Pest Of The Month: White Mold

Pest Of The Month: White Mold

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Identification
Sclerotinia prefers cool, moist weather. High humidity and dewy conditions supports the spread and increases the severity of infections. 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. The Sclerotinia enable the fungus to survive from season to season and are the source of inoculum to infect crops.
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 also can enter the plant through leaves or pods that touch the soil where Sclerotinia or infected plant parts act as inoculum.

Survival And Spread

In tomato, potato, and pepper, infection typically starts at flowering. Water-soaked spots usually are 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 also can 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 Sclerotinia formed by the fungus often are found inside infected stems.
Almost all Sclerotinia diseases are field diseases, but when they occur in postharvest situations, they can be very damaging. In beans, the fungus might create a mass of diseased pods that is stuck together by fungal growth, resembling a nest (hence, the name “nesting”).

Management Methods

In beans, fungicides including Botran 75 W (dicloran, Gowan) Endura 70 WG (pyridinecarboxamide, BASF), Iprodione 4L (Arysta LifeScience) Quadris F (azoxystrobin, Syngenta), Rovral 4F (iprodione, Bayer CropScience) and Switch (cyprodinil, fludioxonil, Syngenta) applied at bloom stage have been effective in controlling white mold. Iprodione and Rovral 4F have been used with good results in lettuce. For potato, Iprodione 4L, Rovral 4F, and Topsin M WSB and 4.5 L (thiophanate, Cerexagri) are recommended for Sclerotinia control; while in tomato, Amistar 80DF (azoxystrobin, Syngenta) has produced good results. Biologicals like Serenade Max (Bacillus subtilis, AgraQuest) and Sonata (Bacillus pumilus, AgraQuest) also have provided various degrees of control alone and in combination with other fungicides.

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