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.
Spider mites attack the plants when weather is hot and dry.
For more specific information on the identification of diseases and insects and spray recommendations, contact your local county agent. Harvesting Determining optimum maturity of a watermelon can be difficult. There are several clues to look for when harvesting. First, inspect the tendril opposite the area at which the watermelon is attached to the stem. This curly structure should be brown or dead.