White Mold
Beginner
Scientific Name
Sclerotinia sclerotiorum
Identification
- Lesions may occur anywhere on the stem
- The stem becomes soft and bleached or light grey and large black fungal bodies (sclerotia) develop in or on the lesion
- As a section of the stem dies, areas of the plant above the affected area also wilt and die
- During cool, moist weather, a cottony growth appears on the affected areas
- Infected fruit rots completely
Often Confused With
Phytophthora blight
Verticillium wilt
Period of Activity
Plant surfaces must remain continuously wet for 48-72 hours for infection to occur. Disease develops most rapidly at 20- 25°C (68- 77°F), and not at all above 30°C (86°F).
Scouting Notes
Look for wilting plants or branches. Light-coloured sections of
stem are diagnostic of white mold. The diagnosis can be confirmed
if sclerotia
(large black fungal bodies resembling rat droppings) are found in or
on the affected area.
Thresholds
None established.
Advanced
Scientific Name
Sclerotinia sclerotiorum
White mold has an extensive host range, infecting more than 300 plant species. In peppers, this disease may be seen in very wet seasons, but is not usually a serious concern.
Identification
White mold symptoms normally first appear at a leaf scar or where a
fallen flower sticks to the plant.
Water-soaked lesions develop on the stem. The lesions enlarge rapidly, girdling the branches and stems, causing leaves to turn yellow and die. The stem lesions appear bleached or pale. White, cottony fungal growth develops on affected stems. Hard, black sclerotia (fungal structures) may be found in the fungal growth on or within the stem. These sclerotia can persist in the soil for many years. Parts of the plant above the infected area wilt and die.
Often Confused With
Phytophthora blight
Verticillium wilt
Biology
White mold overwinters as sclerotia.
Moist soil conditions cause the sclerotia
to germinate and release
spores which then infect the crop. These Sclerotinia
species are weak pathogens and do not usually infect healthy plant tissue.
They often invade through dead or injured tissue, or spent flower
blossoms.
Period of Activity
Plant surfaces must remain continuously wet for 48- 72 hours for infection to occur. Disease develops most rapidly at 20- 25°C (68- 77°F), and not at all above 30°C (86°F).
Scouting Notes
Look for wilting plants or branches. Light-coloured sections of
stem are diagnostic of white mold. The diagnosis can be confirmed
if sclerotia
(large black fungal bodies resembling rat droppings) are found in or
on the affected area.
Thresholds
None established.
Management Notes
- Practice a 3– 4 year crop rotation away from susceptible crops (cucurbits, edible beans, soybeans, carrots and lettuce).
- The inclusion of a cereal crop in the rotation will significantly reduce the amount of sclerotia in the soil.
- Dense canopies and poor air circulation that allow foliage to remain wet for extended periods encourage the development of white mold.
- Sclerotinia species can also cause a collar rot of transplants.