Time For Foliar Fungicide Application Decisions In Corn
DR. KIERSTEN WISE
LEXINGTON, KENTUCKY
Corn is moving through growth stages quickly, and the warm, humid weather in many parts of Kentucky has been conducive for foliar disease development. Fungicides are commonly promoted to reduce the impact of foliar disease in corn, but with tight margins and a difficult market, it is important to pay careful attention to 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 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 and also the best chance for seeing a yield response, compared to applications that occur later in the season. Early vegetative stage applications are less likely to provide an economic return. For southern rust, a fungicide application may be needed through milk (R3). Management of tar spot is on a case-by-case basis at this time.
3. Fungicide Class
University research indicates that fungicide class influences the potential for yield response from foliar fungicide applications occurring at VT. Applications of products containing multiple 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. Fungicide classes and efficacy of specific fungicide products for foliar diseases 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 are less economically viable.
5. Disease identification
It is important to accurately identify foliar diseases before deciding if a fungicide application is needed. Currently there are very few reports of foliar disease in Kentucky. Early symptoms of gray leaf spot have been observed on leaves in the lower canopy of some fields (Fig. 1), and there have been some reports of northern corn leaf blight (Fig. 2) in certain fields. In all instances, levels were low and did not warrant management at that time. The good news is that southern rust, our annually important disease, has not been confirmed in the United States as of June 22. If corn can reach milk stage (R3) before southern rust appears in Kentucky, there is likely to be little to no impact on yield. Real-time monitoring of southern rust can be observed by checking the disease monitoring map on the Crop Protection Network. Tar spot has been found across the Midwest but not yet confirmed in Kentucky. Even if tar spot is detected in the state, we would not expect the disease to develop quickly, because risk of disease development is very low, according to the new Crop Risk Tool, that can forecast disease risk for tar spot and gray leaf spot for corn that is between growth stages V10 and R3. See the previous article in Kentucky Pest News entitled “Time to Scout for Corn Diseases” for more information about the Crop Risk Tool and tar spot. ∆
DR. KIERSTEN WISE
UNIVERSITY OF KENTUCKY