The Latest Technical Methods and Tutorial for Watermelon Pest and Disease Control

Watermelon is an annual trailing vine plant of the genus Citrullus in the Cucurbitaceae family. Its main diseases include watermelon anthracnose, watermelon damping-off, watermelon viral disease, watermelon powdery mildew, watermelon Phytophthora blight, watermelon cottony leak, watermelon southern blight, watermelon gummy stem blight, watermelon brown rot, watermelon root-knot nematode disease, watermelon leaf blight and watermelon Fusarium wilt, etc. Now let us take a look at watermelon pest and disease control techniques together!

Watermelon Anthracnose

[Symptoms]At the seedling stage, semicircular or circular brown lesions appear on the edges of the cotyledons, on which small black dots or pale red sticky material are produced. When young stems are affected, the diseased part turns dark brown and constricts, causing the seedlings to topple over. Leaf lesions are actually circular pale yellow water-soaked small spots that later turn brown, with purple-brown edges and a pale brown center, bearing concentric rings and small black dots. The lesions tend to perforate.

[Occurrence Pattern]The optimum temperature for pathogen growth is 24-25°C, and the humidity is above 90%. Under high temperature and dry conditions, the disease is relatively mild.

[Control Methods]First use disease-free seeds, or disinfect the seeds by soaking them in warm water at 55°C for 15 minutes, or soaking them in a 100-fold dilution of 40% formaldehyde for 30 minutes, then wash them clean with water before sprouting. In the early stage of the disease, spray a 400-500-fold dilution of 70% mancozeb, or a 500-fold dilution of 65% zineb or carbendazim, once every 5-6 days, for 2-3 consecutive sprays.

Watermelon Damping-off

[Symptoms]In the early stage of the disease, the area of the seedling near the ground surface appears yellow and water-soaked, then turns yellow-brown, dries up and shrinks, so that the seedling breaks off as soon as it is pulled.

[Occurrence Pattern]The pathogen spreads with rain and flowing water. Low soil temperature (10-15°C), high humidity in the seedbed, cool nights and insufficient light during the day all favor the onset of the disease. When the seeds and seedbed soil carry many pathogens, the chances of the seedlings becoming infected are also greater.

[Control Methods]① Agricultural control: Strictly choose soil that is high-lying, well-drained and has not previously grown cucurbits. Strengthen seedbed management and do a good job of heat preservation, ventilation and humidity reduction. When the seedbed humidity is too high, a small amount of plant ash or dry soil can be scattered on it, and ventilation can be used to reduce humidity. ② Chemical control: As soon as diseased plants appear, immediately remove the diseased seedlings and spray copper-ammonia mixture to prevent the disease from spreading. A 700-800-fold dilution of 75% chlorothalonil can also be sprayed.

Watermelon Viral Disease

[Symptoms]On melon plants, symptoms first appear on the upper leaves, showing a mosaic mottling of alternating dark and light green, with leaves becoming smaller and curled, stems twisted and stunted, and the plant dwarfed. The melons become smaller, and they also bear mottling of alternating dark and light green. When watermelon is affected, yellow-green mottling appears on the leaves, the leaf surface becomes uneven, newly grown leaves are deformed, and infected leaves are narrow and long, shrunken and twisted; the floral organs develop poorly, and no fruit is set or the fruit is deformed.

[Occurrence Pattern]High temperature and strong sunlight favor the onset of the disease, and melon fields lacking fertilizer and with weak growth vigor often suffer severe outbreaks.

[Control Methods]Kill aphids promptly. Effective agents include a 3000-fold dilution of 20% fenvalerate emulsion, a 2000-3000-fold dilution of 2.5% deltamethrin, and a 1500-2000-fold dilution of 40% dimethoate emulsifiable concentrate. In severe cases, use 4 vials of 800,000-unit penicillin mixed with 15 kg of water for spraying. Alternatively, using 2 vials of antitoxin (20 ml) plus 50 g of zinc sulfate mixed with 15 kg of water to spray the leaf surface also has a notable effect.

Watermelon Powdery Mildew

[Symptoms]In the early stage of the disease, tiny circular white spots appear on the leaves, which later expand into white powdery patches; the lesions connect into continuous sheets, covering the leaves and stems with white powder.

[Occurrence Pattern]When field humidity is high and the temperature is 16-24°C, the disease is severe. Watermelon and melon grown in greenhouses and plastic tunnels often develop the disease earlier and more severely than open-field cultivation because of poor air circulation and high humidity.

[Control Methods]Pay attention to field sanitation, promptly remove diseased leaves and burn them in a centralized manner. Strengthen cultivation management, apply more phosphorus and potassium fertilizers, and improve plant resistance. In the early stage of the disease, spray a 120-200-fold dilution of agricultural antibiotic 120, or a 1500-2000-fold dilution of 15% triadimefon, or an 800-1000-fold dilution of 70% thiophanate-methyl wettable powder.

Watermelon Phytophthora Blight

[Symptoms]Both seedlings and mature plants can develop the disease, affecting leaves, stems and fruits. When cotyledons are infected, dark green water-soaked circular spots first appear, the center gradually turns reddish brown, and the area near the ground constricts or dies. When true leaves are infected, dark green water-soaked circular or irregular lesions first appear and spread rapidly; when humidity is high, they rot or look as if scalded by boiling water, and after drying they become pale brown and easily broken. When the stem base is infected, spindle-shaped water-soaked dark green sunken spots form, surrounding the stem and rotting it, and everything above the affected part dies. When fruits are infected, dark green circular water-soaked sunken spots form, then rapidly spread to the whole fruit, causing the fruit to rot and give off a silage odor.

[Occurrence Pattern]The temperature range for the disease is 5-37°C. The optimum temperature is 20-30°C. During the rainy season and under high temperature and high humidity, the disease develops rapidly; poor drainage, overly dense planting, dense stems and leaves, or poor ventilation lead to severe outbreaks.

[Control Methods]From the early stage of the disease, begin spraying a 700-800-fold dilution of 50% copper hydroxide-metaxyl wettable powder, an 800-fold dilution of 35% oxadixyl-copper wettable powder, an 800-fold dilution of 72.2% propamocarb aqueous solution, or 58% metalaxyl-mancozeb (ridomil-zinc) wettable powder.