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Prevention of corn leaf spot
Corn leaf spot is a common disease that can affect corn plants throughout their entire growth cycle, but it tends to be most severe after the tassels have emerged. The primary damage caused by this disease is to the leaves, although it may occasionally affect the leaf sheaths as well. Initially, the lesions appear as small, water-soaked spots that gradually develop into red-brown areas with a yellowish center. The size and shape of these lesions vary depending on the vascular structure of the leaves, typically measuring up to 2 cm in length—smaller than the larger lesions seen in other diseases. Two distinct lesion types are observed: oval-shaped spots and elongated lesions. In some resistant corn varieties, only small, round necrotic spots may appear.
As the infection progresses, the lesions often lead to early leaf death. A thin layer of black mold develops on the underside of the lesions or on the opposite side of dead leaves. The presence of a large number of overwintering bacteria increases the likelihood of early infestations, especially in fields near villages, which can result in widespread outbreaks. Environmental conditions play a critical role in disease development. When temperatures range between 20°C and 25°C and relative humidity exceeds 90%, spore formation, germination, and spread are greatly enhanced. The disease spreads primarily through wind and rain.
In northern corn-growing regions, heavy rainfall from June to July—often exceeding 80 mm—combined with high humidity creates ideal conditions for disease development. Additional moderate rains in August further contribute to the severity of the outbreak.
To manage corn leaf spot, several preventive and control measures can be implemented. Chemical control is effective when applied at the right time. If more than 70% of the plants in the field show symptoms and the leaf infection rate reaches 20%, spraying should begin immediately. Recommended fungicides include 50% carbendazim wettable powder diluted at 500 times, 50% amitriazole wettable powder at 500 times, 90% mancozeb wettable powder at 500 times, or 40% triazole EC diluted at 800 times. Each mu (approximately 667 square meters) requires 50 to 75 kg of solution, and applications should be repeated every 7 to 10 days, with 2 to 3 sprays usually needed for effective control.
Another important method is the removal of infected leaves. The disease typically affects the lower leaves first. When the infection rate in the lower two leaves reaches about 20%, affected leaves should be removed promptly. Then, 3 to 5 leaves should be removed every 7 to 10 days to reduce the spread of the disease. This method is most effective when implemented on a large scale and quickly. After removing the diseased leaves, it’s also recommended to apply fertilizer with irrigation to promote plant growth and enhance resistance to future infections.
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