How to Manage Pests
UC Pest Management Guidelines
Scientific Name: Anasa tristis
(Reviewed 12/09, updated 6/12, pesticides updated 5/16)
In this Guideline:
Description of the Pest
The adult squash bug is 0.65 inch (1.5 cm) in length. It is brownish yellow but appears black because of a dense covering of black hairs. Protruding margins of the abdomen are orange or orange and brown striped, and the margins of the pronotum are yellow. Shiny, elliptical reddish brown eggs are laid singly or in groups of 15 to 40 on the underside of leaves or on stems. Young nymphs are pale green, while later instars have a blackish thorax and brownish abdomen; they are often covered with white powder.
Injury occurs on squash, pumpkins, and melons. Adults and nymphs cause damage by sucking plant juices. Leaves lose nutrients and water and become speckled, later turning yellow to brown. Under heavy feeding, plants begin to wilt, and the point of attack becomes black and brittle. Small plants can be killed completely, while larger cucurbits begin to lose runners. The wilting resembles bacterial wilt, which is a disease spread by another pest of squash, the cucumber beetle. The wilting caused by squash bugs is not a true disease. Squash bugs may feed on developing fruits, causing scarring and death of young fruit.
Good field sanitation and other cultural practices help to prevent damage by this pest. Treatments may be warranted if the insect is causing damage in the field.
Destroy crop residues and reduce overwintering hiding places.
In desert production areas, exclude squash bugs by applying row covers (plastic and spun-bonded materials) at planting and gradually removing them at first bloom or earlier if needed. Row covers are not recommended for the San Joaquin Valley.
Some plant varietal preferences occur: pumpkins, watermelons and squash are the most seriously damaged; zucchinis are less susceptible. Because squash bugs have a preference for squash, a squash planting can be used as a trap crop near other cucurbits plantings such as watermelon to concentrate an infestation. Treat the trap crop with an insecticide to control the infestation.
Organically Acceptable Methods
Cultural controls are acceptable to use in an organically certified crop along with sprays of PyGanic, insecticidal soaps, and certain oils.
Monitoring and Treatment Decisions
Squash bugs overwinter as adults under dead leaves, rocks, wood, and crop debris. In spring, search for squash bugs hidden in these places, near buildings, and in perennial plants. Inspect young plants daily for signs of egg masses. Start monitoring after transplanting or when seedlings emerge and continue monitoring through fruit development.
While no threshold has been established in California, in the Midwest one egg mass per plant is used to make treatment decisions. If the squash population exceeds the threshold, apply an insecticide early when most eggs are hatching because young nymphs are more susceptible to pesticides than older nymphs or adults. Squash bugs will feed on and damage young and mature fruit, therefore, control may be needed later as the crop matures.
UC IPM Pest Management Guidelines: Cucurbits
Insects and Mites
E. T. Natwick, UC Cooperative Extension, Imperial County
Acknowledgment for contributions to Insects and Mites:R. L. Coviello, UC Cooperative Extension, Fresno County
C. B. Fouche, UC Cooperative Extension, San Joaquin County
L. D. Godfrey, Entomology, UC Davis
J. B. LeBoeuf, AgiData Sensing, Inc., Fresno
M. Murray, UC Cooperative Extension, Colusa and Glenn counties
C. G. Summers, Entomology, UC Davis and Kearney Agricultural Center, Parlier