Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu
This has been a particularly bad year for striped cucumber beetles and squash bugs in watermelon, pumpkin and squash. Some fields have been hit particularly hard with beetles causing 10-15% plant loss due just to their feeding. The biggest problem with these pests and why control sprays have not worked well is that they are consistently hiding in the plastic hole where they are feeding on the stem (Fig. 1). Sprayers are set up usually to cover a lot of leaf canopy and do not do a very good job of putting chemical down in the plant hole. This stem feeding can be severe enough that either pest alone could cause some wilting, but with both feeding on this relatively small area of the stem they are causing considerable damage (Fig. 2). In one case, when the pumpkin plant was pulled up 3 squash bugs refused to move off of it, so intense was their feeding (Fig. 3). It is hard enough to kill squash bug adults with a good cover spray, but when only small amounts of spray are reaching them down in the plant hole they will not be controlled. Often it is possible to walk by plants and even inspect them and still see no beetles or squash bugs, as they will stay down at the base of the plant and only move when the base is exposed. In one field 1 out of every 15 plants was wilting (Fig. 4) due to squash bug and cucumber beetle feeding. These pictures are from a pumpkin field but the same problem is occurring in watermelon fields with both striped cucumber beetles and squash bugs feeding on plants down in the plant hole. If this type of feeding is occurring in your fields, insecticide applications (pyrethroids such as Asana, Warrior, bifenthrin) must be directed down at the base of the plant.
Figure 1. Cucumber beetle feeding at base of plant in plastic hole
Figure 2. Severe feeding on pumpkin stem by striped cucumber beetle and squash bugs
Figure 3. Three squash bug adults refusing to relinquish their pumpkin stem
Figure 4. Wilted plant due to striped cucumber beetle and squash bug feeding at its base