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Corn gray spot disease, also known as leaf spot or corn leaf spot, has become increasingly prevalent in recent years, posing a serious threat to corn crops. This fungal disease affects the leaves and can significantly reduce yield and quality if not managed properly.
**Symptoms:**
The disease primarily affects the leaves. Initially, small, elliptical or oblong lesions appear with unclear borders, ranging in color from gray to light brown. As the disease progresses, these spots turn darker, often brown. Lesions are typically confined between the parallel veins of the leaves, measuring approximately (4–20) mm in length and (2–5) mm in width. When humidity is high, a gray moldy substance may develop on the back of the lesions, indicating active fungal growth.
**Disease Characteristics:**
The disease is caused by several fungal pathogens, including *Sphaceloma* species such as *Cercospora zeae* and *Cercospora sinensis*. These pathogens overwinter in infected plant debris and serve as the primary source of infection for subsequent outbreaks. The disease tends to occur more frequently during wet periods, especially in July and August. In some cases, it leads to excessive drying of the leaves. Under dry conditions, the pathogen can survive on diseased plant material, but it cannot overwinter effectively when the surface is moist. Factors such as topography and planting patterns have a significant impact on disease occurrence, while sowing date, plant density, and fertilizer use have less influence.
**Control Methods:**
1. **Agricultural Control:**
Selecting resistant corn varieties is one of the most effective long-term strategies. Reducing the initial infection sources through proper field management, such as fall plowing and spring cultivation, can help control the spread. Intercropping can improve the microclimate within the field, reducing relative humidity and limiting disease development. Removing infected plant material immediately after harvest, practicing crop rotation over large areas, and maintaining good drainage after rainfall are all important steps in preventing moisture buildup and reducing pathogen survival.
2. **Chemical Control:**
Early application of fungicides is crucial for effective disease management. Commonly used products include 75% chlorothalonil wettable powder diluted at 500 times, 50% carbendazim wettable powder at 600 times, 40% mancozeb emulsifiable concentrate at 800–900 times, 50% benomyl wettable powder at 1500 times, 25% benzofenaple emulsifiable concentrate at 800 times, and 20% triadimefon emulsifiable concentrate at 1000 times. Applying these treatments at the early stages of the disease can significantly reduce its impact and prevent further spread.
By combining cultural practices with timely chemical interventions, farmers can effectively manage corn gray spot disease and protect their crops from yield losses.