Pest Of The Month: Sclerotinia Disease

Pest Of The Month: Sclerotinia Disease

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Identification

A good indicator of Sclerotinia disease is the presence of small, black sclerotia (resting structures) of the fungus. Sclerotinia can form on the surface of plant parts as well as inside the stems of pepper and tomato.

Another common indicator of Sclerotinia diseases is the presence of white, cottony-like mycelium of the fungus when weather conditions are cool and moist.

Symptoms vary between crops. White mold in beans usually appears after flowering. The disease often appears in leaf axils and advances into the stem, producing water-soaked spots that increase in size, girdling the stem, and killing it above the point of infection. The disease can also enter the plant through leaves or pods that touch the soil where sclerotia or infected plant parts act as inoculum.

In tomato, potato, and pepper, infection typically starts at flowering. Water-soaked spots are usually the first symptom, which is followed by invasion of the stem, girdling, and death of the upper part of the stem that turns a light gray. The disease can also begin where the plant contacts the soil or infected plant debris. Large portions of the field may become diseased, producing large, circular areas of dead plants. The black sclerotia formed by the fungus are often found inside infected stems.

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Almost all Sclerotinia diseases are field diseases, but when they occur in post-harvest situations, they can be very damaging. In beans, the fungus may create a mass of diseased pods that is stuck together by fungal growth, resembling a nest (hence, the name “nesting”).

Survival And Spread

Sclerotinia prefers cool, moist weather. High humidity and dewy conditions support the spread and increase the severity of infections. The sclerotia enable the fungus to survive from season to season and are the source of inoculum to infect crops.

Management

In beans, fungicides including Botran 75-W (dicloran, Gowan), Endura 70 WG (boscalid, BASF), Iprodione 4 L, Quadris F (azoxystrobin, Syngenta Crop Protection), Rovral 4 F (iprodione, Bayer CropScience), and Switch (cyprodinil + fludioxonil, Syngenta) applied at bloom stage have been effective in controlling white mold. For potato, Iprodione 4 L, Rovral 4 F, and Topsin M WSB and 4.5 L (thiophanate-methyl, Cerexagri-Nisso) are recommended. In tomato, Amistar 80 DF (azoxystrobin, Syngenta) has given good results. Topsin M WSB has a Section 18 for control of Sclerotinia on tomatoes and other fruiting vegetable in effect until April 2009. Biologicals like Serenade Max (Bacillus subtilis, AgraQuest) and Sonata (Bacillus pumilus, AgraQuest) have also provided various degrees of control alone or in combination.

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