Rindworm is a general term referring to a number of insect larvae that feed on the surface of watermelon fruit. The most common culprits are the larvae of the cucumber beetle or corn rootworm. These larvae live in the soil and feed on the underside of the developing melon. Feeding damage is very superficial and does not affect the eating quality of the melon (Figure 3). Unfortunately, many buyers have a low tolerance for even superficial defects. US industry tolerances are 5 in2 per melon, with no more than 10% of the melons affected.
Chemical controls targeting the larvae are usually ineffective, as it is almost impossible to get contact activity on the underside of the melon. Control of the adult populations of cucumber beetles in the spring may help to reduce summer feeding activity.
Additional types of larvae that occasionally feed on watermelon rinds are European Corn Borer, Armyworm and late-season cutworms such as the Variegated Cutworm and the Western Bean Cutworm. These worms typically feed on the upper surface of the melon, making chemical controls somewhat more effective. Scout all cucurbit fields regularly for signs of insect activity and feeding damage.