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We are starting to receive reports of white mold in soybean. With the exception of later planted soybean, most of the soybean crop is at the R4 into R5 growth stage. As you scout the soybean crop, areas of wilted soybean plants may be indicative of white mold (Figure 1). Closer inspection of the wilted area will often lead to the “white mold” symptom that is diagnostic, which is the fluffy white mycelium (Figure 2). Seeing symptoms of white mold means that the plants were infected weeks earlier and the application of a foliar fungicide for control of white mold is not recommended. Also, as earlier stated, with most of the soybean crop past the R3 growth stage, foliar fungicides are not recommended even if scouting does not show evidence of white mold.

For further information about scouting for white mold, please consult:

White Mold of Soybean in Wisconsin

and

White Mold in Soybeans

Figure 1. Areas of soybean where plants are wilted. This is often indicative of white mold.

Figure 2. White mycelium on the soybean stem are a good diagnostic indicator of white mold.

Drs. Shawn Conley (University of Wisconsin) and Vince Davis (University of Illinois) are conducting a communication methods survey and are asking for your participation. The objective of this survey is to investigate the technology that soybean growers and agronomic consultants use to find and share soybean production and marketing information. This survey is being conducted through the mail via post cards and through an on-line survey program. The research is sponsored by the Illinois and Wisconsin Soybean Marketing Boards through the soybean checkoff. The survey should take less than 10 minutes of your time but will be extremely valuable to us. This survey is completely voluntary and the information you provide will remain anonymous. Please visit www.surveymonkey.com/s/soybeangrowercommunications to take part in this research to help us serve you better.

We sincerely thank you in advance for your participation. – Shawn P. Conley and Vince M. Davis

With the soybean crop moving closer (or in some cases at) flowering, now is an excellent time to review factors that may impact the risk of white mold in 2010 (caused by Sclerotinia sclerotiorum). The first two factors that should be considered have already occurred…knowledge of the field history of the disease and the level of resistance in the soybean variety that was planted. These can be used to provide a baseline assessment of risk. If you are unsure of the level of resistance in your soybean variety, I would recommend consulting with your seeds person to obtain that information. In addition, there are several abiotic and biotic factors that need to be considered to understand if there is an increased risk of white mold. If temperatures are in the moderate range (70’s are optimal), rainfall is normal to above normal, soil moisture is at or above field capacity, and there are extended periods of prolonged fog and leaf wetness at or just after flowering, these can increase the risk of white mold in the field. Also, agronomic practices that are used to promote high yield potential in soybean (in particular those practices that encourage early canopy closure) like early planting date, higher plant populations, and narrow row spacing can also increase of the risk of this disease.

Active scouting should commence as we move into flowering for presence of apothecia, which are tan, cup-shaped mushrooms (0.5-2mm in diameter) that can be found on the soil surface (Figure 1). Apothecia produce the spores of S. sclerotiorum that infect soybean plants. Previous research has shown that apothecia production is related to soil moisture and temperature, and the timing and density of the crop canopy closure.

Figure 1. Apothecia of Sclerotinia sclerotiorum. These small (0.5-2 mm in diameter), tan fruiting structures produce spores that can infect senescing soybean flowers. Parting the soybean canopy and inspecting the soil for apothecia is an important way to determine your risk of white mold.

Management options include foliar fungicides (like Topsin M, Domark, and Endura) or herbicides (Cobra). Several questions have been raised about the efficacy of these products and in 2009 results variable when comparing Marshfield, WI and DeKalb, IL. Also, several questions have been raised regarding the use of other herbicides that cause similar changes to the soybean canopy like Cobra. Keep in mind that white mold suppression is listed on the Cobra label, while this is not indicated in other herbicides in the same chemical class. If the decision to spray a fungicide/herbicide is made, make sure that proper application timing occurs – applications should be made at flowering to protect senescing flowers from infection. Also, make sure that there is excellent spray coverage, which means that canopy penetration is essential to protect the developing soybean flowers.

For further information about white mold, please check Soyhealth and also UWEX YouTube.

2009 was known to many in WI as the “Year of the Yellow Bean“. Growers are again experiencing yellow soybeans in 2010, but for a different reason (Image 1). We must first remember that in soybean, active N-fixtion does not begin until the V2-V3 (2 to 3 open trifoliates) growth stages. Even if you were to properly dig a soybean plant, identify and split a nodule, the red appearance does not necessarily mean that fixation has fully begun (Image 2).

In 2009, dry soils were a contributing factor limiting nodulation and leading to early season low leaf N content. In 2010, our soils have been at or above field capacity for the last 10 days to 2 weeks (Figure 1). If soils are waterlogged depleted oxygen and increases carbon dioxide levels can lead to reduced root growth, shoot growth, nodulation, nitrogen fixation, photosynthesis, biomass accumulation, stomatal conductance, and plant death due to diseases and physiological stress (Oosterhuis et al., 1990; VanToai et al., 1994 and 2003). Given our growth stage and the fact that nodules are present I do not foresee any yield impact in the yellow soybeans. A few days of dry weather and warmer temperatures will quickly alleviate these symptoms.

Figure 1. Rainfall and soil water content at Arlington WI in 2010 (6/42010 to 6/16/2010)

Literature Cited:

Oosterhuis, D.M. H.D. Scott, R.E. Hampton and S.D. Wullschleger 1990. Physiological response of two soybean [Glycine max, (L.) Merr.] cultivars to short term flooding. Env. Exp. Bot. 30:85-92.

VanToai, T.T., J.E. Beuerlien, A.F. Schmithenner, and S.K. St. Martin, 1994. Genetic variability for flooding tolerance in soybeans. Crop Sci. 34:1112-1115.

VanToai, T.T., S. K. St. Martin, K. Chase, G. Boru, V. Schnipke, A. F. Schmitthenner,and K. G. Lark. (2001) Identification of a QTL associated with tolerance of soybean to soil water-logging. Crop Sci. 41,1247-1252.

VanToai, T. Y. Yang, P. Ling, G. Boru, M. Karica, V. Roberts, D. Hua, B. Bishop. (2003) Monitoring soybean tolerance to flooding stress by image processing technique. In T.T. VanToai, et al. (ed) Digital Imaging and Spectral Techniques: Applications to Precision Agriculture and Crop Physiology. ASA Special Publication No 66. The American Society of Agronomy. Madison, WI. Pp 43-51.

Please join us for the annual Pest Management Field Day on July 6 at the Arlington Agricultural Research Station. This will be an excellent opportunity to hear results from new and ongoing research projects and to network with researchers, extension staff as well as your own colleagues.

Speakers and topics are:

Joe Lauer, Agronomy, “A Wisconsin Transgene Walkabout”
Paul Esker, Plant Pathology, “Evaluations of Fungicide Treatments for White Mold in Soybean”
Dave Hogg, Entomology “Interactions Between Host Plant Resistance and Biological Control for Soybean aphid”
Camila Botero, Entomology, “Release of a Soybean Aphid Parasitoid”
Tim Trower, Agronomy, “Fall Dandelion Control”
Branden Furseth and Shawn Conley, Agronomy, “Evaluating 2010 Soybean Seed Treatment Decisions”
Marie Schmidt, Agronomy, “Germination Timing of Pasture Weeds”
Mark Renz, Agronomy, “Switchgrass Establishment: Year Two”

Field tours will depart from the Public Events Facility at 8:30 am and return by noon. In case of rain, “field tours” will be conducted inside. Lunch ($10) will be served after tours return.

The Public Events Facility is located on the Arlington Agricultural Research Station, N695 Hopkins Road. If traveling from the south, exit I 90/94 onto Hwy 51 North. Look for the Arlington Ag. Research Station sign north of Deforest. Turn left (west) onto Badger Lane. Travel 1 mile and turn left (south) onto Hopkins Rd. If traveling from the north, exit I 90/94 onto Hwy 60. Travel east through Arlington and turn south onto Hwy 51. For more detailed driving direction click on http://www.ars.wisc.edu/arlington/directions.html