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The squash bug (Anasa tristis) is common throughout the United States. It mainly attacks squash and pumpkins but can also attack other plants in the cucurbit family, such as cucumbers.
- Squash bugs suck the sap out of leaves and cause yellow spots that later turn brown.
- It is most important to control squash bugs when the plants are young seedlings and when they are flowering.
- They can cause young plants to wilt and die.
- Squash bugs are not a problem if you see them feeding on plants in the fall.
How to identify squash bugs
Adult squash bugs are flattened, large insects. They measure 5/8 inch long and 1/3 inch wide. They are usually dark gray to dark brown. Their abdomens have alternating orangish and brown stripes.
The eggs are oval shaped, 1/16 in. long, and yellowish to bronze.
The nymphs hatching from the eggs range in size from 1/10 to ½ inch in length as they progress through five stages called instars.
At first, the young nymphs have a light green abdomen and black heads and legs. As the nymphs grow larger, they first turn light gray and then brownish gray, with black legs and antennae.
Life cycle of squash bugs
Squash bugs can live through the winter as adults in sheltered places, such as under plant debris, around buildings, or under rocks. When adults come out in the spring, they fly to growing cucurbit plants to feed and mate.
Female squash bugs lay small clusters of eggs (about 20) on the undersides of the leaves, especially between the veins where they form a V. Eggs may also be seen on stems. The females usually start appearing in gardens in early June and continue to lay eggs through mid-summer.
Eggs hatch in about 10 days, and nymphs mature in about four to six weeks. Both adults and nymphs run for cover when disturbed.
One generation develops each year, although it is possible that in some summers there is a partial second generation.
The life stages overlap and all of them can be seen at any given time during the growing season. In the fall, especially after the vines have died, the adults and nymphs group together on squash fruits.
The nymphs die when the temperatures drop to freezing. The adults fly or crawl to sheltered places for the winter.
Damage caused by squash bugs
Squash bugs suck the sap out of leaves with their piercing-sucking mouthparts. Their feeding causes yellow spots that eventually turn brown.
The feeding also affects the flow of water and nutrients, which can cause wilting.
Unlike cucumber beetles, squash bugs do not carry diseases.
Larger, sturdier plants are more tolerant of feeding damage, while young plants may die because of feeding.
How to protect your plants from squash bugs
Keep your plants healthy
Maintain healthy, sturdy plants through proper fertilization and watering to help limit squash bug damage.
Pick bugs off the plant early
Early detection of nymphs is important, as adult squash bugs are difficult to kill.
- Remove and kill nymphs and adults by dropping them into a pail of soapy water. This is effective only if a few plants are affected.
- Removal of squash bugs can be challenging because squash bugs hide under leaves and move quickly when disturbed.
- Crush eggs that are attached to the undersides and stems of leaves.
- Trap squash bugs by laying out boards or pieces of newspaper. Squash bugs will group under the boards at night, you can then collect and destroy them in the morning.
- Remove plant debris during the growing season, to reduce sites where squash bugs can hide.
- Clean up cucurbits and other plant matter in the fall to reduce the number of overwintering sites.
Pesticides should only be applied, if plants are wilting early in the season (due to squash bug feeding).
- The best time to apply pesticides is early morning or late at night (during minimum bee activity).
- Be sure to spray underneath the leaves, where most squash bugs are found.
- It is not necessary to treat squash bugs found in the garden during late summer or fall.
- Active ingredients of commonly available pesticides are:
CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.
Reviewed in 2018