Managing Frogeye Leaf Spot in a New Decade

frogeye leaf spot in soybeans — Frogeye leaf spot in soybeans

I talked with 160 private pesticide applicators at the trainings in Wilber and Saline Center this past week about integrated pest management in regards to frogeye leaf spot, a fungal disease in soybeans. In 2019, the University of Nebraska-Lincoln Extension confirmed this pathogen showed resistance to a common fungicide group 11 or QoI, formerly called strobilurins, in ten different counties in eastern Nebraska.

The fungal pathogen that causes this disease in soybeans is Cercospora sojina. The pathogen survives over the winter in soybean residue. During the growing season, wind and rain spread the fungal spores onto soybean plants where infection occurs. Ideal environmental conditions include temperatures near 80 degrees along with high humidity and extended leaf wetness. The disease then spreads from infected plant tissue. Infection can occur anytime during the growing season, but typically, during when soybeans are flowering in July. The disease can cause significant yield loss if left untreated under heavy pressure.

If you grow soybeans, you need to consider alternative control tactics to manage frogeye leaf spot. Foliar fungicides products applied in July and August need to include several modes of action, such as product with group 3, 7, and 11 modes of action. Examples of products include Revytek, Miravis Neo, Priaxor, and Trivapro. However, just switching fungicides is not integrated pest management. I encourage you to assess the genetic resistance rating to frogeye leaf spot in soybeans that you ordered or plan to order from your seed supplier. Most full season varieties, that is 3.0 relative maturity and above, general have company frogeye leaf spot (FLS) resistance ratings. Contact your seed suppliers to obtain frogeye leaf spot ratings.

I encourage you to take some time to determine the potential disease risk from frogeye leaf spot in each of your fields in 2020 and beyond. For example, if you have a field with a previous history of above average frogeye leaf spot pressure, less yield response to foliar fungicides in the last growing season, and in a corn-soybean or continuous soybean rotation, it is a high-risk field for frogeye leaf spot. Match up these higher risk fields with a variety with better resistance to frogeye leaf spot along with in-season scouting, and well-time fungicide application using a product with multiple modes of action to help control the disease. Do not forget other disease ratings and performance when looking a product placement for each field.

Changing the crop rotation away from the normal corn-soybean rotation on certain fields would be an additional integrated management option. Extended rotations, such as corn-corn-soybean or corn-soybean-wheat, would provide more effective integrated pest management.

There are numerous online and hard copy resources available from Nebraska Extension for you to utilize in managing frogeye leaf spot in a new decade. Please visit my local agronomy website for Saline, Jefferson, and Gage counties at croptechcafe.org or call our office at 402-821-2151. Know your crop, know your tech, know your bottom line.