Managing Squash Bugs


by Karen Weiland, Advanced Master Gardener



An infestation of squash bugs (Anasa  tristis)can inflict quite a bit of damage in the garden.  They feed primarily on fruits such as pumpkins, melon and squash and can destroy the plant by sucking its sap from stems and leaves, causing the leaves to wilt and die.  In the fall, they can feed on unripened fruit, causing the fruit to go bad.

Squash bugs are about 5/8 of an inch long, winged and grayish brown with a flat back.  Orange-brown stripes can be seen on the edges of the abdomen and the undersides.  Squash bugs and stink-bugs are sometimes mistaken for each other.  Their shape and size are similar with stink-bugs being wider and rounder and they both release an odor when crushed.  The difference is that stink-bugs have this name because they can release their nasty odor when disturbed, not just crushed.  In the garden, stink-bugs prefer to feed on legumes and tomatoes.

Squash bug eggs are an orange to copper color, 1/16 of an inch long and are laid in clusters on the top or underside of the leaves and on stems.

I caught this adult laying her eggs. Hand picking the adults and destroying the eggs are very effective at ridding the garden of these pests.

Nymphs hatch in one to two weeks, are 3/16 to ½ inch long and range in color from a mottled white to a greenish gray with black legs.  They later turn brown, resembling an adult, and start growing their wing pads. During a time period of about 4 to 6 weeks, they molt several times, increasing their size each time and then become adults.

Unmated squash bugs overwinter by finding shelter under garden debris, rocks, wood, etc.  In the spring, they fly from their winter habitat to feed, mate and lay eggs.  Search for them early in the season.  They will be hiding under debris, in perennials and near buildings by the garden.

Place wooden boards or shingles randomly throughout the garden.  Squash bugs will use them as a night time shelter.  In the morning check under them for squash bugs, destroying them when found.

The best method for control of these bugs is through keeping the garden clean.  Remove cucurbit plants after harvest and keep the garden free from debris where bugs can overwinter.  During the growing season, pick off and destroy the egg masses as soon as you discover them.  Use protective covers such as row covers, removing them at bloom time to allow for the pollination process to take place.  Growing vines vertically can make cucurbits less vulnerable to squash bug infestations.  There are some squash varieties that are more resistant to squash bug damage than others.  Crop rotation can also contribute to control of the squash bug.

Using insecticides to kill squash bugs can prove to be difficult because they are often hiding near the crown and can be hard to reach with a spray.  Oils, such as neem oil and horticultural oil, are less toxic to the environment and work the best on the very small nymphs.  Good coverage is essential so that nymphs hiding under the leaves and deep within the plant will be reached.  Diatomaceous earth, a natural pesticide made from the fossilized shells of one-celled organisms called diatoms, is abrasive to many insects and can be dusted over plants and applied to the base of plants to reduce their numbers and will periodically need to be reapplied.  There are other, more toxic, pesticides that can be used however they also have a negative effect on bees and beneficial insects throughout the garden.  If an insecticide is used, it should be sprayed in late afternoon or evening to avoid injury to bees.


As always, Happy Gardening!


More information about gardening and related subjects can be found online at Purdue University.  The Purdue University Cooperative Extension Service can be reached at 499-6334 in LaGrange Co., 636-2111 in Noble Co., 925-2562 in DeKalb Co. and 668-1000 in Steuben Co.