How to prevent and control soybean anthracnose? Detailed explanation of occurrence patterns and control techniques

1 Disease symptoms

A considerable portion of infected seeds die in the soil before emergence. The disease can occur from the seedling stage to the maturity stage. The pathogen can invade young stems from the cotyledons, damaging stems and pods, and also damaging leaves or petioles.

1.1 Cotyledon disease symptoms The disease can occur from the seedling stage to the maturity stage. On the emerged cotyledons there are dark brown lesions with slightly lighter edges. After the lesions expand, cracking or sunken areas often appear. When the climate is humid, the cotyledons become water-soaked and quickly wilt and fall off.

1.2 Leaf disease symptoms When leaves are infected, the lesions are irregular in shape, with dark brown edges and light brown interiors. On the lesions, rough bristle-like black dots form, which are the pathogen's acervuli.

1.3 Stem disease symptoms Initially reddish-brown lesions appear, gradually turning brown, and finally gray, irregular in shape, with dense bristle-like black dots on them, often surrounding the entire stem.

1.4 Pod disease symptoms The lesions on pods are round or irregular. The black acervuli are sometimes arranged in concentric rings. Diseased pods cannot develop normally, and the seeds become moldy, dark brown and shrunken, or fail to set seed.

1.5 Petiole disease symptoms When petioles are infected, the lesions are brown and irregular in shape.

2 Occurrence patterns

The pathogen overwinters on soybean seeds and diseased residues. After sowing the following year, diseased seedlings growing from infected seeds produce large numbers of conidia under humid conditions, which spread infection through wind and rain. The optimum temperature for disease occurrence is 25-28°C. The pathogen cannot develop below 12-14°C or above 34-35°C. In production, low temperatures at the seedling stage or excessively dry soil delay soybean germination and emergence, making seedlings prone to disease. Warm and humid conditions at the adult plant stage favor infection by this pathogen.

3 Control techniques

① Select disease-resistant varieties and disinfect seeds to ensure seeds are free of the pathogen, use rational close planting, and adopt scientific fertilization techniques to improve disease resistance. ② Drain water promptly to reduce humidity in the soybean field, avoid applying too much nitrogen fertilizer, and after harvest promptly remove diseased residues, deep plow, and implement crop rotation of more than 3a to reduce overwintering inoculum sources. ③ Strengthen field management, and promptly deep plow and hill up soil during intertillage. After rain, promptly drain accumulated water to prevent moisture retention. ④ Before sowing, dress seeds with 0.5% of seed weight of 50% carbendazim wettable powder, and after mixing, seal for 3-4h. After flowering, it is also possible to spray 25% Tanteling wettable powder at 500 times dilution, or 47% Jiaruinong wettable powder at 600 times dilution, or 1:1:200 Bordeaux mixture.