How to control powdery mildew in pumpkins? Detailed explanation of the latest control methods
Powdery mildew in pumpkins is one of the most common and serious diseases affecting pumpkins, and pumpkins are also the cucurbit most severely affected by powdery mildew among all cucurbits. It mainly damages the leaves. The surface of affected leaves is mostly covered with a white powdery substance, causing photosynthesis to be significantly blocked, and in severe cases the leaves turn yellow and even scorch, affecting pumpkin fruiting. Let us take a look together below at the control methods for powdery mildew in pumpkins!
Damage characteristics
Pumpkin plants suffering from powdery mildew are most severely damaged in the later growth stage. It mainly damages leaves, petioles or stems, and fruit damage is less common. Initially, small white mold spots appear on the leaves or tender stems, then expand into mold patches 1-2 cm in size. When conditions are suitable, the mold patches expand rapidly and connect with one another, and the white powdery substance covers the entire leaf surface, causing the leaves to turn yellow and wither or curl up but not fall off. In late autumn, the mold patches turn gray, and small black granules grow on them, namely the cleistothecia of the pathogen.
Conditions for disease onset
Powdery mildew in pumpkins reaches its peak when high temperature and high humidity alternate with high temperature and dryness. At the same time, fields with more nitrogen fertilizer such as urea applied, excessive planting density, and damp conditions are prone to disease onset or more severe disease. After production ends, the pathogen overwinters on old plants and diseased plant debris. A comprehensive survey of resistance among varieties is still lacking. At present, it is only known that the Phoenix pumpkin bred in Taiwan, China has strong resistance, and the Tanzi pumpkin of Shashi, Hubei, and Jin Pumpkin No. 3 of Taigu, Shanxi are also relatively resistant to powdery mildew.
Control methods
1. Select good varieties: The Japanese Yixiang pumpkin, Jinli pumpkin, and Juhong pumpkin, which are currently planted more widely, have a certain degree of disease resistance, but purification and rejuvenation work should be done well, and disease-free seedlings should be selected.
2. Seed disinfection: Before sowing, first sun the seeds in sunlight for 1-2 days to kill miscellaneous bacteria on the seed coat and improve germination vigor. Soak the seeds in warm water at 50-55°C with stirring for 30 minutes, and when the temperature drops to 30°C continue soaking for 8-10 hours, then place them in a 1% potassium permanganate solution for disinfection for 20-30 minutes. After rinsing clean, germinate at 28-30°C for 48-72 hours, and sow when the radicle emerges.
3. Strengthen management: It is best to carry out a 2-3 year crop 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. Generally no topdressing is applied during the vine extension stage. During the fruit expansion stage, apply 20 kg of potassium sulfate compound fertilizer per mu as topdressing, and keep the soil moist. After rain, clear the ditches and drain water promptly. Remove diseased, old, and yellow leaves at the base in time, and bury them deeply or burn them in a centralized manner. Strengthen field ventilation and light penetration to enhance plant stress resistance.
4. Spray protective film: Before the onset of powdery mildew in pumpkins or in the early stage of onset, spray 99.1% Diphacin 300-500 times dilution on the leaves so that they form a protective film, spraying once every 5-7 days, for 2-3 consecutive sprays.
5. Chemical control: Apply pesticides at the appropriate time from late April to July for control. Before disease onset, 53.8% Kocide 2000 at 1000 times dilution can be used. In the early stage of onset, 10% difenoconazole at 1500 times dilution, or 40% flusilazole at 8000 times dilution can be used, or baking soda at 600 times dilution can also be used for control. Start spraying when 1-2 lesions appear on individual leaves, spraying once every 3-4 days, for 4-6 consecutive sprays. Baking soda can not only prevent disease but also promote growth, and increases pumpkin yield by 10-20%. When spraying, try to use spray nozzles with small apertures to reduce leaf surface humidity.