A second application is warranted if plants are healthy, small fruit is present, and there is little to no weed pressure. Watering is very important in growing watermelons. The key time to water is from the time the fruit is beginning to form until it is half-grown. A lot of water near harvest will reduce the sugar content and cause the fruit to have hollow centers. Diseases Fungus diseases such as gummy stem blight, anthracnose, and alternaria leaf blight can be serious problems in wet seasons.
Most gardeners can harvest fruit without having to apply fungicides.
Watermelons need to be rotated in the garden to reduce soilborne diseases like fusarium wilt. By selecting the most disease-resistant varieties, rotating the crop, and not crowding the plants, most serious problems can be avoided. Insects and Mites Striped and spotted cucumber beetles are the most damaging insects to watermelons. They cause most of the feeding damage early in the season. Aphids or plant lice will feed on the bottom of the leaf, causing it to curl under.