Squash bugs on Plants

Symptoms

Small white stipples appear on the leaves at the spots where feeding first occurs. As the bugs keep feeding, the leaves become speckled and later turn yellow to brown. Under heavy feeding, the leaves look yellow or brown and tattered.

Plants may wilt, and the feeding points become blackened and brittle. This wilting is sometimes called Anasa wilt. In severe cases, plants may wilt and die.

Fruit can be affected too. Young fruit may abort, become misshapen, or show scarring. The damage comes from squash bug adults and nymphs sucking plant juices. Leaves lose nutrients and water and become speckled.

Look for these signs on squash, pumpkin, melon, watermelon and zucchini. Pumpkins, watermelons and squash are the most seriously damaged, while zucchinis are less susceptible. Injury occurs on squash, pumpkins, and melons. Check the leaves, the feeding points and the young fruit together.

Causes

The damage comes from the squash bug, Anasa tristis. Adults and nymphs both feed by sucking plant juices. As they feed, leaves lose nutrients and water and become speckled. Young fruit may also abort or become misshapen.

Adults overwinter in garden debris such as dead leaves, rocks and wood. In spring, they move onto cucurbit plants. Crop residues and garden debris are overwintering sites for adult squash bugs.

Squash bugs also harbor the bacterium that causes cucurbit yellow vine disease, and they transmit it.

The bugs feed on squash, pumpkin, melon, watermelon and zucchini. Pumpkins, watermelons and squash are the most seriously damaged, and zucchinis are less susceptible.

Egg masses can be found on leaf undersides and stems. Squash bugs also shelter under a board or heavy cardboard laid beneath affected plants. They can be concentrated on a squash planting used as a trap crop near other cucurbit plantings. The parasitic tachinid fly Trichopoda pennipes is a natural enemy, and its eggs can be found on the undersides of squash bugs.

Diagnosis

This problem is caused by squash bug adults and nymphs sucking plant juices. So the first test is to look for the bugs on your cucurbit plants.

Place a board or a piece of heavy cardboard under affected plants. Then check each morning for squash bugs sheltering underneath. Next, inspect the leaf undersides and stems for egg masses. Look at the undersides of any squash bugs you find for the eggs of the parasitic tachinid fly Trichopoda pennipes.

Small white stipples where feeding first occurs, followed by speckled leaves that turn yellow to brown, fit squash bug feeding. Wilting with blackened, brittle feeding points is called Anasa wilt. Young fruit may abort, become misshapen, or show scarring when the bugs feed. In severe cases, plants may wilt and die.

Check the host as well, since this problem affects squash, pumpkin, melon, watermelon and zucchini. Squash bugs also harbor and transmit the bacterium that causes cucurbit yellow vine disease.

Treatments

After harvest, remove and destroy crop residues and garden debris such as dead leaves, rocks and wood to reduce overwintering sites for adult squash bugs. Place a board or heavy cardboard under affected plants, check it each morning and destroy any squash bugs sheltering underneath. Inspect plants regularly for egg masses on leaf undersides and stems. Pick off, or tear away and destroy, any you find as soon as you see them.

Cover young plants with row covers to exclude squash bugs, and remove the covers at bloom to allow pollination. You can plant squash as a trap crop near other cucurbit plantings to concentrate squash bugs for removal or treatment. At the end of the growing season, destroy plant debris rather than composting it.

Among organic methods, hand-pick and crush nymphs, or drown them in soapy water. Encourage natural enemies such as the parasitic tachinid fly Trichopoda pennipes, spiders, ground beetles, big-eyed bugs and lady beetles. You can apply an organic-acceptable pyrethrin spray around the base of plants when eggs are hatching and nymphs are young. Small nymphs are the most susceptible stage.

Organic-acceptable insecticidal soap needs thorough coverage of the plant canopy. It works mainly against small nymphs and less well on older nymphs or adults. Narrow-range (horticultural) oil is also organic-acceptable and is effective mainly on small nymphs. Use it with care, since oils can cause phytotoxicity.

Among chemical options, dinotefuran is an early-season soil-applied insecticide that targets aphids and whiteflies and also provides protection against squash bugs. It is subject to state neonicotinoid use restrictions. Lambda-cyhalothrin is a registered foliar pyrethroid insecticide labeled for squash bug control on cucurbit crops. Esfenvalerate is a registered foliar insecticide for squash bug control. It may encourage a buildup of pest mite populations and is highly toxic to honey bees.

The product label is the legal instruction, and it must be followed for the crop and site being treated.

Prevention

Adults overwinter under leaves, wood and other garden debris. Remove and destroy crop residues and debris such as dead leaves, rocks and wood after harvest to reduce those overwintering sites. Destroy plant debris at the end of the growing season instead of composting it.

Cover young plants with row covers to exclude squash bugs. Remove the covers at bloom to allow pollination. A squash planting set as a trap crop near other cucurbit plantings can concentrate the bugs.

Inspect plants regularly for egg masses on leaf undersides and stems. A board or heavy cardboard under your plants lets you check each morning for sheltering squash bugs. Encouraging natural enemies such as spiders, ground beetles, big-eyed bugs and lady beetles is another option.

Plants most often affected

Squash bugs injure squash, pumpkin, melon, watermelon and zucchini. Pumpkins, watermelons and squash are the most seriously damaged, while zucchinis are less susceptible. Adults and nymphs feed on these cucurbit plants by sucking plant juices. After overwintering in garden debris, the adults move onto them in spring.

• Field Pumpkin
• Garden Cucumber