Squash is relatively easy to grow, but insect problems can be a serious concern for any gardener.

Squash (Cucurbitais, a genus in the gourd family Cucurbitacea)  is one of the favorite plants in the Ohio vegetable garden. Cucurbitais includes pumpkins, zucchini, acorn squash, pattypan squash, spaghetti squash, and yellow squash, to name a few. Squash is relatively easy to grow, but insect problems can be a serious concern for any gardener. Two common pests are the squash vine borer and squash bugs.  Gardeners across the region can benefit from gaining an understanding of these insects' individual lifecycles and habits. Further, much can be done to control and prevent them.

Squash bugs (Anasa tristis) damage plants as both nymphs and adults.  Squash bugs feed on plant juices from the leaves and inject a toxin that causes the leaves to die. Plants are more susceptible to damage when they are young.  Rapid wilting is a key sign of squash bug damage, and leaves will turn crispy and black before dying. 

Identifying the squash bug

• Adults are about 5/8" long, gray or brown in color. They are an elongated oval with a pointed head. When squished they have a rather unpleasant smell.
• Eggs are orange to yellowish-brown in color and take 10 to14 days to hatch. Adults will lay eggs until mid-summer.
• Nymphs (instar- immature stages) are the same shape as adults but smaller. Younger nymphs will be green in color and darken with age and growth. They feed on leaf sap and grow for 4 to 6 weeks until they reach maturity.

Squash bugs live and lay eggs on the undersides of the leaves in clusters. They will overwinter under old vines, leaves, in the soil or under rocks. Squash bugs produce one generation a year. 

Control

• Check the undersides of the leaves in mid - in June for eggs and small nymphs. If spotted, hand pick the eggs and nymphs off the leaves and kill them in a container of soapy water. Squash bugs are much easier to deal with when they are young.
• Clean up the garden in the fall by removing remaining plant material and rocks. Don't leave a place for these bugs to overwinter.
• Wood mulch is a great place for these bugs to hide, so refrain from mulching your squash plot.
• Garden rotation is a good prevention method. Rotate squash with non-Cucurbitacea families.
• Using a combination of newspaper, straw and secured row covers will keep adult squash bugs away and prevent them from laying eggs.  This cover may be used at planting and can remain in place until flowering starts. Row covers will need to be removed to allow for pollination.

Varieties that are most resistant to squash bugs include zucchini, acorn, spaghetti, butternut, and green striped Cushaw.

Squash vine borer (Melittia satyriniformis) is a serious insect problem found east of the Rocky Mountains. Larvae cause damage to the plant by eating and destroying the inside of stems, causing the plant to die in sections or as a whole. Adult squash vine borers are moths that fly during daylight hours and rest at night.

• Adults look like wasps, ½ inch long with an orange abdomen and black dots.  Adults emerge from underground and are active for most of the summer, with the abundance of them out in July.
• Larvae are creamy white with brown heads, up to 1 inch in length.
• Eggs are 1/25th of an inch, flat and brown in color, and are found singly near the ground.

Squash vine borers overwinter in the soil (1-5 inches underground) as full grown larvae in cocoons. Adults emerge in June and lay individual eggs at the base of squash plants. Eggs hatch within  9 to 14 days and the larvae will then bore into stems to eat. The larvae feed through the center of the stem, blocking the flow of water and nutrients to the rest of the plant.  They will feed for 4 to 6 weeks, then leave the stem and burrow a couple inches into the soil to pupate and overwinter.  Only one generation is produced a year.

Damage is seen by sudden wilting of the plant. Many times a single plant will wilt while others remain perfectly fine. Because the damage is happening inside the larvae often go unseen. The point of entrance can be spotted by finding a small hole in the stem with yellow sawdust-like frass (excrement of plant-eating insects). The infested plants are weakened and may die, others will struggle the rest of the summer.

Control

• Cover vines at the leaf joints with soil to encourage additional secondary roots that can sustain the plant if damage occurs at the main stem.
• When harvesting is complete, remove all remaining vines so that the late larvae can't complete their lifecycle.
• Turn over soil in the fall or spring to wipe out cocoons.
• Cover stems with nylon stockings or foil to prevent eggs from being laid.
• Remove and kill eggs before they hatch.

Squash varieties that are less likely to be attacked by squash vine borer include summer crookneck, dickenson pumpkin, green striped cushaw and butternut. Least tolerant include hubbard and zucchini.

Vegetable gardening can be fun and very rewarding, but problems arise when some of Mother Nature's insects move in. Don't get discouraged. Work at fixing the problems by using good garden care, responsible garden maintenance and planting resistant varieties.


Barbara Arnold is green corps coordinator at Franklin Park Conservatory.