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.

References:

Grau, C.R., Radke, V.L., and Gillespie, F.L. 1982. Resistance of soybean cultivars to Sclerotinia

sclerotiorum. Plant Dis. 66:506-508.

Planting date effect on winter wheat grain yield and winter survival

As we prepare for the 2009/10 winter wheat production year it is good time to reflect back on the problems that we encountered and devise practical solutions that we can integrate into our upcoming field season. The most widespread issue in our 2009 wheat crop was winter-kill. In our field assessments winter survival was impacted by four major factors, three of which growers have direct control over.

1. The most obvious factor during a drive-by assessment was location within a field. Areas that were sheltered from driving winds as well as areas that held snow such as fence lines or shaded/wooded areas provided protection for crown tissue and increased winter survival.
2. Planting depth: Variability across a field with no topographical effect was mainly driven by planting depth. Wheat that was planted at less than 0.5 inches demonstrated more winterkill than wheat planted at the 1 inch depth. Please see: (Recommendations for winter wheat establishment in 2009 for more information).
3. Genetics (winter-hardiness) played a huge role in 2009. Winter survival ratings ranged from 16 to 69% at our Chilton WI variety trial site and 22 to 73% at our Arlington WI variety trial site. For specific information regarding varietal winter survival ratings please see Wisconsin winter wheat performance tests - 2009.
4. Planting date: Results from our Lancaster and Arlington WI research sites show that yield and winter survival decreased as planting date was delayed (Table 1. and Image 1.). Given the delayed maturity of Wisconsin's field corn and soybean crop and the fact that delayed planting decreases winter survival growers should put greater weight in 2009 on selecting winter-hardy wheat varieties.
   

Table 1. Planting date effect on grain yield and winter survival at Lancaster and Arlington WI, 2009.
Lancaster, WI
Planting date	Grain yield	Winter survival (%)
17-Sep	74.9	88.5
30-Sep	68.3	70.0
13-Oct	54.2	58.0
Arlington, WI
Planting date	Grain yield	Winter survival (%)
18-Sep	101.9	83.8
1-Oct	93.3	55.3
17-Oct	73.9	30.0

Figure 1. Planting date impact on winter survival at Arlington, WI in 2009.