When should fungicides be applied to corn?

By Dave Nanda, 
Director of Genetics and Technology 
for Seed Consultants, Inc.


Farmers have to make many decisions for raising profitable crops. You can make most decisions based on your own knowledge and experience. But for some decisions you need help of unbiased soil and crop agronomists, plant pathologists, and entomologists. Try to contact an Extension educator or a crops consultant who you can trust when you cannot make those decisions yourself. They might cost you a little initially, but if they are knowledgeable and worth their salt, they can save or make you a ton of money!

If deciding when to spray chemicals, it would be great if you had your own sprayer and could spray fungicides and insecticides yourself when you need. However, if you have to get it done by the custom applicators, they have limited time and equipment to cover all the acres contracted in their area. So, they might try to convince you to get it done according to their own schedule. This is especially true for aerial applicators that are dependent on the timing of the planes in their area.

In a recent scouting call for one of our customers, I was told that his custom applicator wants to apply the fungicide the next day otherwise his next chance may be in two weeks. I did see a few small lesions of Grey Leaf Spot on the lower leaves and a couple of lesions of Northern Leaf Blight on the upper leaves, but the corn was still shedding pollen. The applicator had brought a chemical company rep along and they assured the customer that they would guarantee him at least 5 bushels more corn per acre if he sprayed the fungicide next day. With the high temperatures and virtually no rains for the last three weeks, the diseases were not developing but the custom applicator was able to convince the farmer to do it right away or he may be too late. The farmer did a smart thing. He did leave an untreated strip so he can have a yield comparison

Bottom line:

• Get dependable unbiased advice from your crops or seed consultant. 

• Don’t get pressured by people selling the chemicals. 

• Apply fungicides if you see several disease lesions on leaves above the ears. 

• Spray after the silks start to turn brown. You want to protect the leaves during the grain-fill period.

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