Sclerotinia stem rot, commonly known as White mold is a common and destructive disease caused by the fungus Sclerotinia sclerotiorum.
The disease is favored by prolonged wet and cool weather. White, fluffy fungal growth forms on the surface of the infected tissues.
A key characteristic of this pathogen is its ability to produce black resting structures known as sclerotia and white fuzzy growths of mycelium on the plant it infects.
Sclerotiorum can also be known as cottony rot, watery soft rot, stem rot, drop, crown rot and blossom blight.
HOSTS
The host range of this pathogen includes many broadleaf crops and other plants, except corn and small grains.
These include cabbage, common bean, citrus, celery, coriander, melon, squash, soybean, tomato, lettuce, and cucumber, carrots, onions, peas, pumpkins, among others.
DISEASE CYCLE
The lifecycle of Sclerotinia sclerotiorum can be described as monocyclic, as there are no secondary inoculums produced.
Sclerotiorum survives in soil or stems in the form of hard black masses of mycelium called sclerotia, which can remain viable for five years or longer. When conditions are favourable, some sclerotia germinate while others remain dormant.
The sclerotia germinate near the soil surface to form small tan-to-gray mushroom-shaped structures called apothecia, which produce ascospores that spread via air currents to cause infections.
Seed lots can be contaminated with sclerotia, and seeds can be infected with the pathogen.
During harvest these survival structures (sclerotia) are scattered back onto the soil. Thus, inoculum for the next three or more seasons has been distributed.
SYMPTOMS
- sclerotiorum is capable of invading nearly all tissue types including stems, foliage, flowers, fruits, and roots.
The life cycle of the fungus occurs mostly in the soil and thus most host symptoms begin at the soil surface, though the fungus can also be transported by air.
While symptoms can and do differ among host species, there are a number of similarities. The more common symptoms are water-soaked lesions on fruits, stems, leaves, or petioles which usually have an irregular shape. These lesions enlarge and a cottony mycelium covers the affected area. The fungus spreads and the plant becomes a soft, slimy, water-soaked mass. This cottony mycelium usually produces numerous sclerotia, which are black seed-like reproductive structures, which is a reliable diagnostic sign of the fungus.
The host may also exhibit “dry” lesions on the stalk, stems, or branches, with an obvious definition between healthy and diseased tissues. The lesions enlarge and girdle the plant part causing its distal portions to become yellow, then brown, and eventually die. The girdled portion is often the base of the plant which causes the plant to die.
Sclerotia form within the stem pith cavities, fruit cavities, or between tissues.
DISEASE MANAGEMENT
Chemical method
To effectively control the disease, systemic fungicides should be used. These include the following;
- CHANCETYL ELITE 800WDG
- DOMAIN 250EC
- GEARLOCK TURBO 250WP
- MILLIONAIRE 690WDG
- PYRAMID 700WP
- TRINITY GOLD 452WP
- COLINIZER 440WP
- GREEN COP 500WP
Non-chemical approaches
- Where irrigation is used, reduce irrigation frequency during flowering.
- Use certified or disease free planting materials.
- Long-term rotation with non-host crops like corn or small grains may reduce white mold.
- Plant resistant/tolerant varieties whenever possible
- Avoid planting highly susceptible varieties in fields with a history of this disease.
- Plant varieties which are short and do not lodge to reduce disease potential.
- Ensure proper spacing (narrow rows result in more Sclerotinia stem rot).
- Since several weeds can be a host for this fungus, it is important to maintain good weed control.
Tips!
- Incorporate all foliar sprays with INTEGRA 3ml/20l; a sticker, spreader and penetrant which improves the fungicide’s efficacy.
- Ensure timely control of the disease.
- To prevent resistance build up by the fungus, alternate different chemical through the crop season.
- Maintain a proper crop nutrition.
