Squash bugs are the biggest challenge to growing squash in our region. These pests don’t just infest zucchini and winter squash, they also feed on cucumbers and melons—all members of the cucurbit family. 

Squash bugs are about half an inch long, gray to black, with orange and brown stripes along their sides. They use a piercing mouthpart, called a proboscis, to suck fluids from a plant’s xylem and phloem. This damages the plant and often introduces bacterial wilt, a disease that causes leaves to turn yellow and brown and eventually collapse.

MANUAL REMOVAL

Female squash bugs lay up to 250 eggs between June and September. These hatch within 10 days, and the nymphs immediately begin feeding. If left alone, their population can explode in just a few weeks. They overwinter in plant debris and emerge in spring in search of food—often right where you planted squash last year. That’s why it’s important to rotate crops and avoid replanting in the same location.

Squash bugs lay up to 250 eggs between June and September which hatch within 10 days. Look for egg clusters on the undersides of leaves.

If you have just a few plants, look for brownish-copper egg clusters on the undersides of leaves, often near vein junctions. Squash them, scrape them off or press duct or packing tape (sticky side out) against them to remove and dispose away from the garden.

In 1938, Colorado State University conducted a study comparing methods of controlling squash bugs. A field treated with dry pyrethrins (chrysanthemum flower extract) and powdered gypsum yielded 12 tons of winter squash per acre. A second field, where squash bugs were removed by hand, produced 8.7 tons. The untreated control field yielded just 4 tons. It’s worth noting that even hand-picking squash bugs can nearly double your yield compared to doing nothing.

Gardeners who use non-chemical sprays promote agroecosystems, inviting natural predators and birds to help manage insect populations. Native flowers and landscaping attract beneficial insects like ground beetles, rove beetles, big-eyed bugs and wolf spiders—all natural enemies of squash bugs. Cover cropping and crimping (flattening crops after maturity) also encourage beneficial insect populations and fewer pests.

BIOLOGICAL CONTROLS

For true biological control, you can purchase parasitoids such as Hadronotus pennsylvanicus (a wasp) and Trichopoda pennipes (feather-legged fly), which lay their eggs on squash bugs. Their larvae consume the pest from the inside out.

Another popular method is using hoops or tomato cages and covering them with fine mesh netting—orchard netting (1.8 x 6 mm holes) allows pollinators through but blocks adult squash bugs. Thrip screen (0.015 mm openings) offers even tighter protection but blocks all insects, so it must be removed during pollination. Secure the edges well with sandbags, rocks or rebar.

CHEMICAL OPTIONS— USE WITH CAUTION

If manual and biological approaches aren’t working, pesticides like Sevin can control squash bugs, but they also harm beneficial insects, pollinators, earthworms, birds and pets. Its active ingredient, carbaryl, is a neurotoxin and suspected human carcinogen. Always follow label directions carefully.

Squash bug damage causes leaves to turn yellow and brown, wilt, and eventually collapse. They also can feed on cucumber and melon plants.

 Organic sprays are less harmful on the ecosystem but not as effective on squash bugs. Spinosad (from soil bacteria) and azadirachtin (from neem oil) work best on nymphs. Pyrethrins, horticultural oils and insecticidal soaps are mildly effective on nymphs but don’t do much to deter adults.

TRY LATE PLANTING

Another option is to delay planting until early June. Wait for the first wave of squash bugs to emerge and move on in search of food, then plant your crops. Choose 90-day varieties for winter squash or quick-maturing varieties of zucchini and yellow squash, which can be ready in 45-60 days. 

Send your gardening questions to Bryan in care of the BEACON, or email him at [email protected].

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