| Sept. 2009 - Sclerotinia White Mould in Soybeans |
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Sclerotinia White Mould in Soybeans By: Don McLean CCA-On Agronomist FS PARTNERS With the wet season that we have experienced this year there has been a lot of calls about Sclerotinia white mould in soybeans. Sclerotinia white mould is a disease that attacks many broadleaf crops that we grow. They include canola, soybeans, edible beans and many horticultural crops. “Sclerotinia White mould infects soybeans during periods of high moisture when release of spores from apothecia coincides with the presence of fallen soybean blooms. Early development of lesions is often noted at leaf axils. (Apothecia are small mushroom-like structures that originate from hard, black sclerotia in the soil and forcibly release spores to start new infections. Sclerotia are hard dark-coloured masses of mycelia that developed in stems of infected plants during earlier infections.) Once growth of the white mycelia occurs outside the stem, disease diagnosis is much more certain. High plant populations or plant crowding is favorable for Sclerotinia white mould. After infection has occurred the mycelia will begin to appear outside the soybean stem. Spread of the disease will occur when infected plant parts touch uninfected plant parts and mycelia grow from infected to uninfected tissue.” (Production Solutions August, 2009)
Management of Sclerotinia white mould In some crops like edible beans and canola, fungicides are very effective at controlling the disease. Soybeans are more challenging because of their extended flowering period and repeated applications of fungicide would have to occur. Once infection is present fungicides are not very effective at controlling the disease. The best solutions of controlling Sclerotinia white mould is through cultural practices in infected fields. They include: 1/ Plant populations – thick plant stands create an environment conducive to white mould because of reduced air movement and a wetter canopy. 2/ 15” rows or wider will allow more air movement, thus drying the canopy allowing less moisture in the crop and less favorable environment for the disease to establish. 3/ Crop rotation is critical in managing white mould. Rotating to crops that are not affected by Sclerotinia white mould like corn and wheat will help reduce the level of sclerotia in the soil. The sclerotia can survive for a very long time in the soils, the longer the rotation interval between susceptible crops the better. Corn, soybean, and wheat rotation is better than corn and soybean rotation. 4/ Select varieties that have a high level of tolerance to Sclerotinia white mould. 5/ Fertility Management- excessive rates of manure and or nitrogen should be avoided as this may produce excessive vegetative growth leading to thicker plant stands and wetter canopy and a higher risk of Sclerotinia white mould. 6/ Remember that Sclerotinia white mould’s sclerotia can be spread to uninfected fields by combines. Fields with Sclerotinia white mould should be combined after uninfected fields. |
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