How to prevent and control soybean gray leaf spot? Understand the control methods in one article

Soybean gray leaf spot is a commonly occurring disease. In severe cases, it causes leaves to die off, leading to defoliation and reducing yield.

1) Symptoms: Gray leaf spot can occur throughout the entire growth period of soybean. It mainly damages soybean leaves. The lesions are round to elliptical or irregular in shape, with a diameter of up to 2 cm. At the seedling stage, it first spreads from the leaf margin toward the center of the leaf, forming a “V”-shaped lesion. The lesion is initially light green, later becoming light gray to light brown, with a relatively narrow dark brown or purple band along the edge. On older lesions, a large number of black, pinhead-sized spots are produced, which are the fungal pycnidia. The pathogen sometimes spreads from the leaves to the petioles, stems, and pods. The lesions on petioles and stems are striped, light gray or light brown, with brown edges. The lesions on pods are round, with red edges.

2) Pathogen: Soybean gray leaf spot is caused by a fungus. The fungal pycnidia are embedded in the leaf tissue, later breaking through the epidermis, scattered or clustered, spherical, with a membranous wall, brown, 64 to 170 micrometers in diameter, and with an ostiole; the conidia are long elliptical or ovoid, single-celled, and colorless.

3) Control methods: ① Select disease-resistant varieties. ② Seed treatment. Treat seeds with 50% thiram wettable powder or 70% dexon wettable powder at 0.3% of the seed amount. ③ After soybean harvest, promptly remove diseased plant residues from the field. Practice crop rotation with grass-family crops for more than 3 years.