How to prevent and control northern corn leaf blight? A detailed explanation of the latest control measures
Northern corn leaf blight is one of the main diseases of corn, mainly damaging the leaves, and in severe cases also harming the leaf sheaths and husk leaves. After the plant is infected, it starts from the bottom leaves and gradually spreads upward; on the same leaf, large and small spots can occur together, or multiple lesions can merge with each other. When the disease is severe, the leaves dry up, chlorophyll decreases, photosynthesis declines, and grain filling is affected. In ordinary fields, yield is reduced by 15—20%, and in severe cases the reduction reaches more than 50%, greatly affecting corn yield. Therefore, departments at all levels should attach great importance to large and small spot diseases of corn, issue corresponding control measures, and keep the disease under control at the early stage.
Northern corn leaf blight
Northern corn leaf blight, also known as corn leaf blight and corn stripe blight, is one of the important diseases on corn, mainly infecting corn leaves, leaf sheaths and husk leaves, with leaf damage being the most severe. In the field, it generally starts from the lower leaves and gradually spreads to the upper leaves. At the early stage of the disease, water-soaked grayish-green spots first appear on the leaves. Later, they gradually expand along the leaf veins toward both ends, forming large spindle-shaped spots with a yellowish-brown center and brown edges, and in the later stage the lesions often show longitudinal cracking. After most lesions merge, the leaves turn yellow and die, and in severe cases the whole plant turns yellow and dries up early. When the weather is humid, abundant grayish-black mold layers grow on both sides of the lesions, and sometimes grayish-black mold layers also grow on the silks or the glumes of the male flowers. The pathogen of northern corn leaf blight belongs to the class Deuteromycetes, order Moniliales, family Dematiaceae. Generally, a temperature of 20°C to 25°C and a relative humidity above 90% favor disease development. Control should be carried out around the tasseling stage of corn, when the rate of diseased leaves reaches 20%.
Northern corn leaf blight is commonly controlled by the following methods:
1. Spray 500 times dilution of 50% carbendazim wettable powder per mu.
2. Spray 600 times dilution of 50% thiophanate-methyl wettable powder per mu.
3. Spray 500 times dilution of 50% anilazine wettable powder per mu.
4. Spray 800 times dilution of 75% chlorothalonil wettable powder per mu.
5. Spray 800 times dilution of 25% benomyl emulsifiable concentrate per mu.
6. Spray 500 times dilution of 90% mancozeb wettable powder per mu. Spray once every 7~10 days, for a total of 2~3 treatments.
Southern corn leaf blight
Southern corn leaf blight, also called corn spot disease, is one of the important diseases on corn, mainly infecting corn leaves, leaf sheaths, husk leaves and ears, with leaf damage being the most severe. The disease occurs over a long period, and can cause damage from the seedling stage to near maturity, usually being more severe around the tasseling stage and during the grain-filling stage. The leaf spots are smaller, but the number of lesions is greater than that of northern corn leaf blight. After infection, diseased leaves tend to wilt and die. The pathogen of southern corn leaf blight is the same as that of northern corn leaf blight. Generally, a temperature of 20°C to 25°C and a relative humidity above 90% favor disease development. Control should be carried out around the tasseling stage of corn, when the rate of diseased leaves reaches 20%. The control methods are roughly the same as those for northern corn leaf blight.