Sclerotinia sclerotiorum
Class: Fungi
Common Name
White mold and cottony rot
Scientific name
Sclerotinia sclerotiorum
Potential Hosts
Eggplant, strawberry, peppers, tomatoes, basil, tarragon, mint, cabbage, cauliflower, pea, beans, lettuce, cucumber, squash, melon, pumpkin, zucchini, and watermelon
Who am I?
White mold is a common fungal disease that appears on several hundreds of host plants and has worldwide dispersion. White mold favors high moisture conditions and develops primarily during winter time.
White mold infection generally starts with the germination of large black sclerotia (survival bodies) found within the soil. Sclerotia forms apothecia (i.e., spore-bearing structures, tiny saucer-like structures, and cup-shaped mushroom structures).
Changes to the relative humidity, below the canopy, can trigger apothecia to release ascospores into the air. In turn, these spores land on different plant parts. With time, mycelium will grow and invade injured and healthy tissues. Germination on leaves can occur only in the presence of free water such as rain, sprinkler irrigation, and dew.
Dense, fuzzy, cottony-like, white mycelium will develop on infected tissues sometimes accompanied by the formation of sclerotia when humidity conditions permit.
White mold favors relatively low temperatures between 8 and 20°C and exhibits saprophytic potential. White mold can remain in the soil for 8-10 years.
Control measures
Cultural
The sooner the better: It’s easier and more cost effective to overcome infestation by controlling sclerotinia sclerotiorum in its initial stage. Make it a routine to monitor the field regularly and search plants for the presence of white mold on a weekly basis.
As with any moisture-favorable disease, various techniques taken during crop growth can reduce the chances of infection and spread:
Maintain adequate space: Avoid over density planting in order to allow light to penetrate and to promote the quick drying of leaves and fruits on humid days
Recurrence: Year-after-year outbreaks in the same field can point to heavily contaminated soil. This could justify crop rotations and preventive measures such as soil disinfection. Solar disinfection of the soil (solarization or pasteurization) can be implemented in sunny areas. This involves covering prepared and moistened soil with a polyethylene film 35–50 μm thick and keeping it in place for at least 1 month during a sunny period of the year. This will eradicate the presence of white mold on the top layers of soil. It is common for solar disinfection to be accompanied by fumigants such as metam-sodium.
Sanitation: Plant debris must be removed during cultivation, especially affected plants that produce sclerotia, but also at the end of cultivation to avoid fungi from surviving in the soil after burial
Preventive control measures can be considered, including:
Improve air circulation: Promote drying foliage and shorten the duration of wetting periods by introducing net curtain vented areas
Proper soil drainage: The presence of standing water will promote the spread of white mold
Drip irrigation is preferable to other methods of irrigation
Other moisture reduction techniques (during growth) include covering the ground with polyethylene sheets to reduce evaporation from the soil and help isolate vegetation from the soil
Conventional (chemical)
Cultural measures must accompany chemical control.
When conditions for white mold are expected (such as humidity), consider an application of fungicides. The number of applications needed will vary in accordance to the type of crop and the growth environment.
Don’t use products containing the same active ingredient in consecutive treatments. If choosing to use fungicides, make sure they belonging to different groups (with respect to mode of action) to prevent pathogens from developing resistance to a specific chemical.
The following are fungicides used in one or more parts of the world:
Pyrimethanil, cyprodinil+fludioxonil, benomyl, thiram, iprodione, procymidone, vinclozolin, and carbendazim
Organic
Products based on tea tree oil and potassium hydrogen carbonate+copper sulfate can be applied.
Biological
Bacillus subtilis
Caution and careful notice should be taken when using any plant protection products (insecticides, fungicides, and herbicides). It is the grower’s sole responsibility to keep track of the legal uses and permissions with respect to the laws in their country and destination markets. Always read the instructions written on labels, and in a case of contradiction, work in accordance to the product label. Keep in mind that information written on the label usually applies to local markets. Pest control products intended for organic farming are generally considered to be less effective in comparison to conventional products. When dealing with organic, biologic, and to some extent a small number of conventional chemical products, a complete eradication of a pest or disease will often require several iterations of a specific treatment or combination of treatments.