- How to Treat Powdery Mildew on Plants
- What Is Powdery Mildew?
- What Causes Powdery Mildew on Plants?
- Is Powdery Mildew Dangerous?
- Which Plants and Vegetables Are Most Susceptible?
- Can Powdery Mildew Spread to Other Plants?
- How Can I Prevent Powdery Mildew?
- How to Treat Powdery Mildew
- Why Choose Safer® Brand?
- White Mold
- Need help with what to do in your garden?
- Downy Mildew
- Reasons For Rose Leaves Turning Yellow
- Causes of Yellow Leaves on Rose Bush
- Treating Yellow Rose Leaves
- What’s eating the leaves of my roses?
- My roses have white spots on them. What’s wrong?
How to Treat Powdery Mildew on Plants
Though the weather across much of the country may indicate otherwise, spring is on the horizon. That means it’s time to at least start thinking about what to plant in your garden this year and which types of diseases your plants may be susceptible to. Powdery mildew is a relatively common fungus that many plants can contract. If you find powdery mildew on your plants, it’s not necessarily fatal, but you don’t want it hanging around. Fortunately, there are many options for powdery mildew treatment.
What Is Powdery Mildew?
Powdery mildew thrives in conditions opposite those where you would find ordinary mildew. Instead of liking wet and damp conditions, powdery mildew actually prefers warm and dry environments. When it shows up, it’s often first thought to be dust or dirt and can be swept away with your finger – then it returns. It appears as light white or gray spots on the tops and bottoms of the leaves, stems, new growth, flowers and even fruit or vegetables.
What Causes Powdery Mildew on Plants?
Powdery mildew forms when plant foliage is dry, lighting is low, temperatures are moderate and there is high humidity. Ideal conditions for powdery mildew growth is often during the late spring or early summer when evenings are still cool and somewhat humid, but the days are beginning to get warm.
Is Powdery Mildew Dangerous?
In many cases, powdery mildew is not fatal to the plant; instead, it’s more of an aesthetic issue. However, if left untreated, powdery mildew can leech nutrients from the plant, eventually causing leaves to wither and yellow. This can make blooms unsightly and leave vegetables and fruits particularly vulnerable to sunburn. Powdery mildew can eventually reduce the plant’s producing capacity and affect the flavors of fruits and vegetables.
Which Plants and Vegetables Are Most Susceptible?
There is a variety of powdery mildew species and they can affect different types of plants. While no plant is 100% immune, here are some plants that tend to be particularly susceptible.
Here are some fruits and vegetables where you would be most likely to find powdery mildew.
Note that this is not an all-inclusive list, so always keep a vigilant eye on your plants for signs of powdery mildew development.
Can Powdery Mildew Spread to Other Plants?
Powdery mildew spores are spread by the wind and can survive the winter in debris piles or on plants. The good news is that just because you find it on one plant, it doesn’t mean all others nearby will be contaminated. If you catch powdery mildew on zucchinis, roses or other plants, employ preventative measures, like the ones listed below, to ensure your other plants are not in conditions favorable to its development.
How Can I Prevent Powdery Mildew?
One way to prevent powdery mildew is to plant mildew-resistant plant varieties. If that isn’t an option, though, here are some other steps to take:
- Ensure there is enough spacing between your plants to provide enough airflow around all parts of the plant.
- Don’t over fertilize your plants. New growth tends to be very susceptible to powdery mildew development.
- Put plants where they will get enough light and avoid overly shady locations.
- Make sure the soil can drain properly. Inadequate drainage can make soil a breeding ground for disease-causing organisms.
- Use compost to boost the nutrient levels in the soil, which will in turn increase beneficial microorganism populations.
- Keep plants properly maintained by removing any dead or diseased foliage and stems.
- Use preventative treatment options, like a sulfur fungicide, before powdery mildew even forms.
How to Treat Powdery Mildew
If your plants do develop powdery mildew despite your best efforts, don’t worry. There are many environmentally friendly options for eliminating the disease, including:
Baking Soda. Baking soda itself isn’t normally effective as a powdery mildew treatment, but when it’s combined with liquid soap and water, it can be a powerful weapon. It’s normally most beneficial if used as a preventative measure rather than a treatment. Combine one tablespoon baking soda and one-half teaspoon of liquid, non-detergent soap with one gallon of water, and spray the mixture liberally on the plants.
Mouthwash. The mouthwash you may use on a daily basis for killing the germs in your mouth can also be effective at killing powdery mildew spores. Since its function is to kill germs, the powdery mildew spores can’t withstand it. Using three parts water to one part mouthwash has been found to be a good ratio, but new growth can be damaged since mouthwash is potent, so use with caution.
Milk. Milk is making its way onto the scene as a viable means to control powdery mildew. Not all the science is known, but the compounds in milk may be able to act as an antiseptic and fungicide as well as potentially increase the plant’s overall immunity. It tends to be effective as a method of preventing powdery mildew on zucchini and other types of squash, as well as cucumbers. An effective mixture ratio is about one part milk to two or three parts water.
Organic Fungicide Treatments. If you don’t want a do-it-yourself solution, there is a variety of commercial treatment options that are just as environmentally friendly and approved for organic gardening. By going this route, you also know exactly what types of pests the treatment will kill and which types of plants it’s most helpful for.
Water. Since dry conditions coupled with high humidity are often the culprits behind powdery mildew growth, watering your plants overhead and getting the entire plant wet can help. However, it’s important to use this method somewhat sparingly as overwatering can cause other issues for your plants.
Why Choose Safer® Brand?
Sometimes with a do-it-yourself option, it can be difficult to ensure the ratios of ingredients are correct, and if they aren’t just so, the treatment may not work how you were anticipating. You may also need to use caution on which parts of the plants you apply homemade remedies. When trusting your plant’s health to the experts at Safer® Brand, you know for sure what you’re getting in each bottle and that it’s safe and effective for all parts of the plant.
Safer® Brand’s powdery mildew treatments are OMRI certified, which means it’s approved for use in organic gardening. It works by utilizing the power of sulfur compounds, which ultimately alter the plant’s pH. It’s not harmful to the plant, but powdery mildew and other fungi cannot survive.
Another benefit of using a fungicide that’s formulated for organic gardening like those Safer® Brand offers is that it doesn’t harm the soil. Millions of tiny microbes reside in the soil, providing your plant with nutrients and protecting it from pathogens. Using organic disease-control methods can help keep beneficial microorganism populations where they should be and your soil and plants healthy.
So, whether it’s powdery mildew on squash or powdery mildew on roses, Safer® Brand’s line of organic gardening treatments can help your plants, and the environment, stay disease-free and beautiful.
When a plant or part of the plant (leaf, flower, fruit) rapidly collapses and dies this is called blight. Many bacteria, fungi, and viruses can cause blights. Most blights are favored by certain weather conditions, such as hot and humid or cool and moist
White mold is caused by the fungus Sclerotinia sclerotiorum. White mold is common when spring and fall are unusually cool and wet. Under these conditions, plentiful spores are produced and can be carried by air currents to ornamentals. Moist weather is required for stem infection. A small spot appears on the stem, but usually, the disease is not noticed until the plant wilts. At this time a fluffy white mold is produced on blighted stems, and often black, hard sclerotia are found inside stems and on stem surfaces. These sclerotia somewhat resemble black sunflower seeds; they have a thin black outer layer, and inside they are solid and white.
White mold can attack a wide variety of plants but is most serious on composites (aster, sunflower, chrysanthemum, daisy, etc), legumes and crucifers (such as Iberis). The white mold fungus is commonly found on legume forages (alfalfa, clover, vetch, etc.), and is often more of a problem in rural areas located near pastures and forage fields.
Sclerotinia on candytuft
White mold on candytuft
One management option for white mold is to space plants so that they dry after irrigation and rains; closely planted crops maintain a moist environment at the soil line that favors infection. During the growing season, it is very important to remove infected, wilting plants so that the fungal sclerotia are not dropped into the garden to serve as a source of more infections. Fungicide applications can effectively reduce losses, but should be combined with sanitation and plant spacing for best results. Consult your local extension office for the fungicides currently registered for white mold on ornamentals.
The cornerstone for control of all blight diseases is sanitation both during the growing season and in the fall. Wilted and blighted plants and plant parts should be promptly removed from the production area. Do not compost material killed by southern blight or white mold because the sclerotia of these fungi may survive composting. In the fall, all plant debris should routinely be cut at ground level and removed. This material may be composted.
Need help with what to do in your garden?
Q What is powdery mildew?
A A group of related species of fungus causes powdery mildew on different plants. All plants can be affected, and it is particularly prevalent in late summer. A white, powdery covering to leaves, stems, flowers or fruit gives the disease its common name. Sometimes, though, the first symptoms you notice may be yellow or purple discolouration, falling leaves or general poor growth and distortion. Powdery mildew on one type of plant won’t generally spread to other unrelated plants.
Caption: Powdery mildew is common in late summer/autumn
Q How do I spot powdery mildew?
A The first, barely visible, signs are yellow spots or tiny blisters on the leaves or flowers. Beneath these, the infection develops and white patches start appearing on leaves, stems, flowers and fruit. This fine, powdery covering is actually the fungal mycelium throwing out countless spores. Later, whole leaves are engulfed and much foliage is lost. Leaves can be distorted or discoloured, and fruit may crack and split.
Q Which types of powdery mildew am I likely to see in my garden?
A Here are some of the commonest and most damaging species, with tips on identification and individual treatment.
Apple powdery mildew (Podosphaera leucotricha)
Young shoots turn powdery white, older leaves show distortion and white patches.
Aster powdery mildew (Erysiphe cichoracearum)
Upper leaf surfaces turn powdery white, followed by yellowing and foliage loss. It is difficult to treat; keep plants well-watered and choose resistant species such as Aster x frikartii.
Begonia powdery mildew (Microsphaera begoniae)
Ruins indoor plants, with spots appearing on infected leaves that turn brown and dry or yellow and soggy. Control can be difficult. Remove affected leaves, keep roots moist and improve air circulation.
Brassica powdery mildew (Erysiphe cruciferarum)
Causes a white covering on leaves and stems, especially of swedes, turnips and Brussels sprouts where the buttons are spoilt. Water in dry spells and clear up crop debris.
Cucumber powdery mildew (Erysiphe cichoracearum and Spaerotheca fuliginea)
Starts off as round white spots on the upper surface of the foliage, enlarging to cover the whole leaf, which withers and dies. It can also attack courgettes, squashes and pumpkins outdoors. Improve ventilation under glass, and clear up crop debris. Plant more resistant varieties.
Caption: Powdery mildew tends to affect courgette plants in late summer and early autumn
Gooseberry powdery mildew (Sphaerotheca mors-uvae)
Turns shoots white and fruit brown and felty.
Grape powdery mildew (Uncinula necator previously known as Oidium)
Starts on the underside of leaves, then covers foliage and attacks bunches of grapes both indoors and outside. For prevention, thin out growth in winter and ventilate grapes grown under glass.
Pea powdery mildew (Erysiphe pisi)
Affects late-sown peas, covering foliage and pods with moulds. Usually only occurs at the end of the season so has little effect on cropping. Keep plants well-watered.
Rhododendron powdery mildew (Erysiphe species)
Yellow blotches on upper surfaces with matching light-brown, felty ones below. Keep plants well-watered and mulched. Pick off severely affected leaves and avoid the most susceptible varieties. Rose powdery mildew (Sphaerotheca pannosa) White, powdery deposits on young stems, buds and leaves, followed by stunting and dieback with foliage loss.
Rose powdery mildew (Sphaerotheca pannosa)
The symptoms appear mainly on the younger shoots. The leaves become distorted and puckered, and buds fail to open. A greyish, powdery deposit appears on the leaves, stems or buds, and can turn the whole shoot a dirty white. Mildew can weaken roses, and ruin their appearance, but is unlikely to kill them. Water well in dry spells but avoid wetting the leaves. You could also spray with a suitable fungicide.
Strawberry powdery mildew (Sphaerotheca macularis)
Purple areas form on upper leaf surfaces with the tell-tale white covering beneath the leaves. Flowers and fruit can also be affected. Choose resistant varieties such as ‘Cambridge Late Pine’ and ‘Red Gauntlet’. Avoid ‘Aromel’ and ‘Elsanta’ which are very susceptible. Cut off and burn diseased foliage at the end of the season. It can also affect raspberries, blackberries and loganberries.
Tomato powdery mildew (Leveillula taurica)
Occurs mainly on greenhouse crops. It starts as pale, light-grey patches on the upper leaf surface. These are followed by the powdery stage with a yellow surrounding area.
Q How does powdery mildew spread?
A Mildew can be introduced with new plants; low levels of infection may show no symptoms but develop when conditions are favourable. However, the spores are also spread far and wide by the wind.
Q How can I prevent powdery mildew?
A Lush growth, dry roots, cool temperatures, damp air, poor air circulation and too much shade all encourage powdery mildew. Avoid giving susceptible plants too much nitrogen-rich fertiliser (either organic or inorganic) which encourages lush growth. Ensure plants, especially those in containers or growing close to walls, fences or trees, have adequate water. Shade the roots of climbers such as honeysuckle and clematis so their roots stay moist. Incorporating organic matter in autumn and using mulches in spring will help. Avoid overcrowding and reduce competition by keeping plants further apart, or thinning out crowded growth. Under glass, make sure there is a good flow of air at all times.
Caption: Mulching helps keep the soil moist and prevent powdery mildew
Q How do I treat plants affected by powdery mildew?
A First remove the worst-affected parts. If herbaceous plants such as pulmonaria develop mildew after flowering, shear off all the leaves and water well. A new flush of healthy leaves should develop. With woody plants, remove the worst affected leaves and shoots. Do this slowly and carefully, putting the diseased material straight into a container, to avoid shaking spores on to healthy shoots. With annuals you may have to destroy whole plants to prevent the disease spreading.
Secondly, improve the plant’s growing conditions to reduce the factors that encourage mildew (see above).
Thirdly, spray with a suitable fungicide. Scotts Fungus Clear can be used on ornamentals; Bayer Garden Systhane Fungus Fighter or Westland Plant Rescue Fungus Control on ornamentals and some fruit. On vegetables and fruit, use Vitax Organic 2in1 Concentrate or Vitax Organic 2 in 1 RTU.
Q What should I do with plant debris infected by powdery mildew?
A The resting spores of some types of powdery mildew overwinter in plant debris, so clear infected plants away. With strawberries, for example, shear or burn off the foliage in late summer. Other spores overwinter in infected buds of perennial plants. Cutting out sick-looking material at the end of the summer and in autumn may help reduce the level of infection the following year. After getting rid of infected material in the greenhouse, clean up thoroughly using a disinfectant.
By Maurice Koome
Downy mildew is a fungal disease that causes destruction of leaves, stems, and flowers of the infected plant. Downy mildew causal organism is called Peronosporasparsa and as the scientific name indicates, the production of spores is sparse and therefore this disease is difficult to diagnose and control.
Downy mildew (Oomycete fungi) are referred to as a high risk pathogens because of the following factors;
- Oomycetes fungi are able to spread in an explosive manner under favorable conditions.
- Short development cycle (8-10 days under optimum conditions)
- High potential for reproduction (high quantities of spores)
- Wide propagation by water and wind
- Damage is not reversible: The damaged tissues die in general leading quickly to substantial losses at harvest
- High genetic variability: Rapid appearance of strains less sensitive to specifically acting fungicides possible.
Conditions for infection
The optimal conditions for the appearance of Downy Mildew are constant high humidity(RH 85-100%) low night temperatures and moisture on the leaves. The optimal temperatures for spore germination is between 10°C and 18°C no germination take place at temperatures below 5°C and the spores are killed at temperatures above 27°C.
The spores germinate within 4 hours in water, enter the leaves, and reproduce in three days. Spores survive on dried fallen leaves for as long as one month. Wet leaves and high humidity will trigger sporulation overnight. When the sun comes up, leaves start to dry, and spores are released. Most spores spread by wind and infect new leaves before noon. Six hours of constant leaf wetness is enough for spores of downy mildew fungi to germinate and infect leaves.
What factors favour these conditions ?
- Type of greenhouse
- Crop type and density
- Drip irrigation
- Nutrition status
- Human activity; prunning, scouting, spraying, harvesting etc
Downy Mildew symptoms.
- Leaves have reddishblack spots that are angular, tan spots with a very small amount of white crystalline sporulation on leaf undersides
- The leaves develop purplish red to dark brown irregular spots or blotches which might be mistaken for spray burns or possibly black spot.
- Advanced infections will have yellowing of leaves with brown necrotic areas and noticeable leaf abscission.
- Destroy rose debris from previous crops — spores can overwinter in leaves and canes, then the downy mildew can attack new plants.
- Try to water early in the day or whenever leaves will dry quickly, to ensure dry foliage at night
- Even though fans might move spores, you should use them along with venting to reduce humidity and leaf wetness
- Hungry plants are more susceptible to downy mildew. Maintain a balanced fertility program to protect your crops
- Space plants to allow rapid drying of leaves. If the leaves are very touching, the canopy closes in and the humidity increases.
- Use resistant varieties for low maintenance plantings
Choosing the most effective fungicides to prevent or eradicate rose downy mildew can be tough. Downy mildew requires a well-managed chemical spray program starting early with a rotation of chemicals for prevention. Fungicides for use against downy mildew can be categorized as either preventive, early or late curative products.
The disease also overwinters in the crop that was infected in the previous season. The fungus may overwinter in stems as dormant mycelia without oospores as shown alongside. This is the primary inoculum of the disease and upon reaching the favorable conditions, the disease infects new stems. This can be controlled through early drenching of Previcur Energy.
The preventive fungicides (mancozeb, propineb, copper compounds etc) must be applied before an infection period begins. New growth following application will not be protected.
Early curative products e.g Infinito,work against spore germination, sporangia elongation and penetration.
“Late curative products” e.g Verita, deal with intracellular infection level (by this time symptoms are visible to the eye)
- Early curative products that work against spore germination, sporangia elongation and penetration as illustrated below,
- Late curative products” that deal with intra- cellular infection level (by this time symptoms are visible to the eye) These late curative products deal with stages like Cyst germination, mycelium growth as illustrated below in the circle.
Closeup of downy mildew on rose
Early symptoms are usually noticed as light green or yellow angular patches on the upper leaf surfaces. Under high humidity, downy mildews form fluffy or fuzzy (downy) areas of spores only on the lower leaf surfaces. If viewed through a hand lens, these downy areas look like very small bunches of branched hairs. Older leaves near the bottom of the plant are usually infected first and wither and turn brown as the disease proceeds up the stem. Some species can be seed borne and others may cause systemic infections. Some weed species serve as reservoirs of inoculum.
Under high humidity, downy mildews form fluffy
or fuzzy (downy) areas of spores only on the lower
Most foliar diseases can be lessened with proper watering and humidity regulation. Water plants as early in the day as practical to allow foliage to dry before nightfall. Alleviate poor air circulation or crowded conditions with proper plant spacing. Inspect new growth and older foliage regularly for signs of infection to catch infections early. Sometimes simply removing the infected spotted leaves or plants will solve the problem. Selection of resistant varieties will also help to eliminate the application of costly controls.
Impatiens downy mildew a strain of the disease specific to impatiens has been a concern in Maryland since 2012.
Reasons For Rose Leaves Turning Yellow
Yellow leaves on a rose bush can be a frustrating sight. When rose leaves turn yellow, it can ruin the overall effect of the rose bush. Rose leaves turning yellow and falling off can be caused by several things. Below are a few reasons why rose leaves turn yellow.
Causes of Yellow Leaves on Rose Bush
If you notice yellow leaves on a rose bush, you’ll need to determine the likely cause before treatment can take place. Here are some causes of yellow rose leaves:
Light – Rose leaves turn yellow and fall off at the bottom of the rose bushes at times when the upper leaves are shading them. The lower rose leaves are not getting the sunlight they need to, so the rose leaves turn yellow and drop off. When foliage is not getting the sunlight necessary for good growth, the bush simply allows the lower leaves to turn yellow and eventually drop. This is usually an age cycle thing and not harmful to the rose bush.
Heat stress – Another reason for rose leaves turning yellow is the rose bush is under some sort of stress. A common cause of stress is heat stress. The rose bush turns yellow and drops its foliage in an effort to cool down in the case of heat stress. Sometimes with other stressors the rose bush will start dropping foliage until the stress is relieved, whatever stress that may be.
Yellow leaves on rose bushes may also be caused by radiant heat. The ground or area below the rose bush is retaining too much heat, which then radiates up into the lower portions of the rose bush. This radiant heat causes heat stress and the lower foliage will turn yellow and fall off as the rose bush tries to protect itself and de-stress. Dark colored mulch or some rock mulches can hold too much heat in and reflect it back at the rose bushes. If there is a dark mulch or just the bare ground below your rose bushes, try using some shredded cedar mulch or some other light colored mulch all around the base of the rose bush, 24 inches (61 cm.) in diameter for younger rose bushes.
Water – Another source of reflected heat that can cause yellow rose leaves is water. If rose bushes are watered and the water is left to sit at the base of the rose bush, such that the sun’s rays are reflected off the water and up onto the lower foliage, the lower leaves will be somewhat burned. Thus, the rose foliage will turn yellow and fall off. To avoid this, keep your roses well watered but not soaking wet, and keep an eye on the soil moisture. If you do not have a moisture meter, just stick your finger into the dirt as far as you can. If it feels moist, there is no need to water the roses just yet.
Fertilizer – Sometimes, the rose’s foliage can be burned by either too much granular fertilizer of foliar feeding (Miracle Gro) and it will burn the foliage such that it will turn yellow in places and fall off.
Nutrient deficiencies can be to blame too. Nitrogen, magnesium and iron deficiencies can cause yellowing of the leaves. If treated correctly, the leaves regain their nice green color and do not reach the falling off stage. Make sure to research symptoms to recognize what you may be dealing with. Treating the roses for the wrong deficiency will only lengthen the stress period.
Pests or disease – Roses with yellow leaves can also be a sign that the rose has a pest or disease problem, of which there are many that cause yellow leaves. To help determine which it may be, look carefully on the rose bush for other signs of damage or symptoms of disease.
Treating Yellow Rose Leaves
While treating yellowing rose leaves on your plant depends on whatever the specific factor is that’s causing it, there are a few things you can do to help prevent problems by encouraging healthy growth.
Keep your rose bushes well watered but not soaking, soggy wet. Use a moisture meter prior to watering to see if watering is really necessary, or if it can wait two or three more days.
Water your roses either early in the morning or in the evening once the temps have started cooling off. Rinse the bushes off with good clean water after a hot day. Plus, the rinsing of the foliage helps wash off contaminants of the day that can lead to foliage burn or other problems like insects.
Set up a feeding program for your rose bushes and stick to it. I like to alternate what fertilizer I give my roses, thus the program helps me remember which fertilizer gave the best performance. A well-fed and watered rose is far less likely to fall victim to many diseases.
Spend some time in your rose bed or garden checking their foliage (top and bottom of leaves) for any damage or insect presence. Early detection of a possible problem goes a very long way to its cure and to avoiding the frustration of dealing with rose plant leaves turning yellow.
What’s eating the leaves of my roses?
Roses have a reputation for being tricky to grow. Not only do they require specific growing conditions, pruning, and winter protection, but they are also plagued by a long list of insect and disease pests. Although some of the most serious disease problems can be avoided by planting resistant varieties, such as those in the Knock-Out or Easy Elegance series, insect pests aren’t so easily eluded. Keeping roses free of feeding damage involves close observation, careful monitoring, and a basic understanding of the most important and common insect pests.
Roseslug feeding. Whitney Cranshaw, Colorado State University, Bugwood.org
May and June is the time to watch out for a pest called roseslug. Roseslugs are a type of sawfly larva which feed gregariously on rose foliage, eating the tissue between veins and giving leaves a window-pane-like appearance. This transparent layer of tissue eventually turns brown. As the larva continue to develop, they are capable of chewing larger holes in leaves, eating everything but the mid-rib. Roseslugs themselves are smooth with yellowish-brown heads and translucent yellowish-green bodies. They are most often found on the undersides of foliage, which is where you should look when scouting.
Since roseslugs can cause significant aesthetic damage and have the potential to reduce plant vigor if left unchecked, monitoring for them in the spring is essential. Small numbers of roseslugs can be hand-picked from leaves and either squished or drowned in a bucket of soapy water. Heavier infestations may warrant the application of a registered insecticide such as insecticidal soap or spinosad.
Japanese beetle damage. Whitney Cranshaw, Colorado State University, Bugwood.org
If damage to rose foliage doesn’t start until the end of June or beginning of July, adult Japanese beetles are probably the cause. Japanese beetles will feed on both rose flowers and foliage, consuming petals and skeletonizing leaves, making them appear lace-like. If it weren’t for their destructive behavior, Japanese beetles could easily be considered beautiful. They are easily recognized by their metallic green bodies and shiny, bronze wing covers.
In the home garden, one of the best control methods for Japanese beetles is handpicking. It is usually easier to handpick beetles in the morning and evening when the insects are less active. When handpicking, look to see if there are any white spots on the beetle’s backs. These are the eggs of a beneficial Tachinid fly whose larva will bore into the beetle and eventually kill it. Although there are a number of pesticides registered to control this pest, their effectiveness is often limited. Repeated spraying is often necessary, and many of the most effective options are highly toxic to bees and should not be applied to flowering plants.
Leaf cutter bee damage
When precise ovals or circles are cut from rose foliage, leafcutter bees may be active in the garden. Leaf cutter bees are native species that are largely beneficial, only causing minor damage to roses. They are solitary bees, which means they do not form colonies. Females make their nests in hollow twigs, rotting wood, or other existing holes like those in bee nest boxes. Once the female has excavated a tunnel that is several inches deep, she will begin cutting pieces of leaves to create individual nest cells for each of her eggs.
Leafcutter bees are important pollinators of many crop plants as well as native wildflowers, so no chemical controls should be used. Instead, appreciate that you’ve created the right habitat for a native pollinator to thrive.
Do you love learning about stuff like this?
Subscribe to NH Outside with Emma Erler
My roses have white spots on them. What’s wrong?
White spots on your roses could be two things – insects or fungus. To test whether it is a problem with insects or fungus, try and scrape it off with your finger. If it scrapes off it’s an insect. If not, it’s a fungus. If it’s an insect, it’s very likely scale. To get rid of it, scrub it off with warm soapy water and then apply lime sulphur (you can get lime sulphur from your local garden centre). Ideally you should apply lime sulphur in May/June when there are no leaves. If your rose has leaves, just be careful not to get the spray on them – otherwise it might burn them. An alternative to lime sulphur is conquor oil – this is not as harsh on leaves. If the white spots don’t scrape off, it’s a fungus. To fix this you will need a copper based fungicide (also available at your local garden centre or super market).
To prevent both insects and fungus getting at your roses, it’s a good idea to spray them around spring every year with a mix of copper and conquor oil. This will kill the insects and prevent the roses getting fungus as the weather warms up. Again, try to avoid getting it on the leaves.