First, the damage symptoms of corn leaf spot mainly damage the leaves, but also seriously damaged leaf sheath and temporal lobe. The disease begins with the lower leaves of the plant and expands upward. The lesions are long spindle-shaped, gray-brown or tan-colored, 5-10 cm long and 1 cm wide. Some lesions are larger, or several lesions are connected to a large, irregular, spot-like spot. Rainy and wet weather, dense gray mold layer can be densely stained. In addition, there is a lesion that occurs on disease-resistant varieties, spreading along the veins, showing a brown necrotic streak, surrounded by yellow or light brown chlorotic circles, with no spores or very few spores. National corn production areas have occurred. Second, the morphological characteristics of pathogenic bacteria on the lesion generated on the gray mold layer is the pathogen of the conidia stems and conidia. If the mold layer on the lesion is not obvious, moisturizing can be used to promote sporulation. Conidiophores solitary or several bunched, unbranched, bluish-brown, conidiogenous on spore pedicel tip, pale bluish, fusiform or long spindle, erect or slightly curved to one side, with multiple divisions The umbilical spot clearly protrudes beyond the basal cell. Third, the incidence characteristics of the surface of the field and corn stover in the diseased leaf tissue in the mycelium and attached conidia can overwintering, become the second year of incidence of primary infection. The mycelium buried on the diseased leaves at the depth of 10 cm in the ground all died after winter. In the corn growing season, the overwintering bacteria produced spores, which spread to the leaves of the corn with rain or spatter, and are suitable for germination under conditions of temperature and humidity. Infected varieties, the bacteria quickly expanded after invading, about 14 days or so, you can cause local wilting, tissue necrosis, and then form dead spots. In moist climate conditions, a large number of conidia can be produced on the lesions, which spreads with the air flow and re-infects them several times, causing disease epidemics. Due to the coincidence of climatic conditions with the silking filling stage during the disease stage of the corn, the condition of the summer corn develops quickly and the victim is heavy. Disease conditions 1. Disease resistance of varieties is an important factor influencing the epidemic of large-scale disease. In the 1970s, due to the large-scale planting of susceptible corn hybrids, the spread of large-scale spot disease was caused in some areas and the losses were serious. 2. The land near the corn and in the vicinity of the village, due to the large amount of bacteria in the overwintering, the early infestation occurred more frequently, and the infection was more frequent, and it was easy to cause epidemic. 3. The climatic conditions are also important factors in the occurrence of diseases. Temperatures of 20-25°C and relative humidity of over 90% are favorable for spore formation, germination, and infection. Therefore, moderate-temperature and high-humidity climatic conditions are conducive to the spread of large-spot disease. Fifth, the prevention and control methods 1, selection of resistant varieties and resistance to large-scale spot maize hybrids. 2. Implement crop rotation and dumping system: Avoid continuous cropping of corn, deep-fall soil in autumn, deep-fall diseased plants, eliminate sterilization sources, and use corn straw as fuel, treat it as soon as possible after the beginning of spring, and can also treat corn borer; Composting is fully decomposed and straw fertilizer is best not applied in corn fields. 3. Improve cultivation techniques and enhance corn disease resistance: Early sowing of summer maize can reduce the incidence; Intercropping with wheat, flowers, raw sweet potato, and wide and narrow rows of plants; Reasonable irrigation, and attention to field drainage. 4, spraying control: Before and after corn tasseling, the field disease rate of more than 70%, when the disease leaf rate of 20%, began spraying. The effect of a good agent: 50% carbendazim WP, 50% enemy Diclosporin wettable powder, 90% mancozeb, all 500 times more water, or 40% grams of loquat cream 800 times spray. 50-75 kilograms of liquid per acre, spray once every 7-10 days, a total of 2-3 times control.
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