Wednesday, September 9, 2009

Yield Loss and White Mold

We have been receiving multiple questions about the potential yield loss in soybean fields where white mold has been observed in 2009. As soybean moves into the R6 and R7 growth stages, this is an excellent time to assess your fields for plant mortality. Measures to consider include incidence, or the percentage of plants showing symptoms of white mold divivided the total number of plants assessed (multiplied by 100 to obtain the percentage). Also, the severity of white mold can be assessed by examining individual plants and rating each plant using a 0-3 scale (Grau et al. 1982), where:

0 = no symptoms
1 = lesions on lateral branches only
2 = lesions on main stem, no wilt, and normal pod development
3 = lesions on main stem resulting in plant death and poor pod fill

As you scout your fields, the more plants that are rated as a 3 would indicate a increased severity of white mold in the field.

What does this all mean in terms of potential yield loss? Previous studies across Wisconsin has indicated that for every 1% plant mortality, yield loss is 0.25-0.50 bushels per acre. So, for example, if there was 10% plant mortality, yield loss may be from 2.5 to 5 bushels per acre.

For further information, a new video available through UW-Extension YouTube discusses symptoms and risk factors associated with white mold.


Grau, C.R., Radke, V.L., and Gillespie, F.L. 1982. Resistance of soybean cultivars to Sclerotinia
sclerotiorum. Plant Dis. 66:506-508.