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Angie Peltier


Angie Peltier
Former Extension Educator, Commercial Agriculture



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Hill and Furrow

Current topics about crop production in Western Illinois, including field crops research at the NWIARDC in Monmouth.
Figure. Marty Johnson and Brian Mansfield plant corn at the NWIARDC on April 21, 2014.
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Forecasted cool, wet weather + closing canopies + flowering soybeans = white mold risk


Despite the timely soybean planting in the Western Illinois crop reporting district, torrential rains and cloudy days have since delayed crop progress throughout much of the region. As of June 29, only the earliest planted soybeans at the Northwestern Illinois Agricultural Research & Demonstration Center (NWIARDC) have open flowers (Table).

Table. Growth stage of soybeans planted at different dates in a 2015 planting date trial at the NWIARDC.

Planting Date

Growth Stage

(June 29)

April 15

R2

May 12

V7

May 22

V5

June 5

V2


According to the USDA-NASS, an estimated 10 percent of the western crop reporting district's soybeans have begun flowering as of June 28. Soybean crops that are nearing the beginning flowering, or R1, growth stage in the near-term may be at risk for white mold as this week's weather is forecast to be unseasonably cool and moist. Other white mold risk factors include: growing a susceptible soybean variety, in a field with a history of white mold and soybean canopies that are beginning to close.

White mold fungus. The fungus that causes white mold of soybean is called Sclerotinia sclerotiorum. This fungus spends its life in the soil as hard, black structures called sclerotia. Sclerotia, which resemble mouse droppings, help the fungus survive over harsh winters and dry soil conditions. Under cool, wet, humid, and low-light conditions (conditions which are more likely to occur under a full soybean canopy) sclerotia germinate to produce small, cup-shaped mushrooms called apothecia (Figures). Apothecia release sexual spores called ascospores that can infect soybean. Soybean plants are susceptible to infection during flowering as ascospores use dead and dying flowers as a food source and then infect the soybean stem at nodes (where leaves meet the stem).

White mold disease in soybean. Symptoms of white mold are typically scattered in patches throughout the field and include lesions that start at stem nodes. Lesions initially have a water-soaked appearance and become bleached and stringy with time (Figure). The name "white mold" came about because sometimes, under very wet, humid conditions, a white, fluffy mold can be seen growing out of the lesions. Severe infections can result in plant wilt and death and significant yield loss.

What does the research say about fungicides and white mold? Provided that fields dry enough to minimize the risk of a spray-rig both causing significant soil compaction and getting the spray rig stuck, there are several aspects to consider when making the decision about whether to apply a foliar fungicides to protect soybean flowers from S. sclerotiorum. To provide a good measure of protection, fungicides that target white mold, are applied a little bit earlier than is recommended for foliar diseases - beginning flowering rather than beginning podding. Additionally, spray equipment must be carefully calibrated in order for fungicides to penetrate into the canopy and reach flowers. The university trials researching different fungicide active ingredients and application timings have applied fungicides using either small back-pack mounted sprayers or ground-based spray rigs. To my knowledge no university research has compared efficacy and canopy penetration of ground-based versus airplane or helicopter applied aerial applications of fungicides for white mold management.

Dr. Carl Bradley, former University of Illinois Plant Pathology Extension Specialist, previously posted a Bulletin article in which he detailed the results of his trials researching foliar fungicides for white mold management in Illinois.

Additional resources:

Kiersten Wise. 2015. Fungicide Efficacy for Control of Soybean Foliar Diseases. Purdue Extension publication: BP-161-W.

Mike Staton and Martin Chilvers. 2015. Applying Fungicides for White Mold Management in Soybeans. Michigan State University.

Check out this NCSRP-sponsored online publication White Mold in Soybean. Anyone who is interested in a hard-copy of the NCSRP publication Management of White Mold in Soybean is urged to either stop in to the Warren County Extension Office and pick up a copy or contact me to receive one through the mail.



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