Continuing conducive conditons are ripe for soybean diseases

• By Lindsey Thiessen •

frogeye leaf spot
Severe frogeye leaf spot in soybeans — photo courtesy Mississippi State University

Early planting conditions for soybeans were cool and wet, which has lead to numerous reports of stand loss to damping off pathogens. Farmers who have not yet planted soybeans should also be mindful of the impacts of seedling diseases.

Current conditions are warm and extremely wet in most growing regions of the state. These conditions favor pathogens like Pythium spp., Phytophthora sojae, Rhizoctonia solani and Fusarium spp.

There are several options for reducing seedling disease, which may include the use of seed treatments. Choosing a chemical management strategy is reliant on good diagnosis to make sure that the seed treatment includes active ingredients that are effective on the prevalent pathogen populations.

More information on seedling disease management can be found in our fact sheet. For accurate diagnosis of seedling disease pathogens, contact your local Extension agent.

Disease considerations moving forward

This growing season continues to be challenging, with continued rainy conditions in most of the state. As our weather continues to become warmer with these excessively wet conditions, we may be faced with several foliar diseases that could be yield limiting.

Cercospora leaf blight, frogeye leaf spot and target spot may be potentially yield-limiting if plants are affected between R3 and R5. Fungicides may be needed for susceptible varieties during that period of time.

A further potential concern is soybean rust in late-planted soybeans should weather patterns favor its movement and development. Currently, the closest report of soybean rust is in Hampton County, South Carolina.

To monitor soybean rust reports, visit the Soybean ipmPIPE website. When a report of soybean rust is within 100 miles of North Carolina soybean production, announcements will be made to the portal and through other communication outlets.

Scouting for foliar diseases, especially during R3 and R5 growth stages, may be particularly important this year to make foliar disease management decisions.

Root rot diseases, like those caused by Fusarium oxysporum, Fusarium virguliforme and Phytophthora sojae, may be more severe given extended periods of saturated conditions. Scouting regularly, especially areas with low lying areas and areas with high yield potential, is important.

Fungicides may be a necessary part of a disease management program this year due to weather conditions. Fungicide efficacy is reevaluated each year across the state, and a joint fungicide efficacy table has been generated through the Crop Protection Network. Again, regular scouting will help to determine fungicide needs.

Dr. Linsey Thiessen is a North Carolina State University Extension plant pathologist. She may be reached at ldthiess@ncsu.edu

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