What are the main diseases of onions? And how should they be prevented and controlled?

Onions are widely planted and cultivated in China and are one of the main vegetable crops grown in the country. So what diseases do onions have during cultivation? And how should they be prevented and controlled?

Although onions are widely grown, in China they are still mainly concentrated in Fujian, Shandong, Gansu, Inner Mongolia, Xinjiang and other places. Onions contain prostaglandin A, which can reduce peripheral vascular resistance and lower blood viscosity, and can be used to lower blood pressure, refresh the mind, relieve stress and prevent colds. Onions can also remove oxygen free radicals from the body, enhance metabolic capacity, and effectively prevent aging factors, making them a health food suitable for middle-aged and elderly people.

Since onions have so many benefits, what diseases occur during onion cultivation, and how can they be prevented? Then let us learn about onions together.

1. Downy mildew

This disease can occur at all stages of onion growth, from seedling to harvest, with adult plants suffering more severe damage. This disease generally occurs on the leaves, spreading slowly from the leaf base toward the leaf. When air humidity is too high, a frost-like mold layer visible to the naked eye appears on the underside of the leaves. In severe cases, the outer leaves all turn yellow and die, very similar to Fusarium wilt. After discovering this disease, on the one hand humidity must be reduced, as excessive air humidity is one of the main triggers of the disease; on the other hand, 75% chlorothalonil wettable powder at 600 times dilution can be used for control.

2. Purple blotch

When purple blotch occurs, it is mostly concentrated on the leaf area and then slowly spreads. The onset time is mostly concentrated in the rainy season, so everyone must do a good job of drainage. In the early stage of the disease, some light purple spots appear at the top of the leaves. As it spreads, purple becomes the core, with brown drying appearing around it, and finally the whole plant withers and dies. For control, 2% polyoxin at 30 ppm can be selected for spraying, with emphasis on spraying the leaf tip area, about one hour before nightfall.

3. Gray mold

This disease mainly harms the fruit, with green fruit suffering severe damage. In the early stage of the disease, the remaining stigma or petals are infected first, then it spreads to the fruit, causing the peel to become grayish white and develop a thick gray mold layer, appearing water-rotted. When the disease becomes severe, the leaves begin to be affected. The main symptom starts from the leaf tip and extends inward along the veins in a “V” shape, forming grayish brown bands with alternating light and dark striated lines, and the boundary between diseased and healthy tissue is distinct. After the disease occurs, assess the situation; severely affected plants can be directly removed and taken away to avoid contagion, while for milder cases, 1.5% ningnanmycin? — no, 1.5% zhibingling emulsion at 1000 times dilution can be used for control.

4. Anthracnose

This disease also mainly occurs on the leaves. In the early stage of the disease, round or oval reddish brown small spots appear on the leaves. In the later stage, when the disease is severe, they expand into dark brown lesions, with the center turning from grayish brown to grayish white, while the edges are purplish brown or dark green, sometimes with a yellow halo at the edges, and finally the lesions turn dark brown and produce small black dots arranged in concentric rings. During management, the seedbed and greenhouse should be disinfected. For the seedbed, quintozene and carbendazim are generally mixed at a 1:1 ratio and blended with fine soil as bedding soil and covering soil for the seed. For greenhouse disinfection, it is best to fumigate with sulfur powder overnight.

After reading this article, do you understand the diseases during onion growth and the methods of prevention and control?