How to Treat Downy Mildew in Melons? A Detailed Guide to the Latest Control Methods
Downy mildew in melons is a fungal disease that affects melons, mainly targeting cucurbit crops grown year-round in greenhouses; it can occur continuously, and once it appears it is usually uncontrollable, spreading extremely fast, causing the middle and lower leaves to dry up and quickly spreading upward, resulting in major losses. It can be controlled through field management or chemical spraying, and other methods. Let's take a look together at the control methods for downy mildew in melons!
Damage Symptoms
Downy mildew in melons mainly damages the leaves. When infected at the seedling stage, water-soaked small spots appear on the cotyledons, which later expand into light brown lesions, and under high humidity a grayish-purple mold layer grows on the underside of the leaves. When infected at the adult plant stage, light yellow lesions appear on the leaf surface, expanding along the leaf veins into a polygonal shape; when there is dew or guttation on the leaf surface in the early morning, the lesions appear water-soaked, and later the lesions become light brown or yellow-brown polygonal spots. Under continuous rainfall conditions, the lesions rapidly expand or merge into large patches, causing the leaves to curl upward or dry up, with all the lower leaves drying up, sometimes leaving only a few green leaves near the growing point. If the disease enters the rainy season during the fruit development period, it spreads rapidly, reducing yield by 30 to 50%.
Conditions for Onset
The pathogen of downy mildew in melons has a wide temperature tolerance, with 15 to 24°C being suitable for disease onset. In production, excessive watering or moderate to heavy rain after watering, a high groundwater table, and dense plants and leaves make the disease more likely to occur. It mostly starts on the leaves near the roots, and the pathogen spreads through wind and rain or irrigation water. Pathogen germination and invasion have high humidity requirements; the pathogen can only invade when there are water droplets or a water film on the leaves, and the disease develops rapidly when the relative humidity is above 83%.
Control Methods
1. Agricultural control: Choose downy mildew-resistant varieties such as Yellow River Honey Melon, Red-Fleshed Netted Melon, Snow White, and Suizhou Large White Melon. Practice crop rotation, drain promptly after rain, and never flood-irrigate. Fertilize reasonably, train the vines in time, and maintain ventilation and light penetration. Avoid neighboring or continuous cropping with cucurbit crops, and where conditions permit, use rain-shelter cultivation. From July to August, do not water after rain; if water is needed, water half the furrow, and never flood-irrigate.
2. Nutritional control: After melons flower, apply 0.2 kg of urea and 0.5 kg of white sugar (or brown sugar) per mu, mixed with 40 to 50 kg of water, as a foliar spray, once every 5 to 6 days, for 4 to 5 consecutive sprays; or apply 500-fold diluted organic active liquid fertilizer such as "Gaomeishi UA-102 Nutrient" at 50 to 70 kg per mu to the leaves and root soil, once every 7 to 10 days, for 2 consecutive sprays, to enhance plant resistance and prevent disease onset.
3. Chemical control: At the early stage of disease onset, spray 70% phosethyl-aluminum · mancozeb wettable powder at 500-fold dilution, or 18% metalaxyl · mancozeb wettable powder at 600-fold dilution, or 64% oxadixyl · mancozeb wettable powder at 400 to 500-fold dilution, or 72% kekangling wettable powder at 800-fold dilution, or 50% thiram wettable powder at 600-fold dilution, or 25% ridomil wettable powder at 800-fold dilution, or 20% benalaxyl emulsifiable concentrate at 350-fold dilution, or 72% kelü wettable powder at 700-fold dilution, once every 7 to 10 days, for 3 to 4 consecutive treatments.