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Extension Specialists: Spray Fungicide on Corn

No guilt trip from Extension specialists on spraying fungicide on corn, but they do recommend scouting for disease presence.


Farmers who spray fungicide on corn “just as a precaution,” don’t have to worry this year about Extension specialists applying a guilt trip to them. Plant pathologists from several Corn Belt universities are suggesting fungicide applications on corn and others are recommending it. But farmers who apply a fungicide are doing it because there is more of a threat this year, than just doing it because it might boost the yield.

It has been a fun dance to watch for a number of years. Farmers have increasingly sprayed fungicides on corn because chemical dealers have suggested it might boost yields. There has never been proof of that, and somewhere between 40% and 60% of the time it will pay for the cost of the chemical and the application. However, there seems to be sufficient threats to corn this year that Extension specialists are suggesting a fungicide application is a good idea. So if you have already done it, you don’t have to go to bed with a guilty feeling (as if you really ever did!)

The issue this year is delayed planting and a wet spring, which favored the development of some foliar diseases in the corn canopy says Iowa State Plant Pathologist Alison Robertson. Looking at the state of Iowa where corn has some significant delays, she says it will be late July before most of it tassels and when diseases start during the early grain fill stage, there is an increased risk of reduced yield. But she says consider whether your field is at risk:

  • Hybrids vary in their tolerance to diseases and fields with a susceptible hybrid should be sprayed with a fungicide.
  • If scouting has found either gray leaf spot or northern corn leaf blight in the lower canopy, that is a signal for spraying. You might find either common or southern rust in the mid- to upper canopy and those are not as serious.
  • Certain environmental conditions will foster development of one disease over another.

So what do you use to control fungal issues? Since last year, researchers from across the U.S. have created a decision guide for farmers on what is available for use and what should be used. The recommendations are available from the Corn Disease Working Group, which produced a Fungicide Efficacy Table with recommendations that are applicable to most corn producing states.

Read more about spraying fungicides this summer at the


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