Squash Bugs in the Garden

By David Fuller, Colorado Master Gardener, Tri-River Area

Squash bugs (Anasa tristis) are a common pest in gardens that attack various types of cucurbits, including all types of squashes, zucchini, pumpkins, gourds, melons and cucumbers. Squash bugs cause significant damage to plants by sucking the sap from within leading to wilting and death.

Squash bug adult, Whitney Cranshaw,
Colorado State University, Bugwood.org 

The adult squash bugs are a flat, oval shape roughly half an inch long and have a brown or grayish-black appearance. They also have distinctive orange-yellow markings on their legs and antennae. Some also have an inverted V or diamond shape in the middle of their backs with white dots around the perimeter. While mainly seen walking on plants, squash bugs can also fly.

Squash bug nymphs, Gerald Holmes, Strawberry Center,
Cal Poly San Luis Obispo, Bugwood.org 

Adults hibernate under debris in the garden and surrounding areas through the winter. Adults become active and first appear in June when they start feeding on young plants. Once they wake and begin to feed, they then begin to look for mates. An adult female squash bug can lay up to 200 eggs in clusters primarily found on the underside of leaves. Eggs hatch in one to two weeks. After hatching the nymphs have green bodies that change to gray after a few weeks. The nymphs usually feed together in groups on the underside of plants. Nymph to adulthood takes 4 to 6 weeks depending on temperature, relative humidity, and availability of food. Pest populations grow quickly during hot and dry conditions and depending on the location there can be one, two or three generations per season. Adults that develop late in the season do not lay eggs.

Squash bug eggs on the underside of a leaf, 
Whitney Cranshaw, Colorado State
University, Bugwood.org 

Using some of the following methods of control will help reduce the population.

Maintaining healthy plants is the best defense against pest in the garden. Crop rotation, removing plant debris, and covering crops with floating row covers are some effective ways to prevent a buildup of squash bug populations. Good weed control is also crucial to reducing squash bug habitat in the garden.

Another solution is planting nasturtium, natural companion plants that work to repel squash bugs, between plants that are affected by the pests. The parasitic fly Trichopoda pennipes is a predator of squash bugs. The larva will burrow into the body of the host, where it will live for approximately two weeks, at which point it will emerge from the host, killing the squash bug.

Handpicking and destroying squash bugs, as well as their eggs, is an effective way to control them. You can also capture them by using a piece of duct tape. Eggs are usually laid in clusters on the undersides of leaves and are yellow to bronze in color. Once you catch them simply drop them into a bucket of soapy water or step on them.

Neem oil is a natural pesticide that can be used to control squash bugs. It works by interfering with the bug’s feeding and reproductive abilities.

Insecticidal soap is a contact insecticide that works by suffocating the bugs on contact. It is effective against all stages of the bug’s life cycle and is safe for use in gardens. You can also mix your own homemade spray using tsp mild liquid soap to a liter of water (always spot-test sprays before using them on any plant).

Chemical insecticides, such as carbaryl (Seven XLR), permethrin (Permethrin SFR 36.8%) and lambda cyhalothrin (Warrior, Matador) can also be used to control squash bugs. However, it's important to follow the label instructions carefully and to rotate insecticides to prevent the development of resistance.

Squash bug damage, Whitney Cranshaw,
Colorado State University, Bugwood.org 

I have learned that the best time to control squash bugs in the summer heat is after a rain or an irrigation because the bugs will come to the surface, where they can be easier to spray or hand pick. During the summer they will bury down into the soil to get away from the heat, which is why after a rain is the best time to remove the pest.

In conclusion, controlling squash bugs requires a combination of cultural, mechanical, and chemical control methods. Early detection and control are crucial to minimize damage to plants and to prevent the buildup of populations.

Learn more about squash bugs and  from the CSU Extension factsheet: Squash Bug: Management in Home Gardens and find out more about growing squash at this CSU Extension fact sheet Cucumbers, Pumpkins, Squash, and Melons.