What are the latest control methods for white blight of Welsh onion?
White blight of Welsh onion is a fungal disease. The pathogen mainly overwinters in the soil as chlamydospores, and in the following spring when conditions are suitable it produces sporangia, which spread via irrigation water or wind and rain. Newly produced zoospores on the lesions and those on the soil surface spread via raindrop splash. The disease can occur at both the seedling stage and the adult plant stage, and the affected part is the leaves of the Welsh onion. Let us take a look together at how to control white blight of Welsh onion!
Symptoms of white blight of Welsh onion
White blight of Welsh onion can occur at both the seedling stage and the adult plant stage. When seedlings and adult plants are infected, oily, dark green lesions with indistinct margins appear on the leaf sheaths and leaf blades, later gradually expanding into large oily, greenish-white lesions 5-10 cm in size. The center of the lesion is white to grayish-white, and as the lesion extends to the leaf tip the leaf gradually dries up and droops. On a single plant, in the early stage of the disease the lesions mostly appear at the same height, which distinguishes it from late blight and gray mold.
Conditions for the onset of white blight of Welsh onion
The pathogen mainly overwinters in the soil as chlamydospores, and in the following spring when conditions are suitable it produces sporangia, which spread via irrigation water or wind and rain. Newly produced zoospores on the lesions and those on the soil surface spread via raindrop splash. It generally first occurs in May to June, and as the rainy season arrives the disease worsens. It is prone to occur in summers with many consecutive overcast and rainy days. After heavy rain, if drainage is not timely, water accumulates at the field edges, or there is excessive nitrogen fertilizer or excessive vegetative growth of the plants, the disease is more severe.
How to control white blight of Welsh onion?
1. Choose disease-resistant or disease-tolerant varieties such as Gaojiao Bai, Jitui Cong, Wuye Qi, Bikeqi Welsh onion, and Zhangqiu Wutong.
2. In affected land, onion and garlic vegetables should not be planted within 2-3 years. After harvest, take care to remove diseased plant residues and bury them deeply in a centralized manner or burn them.
3. Use high beds or ridge cultivation, carry out timely intertillage and hilling, and avoid contact between onion seedlings and water as much as possible.
4. Apply compost fermented with enzyme bacteria, and apply less quick-acting nitrogen, so as to enhance the disease resistance of the plants.
5. In the early stage of the disease, spray 30% Ludebao suspension concentrate at 400-500 times dilution, or 77% Keshade wettable microgranule powder at 500 times dilution, or 60% disodium edetate · phosethyl-Al wettable powder at 500 times dilution, or 72% Kelu wettable powder or 72% cymoxanil mancozeb wettable powder, or 72% Keshuangqing wettable powder at 800 times dilution, once every 10 days or so, for 1 or 2 applications. When resistance to the above fungicides develops, switch to 69% Anke mancozeb wettable powder or water-dispersible granules at 1000 times dilution.