Pennsylvania Soybeans: Start Scouting Fields for Disease Symptoms

Those soybeans that made it through the tough seedling stages this year can consider themselves lucky. The next thing we need to concern ourselves with is foliar disease.

As you are evaluating your soybean stands, it would be worth your time to check on your plant health as well. This early in the season, our beans are usually pretty clean. The first foliar disease we normally spot is downy mildew. We don’t typically see this disease in levels that would require fungicide application.

Our next common foliar disease is brown spot. I wouldn’t expect to see much right now on our plants, but it will inevitably arrive for us. Fungicides are typically recommended only if it becomes severe early in the season.

Finally, a disease to track closely this year is frogeye leaf spot. Last year we saw more frequent and higher levels of infection for this disease across the state. This year, we haven’t spotted it yet, but the earlier it shows up, the more damage it can do. If you see something that looks like frogeye on young beans, don’t panic. There are a few things that to the unaided eye are indistinguishable from frogeye. I have seen some phyllosticta leaf spot in some plots here at SEAREC (Fig 1).


Fig. 1 Phyllosticta leaf spot

This, or sometimes herbicide damage, may mimic the symptoms of frogeye. This happens every once in a while. The good news is, phyllosticta is very unlikely to cause any long term problems. The plants just tend to grow out of it.

As you move through the season, you may make the decision to apply a fungicide on soybeans. If that becomes the case, you can refer to this fungicide efficacy chart to choose an appropriate chemistry. This chart is a result of hundreds of university trials from across the country, and is updated each year.If a fungicide is not listed here, it probably means it is just too early to have results from many independent field studies yet.

There is a new reference book for soybean diagnosis available that you may want to check out. “A Farmer’s Guide to Soybean Diseases” is an affordable and easy-to-use alternative to the “Compendium of Soybean Diseases and Pests” that you may be familiar with. This new guide is geared toward the grower and consultant rather than the scientist. It, along with its counterpart for corn, is currently on sale at APS Press.

Finally, have you heard about the Crop Protection Network, yet? Extension specialists and USDA have joined forces, supported by the industry to compile the best resources for crop disease management in one place. The site is still building, but there are already some excellent soybean publications with great pictures and information for crop consultants and progressive growers available.

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