Fungicides: Consider Risks Vs. Rewards

With grain prices at unprecedented levels and some fungicide companies implementing aggressive marketing campaigns, many corn and soybean producers are considering applying a fungicide to increase yields. Extension experts recommend taking a closer look at the risks involved, not just results promised.

University of Kentucky College of Agriculture plant pathologists Don Hershman and Paul Vincelli say dealership agronomists and their grower-customers should consider the risks before applying fungicide to crops because its effects are unpredictable and in many cases, applications are not warranted.

“Historically, corn and soybeans are not grown under conditions that favor the development of foliar fungal diseases — the primary target of fungicide applications,” Hershman says. “Most acreage that is being treated in Kentucky does not need it for disease control.”

Producers are also treating to maximize plant health as a hedge against crop stress, Hershman says. “Some fungicides have produced higher yields compared to non-treated crops in the absence of disease, but university research trials indicate that statistically higher yields are produced only about 25 to 30 percent of the time when disease is not a factor,” he says. “Marketing literature from fungicide manufacturers suggests a much more favorable outcome than what we find in replicated studies in Kentucky and across the Midwest.”

Applying fungicide to soybeans has been done for some time now, but widespread applications to corn have only occurred during the last two years. During this time, crop prices have sharply increased; fungicide companies vamped up their marketing efforts to target corn and soybean producers, and many grain producers have had favorable results when applying fungicides. The result is an estimated 50 million acres — about 30 percent — of corn and soybeans in the U.S. will be treated with a fungicide in 2008.

If yields do increase, producers can easily recoup the cost of the fungicide and application, which is averaging about $22 an acre. But while fungicides may produce yield increases for some producers, it may result in yield loss for others.

In 2007, Vincelli and Chad Lee, UK Extension grain crops specialist, conducted experiments to test the effectiveness of fungicides on increasing corn yields under low disease and good growing conditions. The results showed no significant difference between treated and untreated plots. Vincelli says he conducted similar tests several years ago and received similar results.

Their findings are consistent with other research from across the country, which has shown fungicide applications caused modest gains in average yields for both corn and soybeans, but results greatly varied depending on the treatment and the individual crop. For example, in university studies conducted for corn in 2007, some applications produced as much as 27 more bushels per acre, but some resulted in a loss of 29 bushels per acre.

In addition to its unpredictability, fungicides could have other adverse effects. Hershman says there have been several documented cases where insect populations have soared because fungicides killed beneficial fungi, which kept populations down. This could result in growers taking on additional costs by having to purchase an insecticide. The “greening effect” of strobilurin fungicides could slow or delay harvest because grains harvested at higher moisture may require more drying. Producers should weigh these risks before deciding if the fungicide would be economical for their operation.

If your growers do decide to apply fungicide, it is important to have excellent spray coverage. Either aerial or ground spraying can accomplish this. Be sure to follow label instructions and leave an untreated strip large enough to determine the impact of spray applications.

Hershman and Vincelli encourage producers to use fungicides only when there is a significant risk for disease. Producers will get the best results from fungicides when diseases are present or likely to occur. Local Cooperative Extension Service offices can provide more information on the factors that contribute to disease risk in corn or soybeans.

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