Soybean downy mildew mainly occurs in the northeast and north China, and is most serious in Heilongjiang and Jilin. The disease harms seedlings, leaves, pods, and grains. The rate of infected seeds is as high as 10-50%, causing the seed germination rate to decline, oil content to fall, quality deterioration, and product devaluation. Leaf disease can cause early leaf loss, resulting in reduced yield. General production cuts are 6-15%, and serious diseases can reduce production by more than 50%.
Symptom identification: Pseudoperonospora sojae mainly damages seedlings or adult plants, pods and beans. Seedlings growing from diseased seeds can develop systemic disease, and the cotyledon is asymptomatic. The chlorotic plaques appear from the base of the first pair of true leaves, spreading along the main veins and lateral veins, causing chlorosis of the entire leaf. When the leaves are re-infested, small spots of chlorosis appear, and later become brown dots. Afterwards, the leaves of the whole plant can show symptoms. The lesions on the leaves are scattered and appear to be round or irregular, with chlorotic macules at the beginning and yellowish-brown or spotted spots later. Before and after the flowering period, there was a lot of rain or humidity, and there was a gray moldy layer on the back of the lesion. Later diseased leaves turn brown and dry, causing early defoliation. The external symptoms of bean pods are not obvious, but the yellow mold layer is often present in the larvae, namely the pathogen mycelium and oospore. The affected beans were shiny and black, with a layer of yellow-white powdery mildew on the surface.
Control methods:
1, choose resistant varieties. The disease resistance of the varieties is obviously different. The selection of high-yield, high-quality and disease-resistant varieties is an effective prevention and control method.
2, seed processing. Pre-sowing seed dressing with 72.2% Preclo®, 35% Metalaxyl (Drumys) powder, 80% triethylaluminum phosphate (ethylaluminophosphate) wettable powder, 70% Dukesson wettable powder And so on, the dosage is 0.1-0.3% of the seed weight. 70% Antecan wettable powder can also be used. Seed dressing at 0.5% seed weight.
3, a reasonable rotation. Rotate with other crops for more than 2 years.
4. Eliminate diseased plant residues. Ploughing buries the diseased body in the deep layer of the soil and eliminates the source of sterilization.
5, pharmaceutical control. At the beginning of the disease, Tiantian sprayed medicine. Commonly used agents: 58% metalaxyl MnZn WP 600 times, 72% Kelu WP 700 times or 64% WP WP 500 times, spray once every 7-10 days, even spray 2-3 times. It can also be used per hectare 72% cream urea-manganese zinc wettable powder 2.5-2.7 kg, 72% g / liter rapemil hydrochloride salt water agent 0.9-1.5 liters, 68% fine nail cream-manganese zinc water dispersant 1.0-1.5 Kilograms, 64%?f cream-manganese zinc wettable powder 2.5-3.0 kg, 80% glyphosate wettable powder 3 kg per hectare, 3 sprays of water spray, interval 7-10 days. Can also be used 69% Anke Zinc WP 900-1000 times spray.
6, biological control. 3% polymyxin wettable powder 600 times spray.
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