Purple onion caused by high humidity conditions

Purple spot disease is one of the most important diseases on the production of onions. It mainly harms the leaves and pedicels, and also affects bulbs during onion storage. The diseased part first appeared as a water-soaked white spot, then expanded into an oval or spindle-shaped, gradually changed from light brown to gray-brown or gray-purple, with a slight depression in the middle and a yellow halo around it. When the humidity was high, the diseased part produced concentric circles. Stains arranged in grayish black mould (spores and conidia of pathogens), the upper parts of the lesion often necrosis or break. Onions in storage and transportation often start from the top of the onion and decay when wet.

Onion purple spot is a fungal disease. The pathogen can be contaminated in the southern warm area. It is harmful to the annual conidium in the warm southern area. In the cold regions of the north, the mycelium is in the host or overwinters in the soil with the diseased body, and conidia are produced in the next year when conditions are suitable. , spread through air currents or rain. The bacteria can invade through the stomata or wounds of plants, and can also penetrate directly into the epidermis. After the onset of disease, the diseased part produces conidiospores for reinfection. The optimal temperature for disease onset is 25 to 27°C, and no disease occurs at 12°C or below. The germination and invasiveness of germs requires rain or dew, rain, condensation for a long time, and heavy fog. Diseased fields, low-lying land, excessive watering, insufficient fertilizer, poor growth, and many wounds caused by pests also cause severe disease.

Purple spot disease occurs during onion growth. The diseased leaves should be removed in time to bring deep burial outside the field. In the initial stage of disease, 58% methine zinc WP or 64% Mn Zn wettable powder 500 times, or 50% isoprenil wettable powder 1500 times, or 75% chlorothalonil wettable powder 500 ~ 600 times spray, every 7 to 10 days once, continuous control of 3 to 4 times, pay attention to alternate medication. Adding 5 to 10 grams of neutral laundry detergent per 10 kilograms of liquid can increase the adhesiveness of the liquid. In order to prevent purple spot disease from continuing to harm during the storage period, the onion should be harvested after ripening on the top of the onion, dried and stored outside until the bulbs are dry, the cellar temperature is controlled at 0°C, and the relative humidity is controlled below 65%.

To prevent Onion purple spot disease, we should strengthen the management and cultivation of strong seedlings to enhance plant disease resistance. The sowing date is appropriate from late September to mid-October. We choose the plots with loose soil, fertile soil, and strong water-holding capacity. We choose the fields with high dryness, fertile soil, and easy drainage. Apply organic fertilizer and increase phosphorus and potassium fertilizers. In addition, the onion seeds can also be borne with bacteria, and can be soaked with warm water of 50°C before sowing, so as to eliminate the source of sterilization.