By Whitney Cranshaw, Colorado State University Cooperative Extension, Entomology
Squash bugs are the most important insect pest of squash in much of the state, particularly in the southeast and West Slope areas. Damage is caused by the feeding of the insects which use their piercing mouthparts to lacerate and destroy pockets of plant tissue. As infestations progress, large areas of the plant become girdled and wilt. Feeding on the fruit also occurs and the sunken wounds are ready entry courts for rots. Although hard "winter type" squashes (including pumpkins) are particularly susceptible, zucchini and other summer squashes are also damaged.
The adult squash bugs (left) are strong fliers and migrate to fields and gardens in early summer. Squash bug eggs (right) are shiny brown and elliptical, attached in groups to the underside of leaves.
Squash bugs are among the more difficult insects to control. This is in part due to the difficulties of spraying large plants such as squash. But squash bugs are also inherently resistant to most insecticides. Sevin is the standard insecticide for control in gardens; pyrethroids (e.g., Asana, Ambush, Pounce) or endosulfan (Thiodan) in commercial production.
An optimal timing for managing squash bugs involves early season control. A spray applied when the first eggs are observed and again 10-14 days later should provide good season-long control. This approach has the further advantage of having to treat fairly small plants so coverage should be good and to avoid insecticide use after flowering or near harvest.
However, it may be possible to further restrict the amount of insecticide needed by targeting the applications to the base of the plant. During the day, squash bugs usually seek shady cover and aggregate around the base of the plant. In addition, a few applications of diatomaceous earth around the plant base were also effective, providing an "organic" alternative.
Management around the base of the plant seems to be very important in other respects. When mulch is provided, an additional source of cover, squash bug injury increases. Therefore, it appears that a better approach is to try to open up the area of the plant base through plant training to reduce its suitability to squash bugs.
Photos: Whitney Cranshaw, Colorado State University, Bugwood.org
© CSU/Denver County Extension Master Gardener 2010
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Date last revised: 01/05/2010