Squash bugs (Anasa tristis) are common pests on plants in the cucurbit family, including squash, pumpkin, melon, cucumber and zucchini. Leaves may develop small specks that turn yellow, then brown beyond the point of attack. Vines start to wilt, and parts of the plant blacken, turn crisp and die. Young plants may completely succumb to a squash bug infestation. If infested plants survive, their yield can be greatly reduced.
Squash bugs usually hide in leaf axils, along leaf veins or on the undersides of leaves. In some cases, the population density is so high the bugs are obvious. The five-eighths-inch- long, winged adults are gray, yellow-brown or black. They are flat-backed, often speckled and may have a covering of dense black hairs. An orange or orange-brown stripe borders the abdomen. The wingless nymphs are smaller versions of the adults but have a reddish head and pale green to almost white abdomen without a stripe. As they age, squash bugs turn brown.
The eggs, laid in clusters of a dozen or more from late spring through midsummer, are yellow-brown to bronze ellipses. They hatch into nymphs within approximately 10 days. The nymphs turn into adults within four to six weeks.
Adults are active from when the vines start to spread through the harvest season. There is one generation per year.
Squash bugs are sometimes called “stink bugs” because of the foul odor they exude when crushed.
Squash bugs have sucking mouthparts feeding on leaves and stems by inserting their straw-like mouthpart into plant tissue. They suck out the sap causing a speckling effect around the point of insertion. Damage tends to be localized.
MANAGEMENT: Squash bugs are challenging to control. Early plantings are more susceptible to damage. Choose resistant Cucurbit family varieties. Rotate crops and avoid planting cucurbits in the same place as the previous season. Alternatively, if you have had an infestation, take a break from planting these family members for one year.
Closely monitor areas where cucurbit crops are planted and remove bugs and eggs. Trap them by placing boards in and near the garden. Turn the boards over daily and kill or vacuum up the bugs. Handpicking the bugs off plants is another effective technique. When the bugs congregate on just a few leaves, simply cut the leaves off and put them in the garbage. Do not compost infested plant parts. In spring and early summer, search out the egg masses and destroy them.
Since these bugs overwinter as unmated adults in protected places in mulch, old plants or weeds, remove all plant debris from the garden after harvest. Leave the garden site clean and free of hiding places for overwintering bugs. Natural predators such as the tachinid fly and wolf spiders can help to control squash bug populations. Chemical insecticides are only temporary solutions to a squash bug problem, because populations resurge within a few days or weeks. Insecticides can also damage cucurbits. Better alternatives are to reduce the numbers of reproductive adults and practice good sanitation in the garden.