Native to Central America, squash bugs are now found wherever squash is grown.
Illustration By Keith Ward
This article is part of our Organic Pest Control Series, which includes articles on attracting beneficial insects, controlling specific garden pests, and using organic pesticides.
Squash Bugs (Anasa tristis)
One of the most common pests encountered when growing pumpkins or squash, squash bug (Anasa tristis) adults and larvae feed on the leaves, stems and fruits of squash and pumpkins; late in the season fruits may be swarmed by immature nymphs. Badly hit plants produce poorly because so many leaves are consumed and fruits are damaged. Organic controls for squash bugs include crop rotation, using row covers and dedicated handpicking. Trap cropping also can be used to manage squash bugs in the vegetable garden.
What Are Squash Bugs?
Native to Central America, squash bugs are now found wherever squashes are grown. Emerging in mid to late spring, just as pumpkin and squash begin growing vigorously, squash bug adults are gray, oval-shaped stink bugs capable of flying on warm days. Adults are often seen lurking in squash foliage, looking for mates. Much more visible are the dark brown egg clusters attached to either side of leaves, often between leaf veins. Small, gray nymphs with long black legs appear a few weeks later, along with many additional egg clusters.
What Squash Bug Damage Looks Like
Squash bug larvae and adults feed by inserting their needle-like mouth parts into squash or pumpkin leaves, stems or fruit to suck plant juices. As they feed, they release a toxin that causes injured tissues to turn black or brown and die. When plants develop fruits, adults and nymphs often damage them by making numerous pinprick holes. In some areas, squash bugs vector a viral disease called Cucurbit Yellow Vine disease, which causes plants to turn yellow and stop growing.
Squash Bug Life Cycle
In fall, squash bugs fly to nearby wooded areas and overwinter beneath bark or other cover. In spring, they emerge and search for squash, pumpkins or other suitable host plants in the squash family. After a little light feeding, mated females lay clusters of glossy brown eggs on both sides of leaves. The eggs hatch about two weeks later, and the nymphs feed for a month or more before reaching adulthood. Meanwhile, the adult females continue laying eggs. A six week complete life cycle is typical. This means a second generation can emerge at the perfect time to sabotage fall pumpkins or winter squash.
Squash Bug Predators
Numerous natural predators can assist in the struggle to manage squash bugs, though most of them are most active late in the season. Natural enemies of the squash bug include Tachinid flies and tiny egg parasites that resemble flying ants.
Organic Squash Bug Control
Good organic control of squash bugs involves using several different methods. Yellow summer squash are generally very attractive to squash bugs, as are buttercup squash and large pumpkins. When grown as crop plants, these attractive strains should be protected with floating row covers until they start to bloom heavily. You also can use a small planting of early yellow squash as a trap crop for squash bugs. When a number of squash bugs have gathered on the plants, place a bag over them and pull them up. Pull only one plant at a time, which forces surviving squash bugs to move to neighboring plants.
You also can use the opposite approach by including butternuts and other C. moschata species in your garden, which are slightly less attractive to squash bugs compared to other squash. However, when they are the only squash grown, squash bugs will feed on them quite happily.
Squash bugs are naturally attracted to the shelter near the base of squash plants, and both organic and plastic film mulch can provide them with convenient hiding places. You can exploit this behavior by placing boards or thick pieces of cardboard beneath plants. Early in the morning, squash bugs found hiding beneath the boards can be quickly scraped off into a bucket of soapy water.
Handpicking adults and nymphs, and removing egg clusters from leaves, are required activities after row covers have been removed in midsummer. Spraying the plants with water causes adults to move toward high leaves, where they are easy to grab. In situations where squash bugs are out of control, many gardeners gather them using small shop vacs with an inch or two of water in the reservoir. As for squash bug eggs, you can scrape them off with a wet fingernail or table knife (the glue that attaches them to the leaf is water soluble), or by using small pieces of duct tape, wrapped around your finger with the sticky side out.
More Advice on Organic Squash Bug Control
Keep a close watch on your growing squashes and pumpkins in late spring, and pick and destroy any adults in search of host plants. Use floating row covers to protect plants until they start to bloom. Do all you can to provide food and habitat for wasps, tachinid flies and other beneficial insects. When adults are seen, immediately start scouting for eggs.
Some gardeners combine handpicking with sprays made from natural soaps, which can desiccate young squash bugs.
If you keep chickens or other poultry, allow them to clean up beds where you plan to grow squash or pumpkins before the crops are planted, and again at the end of the season.
More information on organic squash bug control is available from Colorado State University, University of Minnesota and North Carolina State University.