Corn brown spot control

Maize brown spot disease is a new corn disease discovered in recent years. It occurs in all the corn producing areas in the country, among which there are heavy damages in Hebei, Shandong, Henan, Anhui and Jiangsu. Warm and humid areas occur more often, and in some years, they suddenly become popular in the field of planting corn. In severe cases, they can cause deforestation and harm corn and plants of the genus Eucalyptaceae. 1. The pathogen belongs to the genus Thraustochyliaceae. It is an obligate parasite on corn that inhabits parenchyma cells. Dormant sporangia wall thickness, nearly round to ovoid or spherical, yellow-brown, slightly flat, capsular. 2. Symptoms occur in corn leaves, leaf sheaths and stems. They occur at the tip of the top leaf. Lesions are the most common at the junction of the leaves and leaf sheaths. They are often densely integrated. The first is yellow-brown multi-functional or red-brown small spots. The lesions are Round or elliptical to linear, the leaf tissue near the uplift is often red, small lesions often come together, and when severe, several or even all lesions on the leaves are full of lesions, appearing larger brown on leaf sheaths and veins. Spots, lesions of epidermis rupture at the late stage of disease, necrotic tissue of leaf cells, brown powder (sporangia of pathogenic bacteria) were scattered, and diseased leaves were scattered, and veins and vascular bundles remained filamentous. Stem disease occurs in the vicinity of the festival. 3. The onset of disease The pathogenic bacteria spores (sac) overwintering in the land or in the diseased body. In the second year, the pathogens are transmitted to the corn plants by airflow, germinate under suitable conditions to produce a large number of zoospore, zoospore on the surface of the blade. On the water droplets swim, and the formation of infestation silk, damage the tender tissue of corn. In July and August, if the temperature is high, the humidity is high, and there is more rainy day, it is beneficial to the onset. In the thin soil plot, the leaves are yellow and 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. In addition, according to the survey, the parents have susceptibility diseases such as Shendan16, Shandan911, Yuyu26, etc. 4. The cause of the disease 4.1 The brown spot pathogens are found in the soil and in the diseased tissues. First, when the high-susceptibility varieties are continuously cropped, the amount of bacteria in the soil increases by 5 to 10 times per year. Secondly, in the aspect of fertilization, the use of the sick Straw returned to the field, the application of unfamiliar manure compost or bacterial farm manure so that the pathogen was introduced into the field, resulting in a corresponding increase in the number of bacteria. 4.2 Maize 5-8 leaves, soil fertility is not enough, yellow maize leaves, defertilization phenomenon, corn disease resistance is reduced, is the main reason for the occurrence of brown spot. 4.3 The air temperature is high and the humidity is high. The summer corn area is generally susceptible to disease if it is cloudy and rainy in the middle of June to early July. 5. Control methods 5.1 Agricultural measures 1 After the harvest, the corn completely removes the diseased body tissue, and deep-deep the soil; apply enough base fertilizer and timely fertilizer. Generally, Miaofei should be applied at the 4th to 5th leaf stage of maize, and topdressing urea (or N, P and K compound fertilizers) should be 10 to 15 kg/667 m2. If diseases are found, fertilizers should be immediately applied, and nitrogen, phosphorus, and potassium fertilizers should be taken care of. 3Select disease-resistant varieties and implement rotation for more than 3 years; 4Apply Japanese compost compost compost or fully mature organic fertilizer; timely top-dressing, cultivating grasses to promote plant robust growth and increase disease resistance; 5 appropriate planting density , 667 square meters less than 3500 strains, improve field permeability. 5.2 Chemical control 1 Early prevention. In the 4 to 5 leaf stage of corn, 25% triadimefon 1500 times foliar spraying is applied every 667 square meters to prevent the occurrence of corn brown spot; 2 timely control. Immediately after the onset of corn, spray 25% of triadimefon(triazole copper) wettable powder 1500 times on the stems and leaves or use fungicides to spray. In order to improve the prevention and control effect, some foliar treasures, potassium dihydrogen phosphate, urea, etc. can be properly added in the liquid medicine. Combining with topdressing available fertilizers, the spread of diseases can be controlled, and the robustness of corn can be promoted to improve the disease resistance of corn. According to the current rainy weather characteristics, spraying bactericide should be 2 to 3 times, 7 days apart, within 6 hours after spraying, rain should be added after the rain. (Author: Hou Venus Unit: Agricultural Bureau Chiping County, Shandong Province)

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