A Detailed Guide to the Latest Control Methods for Watermelon Gray Mold

Watermelon gray mold occurs throughout the country and is caused by infection with Botrytis cinerea of the genus Botrytis in the Deuteromycotina. It is severe in the humid and rainy regions of the south, causing seedling death and fruit rot that reduce yield. Besides watermelon, it also harms cucumbers, eggplants, tomatoes, common beans, and many other vegetables. Now let us take a look together at the control methods for watermelon gray mold!

Damage Symptoms

Watermelon gray mold mainly harms leaves, stems, and fruits. On young leaves, water-soaked dirty spots first appear, then expand into brown or ink-colored patches and tend to perforate. On stems, elliptical or longitudinally elongated sunken black spots appear, with cracking in the middle. Young fruits first develop dark brown sunken spots, and later their development is hindered, forming deformed fruits. Fruit lesions are mostly scab-like, and some crack or rot into holes. The diseased parts secrete a translucent gelatinous substance that later turns into amber-colored lumps. When humidity is high, dense soot-colored mold layers grow on the surface of all diseased parts. Watermelon gray mold can be called a devastating disease of watermelon. It is widespread, difficult to eradicate, and seriously affects yield and quality, with yield loss reaching more than 50%, up to total crop failure.

Disease Pattern

The pathogen overwinters in the soil as mycelium and sclerotia with diseased residues. In the spring of the following year, the mycelium produces conidia, and the sclerotia germinate to produce conidiomata and release conidia, which spread by airflow and rainwater, harming watermelon seedlings, flowers, and young fruits and causing primary infection. Mold layers are produced on diseased parts, further producing large numbers of conidia that reinfect watermelon and expand the spread. When temperatures drop in early autumn, sclerotia are again produced and lie dormant in the soil to overwinter. The suitable temperature for pathogen growth is 22-25°C, and the survival temperature is -2-33°C. The relative air humidity for conidia formation is 95%. Therefore, under conditions of high temperature and high humidity, the disease occurs more severely.

Chemical Control

1. Biological agents: 1% Wuyimycin aqueous solution at 200 times dilution can be selected, spraying 20-30 kg per mu, once about every 7 days, for 2-3 consecutive sprays.

2. Chemical pesticides: In the early stage of the disease, 50% procymidone or iprodione wettable powder at 1000-1500 times dilution, or 60% Fangmeibao wettable powder at 500 times dilution, or 70% thiophanate-methyl wettable powder at 800 times dilution can be selected, spraying once about every 7 days, for 2-3 consecutive sprays. 40% Shihuile suspension concentrate, or 21% Baijundi, or 20% propiconazole emulsifiable concentrate can also be used, all with very good control effects.

Agricultural Control

1. Crop rotation: Carry out crop rotation and changing of crops for more than 3 years, and apply fully decomposed organic fertilizer.

2. Seedling soil disinfection: For each square meter of seedling bed or planting hole, irrigate with 4-5 kg of 70% fenaminosulf technical powder at 1000 times dilution.

3. Greenhouse disinfection: Use Baijunqing smoke agent or iprodione smoke agent to fumigate the greenhouse, using 0.25 kg of pesticide per large greenhouse, fumigating once every 8-10 days, for 2-3 consecutive fumigations.