Kentucky Corn: 5 Considerations Before Applying a Fungicide

Corn is moving through growth stages quickly, and April planted corn is at or approaching tasseling in many fields across the state. Pre-tassel and tasseling fungicide applications are common, although fungicide use in corn is not always an automatic decision. This article discusses some of the factors that influence the profitability of a fungicide application.

1. Crop Production Factors

Check hybrid ratings for foliar diseases such as gray leaf spot and northern corn leaf blight prior to foliar fungicide application.  Fungicide applications to hybrids with good foliar disease resistance are less likely to provide economic returns.

Hybrids susceptible to foliar diseases are more likely to respond to foliar fungicides, especially if planted in continuous corn or fields under conservation tillage. These fields are at higher risk for foliar disease development since the fungi that cause several foliar diseases survive in residue.

Additionally, irrigated fields are at higher risk for foliar diseases since irrigation creates an environment favorable for disease development.

2. Fungicide Timing

University research indicates that foliar fungicides applied at tasseling or early silking (VT-R1) provide optimal foliar disease control for gray leaf spot and northern corn leaf blight and also the best chance for seeing a yield response, compared to applications that occur after “brown silk” (R2) in corn.

Early vegetative stage applications (V6) are less likely to provide an economic return. A recent national summary of foliar fungicide trials comparing yield response of early fungicide applications to applications that occur at VT-R1 can be found here.

Recent UK research has indicated that V12 or pre-tassel fungicide applications provide comparable foliar disease control and yield response as VT-R1 applications under low to moderate levels of foliar diseases like gray leaf spot. Fungicide applications that occur at brown silk or later may be too late to realize the full benefit of fungicide application for diseases like gray leaf spot.

However, if the disease southern rust arrives in Kentucky before corn is through milk stage (R3), later fungicide applications may be needed to manage this disease.

3. Fungicide Class

Recent University research indicates that fungicide class influences the potential for yield response from foliar fungicide applications occurring at VT. Applications of products containing both strobilurin (QoI; FRAC group 11) and triazole (DMI; FRAC group 3) fungicide classes are more likely to result in a positive return on fungicide investment compared to applications of products containing only a strobilurin or triazole fungicide active ingredient.

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Fungicide classes and efficacy of specific fungicide products for foliar diseases like gray leaf spot are described in the updated fungicide efficacy table for management of corn diseases, which is developed by the national Corn Disease Working Group and posted on the Crop Protection Network website.

4. Yield potential in damaged corn

Flooding, hail damage, and other weather events have reduced corn yield potential in certain fields in Kentucky. Before applying a fungicide to these fields, assess yield potential and determine if additional investment in the crop is warranted.

Remember that fungicide applications are most successful when used to help protect yield from foliar diseases. Fungicide applications used to “recover” yield in a compromised crop may be less economically viable.

5. Disease identification

It is important to scout corn and determine if foliar diseases are present and at levels that need management before deciding if a fungicide application is needed. If help is needed identifying diseases present in corn, have your county agent submit samples to the University of Kentucky Plant and Pest Diagnostic Laboratory. This lab can provide an accurate diagnosis that can aid in management decisions.

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