One of the most severe diseases affecting rapeseed is downy mildew disease. Improper control of downy mildew disease can lead to serious yield reduction in rapeseed. Let's learn about the symptoms and control measures of downy mildew disease in rapeseed.
Symptoms of Downy Mildew Disease in Rapeseed
Downy mildew disease mainly affects the leaves of rapeseed, spreading from the outer leaves to the inner leaves. Initially, pale yellow, nearly circular to polygonal lesions appear on the leaves. Later, white downy mildew grows on the lesions on the undersides of the leaves, which are fungal spore stalks and spore sacs. Under suitable conditions, the pathogen can spread to the upper surface of the leaves. In the later stages, the lesions become brown and connect into patches, leading to rapid wilting and death of entire leaves. In high humidity, white mold-like structures, including mycelium, spore stalks, and spore sacs of the pathogen, grow on the undersides of the leaves and sometimes spread to the upper surface.
Control Measures for Downy Mildew Disease in Rapeseed
-
Crop Rotation: Rotate with cereals such as wheat and rice for two years to significantly reduce the number of oospores in the soil and decrease the source of infection.
-
Proper Planting Density: Plan the spacing properly when transplanting rapeseed, with an average spacing of about 15-20cm. This spacing allows rapeseed plants to grow without overcrowding, reducing humidity inside the greenhouse.
-
Appropriate Fertilization: Avoid excessive nitrogen fertilization. Before transplanting rapeseed, use high-quality organic fertilizers or microbial fertilizers as base fertilizers. For top dressing, apply high-nitrogen water-soluble fertilizers according to growth, using balanced fertilizers for moderate growth and potassium-rich fertilizers for vigorous growth. Additionally, supplement with foliar micronutrient fertilizers as needed.
-
Humidity Management: Focus on controlling temperature differences, reducing humidity, and increasing light intensity in the greenhouse. Open the greenhouse for ventilation at suitable temperatures in the morning to reduce humidity.
-
Chemical Control: In the early stages of infection, spray with fungicides such as 69% acylalanine manganese zinc, 72% oxycarboxin manganese zinc, 25% metalaxyl, 72.2% propamocarb, 70% ethoprophos aluminum manganese zinc, 50% acylalanine, or 58% metalaxyl manganese zinc every 7-10 days, rotating and alternating treatments 2-3 times.
Above are the introduction and control measures for downy mildew disease in rapeseed. Downy mildew disease is a major threat to rapeseed, and proper control measures are essential.
