How will late-planted soybeans be impacted by fungal pathogens?

Fungal disease may be elevated this year due to excessive soil moisture in late planted soybeans, especially seedlings. Generally, improving field drainage and loosening compacted areas when possible helps the soybean fight soil fungal pathogens. Proper seed treatments along with genetic resistance can be effective at suppressing many fungal diseases.

When rotten soybean seed is found in the soil with no insect presence, chances are good that it’s caused by disease.  

Soybeans planted in cold, wet soil are most likely to be impacted by Fusarium or Pythium. If disease occurs in warm conditions, it is more likely Phytophthora and Rhizoctonia.

• Fusarium can cause damping off, stunting and root rot.

• Pythium and Phytophthora cause similar symptoms - rotten seeds, soft brown dying tissue, etc - and can only be distinguished from each other through lab testing.

• Rhizoctonia is often seen in late planted soybean fields and often displays as decay or lesions on the root or lower stem.

It is difficult to diagnose sudden death syndrome early, but cool, wet conditions in the early growing season, combined with high moisture levels at flowering, seem to amplify the risk.

The best preventative steps farmers can take are to select varieties with genetic resistance and to utilize seed treatments to lower risk. If fungal disease pressure is noted, capture this information to help make more informed seed choices in future crop years.

For most blights, beginning pod fill (R3) is an important time to consider fungicide.

Protecting the plant leaf area will maximize the pod fill period. If you know your varieties have low ratings for frogeye leaf spot or white mold, a fungicide application may be needed. Limited tillage or no-till practices may increase fungal disease presence, because pathogens can overwinter in residue. White mold may show up earlier in heavy canopies with high moisture.

Late season fungal disease concerns are unclear at this point, but we can expect that if higher moisture levels persist through the growing season, molds, pod blights, and stem and root rots may be prevalent.

Focusing on season-long scouting will help you catch infection early so timely treatment can be performed. Remember to always read and follow label instructions to achieve optimum control.

ALWAYS READ AND FOLLOW LABEL DIRECTIONS. It is a violation of federal and state/provincial law to use any crop chemical product other than in accordance with its label. The distribution, sale and use of an unregistered pesticide is a violation of federal and/or state law and is strictly prohibited. It is your responsibility to confirm prior to purchase and use that a product is labeled for your specific purposes, including, but not limited to, your target crop or pest or weed, and its compatibility with other products in a tank mix.

Sources: https://www.apsnet.org/edcenter/disandpath/oomycete/pdlessons/Pages/PhytophthoraSojae.asPx

https://crops.extension.iastate.edu/cropnews/2009/05/scouting-soybean-seedling-diseases

https://cropwatch.unl.edu/2019/root-disease-update

https://www.ilsoyadvisor.com/on-farm/ilsoyadvisor/can-you-get-hold-your-soybean-mold-threshold