First, the symptoms
It mainly occurs in corn leaves, sheaths and stems. Lesions first occur at the tip of the top blade, initially light yellow, gradually turning yellow-brown or dark brown, round or oval, small lesions often come together, and in severe cases there are several or even full patches on the leaves. The lesions showed large brown spots on leaf sheaths and veins, and the lesions showed a rupture at the late stage of disease. The leaf cell tissue was necrotic and brown powder was scattered. The veins and vascular bundles remained filamentous. Once infected with pathogenic bacteria, the leaves of the whole plant quickly produced a large number of small yellow spots with a diameter of about 1 mm, and the leaves quickly dried up.
Second, the law of occurrence
In the middle period of corn growth (July to August), the temperature is higher (23°C～30°C), the humidity is higher (relative humidity more than 85%), and when there is more rainy day, it is conducive to the disease; the density is too high and the incidence of field canopy closure Heavy; low-lying and damp, after the rain there are plots of water and continuous plots, the incidence of heavier; soil infertile land heavier incidence.
Third, the cause of the disease
1. There are brown spot pathogens in the soil and in the diseased body tissue; when highly susceptible species are continuously planted, the amount of bacteria in the soil will increase by 5 to 10 times per year; in the aspect of fertilization, if straw is used to return diseased residues, application is not Decomposing manure, compost, or farmyard manure with bacteria will cause the pathogen to be introduced into the field, causing a corresponding increase in the number of pathogens.
2. In the period of 5-8 leaves of maize, the soil fertility was not enough, the yellow color of maize leaves appeared, the phenomenon of defertilization appeared, and the disease resistance of maize was reduced, which was the main cause of brown spot disease.
3. The air temperature is high and the humidity is high.
Fourth, control methods
1. Agricultural measures. After the harvest of corn, the diseased body tissue was completely removed, and the soil was deeply plowed; the disease-resistant varieties were selected; the base fertilizer was applied adequately, and the fertilizer was timely applied. Summer corn, if no base fertilizer or seed fertilizer is applied, shall be applied at the 4th to 5th leaf stage of maize, and 10~15 kg of urea will be applied per acre. Nitrogen, phosphorus, and potassium fertilizer shall be used for fertilization, and organic fertilizer must be used fully. Decomposition; appropriate density should be selected according to the characteristics of the varieties, appropriate sparse, improve field permeability.
2. Chemical control. In the initial stage of disease, use 25% triadimefon WP for 1500 times or 70% thiophanate-methyl for 70 grams per mus, or 12.5% ​​for licorice powder 30 grams per acre, spray 30 kg of water. Such as the combination of large and small spot disease prevention and control, available 25% Benzosterine EC 800 times. When Curvularia spp. is added, 5% trehalose can be added. The drug should be taken once every 7 days and the drug should be administered 2 or 3 times continuously. In order to improve the control effect, some potassium phosphate, urea and other foliar fertilizers can be properly added to the medicament to promote robust growth and improve disease resistance.
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