By: Kevin Ong and Ashley Brake

Botrytis blight is a fungal disease found worldwide that infects a wide range of plants, creating devastating losses for ornamental plant and vegetable growers. On roses, the fungus botrytis cinerea causes the disease also known as gray mold. Botrytis thrives in cool, humid weather, especially during the spring and fall. In Texas summers, it rarely occurs on outdoor roses when conditions are hot and dry.

Symptoms

Symptoms of Botrytis blight include flower blight, bud rot, stem rot, and leaf blight. The fungus can invade and damage almost any plant part, but prefers tender tissues such as petals and buds. Weakened or injured tissues such as wounds and aging or dying plant tissue are also susceptible to infection. Initial symptoms on soft plant tissues (leaves or pet a ls) appear as water-soaked brown spots that develop into gray, fuzzy mold as the tissue ages and rot s (Figs. 1 and 2). Heavily infected flower petals may become matted and stick together (Fig. 3). Such blight ing of blossoms and buds is common in roses when favorable conditions persist. Stem lesions can develop and eventually girdle (encircle) the stem, causing wilting and dieback on the part of the plant above that point.

Cause

B. cinerea is most aggressive in high humidity and cool and cloudy (low light) conditions. Grape-like clusters produce many tiny spores that are dispersed primarily by air or water. These spores give a fuzzy, moldy appearance to infected plant tissue. This fungus can also produce sclerotia, which look like tiny black pellets. A sclerotium is a structure that allows the fungus to survive unfavorable conditions (such as over the winter). Botrytis can also survive as mycelia and spores on diseased plant parts or plant debris.

Management

Because Botrytis can produce many spores in a short time under favorable conditions, the best prevention is good sanitation.

  • Make sure the growing area is free from diseased plant materials.
  • Remove affected blooms, canes, or stems. Bag and destroy diseased plant parts to reduce inoculum. Do not place them in a compost or trash pile near roses.
  • Irrigate carefully to reduce excessive wetness and humidity on the plants.
  • Plant and space rose plants so they have good air circulation.
  • Avoid unnecessary wounding of the plants when pruning. These wounds create entry sites for the fungus to infect the plant.

Fungicides are available to manage this disease. Natural products such as potassium bicarbonate,when used as a preventive measure,can provide some protection when disease is not prevalent. Some biological fungicides, such as those containing Streptomyces lydicus (Actinovate) or Trichoderma harzianum (PlantShield) can also provide some protection when used preventively. Conventional chemicals labeled for use against Botrytis include chlorothalonil (OrthoMax Garden Disease Control), fludioxanil*(Medallion), and fenhexamid* (Decree). Fungicidal product labels should note the target pest and host plant. Read the label to select the proper product and for correct rate and application information.

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Botrytis Control On Roses

By Stan V. Griep
American Rose Society Consulting Master Rosarian – Rocky Mountain District

Botrytis blight fungus, also known as Botrytis cinere, can reduce a blooming rose bush to a mass of dry, brown, dead flowers. But botrytis blight in roses can be treated.

Symptoms of Botrytis on Roses

The botrytis blight fungus is sort of grayish brown and looks fuzzy or wooly. The botrytis blight fungus seems to attack mostly hybrid tea rose bushes, attacking the leaves and canes of the subject rose bush. It will prevent the blooms from opening and many times causes the bloom petals to turn brown and shrivel up.

Botrytis Control on Roses

Rose bushes under stress will be extremely vulnerable to this fungal disease. Make sure that you are caring for your roses properly, which means making sure your roses are getting enough water and nutrients.

Rainy and high humidity climatic conditions create just the right mix to bring on an attack of botrytis on roses. Warmer and drier weather takes away the humidity and moisture that this fungus loves to exist in, and under such conditions this disease will usually discontinue its attack. Good ventilation through and around the rose bush helps keep the humidity buildup within the bush down, thus eliminating a favorable environment for the botrytis disease to get started.

Spraying with a fungicide can give a bit of temporary relief from botrytis blight in roses; however, the botrytis blight fungus does become quickly resistant to most fungicidal sprays.

Make sure that if you have a rose with botrytis blight you are careful to discard any dead material from the plant in the fall. Do not compost the material, as botrytis fungus can spread the disease to other plants.

by Nanette Londeree, Master Rosarian

April showers bring May flowers, and along with it, the potential for Botrytis – the disease that can turn beautiful spring blooms into a brown, soggy mush. This ubiquitous disease is also know as Botrytis blight, bud rot, gray mold, wooly mold and when growing on grapes, the “noble rot” where it can either ruin a crop of grapes, or produce excellent dessert type wine. In our mild Mediterranean climate, we don’t see this disease too much during the dry summer months, but once the rains begin again in the fall, the wooly gray fungus returns with a vengeance.

The disease is caused by several strains of the fungus Botrytis cinerea and attack blooms and canes, but is rarely seen on rose leaves. It has a wide range of host plants in addition to roses and grapes – dahlias, gladiolus, tulips and marigolds are very susceptible to the disease.

During the growing season, the disease affects rose buds and petals – you may see spotted flower petals or the tips and edges of the petals turn soft and brown. The spots look like water spots on the petals, however, the spots are actually caused by the plants’ reaction to the invasion of the fungus at the spot where the petal has been damp. Other times, the flowers simply fail to open, or result in a shattered mess of brown petals. This can be followed by wooly gray fungal spores on decaying tissue. Twigs may die back and large, diffuse, target like splotches form on canes.

Botrytis is also seen on bareroot roses that are handled via mail order since the cool, moist conditions in the shipping container are just right for the fungus to grow. It is important to remove your bareroot roses from their shipping containers as soon as you can to reduce the potential for the disease. While it thrives in warm, humid conditions, it can overwinter even in cold climates. It can remain dormant on a plant until the weather conditions are right then spring to life.

Since it is such a prevalent fungus, prevention is the best approach – plant roses that are not susceptible to botrytis blight; reduce the humidity around plants by providing good air circulation, modifying irrigation and reducing ground cover; deadhead any infected flowers immediately and dispose of fallen leaves and petals; prune out infected canes, buds, and flowers and generally maintain good garden sanitation.

The disease can be controlled by spraying with fungicides like chlorothalonil (Daconil 2787, Fungi-gard), or mancozeb (Fore). This disease is notorious for rapidly developing resistant strains, so if you spray, it is important to alternate spray materials. Remember that fungicides are among the most toxic chemicals in the gardener’s pest control arsenal, so use caution when spraying and follow the directions on the product label.

Plant die back

There’s nothing more disconcerting than seeing plants that you’ve nurtured, suddenly collapse and start to die back – especially if it followed by complete death!

Description

Shoots, stems and leaves may die back for any number of reasons – including waterlogging at roots, drought conditions, frost damage, very hot weather, disease problems or general lack of plant nutrients such as potash or phosphates.

Wilting at the tip of the shoots gradually moves down the stem and to the rest of the plant.

Treatment and control

Obviously work out what conditions have caused the collapse and die back and do everything to remedy them. If done quickly, the plant may recover.

Cut back affected stems and growth below the dead area, but just above a bud or leaf joint. Don’t be tempted to do this quickly, in case the plant makes a recovery. For instance, frost damaged shoots may recovery and start re-growing as late as June or July.

Feed the plant in spring and summer with a balanced, liquid plant food to encourage strong new growth.

Phytophthora dieback

Phytophthora dieback devastation – Photo © Parks and Wildlife

What is Phytophthora dieback?

  • Phytophthora dieback is caused by the plant pathogen, Phytophthora cinnamomi, which kills susceptible plants, such as banksias, jarrah and grass trees, by attacking their root systems.
  • Dieback is a symptom of a Phytophthora infection, and affects more than 40 per cent of the native plant species and half of the endangered ones in the south-west of Western Australia.
  • The plants die because they cannot take up the water and nutrients they need.
  • It’s is not easy to detect as infected plants often appear to be dying from drought.
  • There is no known cure for the disease.
  • Phytophthora disease also affects many agricultural crops and garden plants.
  • The fungus is spread through the movement of soil and mud, especially by vehicles and footwear. It also moves in free water and via root-to root contact between plants.
  • Help prevent the spread of Phytophthora dieback.
  • It can devastate bushland by removing particular plants and changing the nature of the landscape, possibly driving rare species toward extinction. Changes in the composition of bushland also represent habitat change to animal communities with flow-on effects to their survival potential.
  • There are several species of Phytophthora, but Phytophthora cinnamomi is the most widespread and destructive. It was probably introduced by early European settlers in the soil of plants they brought with them.

Spread of dieback in WA
Larger map

Its impact in Western Australia

More than 40 per cent of Western Australian native plants are susceptible to the disease, particularly those in state’s south-west.

The area of land infected in Western Australia by Phytophthora dieback is equivalent to 500 times the size of Rottnest Island or over one million hectares.

Twenty per cent of the state’s jarrah forest and up to 80% of the Stirling Range National Park infected.

Where it is

Phytophthora dieback has been found in many of south-west Western Australia’s national parks, nature reserves and metropolitan bushland:

  • along the coast (such as Two Peoples Bay Nature Reserve
  • in metropolitan Perth bushland areas (such as Lightning Swamp Bushland)
  • in National Parks (including Stirling Range, Bagingarra and Fitzgerald River National Parks.

How it affects the environment

Dieback can cause:

  • loss of biodiversity
  • extinctions of threatened plant and animal species that rely on susceptible plants for food and habitat, such as dibblers, western ground parrots and honey possums.
  • reduced variety of native plants
  • loss of key understorey species
  • disruption to woodland vegetation structure
  • the increased dominance of resistant plants such as grasses, rushes and sedges, or introduced weeds.

Dieback shoe cleaning station – Photo © Parks and Wildlife

Stopping dieback

Phytophthora cinnamomi lives in soil and in plant tissue, and can survive in plant roots during the dry summer months.

  • The warm moist soils of the state’s south-west provide ideal conditions for Phytophthora cinnamomi to produce millions of spores.
  • The disease is spread through infected soil and mud, especially by vehicles and footwear, as well as through water and root- to root contact between plants.

Managing the disease

There is no known cure for Phytophthora dieback.

The department is carrying out research into the fungicide phosphite, a biodegradable fungicide that protects plants against Phytophthora dieback. Phosphite works by boosting the plant’s own natural defences, allowing some susceptible plants to survive in Phytophthora dieback infected areas.

Prevention

Prevention is still they key. Limiting the spread of Phytophthora dieback is cheaper and far more effective than managing the impacts of the disease once introduced to a bushland.

Phytophthora dieback is most rapidly spread through human activity resulting in the movement of infected soil on vehicles, equipment and footwear.

Forestry and mining industries, as well as recreational bushland users (such as off-road vehicles, mountain bikes and bush walkers) need to take particular care not to spread the disease.

Management practices to prevent the spread of Phytophthora dieback into uninfected areas include strict hygiene measures such as:

  • cleaning stations to avoid transport of contaminated soil
  • cleaning footwear and washing down vehicles and equipment
  • use of dieback free construction materials
  • seasonal and permanent road and trail closures
  • information signs and education.

Vehicle at washdown station – Photo © Parks and Wildlife

What you can do

You can play a vital role in stopping the spread of Phytophthora dieback:

  • look out for information signs around dieback-affected areas and follow the instructions
  • do not move soil or plant material
  • use clean-down stations and boot cleaning stations
  • stay out of quarantined areas in bushland and forest
  • do not enter disease risk areas during, or for three days after, rain
  • follow local regulations when gathering firewood

Dieback free areas:

  • use clean-down stations to remove or sterilise mud and soil from footwear, equipment and vehicles before entry
  • avoid travel during and after rain, when the soil is damp
  • always stay on roads and tracks
  • apply for permits when required (such as when gathering firewood)
  • be prepared for and observe restrictions on access.

The department’s role

Phytophthora dieback research is a major component of the department’s work.

Our research includes:

  • detecting and identifying new Phytophthora species in Western Australia
    • monitoring the spread, and rate of spread, of Phytophthora pathogens
    • investigating the genetic makeup and survival capacity of Phytophthora species
  • investigating the susceptibility of Western Australian plants to Phytophthora cinnamomi and other Phytophthora species
    • researching the biology and epidemiology of Phytophthora species in native plant communities
  • investigating ways to reduce the spread of Phytophthora dieback.
    • investigating ways to optimise current control methods including phosphite treatment, and hygiene and quarantine protocols
    • researching the role of fire in managing species susceptible to Phytophthora
    • translocating plant species at risk. This involves deliberately transferring plants from one area to another to help conserve it.
  • seed banking rare and endangered flora that is susceptible to Phytophthora disease. Seed banking offers us an efficient and cost effective way of conserving genetic diversity for future conservation work
  • researching and understanding the long-term impacts of Phytophthora cinnamomi in Western Australian ecosystems.

The department has an active program to detect, diagnose and map the occurrence of dieback on lands managed by Parks and Wildlife. This includes interpreting and mapping areas for Phytophthora dieback prior to disturbance operations to manage or contain the spread of dieback. Visit the department’s Vegetation Health Service to identify and detect Phytophthora species.

Links and resources

Parks and Wildlife information

Links

  • Dieback Working Group
  • Centre for Phytophthora Science & Management (Murdoch University)
  • Project Dieback (NRM) Natural Resource Management WAa
  • Phytophthora cinnamomi disease (Department of the Environment)

Dieback

SERIES 16 | Episode 15

Jarrah trees grow only in the south west of Western Australia….they live for up to 500 years, but a major disease is killing these magnificent specimens, and tragically others as well. It’s called phytophthora, or dieback. It’s found all over the world, and to date there is no definitive cure.

There are approximately 60 known species of dieback, which can ultimately be more devastating than salinity to our forests and hinterland. Dieback is a soil fungus like organism that invades the roots of plants, starving them of water and nutrients.

Associate Professor Giles Hardy from the Centre for Phytophthora Science and Management at Murdoch University is a world leader in this field. He says: “Dieback spreads mainly in soil or on plant material and can be moved by vehicles, on people’s feet, bushwalking, by feral animals like pigs….essentially anything that moves soil.”

Dieback occurs throughout Southern Australia, Queensland and in areas with 600 millimetres of rainfall and above – like Wilsons Promontory in Victoria, the Brisbane Ranges in Tasmania, and Kangaroo Island.

Banksias are really susceptible to dieback and once infected, can die in about three weeks.

It’s possible to identify phytophthora in the home garden environment quite easily. There are indicator species which include most of the Proteaceae family, so the banksias, grevilleas, macadamias, avocados are all highly susceptible. They die very quickly and they show typical symptoms of water and nutrient starvation in a short time.

How is this different from water stress? Find a plant that’s beginning to die and remove the bark at the base of the tree. If the pathogen is present you will see a dark, dead area joining a healthy area. It’s in this dark area that the pathogen is active and it’s blocking the water and nutrient transport system in the plant, and they die.

The spores can survive for many years in the soil as resistant structures, resting spores, or in resistant plants.

There are many strategies to control this pathogen. One is through the use of a chemical called phosphite. Phosphite is an environmentally benign chemical so it’s safe to use. It’s applied as an injection into the trunks of larger trees, it can be sprayed from backpacks onto smaller plant species, and in the natural ecosystem can be sprayed from aircraft.

Buying plants from accredited nurseries that follow strict hygiene procedures is a good way to reduce the risk of introducing dieback into your garden.

The disease can be spread in nurseries by contaminated potting mix, and when pots are placed on the ground the organism can literally spread between pots. Pots should be kept off the ground and have good drainage.

Transplanting established plants from one garden to another can also spread the disease. Propagating from seed and cuttings is safer because there is no soil transported with stock.

Dieback is a serious disease and its full impact on natural ecosystems, agriculture and, of course, the gardening industry, is yet to be fully realised.

The Meaning Behind 8 Different Types Of Popular Funeral Flowers

When choosing flowers, the arrangement you pick should tell the same story as the relationship you had with the person. Was the deceased the love of your life? A close or distant family member? A dear friend? Here’s some tips to help you make the right floral decision.

Lilies

When someone says, “This place smells like a funeral home” chances are there is a lily nearby. This is often considered the go-to funeral flower and there’s significant meaning behind this strongly aromatic blossom. Lilies suggest that the soul of the deceased has returned to a peaceful state of innocence.
Guru Tip: Christians think this flower symbolizes purity, virginity, and the radiance of the soul. It’s believed that the Virgin Mary’s tomb was covered in this flower.

Peace Lily Plant

Similar to the flower, the peace lily plant symbolizes innocence and rebirth of the departed’s soul from the complex physical world to a greater place.

Guru Tip: This is what I usually send to people I know who are grieving. I love how this plant will last for a while in the person’s home of office.

Roses

Just like lilies, roses are a very common and appropriate funeral flower, and each color rose has a slightly different connotation. White roses are the ultimate symbol of spirituality, purity, and innocence. At a funeral, the classic deep red rose evokes love and grief. The yellow rose is often given by friends to show their bond. The rarer dark pink roses are used to express thankfulness to the deceased.

Guru Tip: Roses can be mixed in with other flowers or uses in a casket spray, standing spray, or wreath.

Orchid

No matter what color, orchids have a universal meaning: “I will always love you.” Take it away, Whitney…

Guru Tip: Orchid plants make particularly special gifts. Unlike orchids in an arrangement, these last longer in the home or office.

Chrysanthemums (“Mums”)

Unlike other flowers, the meaning behind chrysanthemums varies globally. In America and Europe, the meanings focus on sympathy and honor. The color plays a role in the meaning as well. Red symbolizes love, while white symbolizes innocence.

Guru Tip: In Asia, chrysanthemums symbolize rebirth and are more often given at baby showers than funerals.

Carnations

Carnations are often used in funeral wreaths and standing sprays. As with other flowers, each of the colors has its own meaning. The red shows affection and the white tends to symbolize innocence. For Catholic and many other Christian funerals, pink carnations might be a good choice since it’s believed they were created from the Virgin Mary’s tears.

Guru Tip: Talented florist use carnations to create beautiful arrangements replicating sports logos, favorite activities and other personalized tributes. For some very good examples, .

Hyacinth

These are mostly added into an arrangement of assorted flowers. There are a variety of thoughts behind the meaning, ranging from “you’re included in my prayers” to deep anguish.

Guru Tip: Some believe this flower symbolizes sports, games, and rashness so be careful not to insult!

Hydrangea

The meaning behind this flower is not as well-known as the others, but many believe it symbolizes true heartfelt emotions.

Guru Tip: As with the peace lily, the plant version of this flower will always last longer than the cut arrangement.

Identify And Fix Rose Canker Fungus

By Stan V. Griep

American Rose Society Consulting Master Rosarian – Rocky Mountain District

Rose canker is also known as Coniothyrium spp. This is the most common of the several kinds of rose canker fungi that can affect the canes of roses. When left unmanaged, not only can rose cankers eat away at the beauty of your rose bushes, but they can eventually kill your rose plant.

Identifying Rose Canker Fungus

Rose canker is what is known as pathogenic fungi, while it is not really all that complicated a fungus, it can still cause a lot of damage. Rose cankers will often show itself as black splotches on the canes of rose bushes.

Many times after a recent pruning rose stem cankers will show up, especially when the pruners have not been cleaned between the prunings of different rose bushes. Rose canker can spread from a rose bush where it was just pruned out to an uninfected rose bush by using the unclean pruners.

Canker is most active during cold times of the year when rose bushes are less active.

Preventing And Curing Rose Canker

Removal of the infected cane or canes to good clear cane tissue below the canker followed by the spraying of a good fungicide will help in getting rid of or reducing the canker problem. Remember to wipe off the pruners with the disinfectant wipes or dip them in the Clorox solution after each pruning of a diseased cane! Always wipe down your pruners with Clorox or Lysol disinfectant wipes or dip them into a mixture of Clorox and water before pruning each rose bush.

Promoting vigorous growth helps as well, as a healthy thriving rose bush fights off the canker attacks well.

Using a good preventative fungicidal spraying program goes a long way to not having to deal with the frustrations of a fungal infection and the elimination of it. A rotation of fungicidal sprays is recommended to help keep the different funguses from becoming resistant to the fungicides effects.

Stem canker of rose

Introduction:

Rose cankers appear any time of year but especially when the plants are under stress. Three canker diseases (brown canker, stem or common canker, and brand canker) are common in Illinois and are generally confused with weather injury or other problems. Cane infections may approach 100 percent (all canes infected) where control measures are not practiced. Identifying particular canker species is not important, but it is important to identify a problem as a canker.

Causal Agent:

Coniothyrium spp

Symptoms:

  • The first symptoms are small, roundish lesions in the canes the spots are pale yellow, reddish, or bluish purple.
  • They gradually enlarge, turn brown or grayish white (often with a darker margin), and may partially or completely girdle the cane.
  • Complete girdling results in dieback or poor growth of the plant parts above the affected areas.
  • Cankered areas are sprinkled with black, speck-sized, fungus-fruiting bodies.
  • When left unchecked, infections may spread downward into the crown, causing entire rose plants to wilt, wither, and die.
  • Infection occurs chiefly through a wide variety of wounds, including thorn abrasions. Infections may also occur on the leaves and flowers.

Disease cycle:

The fungi causing stem canker and die back usually survive the winter on diseased canes or plant debris. Spores of the causal fungi are usually spread by wind-blown rain or irrigation water. Rose canes are infected through wounds during periods of humid, wet weather. The disease may also be spread by fungus-contaminated pruning tools. Cankers often form on the stub of pruned canes, but they may also be seen around leaf or thorn scars, winter injury, or other damage on the canes. Stem canker and dieback are most damaging to weak, slow-growing roses.

Control:

  • Removal of the infected cane or canes to good clear cane tissue below the canker followed by the spraying of a good fungicide will help in getting rid of or reducing the canker problem.
  • Remember to wipe off the pruners with the disinfectant wipes or dip them in the Clorox solution after each pruning of a diseased cane.
  • Always wipe down your pruners with Clorox or Lysol disinfectant wipes or dip them into a mixture of Clorox and water before pruning each rose bush.
  • Promoting vigorous growth helps as well, as a healthy thriving rose bush fights off the canker attacks well. Using a good preventative fungicidal spraying program goes a long way to not having to deal with the frustrations of a fungal infection and the elimination of it.
  • A rotation of fungicidal sprays is recommended to help keep the different funguses from becoming resistant to the fungicides effects.
  • As stated above, keep canes from crossing each other. Even if they appear not to be touching, wind and growth can change that condition.
  • Pruning out dead or dying wood during your regular visits to the garden is also essential.
  • when planting new plants, use care not to damage canes. If you should damage a cane seriously, consider removing the cane entirely.
  • Likewise, when pruning or deadheading, cut back to the node. Failing to do so, results in dieback to the node, and the resulting dead wood is an invitation to canker spores.
  • As for fungicides, those that control black spot on ornamentals will also control canker.

Favorable conditions:

  • Wet weather
  • Humid conditions
  • Low plant to plant distance
  • Less air circulation

Also Study:

Black Spot of Rose | Symptoms | Survival and Dispersal Management

Prevent and manage rose cankers

Question: I have several pink Knock Out roses that I’ ve had for several years, and they have always been healthy and lovely. I make sure I care for them properly. Recently I noticed that all of them have cankers and discoloration (black and dark brown) up and down the stems. I have done research on this and ha ve been getting mixed messages. Some say it is a fungus that cannot be treated and will eventually kill the plant. Some say a soap insecticide will help. Others say something different. We have had harsh winters before, but I do not recall any as wet as we’ve had this year since I put the roses in. Is that what is causing this? What can I do — if anything?

Answer: Rose cankers are a problematic issue for rose growers, regardless of which types of roses you grow. Though Knock Out roses are far more disease resistant than many other types of roses, they are not immune to rose cankers.

There are four primary canker diseases of roses, including brown canker, common canker, cane blight canker and brand canker. All are caused by pathogenic fungi. Cankers can easily be confused with winter injury. The presence of new cankers during the growing season is a sign that winter injury is not to blame.

The first signs of a canker infection are small, round lesions on the canes. They can be reddish, yellow or near black. The lesions enlarge over time, turning brown with a dark outer edge. They may spread to cover the complete circumference of the stem. When this happens, the entire stem may die.

Infections typically start when the plant is injured through poor pruning, flower harvest, or another tissue-damaging action. It is also easily spread via infected pruning equipment.

If left untreated, a canker infection can spread down into the crown of the rose and cause complete plant death. Unfortunately, infections are more prevalent during wet season such as the one we had last year.

To prevent and manage rose cankers, you must clean your pruning shears with a 10% bleach solution or another disinfectant between each clip because the pathogen is easily spread on “dirty” tools. Prune the plant only when necessary and remove all infected branches and dispose of them in the garbage. Do not put them on the compost pile. When cutting off a branch with a canker, remove all of the stem down to about 2 inches below the lowest canker. Always prune in dry weather.

You can help protect your roses from cankers this coming season by applying an organic biofungicide based on Bacillus subtilis to all sides of all stems every 14 to 21 days throughout the growing season. One common brand name is Serenade. This organic fungicide is useful for preventing cankers, black spot, powdery mildew and other fungal diseases. Insecticides will do nothing to prevent or control rose stem cankers as they are not an insect-caused problem.

  • Horticulturist Jessica Walliser is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden,” “Good Bug, Bad Bug,” and her newest title, “Container Gardening Complete.” Her website is jessicawalliser.com. Send your gardening or landscaping questions to or The Good Earth, 622 Cabin Hill Drive, Greensburg, PA 15601.

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