Fungicide Decisions Nearing for Corn and Soybean

July 14, 2008
ICM News

By Daren Mueller, Department of Plant Pathology

With both corn and soybean fields finally reaching the reproductive growth stages, decisions to apply foliar fungicides need to be made. On July 3, Alison Robertson wrote an article about foliar diseases on corn (see Robertson article) and XB Yang has weighed in on soybean (see Yang article), but I want to throw in my two cents-worth on this issue.

If you want to get some different angles on making this decision, there have been several excellent articles written from other states (click on the title to see the article).

• Foliar Fungicides for Corn and Soybean – Don’t Rush to Spray - University of Wisconsin

• Fungicide use in corn and soybean: to apply or not to apply? That is the question - University of Kentucky

• Some Fungicide Application Basics – how not to blow a great tool - Ohio State University

• Making Profitable Fungicide Applications in Corn - University of Illinois

• Should Hail-Damaged Corn be Treated With Foliar Fungicides? - University of Nebraska

Here are my two cents. If your mind is already made up to apply fungicides to corn or soybean, then try to follow two simple IPM approaches to select which fields get fungicides.  My first cent: Data from both university and industry sources continue to show that the greatest yield responses have come from fields with the most disease pressure.  So, target fields that are planted to a susceptible hybrid or cultivar and have disease present at the time of application.

For this year, foliar diseases of soybean have been more prevalent than years past. Brown spot and bacterial blight commonly have been reported and frogeye leaf spot and Cercospora leaf blight have been identified from scattered fields.  While fungicides will not affect bacterial blight, fungicides can manage brown spot, Cercospora leaf blight and frogeye leaf spot.

And now for cent number two. Selection of the fungicide product should be based the fungal diseases that are present.  While triazoles are a bit more effective against soybean rust (not currently a threat), strobilurins are more effective against frogeye leaf spot and Cercospora leaf blight (see article and Table 11.2).

Another important consideration, especially for this year, is yield potential.  Several of these above articles touch on this, but it doesn’t hurt to say it again.  Fungicides will not recover lost yield.  If you want to improve your chances of recouping your cost of fungicides, then target fields that have higher yield potential.

Daren Mueller is an extension specialist with responsibilities in the Corn and Soybean Initiative.


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Daren Mueller Associate Professor

Daren Mueller is an associate professor and extension plant pathologist at Iowa State University. He is also the coordinator of the Iowa State Integrated Pest Management (IPM) program. Daren received his bachelor's degree from the University of Wisconsin-Madison in 1996, and his master's degree a...