How to Manage Pests

UC Pest Management Guidelines


Squash Bug

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.

Cultural Control

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.

  • Do not remove the entire plastic row cover at one time because a drastic reduction in humidity will shock plants and can lead to collapse. Instead vent the covers and remove them gradually. Covers made of spun-bonded materials do not need venting because hot air is able to escape.
  • Remove row covers if the air temperature underneath reaches 104° F before bloom.
  • Remove row covers before plants grow high enough to touch hot plastic.

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.

Common name Amount per acre REI‡ PHI‡
(Example trade name)   (hours) (days)

Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Not all registered pesticides are listed. Always read the label of the product being used.
  (Venom) 1–4 oz 12 1
  COMMENTS: An earlier season soil application that targets aphids and whiteflies can provide protection for about 40 days. Make a foliar application later in season after soil application has lost its effectiveness.
  (Warrior II with Zeon)* 1.28–1.92 fl oz 24 1
  (Asana XL) 5.8–9.6 oz 12 3
  COMMENTS: Repeat as necessary to maintain control. Do not exceed 0.25 lb a.i./acre per season. May encourage the buildup of pest mite populations. Highly toxic to honey bees.
  (PyGanic EC 1.4) 16–64 oz 12 0
  COMMENTS: Apply round the base of plants a few days after eggs are first laid and nymphs are beginning to hatch. Follow with a second application 10 days later. Buffer final spray to a pH of 5.5 to 7.0.
  (M-Pede) 1–2% solution 12 0
  MODE OF ACTION: A contact insecticide with smothering and barrier effects.
  COMMENTS: Thorough coverage is important. Can control small nymphs; not as effective on older nymphs or adults.
  (TriTek) 1-2 gal/100 gal 4 0
  (Organic JMS Stylet Oil) 3–6 qt/100 gal 4 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: Thorough coverage is important. Can control small nymphs; not as effective on older nymphs or adults. Oils may cause phytotoxicity problems; exercise care when using these materials. Check with certifier to determine which products are organically acceptable.
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
1 Rotate chemicals with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; chemicals with a 1B group number should be alternated with chemicals that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).
* Permit required from county agricultural commissioner for purchase or use.
# Acceptable for use on organically grown produce.



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Cucurbits
UC ANR Publication 3445

Insects and Mites

E. T. Natwick, UC Cooperative Extension, Imperial County
J. J. Stapleton, UC IPM Program, Kearney Agricultultural Center, Parlier
C. S. Stoddard, UC Cooperative Extension, Merced & Madera counties

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

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