By: Sarah Adams
Member of the Big Country Master Gardeners
This month’s bug is the squash bug. Squash bugs are in the Animal Kingdom, Phylum Arthropoda, Class Insecta, and the Order Hemiptera making them a “true bug.” Squash bugs are in the family of Coreidae. Coreidae is a large family of predominantly sap-sucking insects in the Hemipteran suborder Heteroptera. The name “Coreidae” derives from the genus Coreus. Squash bugs (Anasa tristis) are a common pest affecting gardens in our area, particularly for gardeners who grow plants in the cucurbit family. The cucurbit family includes vegetables such as squash, pumpkins, cucumbers, and melons. These insects can cause significant damage to plants and fruit production. As a vegetable specialist the number one question I get from gardener is “How do I get rid of squash bugs?” First, we need to learn about the squash bug and how it lives.
Adult squash bugs are dark brown, 1/2 to 2/3-inch long, 1/4-inch wide with fully developed flat wings held over the back of the body that look like a shield on the back of the bug. Squash bugs have an incomplete life cycle, meaning the insect hatches from an egg and then goes through several nymphal stages before becoming an adult. Squash bug eggs are oval shaped and yellowish-brown. After oviposition they are fairly light and will darken with age. Eggs are oviposited in clusters of 4 to 40 in fairly uniform rows, often on the underside of leaves between the forks of the veins. Nymphs are approximately 1/8 inch long. The young nymphs are boldly colored with a red head, antennae, thorax and legs, and a green abdomen. Nymphal color fades with age to a gray/white with black legs and antennae. The 5th instar nymph appears very similar to the adult with wing buds instead of complete wings. The adult squash bug has a gray/white body with black legs and antennae.
During the winter months, adult squash bugs survive in plant debris, under piles of leaf litter, firewood, boards, and other protected sites. They become active in spring after host plants emerge. They mate and lay eggs on the underside of leaves. Nymphs hatch from eggs in about 2 weeks. Upon hatching, they are about 1/8-inch long and green and reddish in color. Initially they stay in groups, but, as they develop, the grayish-white nymphs gradually disperse throughout the plants. Development from egg to adult occurs in 45 to 60 days, and up to three generations may occur annually.
Like all true bugs the squash bug has piercing-sucking mouthparts. Squash bugs cause damage to plants by feeding on their sap. They use their piercing-sucking mouthparts to extract fluids from leaves and stems, which can result in wilting, yellowing or grayish appearance, and even death of the plant. This damage is particularly harmful to young plants, which may not survive an infestation. In addition, their feeding can introduce pathogens that cause disease. Squash bug populations increase during the season and large numbers of nymphs may occur on the fruit. Adults are more solitary and tend to occur around the base of the plant near the ground. When crushed, a disagreeable odor is released by this insect. Another insect to be aware of in the Coreidae family is the Phthia picta (Drury). It is quite common in gardens and is similar to a squash bug. This insect is often confused with the squash bug because it causes the same type of damage.
Controlling squash bugs, as with all garden pests, requires an integrated approach that includes monitoring, cultural practices, and chemical control when necessary. Proper monitoring and cultural controls can significantly reduce squash bug populations minimizing the probability that populations will increase to damaging levels. Removing debris after harvesting the garden can kill overwintering squash bug and reduce the following year’s population. All vegetables should then be monitored carefully. The best control method is to kill the bugs while they are still eggs. Carefully examine the underside of the leaves. Compare the eggs to pictures of squash bug eggs to ensure that you are not killing a beneficial insect, and then scrape them off or just squish them. Once they hatch, they are mobile, already causing damage, and much harder to control. The bugs are very stealthy, move fast and will often attempt to hide behind stems and leaves. The most critical time for squash bug control is when plants are at seedling stage, as young plants do not have the strength to tolerate significant feeding. If you suspect squash bug damage but are having difficulty finding the bugs, be sure to check early morning before squash bugs spending the night there disperse. This is the most effective way to control squash bugs. Once you see a squash bug without intentionally looking for it, your garden is overrun and there is not too much that can be done without causing substantial damage to the garden’s entire ecosystem.
Squash bugs get comfortable if a gardener plants the same vegetables in the same place every year. Planting in different places in the garden every year is also a way to reduce the chances of squash bugs building up in the soil. Encouraging natural predators of squash bugs, such as spiders may also help control the population of squash bugs long term.
And remember if you use pesticides in the garden to kill the squash bugs or any pests, then you are likely to kill other beneficial insects disrupting the delicate balance of bugs in your garden. Further, pesticides could be absorbed by the vegetables that you are growing for food. Insecticidal soaps can help control the population of any soft bodied insect including the nymph stage squash bugs by penetrating the body and dehydrating them until they die. Diatomaceous earth (DE) could also be used to control squash bugs, but it needs to be applied directly on the squash bug, which can be difficult. Further, DE will harm many insects in the garden including beneficial insects. Of course, always read the label of anything that you put in your garden or on your plants because no product does just one thing. Some insecticidal soaps can negatively affect plants. Always try the product on a small test area of the garden or plant and see how the plant reacts to the product.
Squash bugs can be a challenging pest for gardeners in West Texas, but with careful monitoring and an integrated pest management approach, they can be managed effectively. By combining cultural practices, natural predators, and targeted control measures, gardeners can protect their crops and enjoy a healthy harvest.
If you have any questions, call the Taylor County Extension Office at 325-672-6048 or email us at mgardeners@yahoo.com. We hope you visit bcmgtx.org for information on all Big Country Master Gardener events, like us on BCMGA Facebook, and check out training presentations on BCMGA YouTube. We are here to help you.
