Field Facts: Gray Leaf Spot
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Gray leaf spot is an annual threat in cornfields from the Midwest to the Atlantic Coast. All corn hybrids in this region, regardless of type, have some susceptibility.
- Common name: Gray leaf spot
- Scientific name: Cercospora zeae-maydis
- Symptoms: Thin, rectangular lesions, up to 2 inches in length, appear on leaves. The lesions start out tan and usually turn gray.
- Conditions for development: Warm temperatures and high humidity create an optimum environment for gray leaf spot.
- Periods of fog can trap moisture in the canopy, sparking an outbreak.
- Heavy wind and rain aid spread of disease from soil to and among developing plants.
Fast facts
- The disease appears in cornfields most growing seasons without significant effect on yield. However, when conditions favoring the disease are persistent, yield losses of more than 50% can occur if left untreated.
- In its early stages, gray leaf spot may be confused with other foliar fungal diseases, including northern corn leaf blight, anthracnose leaf blight, eyespot and common rust.
- To verify, hold a leaf up to the light and look for a yellow halo around pinpoint lesions.
- There are many factors that contribute to the risk of gray leaf spot damage in corn. Climate, moisture, cropping system, weed pressure, timing and tillage practices are other factors that impact disease risk.
- Weeds block air movement through the canopy, holding humidity and preventing leaf surfaces from drying, which increases disease risk.
- Gray leaf spot fungus overwinters in corn residues, making the threat of infection greater with continuous corn.
Control tips
Significant yield loss can occur if leaf area is destroyed before grain fill is complete, so it’s critical that your customers are taking steps to mitigate diseases like gray leaf spot. Early infection also allows more time for secondary outbreaks, disease spread and leaf damage — resulting in even greater yield losses.
For optimum disease control, work with customers to implement the following strategies:
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- Choose disease-resistant corn varieties.
- Rotate crops and till fields to encourage decomposition of infected residue.
- Apply a fungicide preventively or, if necessary, curatively. Aproach® Prima fungicide is very effective at controlling gray leaf spot with preventive and curative modes of action.
For more information on gray leaf spot and other common corn diseases, check out the Corn & Soybean Disease ID Guide from Corteva Agriscience.
Aproach® Prima is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions.