Fungicides on corn: Worth the investment? (Jon Urness)

Posted on August 4, 2014 in Forage Foundations
By Jon Urness, Vita Plus national forage specialist
The strategy of applying fungicides to growing corn has received a lot of attention in recent years and producers have been asking themselves, “Should we get on board with this or is it a waste of my crop input dollars?”

Like many new technologies, the answer seems very non-committal…maybe.

Let’s start by looking at what created this trend.  First, high corn grain prices fueled by global demand had producers wanting to maximize yields and the added cost of applying fungicide didn’t seem too high. Second, we saw a greater foliar disease threat in recent years because of reduced tillage and continuous corn production. In addition, we are seeing more new fungicidal products on the market. And finally, those products are well promoted by their manufacturers.

Stan McGraw, agronomist at Vita Plus Dodgeville, sheds some light on this question based on his experiences in southwest Wisconsin. He said he agrees that the corn price drove some of the interest in applying fungicides and that’s based on simple economics.  The general consensus had been that the breakeven benefit of applying fungicide was six additional bushels of corn.  According to McGraw, that worked well when corn was priced at $6 to $7 per bushel. The cost for applying fungicide ranges from $25 per acre to as high as $30, depending on application, so five to six extra bushels of corn easily paid for the application with strong corn grain prices.

But now, with corn at $3.60 (mid-July 2014), the breakeven is more like eight to nine bushels in McGraw’s estimation.

Producers seem to benefit most from fungicide applied to corn during years of ample or excessive moisture. McGraw estimated that you might see a difference three out of five years.  And quite possibly, with the moisture experienced early this summer in Wisconsin, this might be one of those years.

Still, it’s hard to predict.

Data from Michigan State University backs up McGraw’s estimate.  From a well-conducted set of 39 field trials from 2008 to 2010 in the Midwest Cornbelt, researchers saw a significant positive difference in yield only 46 percent of the time. Although, statistics can be tricky because the same study showed a positive yield response 80 percent of the time, but the data was not considered statistically significant. Producers need to be cautious when trial data numbers are thrown around.

McGraw also suggested that seed companies have done a good job of providing disease resistance data on their hybrids and many have a high degree of resistance to threats like anthracnose. Going over that information makes a lot of sense prior to making application decisions. However, Michigan State researchers suggest that, because of high corn prices, some producers have chosen hybrids based only on yield potential and sometimes ignored the disease resistance data.

University of Wisconsin agronomists, in their 2014 publication “Pest Management in Wisconsin Field Crops,” pointed out that, if any leaf diseases threaten during the period between tasseling and dent (approximately 35 days), then the economics could swing in favor of treating because this is such a critical time in the formation of kernels.  This obviously requires special application equipment, such as aerial sprayers. Their suggestion is to monitor fields closely as early detection is key.  Be especially cognizant of hybrids that don’t indicate resistance to diseases such as leaf blight, leaf spot, eyespot, gray leaf spot and rust.

For more information on specific fungicides and their uses, consult the following resources:

Category: Crop varieties
Forage Foundations