Soybean Disease Calendar

Disease presence in a field can drastically reduce yield potential and can be extremely difficult to manage. It is crucial to scout early for diseases before the full bloom and full pod stages in order to maintain high yield potential. Be sure to note which field has been contaminated in order to avoid recurring diseases in future growing seasons. Foliar fungicides can also be used to protect against major foliar diseases. Full bloom (R2) to full pod (R4) are crucial periods to help maximize yield potential, so reducing plant stress during these stages is essential. Rotating to a non-host crop can help eliminate disease presence. Some diseases to be aware of include1:

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  • Charcoal Rot can infect soybeans at any growth stage, but the worst infection is typically seen during the reproductive phase. It is more common in light soils with low organic matter and causes rapid plant death. The distinguishing characteristic is black speckling on the lower stem from the fungal tissue.
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  • Sudden Death Syndrome infects soybeans during the late vegetative growth stages and usually occurs in the root system. It is often associated with highly productive soils, cool temperatures during flowering, and significant rainfall before and during flowering. Key characteristics of this disease are yellow blotches which form between the veins on the uppermost leaves eventually turning brown. The leaves may roll inward due to lack of water and eventually drop off.
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  • Frogeye Leaf Spot (also known as Cercospora leaf spot) can survive on residue and infected seeds. It thrives in warm and humid environments while rain and wind can disperse infected spores to other leaf tissues. When spotted, leaf lesions are eye-like with purplish-brown to red margins and gray to tan centers.
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  • Phytopthora Root Rot is most prevalent in low, poorly drained areas. However, it can also be spotted on high ground in areas of high moisture. The fungus survives in the soil or plant debris for extended periods and thrives in soil temperatures of 70 to 80 degrees. Key characteristics include a chocolate brown discoloration of the stem from the soil line up.
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  • White Mold (or Sclerotinia stem rot) is located two inches below the soil surface and will begin to germinate when soil temperatures are less than 65 degrees and moisture levels are high. Infection occurs when plant wounds contact neighboring infected plants. Key characteristics of this disease are water-soaked lesions at the stem nodes. They surround the stem, cutting off moisture and nutrients to the upper plant parts.
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It is never too early to begin scouting for diseases throughout the growing season. Infection can affect soybean seedlings, foliage, roots, stems, pods, and seeds, drastically reducing yield potential. For more information on soybean diseases, be sure to visit the Asgrow® website, click on ‘protect’ and then ‘reduce plant stress.’