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Start pondering fungicides now

Soybeans don’t go in the ground for three months. Then it’s another couple of months before you would spray fungicides. However, it’s not too early to weigh your options.

This month’s Crops Corner question asks for opinions about fungicides. The Indiana Certified Crop Advisers panel includes Greg Kneubuhler, G & K Concepts Inc., Harlan; Jeff Nagel, Ceres Solutions, Lafayette; and Darrell Shemwell, Posey County Co-op, Poseyville.

I’m thinking about spraying foliar fungicides over soybeans. What diseases am I really targeting? Should I spray all fields?

Key Points

• Know which diseases fungicides can control.

• Look at reputable plot data to compare possible returns vs. costs.

• Many plot trials conducted over time often show inconsistent results.

Kneubuhler: This is a million-dollar question every year. From our clients’ plots we’ve seen some overall positive benefits. In my opinion, you’re not targeting any one disease. Timing on fungicides comes before diseases are apparent. Typically, if diseases are prevalent, the benefit of the fungicide has already diminished.

Over time, treatment with fungicides offers a return on investment, with some years being better than others. A fungicide will not make 30-bushel soybeans into 50-bushel soybeans.

You apply fungicides in anticipation of the potential for disease. So if weather conditions are favorable for disease, payback will likely improve.

Nagel: Most foliar fungicides are labeled for activity on these diseases: Asian soybean rust, brown spot, cercospora blight, frogeye leafspot, and pod and stem blight. We’ve seen all of these diseases, except for rust. But severity varies based upon growing season, soybean variety and field history.

Brown spot can be found in just about every field. Most pathologists don’t feel it causes much yield loss, but we’ve occasionally observed fields with significant early-season defoliation on lower leaves. Frogeye is rather new to central and northern Indiana. We haven’t seen significant yield reduction.

Thresholds are generally vague for many foliar diseases. Work with a trusted CCA to monitor for foliar diseases. Treat as necessary. Replicated strip trials help evaluate potential returns for fungicide applications.

Shemwell: Some diseases controlled are powdery mildew, downy mildew, rust, cercospora leaf spot, frogeye leaf spot, anthracnose, brown spot, and pod and stem blight. In most years we see one or more of these here, but it may not be economically feasible to make a fungicide application. Over the past few years we’ve seen inconsistent results from fungicides that were sprayed. We’ve seen a range from negative yield results to yield increases up 15 bushels per acre. On average, the yield increase is about 2 bushels per acre.

Environmental factors should be considered. If you’re experiencing dry conditions, you’ll be less likely to have disease pressure compared to if it’s wet.


CLEAN BEANS: Jeff Phillips, Tippecanoe County Extension educator, finds cleaner beans at harvest whenever he sprays fungicides in plots. However, the difference doesn’t always show up as significant yield gains.

This article published in the February, 2010 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.