Pumpkin leaves covered with white spots, dried and curled: how to prevent and control powdery mildew?

    Pumpkin powdery mildew can occur throughout the growing period, but is most severe in the middle and late stages. It mainly infects the leaves; the petioles and stems can also be affected. In the early stage, nearly circular small white powdery mildew spots appear on both sides of the pumpkin leaves, mostly on the upper surface, and then gradually expand, with the powdery white patches merging into large areas. In severe cases, the entire leaf is covered with white powder, and the leaf tissue beneath the white powder first turns pale yellow, then brown, then grayish white, and the leaf dries up and curls. The symptoms on the petioles and young stems are similar to those on diseased leaves, but with less white powder.

Pumpkin

    Disease conditions: Pumpkin powdery mildew peaks when high temperature and high humidity alternate with high temperature and dryness. Fields with heavy application of nitrogen fertilizer such as urea, overly dense planting, and damp conditions are prone to the disease or suffer more severe attacks. After production ends, the pathogen overwinters on old pumpkin plants and diseased plant debris.

    Integrated control:

   (1) Choose good disease-resistant varieties. The Japanese Yixiang pumpkin, Jinli pumpkin, and Juhong pumpkin, which are currently widely grown, have a certain degree of disease resistance, but purification and rejuvenation work is indispensable, and disease-free seedlings should be selected.

   (2) Seed disinfection: Before sowing, sun the seeds for 1-2 days to kill surface microorganisms and improve germination vigor; soak the seeds in 50-55 degrees C warm water with stirring for half an hour, then when the temperature drops to 30 degrees C continue soaking for 8-10 hours, then place them in 1% potassium permanganate solution for disinfection for 20-30 minutes, rinse clean, and germinate at 28 degrees C-30 degrees C for 48-72 hours, sowing when the seeds show white.

   (3) Strengthen management and fertilize rationally: Carry out a 2-3 year rotation with gramineous crops. Apply 5000-7000 kg of decomposed farmyard manure, 20 kg of ternary compound fertilizer, 15 kg of potassium chloride, and 5 kg of urea per mu. Do not apply topdressing during the vine extension stage; during the pumpkin swelling stage, apply 20 kg of potassium sulfate compound fertilizer per mu as topdressing, and keep the soil moist, draining promptly after rain. Promptly remove diseased, old, and yellow leaves at the base, and bury them deeply or burn them. Strengthen field ventilation and light penetration to enhance the stress resistance of pumpkin plants.

   (4) Spray a protective film on the leaves: Before disease onset or in the early stage of disease, spray 99.1% Disichong 300-500 times dilution on the pumpkin leaves to form a protective film, spraying once every 5-7 days, for 2-3 consecutive sprays.

   (5) Chemical control: From late April to July, apply pesticides at the appropriate time. Before disease occurrence, 53.8% Keshade 2000 type 1000 times dilution can be used. In the early stage of disease, 10% Shigao 1500 times dilution, or 40% Fuxing 8000 times dilution, or 43% Pulike 5000 times dilution, or 12.5% Subaoli 2000 times dilution, or 2% Jiasoumi 600 times dilution can be used for spraying, spraying once every 7-10 days, for 2-4 consecutive sprays. Baking soda 600 times dilution can also be used for control, starting spraying when individual leaves have 1-2 disease spots, spraying once every 3-4 days, for 4-6 consecutive sprays. Baking soda can both prevent disease and promote growth, and increase pumpkin yield by 10-20%. When spraying, use a nozzle with as small an aperture as possible to reduce leaf surface humidity.