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Frogeye Leaf spot

Soybean problems showing up

By Anne Dorrance, Ohio State University Extension plant pathologist

We have multiple planting dates in Ohio this year with soybeans in all different growth stages. This can create challenges when management decisions are based on the stage of crop development.

For soybeans that are flowering, there was a confirmed report of frogeye leaf spot. If the soybeans in the field are in good health then managing this disease is often cost effective on susceptible varieties. Scouting between R2/R3, if frogeye is easy to find on the newly expanded leaves a fungicide application is warranted. There are many fungicides available with fair to very good efficacy. The one caveat is in Ohio we have identified strains of the fungus that causes frogeye leaf spot that is resistant to strobilurin fungicides, so choose a product that has another mode-of-action.

For soybeans that are in the early seedling stages that have continued to get these saturating rains, damping-off is occurring. So these fields will continue to decline until about V2, then the resistance in the plant will take over. So continue to monitor stands in these fields. If stem rot develops at the later stages, then that is from Phytophthora sojae. In these cases, a better variety is needed for the future that has higher levels of quantitative resistance.

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