Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu
Many of the pumpkin fields in the Delmarva area I have visited in the last two weeks were just coming up or had 2-5 leaves on them. I was surprised to see several squash bugs on these small plants. I also found many egg masses (Fig. 1) on the underside of leaves, usually in the crotch of two veins. In some fields with plastic the squash bugs were feeding below the plastic mulch causing the plants to wilt (Figs. 2 and 3) and eventually die. Normally there are only a few fields that will have squash bugs this early, but just about all of the fields I looked at had enough squash bugs to justify treatment. Growers need to watch for squash bugs on their early pumpkin plants, especially down in the plastic hole. A spray may be needed if the plants are stressed (like they were last week from the intense heat) and there are 2 bugs or 1 egg mass per plant.
Figure 1. Squash bug adult and egg mass
Figure 2. One pumpkin plant (top) wilting due to squash bug feeding
Figure 3. Squash bugs at the base of wilted pumpkin plant under plastic mulch
One interesting aspect of these fields with squash bugs is that all the fields that had not been sprayed had many Trichopoda pennipes Tachinid fly parasitoids (Fig. 4) in them. These medium sized, orange bellied, black winged flies will lay white eggs on the underside or “shoulder” of squash bugs (Fig. 5). The eggs will hatch on the side attached to the insect and the maggot will enter the bug and feed inside, eventually killing the pest. While useful under moderate to low infestation levels of squash bugs, these parasitoids will not keep a large population of squash bugs below thresholds.
Figure 4. Trichopoda pennipes adult
Figure 5. T. pennipes eggs on squash bug