During the period of emergence and jointing of summer maize, high temperature and high humidity weather are very favorable for the occurrence of brown spot disease. After the sowing period is delayed, the chance of encountering high temperature and high humidity weather at the seedling stage is increased. Therefore, the occurrence of brown spot disease in summer corn this year may be biased. Symptoms mainly occur in the leaves, leaf sheaths, and stems of corn. Occasionally, there are small oblong to round spots on the outer leaves and male flowers of the ear. Occurred at the tip of the top leaf, lesions at the junction of the leaf and leaf sheaths were the most numerous, with transverse band-like symptoms. Initially yellowish-brown or reddish-brown small spots with round, elliptical to linear or fusiform lesions. Leaf tissue near the bulge is often red. Small lesions often come together. In severe cases, several or even all of the leaves appear on the leaves. Covered with lesions, lesions on the leaves often appear white and transparent; larger brown spots appear on leaf sheaths and veins; lesions of epidermis rupture at the late stage of disease; leaf tissue is necrotic; brown powder is emitted (spore of pathogenic bacteria) Sac). The diseased leaves are partially spalled and the veins and vascular bundles remain as filaments. Stem disease occurs in the vicinity of the festival and often breaks at the infection center. Second, the law of pathogenic bacteria in the dormant spores (sac) in the ground or debris in the winter, the second year by the air flow spread to the corn plants, met the right conditions to produce a large number of zoospores germinate, zoospore on the leaf surface Water droplets swim and form infested silk, invading young tissues of corn. In July and August, high temperatures and high humidity are conducive to disease. In the barren soil, the disease is serious. In the soil where the soil fertility is high, the corn is robust, the leaves are dark green, and the disease is mild or even not. It is easy to produce diseases when there are 8 to 10 leaves of corn, and it will not happen again after 12 leaves of corn. Third, the cause of the disease 1. In the soil and diseased bodies have brown spot pathogens; First, when high-susceptibility varieties continue to work, the soil bacteria in the annual increase of 5 to 10 times; Second, fertilization, use the sick Straw returned to the field, the application of unfamiliar manure compost or bacterial farm manure so that pathogens were introduced into the field, resulting in a corresponding increase in the number of bacteria. 2. In the period of 5-8 leaves of maize, the soil fertility was not enough, the yellow color of maize leaves appeared defertilization, and the disease resistance of maize was reduced, which was the main reason for the occurrence of brown spot. 3. The air temperature is high and the humidity is high. Summer corn areas are generally rainy and rainy in July and August, and they are susceptible to high levels of rainfall. IV. Control methods 1. Agricultural measures: (1) After the corn is harvested, the diseased body tissue is completely removed, and the soil is deeply turned. (2) Note the combination of nitrogen, phosphorus, and potassium fertilizers. Appropriate top-dressing, timely watering, timely cultivation and weeding, and other measures can promote the healthy growth of corn, enhance disease resistance, and eliminate hosts and reduce disease. 2. Chemical control: (1) Active prevention: Corn brown blotch should be mainly prevented. In the 4 to 5 leaf stage of corn, 25% triadimefon WP can be sprayed 1500 times to prevent the occurrence of corn brown spot. . (2) Timely prevention and control: When the corn is onset, use 25% triadimefon WP for 1500 times foliar spray. The spraying should be even and thorough, and protect the upper leaves, especially the leaves above the ear. In order to improve the control effect, some potassium dihydrogen phosphate, urea, etc. may be properly added in the liquid medicine to promote the robustness of corn and improve the disease resistance of corn. Spray bactericide should be 2 to 3 times, 7 days apart, within 6 hours after spraying, rain should be added after the rain.