What are the control methods for soybean frogeye leaf spot?

Frogeye leaf spot occurs commonly in all soybean-producing regions in our country, but it is most severe in the Northeast production region. All parts of the plant can be affected, and affected soybean seeds become smaller with reduced oil content.

Main symptoms: after the plant and some pods are infected, lesions form on all of them. Lesions on mature plant leaves are round, oval, or irregular, mostly grayish brown, and sometimes gray or reddish brown, with the area around the lesion dark brown and clearly demarcated from healthy tissue. Lesions on stems are round or spindle-shaped, gray, with dark brown edges. Lesions can also form on pods, seed coats, and cotyledons.

This disease is a fungal disease. It overwinters as conidia or mycelium on diseased seeds or diseased plants. After diseased seeds grow into seedlings, lesions form on the cotyledons and produce conidia, which spread with wind and rain and repeatedly spread to damage all parts of mature plants. In the Northeast, the disease generally occurs in early to mid-June, enters its peak period in mid-July, and occurs severely when the temperature is relatively high, humidity is relatively high, and there is abundant rain. In years with a lot of rain in August and September, the rate of seed-borne disease is high.

Control methods: First, choose disease-resistant varieties; second, choose soybean seeds produced in uninfected fields; third, chemical control. You can use 50% carbendazim wettable powder plus 50% thiram wettable powder (3:2), with the total amount of pesticide being 0.5% of the seed weight, for seed dressing; if the disease occurs after the seedling stage, use 100 ml of 40% miebingwei suspension concentrate per mu, and you can also use 100 grams of 50% carbendazim wettable powder or 50% thiophanate-methyl wettable powder mixed with water for spraying.