Interest in the use of foliar fungicides on corn throughout the U.S. has expanded dramatically in the past two years.

Prior to 2006, less than 300,000 acres of corn were treated with fungicide. Estimates for the 2007 growing season are that a whopping 14 million acres (=10-12%) of U.S. corn crop were treated!

In an ongoing effort to address questions about the role of foliar fungicides on corn, university-based corn pathologists and agricultural professionals throughout the Corn Belt expanded their research efforts to evaluate the most important fungicides in field trials. This article gives a brief summary of the “state of the art” with respect to corn fungicides.

University Trials

A total of 89 replicated trials were conducted in 2007 in Illinois, Indiana, Iowa, Kansas, Kentucky, Maryland, Minnesota, Missouri, Nebraska, North Dakota, Ohio, and Wisconsin, as well as in Ontario, Canada. Many of these were conducted on commercial farms. Almost all trials were sprayed by ground rig; all were sprayed between VT and R1 stages, the optimal time period for fungicide application. For economic calculations, fungicide treatment was assumed to cost $20/acre and the market price of corn used in the analysis was $3.50/bu, resulting in a “break-even” yield difference of around 6 bu/acre. Dr. Carl Bradley of the University of Illinois conducted the combined analysis of these trials.

Overall, in trials conducted in 2007, foliar fungicides provided an average increase of 3 bu/acre over untreated corn; results in individual trials ranged from a 29 bu/acre yield loss to a 27 bu/acre yield increase in fungicide-treated corn. Out of the 168 different treatments evaluated , 63 (= 38% of the time) had a yield increase of at least 6 bu/acre. Thus, in these analyses, foliar fungicides did improve yield on average, but not enough to pay for the application in the majority of instances.

Looking at the performance of individual products, Headline applied at 6 fl oz/acre provided a yield increase exceeding the break-even point of 6 bu/acre in 39 out of 89 (=44%) trials. Quilt applied at 14 fl oz/acre exceeded the break-even point in 13 out of 37 (=35%) trials, whereas Stratego applied at 10 fl oz/acre exceeded the break-even point in 11 out of 42 (=26%) trials. These results suggest that Headline may provide a most consistent benefit of these fungicides, though future studies on this question are needed.

Not surprisingly, the benefit of fungicide application was greater in corn hybrids which were more susceptible to disease. In hybrids with good to excellent resistance to gray leaf spot, foliar fungicides produced an average yield increase of 3 bu/acre. In contrast, in hybrids with fair to poor resistance to gray leaf spot, foliar fungicides produced an average yield increase of 6 bu/acre.

Interestingly, corn-after-corn did not increase the yield gain obtained by foliar fungicide. In trials with corn following corn, the break-even point was exceeded in 28% of trials, whereas it was exceeded in 41% of trials where the previous crop was something other than corn.

Pioneer Analysis

Scientists from Pioneer conducted an analysis similar to that done by university scientists, using data from a total of 189 studies, including university tests from 2006 plus on-farm strip trials from 2006 and 2007. Their results were generally more favorable for the fungicides. For example, the Pioneer results reported an overall yield benefit of 8.7 bu/acre from fungicide application, with 60% of trials providing a yield boost exceeding the break-even value. (In the Pioneer analysis, a market value of $3.75/bu was assumed, as was a fungicide cost of $20.00/acre, resulting in a break-even value of 5.3 bu/acre.) Compare this—60% of trials exceeding the break-even point—with 38% for the university data for 2007. Certainly some of that difference is due to the higher market price assumed in the Pioneer analysis ($3.50/bu in the university analysis vs. $3.75/bu in the Pioneer analysis), but that doesn’t account for the entire difference. The Pioneer analysis incorporated data for 2006 and 2007, whereas the university analysis only considered results obtained last year. It is possible that some of the difference is due to the fact that 2007 was a rather dry season in many areas, and that a stronger yield benefit will show up in university testing if we get a more normal weather pattern in 2008. This remains to be seen, but it is a possibility.

Another interesting aspect of the Pioneer analysis is that it compared the yield “boost” from a fungicide in trials with vs. without significant disease pressure. Where disease pressure was significant, the average yield boost from fungicide was 15.3 bu/acre. Where disease pressure was insignificant, the yield boost from fungicide was only 3.5 bu/acre, less than the break-even point. This is consistent with UK studies conducted in 2007 and previously, in which we found no significant yield increases in corn crops where disease pressure was insignificant. This is important because certain fungicides are being marketed both for disease control as well as for improving the overall health and physiology of the plant (Plant Health™ and Plant Performance™ trademarks). While products containing strobilurin fungicides (Headline, Quadris, Stratego, Quilt) provide excellent disease control, so far, there seems to be little third-party evidence that these fungicides improve the health of corn unless diseases are active.

Misc. Note

In a very low percentage of cases, pretassel applications of strobilurin fungicides on corn have been associated with damage to the ears, called “beer can ears”, “blunt ear syndrome”, or “hollow husk”. You can see images of these symptoms at a web resource called Abnormal Corn Ears. This symptom forms when male flower parts form on the upper half of the ear instead of female parts. This is thought to occur only in a very low percentage of treated fields, but it does raise concerns about applying fungicides prior to tasseling.

Conclusions

As it stands now, the benefit of foliar fungicides in corn rests on their ability to control diseases. Therefore, growers should consider the risk of disease in their fields before deciding whether or not to treat. The more of these are in place by the time of tasseling, the greater the possible benefit of a fungicide spray.

SOURCE: by Paul Vincelli and Don Hershman

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