Foliar fungicide use in corn

Do insurance fungicide applications on corn in the absence of a justifiable disease threat really pay?

In order to address the question if foliar fungicides can be justified for uses other than disease management in corn, Kiersten Wise of Purdue University and Daren Mueller of Iowa State University published an article called “Are Fungicides No Longer Just For Fungi?: An Analysis of Foliar Fungicide Use In Corn.” Much of the content of the article results from discussions of the Corn Disease Working Group, a group of corn pathologists within the United States and Canada who meet annually to discuss important issues related to corn disease. A summary of the article’s findings follows.

The use of fungicides in hybrid corn increased dramatically in 2007 and is currently higher than five years ago. Several factors resulted in this increase:

  • Increase in the market price of corn.
  • Increased foliar diseases in parts of the United States.
  • New fungicides becoming available for use on field crops.
  • Fungicide manufacturers marketing of fungicides for use in hybrid corn.

Demand for corn has increased due to global markets and the use of alternative fuels, including ethanol. Increasing demand has resulted in a high value for corn, providing the economic justification for increased input costs, including fungicides.

There is an increased need for foliar disease management for several reasons including increased use of reduced or no-till practices and increased acreage of continuous corn. Both of these factors result in an increase in corn residue which can serve as a source of disease inoculum. Also, because of the high price received for corn, producers are prone to select hybrids based on maximizing yield instead of disease resistance than depend on fungicides to limit losses due to foliar disease.

Some fungicide manufacturers suggest that their products can increase yield even in the absence of disease, for example, by using QoI (strobilurin) fungicide to improve stalk strength and harvestability. As a result, some farmers are applying fungicides to corn in anticipation of perceived harvest problems, not in response to disease or a disease threat. Also, the widespread use of glyphosate-tolerant soybeans, corn and other crops may be contributing to an increased general reliance on pesticides, with less emphasis on scouting and IPM practices.

Prior to 2008, little replicated research was available to help develop dependable recommendations for fungicide use in hybrid corn. Much more work was published between 2008 and 2010. Data from 39 high-quality trials across the Corn Belt between 2000 and 2010 was compiled. In only 46 percent of these trials, QoI fungicide application had a statistically significant positive effect on yield. However, 80 percent of the treatments had a positive yield response when strict statistical significance was not considered. Keep in mind that a positive yield response does not necessarily pay for the fungicide application.

Based on this data from across the Corn Belt, the yield increase per acre needed to break even from a fungicide application in 2009 and 2010 was 6 bushels per acre. The 6 bushels per acre needed to break even was achieved 45 percent of the time when a single fungicide application was made between the V15 and R2 growth stages of corn.

The research indicates that even if fungicide applications have the potential to increase corn yield or improve standability in the absence of disease, they may not be profitable. “Insurance” applications of fungicides also have the capacity to increase the development of fungicide resistance, especially for chemistries at high risk of fungicide resistance, such as the strobilurins.

In conclusion, Wise and Mueller state that the profitability of fungicide use in the presence of corn disease pressure is well-established. Scouting, correct disease identification and optimum application timing are important. Economic thresholds to justify fungicide application have not been developed for all foliar diseases and may be difficult to establish, and growers may be persuaded to apply fungicides as “insurance” for the crop. However, research indicates that fungicide use in corn is most profitable when there is high risk for foliar disease, and disease develops to levels that warrant management. The decision to apply a fungicide should be based on disease factors, not on presumed yield enhancements that might occur in the absence of disease.

If you’re wondering whether to use fungicides on corn with or without disease problems, Michigan State University Extension recommends giving “Are Fungicides No Longer Just For Fungi?: An Analysis of Foliar Fungicide Use In Corn” a read. It’s well worth the time.

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