Controlling onion diseases requires good symptom identification, scientific management, and timely application of treatments

During growth, onions are easily infected by a variety of pathogens, and under conditions of high humidity, frequent rain, and poor field ventilation, downy mildew, purple blotch, rust, gray mold, and soft rot are relatively common. Effective disease control is an important part of ensuring onion yield and quality.

Identifying the disease is the first step in control. Downy mildew mostly forms yellow-white to gray-white mold layers on the leaves, and diseased leaves tend to wither and droop; purple blotch often produces purplish-brown lesions on leaves and flower stalks with obvious concentric rings; rust forms orange-yellow blister-like spots on the leaf surface, which later rupture and release rust-colored powder; soft rot mostly starts as decay at the base of the leaf sheaths, accompanied by a foul odor, and in severe cases the whole plant collapses.

Agricultural measures are the foundation of disease prevention. When planting, choose varieties with relatively good disease resistance, practice rotation with crops other than onions and garlic, and avoid continuous cropping year after year. In the field, plant at a reasonable density, maintain ventilation and light penetration, drain promptly after rain to reduce humidity, and avoid excessive nitrogen fertilizer while appropriately increasing phosphorus and potassium fertilizer to strengthen plant resistance. Diseased leaves and plants should be removed promptly and taken out of the field for centralized disposal to reduce the spread of pathogens in the field.

Chemical control should adhere to early detection and early application. In the early stage of disease, appropriate fungicides can be selected for spraying or root drenching, and care should be taken to rotate agents with different modes of action to avoid pathogen resistance; the pre-harvest interval for pesticides must be strictly observed before harvest. When controlling bacterial diseases such as soft rot, it is also necessary to combine this with insect control to reduce transmission opportunities caused by insect wounds. As long as management is in place and treatments are applied scientifically, most onion diseases can be effectively controlled.