older leaves of the plant can be moved to solve a deficiency in another part of the plant. Immobile nutrients will remain very close to where they were initially deposited.

Mobile nutrient deficiencies will show symptoms in the older leaves at the base of the plant, while immobile nutrients will show the first signs of deficiency in the newer growth at the top and outer branches of the plant. Knowing which nutrients are mobile and which are immobile will help you diagnose potential deficiencies.

Essential Cannabis Nutrients and Symptoms of Deficiency

Your plant needs several essential nutrients, so be sure to keep an eye on these signs and visual cues that could indicate a potential deficiency.

Nitrogen (Mobile)

The most common nutrient deficiency in cannabis, nitrogen is essential throughout the lifecycle of the plant, but especially during vegetative growth.

Nitrogen Deficiency Symptoms:

  • An overall lightening and then yellowing in older, mature leaves, especially near the base of the plant
  • Severe deficiency will see continued yellowing, progressing up the plant, with possible discoloration and brown spots at leaf margins; eventually leaves curl and drop
  • Decreased bud sites and earlier flowering with substantially reduced yields

Phosphorous (Mobile)

Phosphorous is essential for photosynthesis and the release of stored energy in carbohydrates. While deficiency is uncommon (usually developing due to pH being above 7.0), the result can be catastrophic for young plants, and lead to stunted growth, delayed flowering, low yields, and poor resin production in mature plants.

Phosphorus Deficiency Symptoms:

  • Purpling of the petioles (leaf stems) on older leaves, followed by leaves taking on a dark blue-green hue
  • As deficiency progresses, both upward and outward growth slows drastically, blackish-purple or dark copper colored spots appear on leaves, and dead spots develop on petioles while leaves curl and drop
  • Sometimes leaves turn metallic purple or dark bronze in color

Potassium (Mobile)

Crucial to the production and movement of sugars and carbohydrates, potassium is also indispensable to the process of cell division as well as transpiration, root growth, and water uptake. Simply put, without it plants can’t grow. Deficiency leads to increased internal temperatures in the foliage of the plant, which causes the plant to evaporate more moisture through its leaves to cool down.

Potassium Deficiency Symptoms:

  • Dull, overly green leaves, followed by “burnt” rusty-brown leaf tips, chlorosis (yellowing), and brown spots, particularly on older leaves
  • Further deficiency shows in leaf burn, dehydration, and curling of younger growth
  • Left unchecked, potassium deficiency will result in weak plants, high susceptibility to pests and disease, and drastically reduced flowering

Calcium (Immobile)

Essential to cell integrity and growth, calcium aids the flow of nitrogen and sugars through the plant. Deficiency is usually found in hydroponic gardens or outdoors in very wet, cool climates with acidic soil.

Calcium Deficiency Symptoms:

  • Lower leaves curl and distort, followed by irregular brownish-yellow spots with brown borders that grow over time
  • Root tips will start to wither and die, and the plant will become stunted with decreased yields

Magnesium (Mobile)

Magnesium is the central atom in every molecule of chlorophyll, meaning that plants use it in very high amounts. It is crucial for absorbing energy from light, as well as helping enzymes create the carbohydrates and sugars that produce flowers.

Magnesium Deficiency Symptoms:

  • Plants will not show signs of a magnesium deficiency until 3 to 6 weeks after it has begun, at which point you’ll see the areas between the veins of older leaves turn yellow (interveinal chlorosis) and the formation of rust colored spots
  • These symptoms will progress through the whole plant, with more and larger spots developing in the interveinal areas as well as tips and margins of leaves
  • Some leaves will curl, die, and drop, while the whole plant looks sickly and droopy
  • Symptoms of magnesium deficiency will quickly escalate during flowering, leading to a reduced harvest

Sulfur (Semi-Mobile)

Essential to plant respiration and the synthesis and breakdown of fatty acids, sulfur plays a huge part in the production of oils and terpenes. It is uncommon to see a sulfur deficiency in cannabis, but these deficiencies are usually the result of a loss of phosphorous due to a high pH level in the root zone.

Sulfur Deficiency Symptoms:

  • Look for young leaves to turn lime green then yellow with stunted growth, followed by the yellowing of leaf veins accompanied with drying and brittleness
  • Continued deficiency results in slow, weak flower production with lowered potency

Copper (Semi-Mobile)

Needed only in trace amounts, copper aids in nitrogen fixation, carbohydrate metabolism, and oxygen reduction.

Copper Deficiency Symptoms:

  • Deficiency is very rare, and first symptoms are seen in the slow wilting, twisting, and turning of new growth
  • Dead spots appear on leaf tips and margins, and sometimes the whole plant wilts

Iron (Semi-Mobile)

Iron is essential for nitrate and sulfate reduction and assimilation, and a catalyst for chlorophyll production. Deficiencies are usually the result of improper pH levels or excess levels of manganese, zinc, or copper.

Iron Deficiency Symptoms:

  • Initial symptoms appear in younger growth, with interveinal chlorosis showing at the base of new leaves
  • Symptoms then progress through the leaves and into older growth, with overall yellowing between leaf veins

Manganese (Immobile)

Manganese helps utilize nitrogen and iron in chlorophyll production as well as aiding in oxygen reduction. Deficiency is rare and usually caused by high pH or an excess of iron.

Manganese Deficiency Symptoms:

  • As with other immobile nutrients, symptoms start in the new growth, initially showing interveinal chlorosis followed by necrotic spots, gradually spreading to older leaves
  • The most obvious sign is when leaf margins and veins remain green around the yellowing of the interveinal areas

Molybdenum (Mobile)

A player in two major enzyme systems that convert nitrate to ammonium, molybdenum is used by cannabis in very small amounts. Deficiencies are rare and can occur as the result of cold weather.

Molybdenum Deficiency Symptoms:

  • Older leaves yellow, sometimes developing interveinal chlorosis and discoloration at leaf edges
  • Eventually leaves cup and curl up before twisting, dying, and dropping

Zinc (Immobile)

Zinc is crucial for sugar and protein production, as well as in the formation and retention of chlorophyll and for healthy stem growth. Deficiency is quite common, especially in alkaline soils and dry climates, and is usually the result of high pH levels.

Zinc Deficiency Symptoms:

  • Young leaves and new growth exhibit interveinal chlorosis, with small, thin leaf blades that wrinkle and distort
  • Leaf tips will discolor and burn, followed by leaf margins and then brown spots
  • The most obvious sign is leaves that turn 90 degrees sideways

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Leafly Staff

Leafly is the world’s largest cannabis information resource, empowering people in legal cannabis markets to learn about the right products for their lifestyle and wellness needs. Our team of cannabis professionals collectively share years of experience in all corners of the market, from growing and retail, to science and medicine, to data and technology.

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