I was out at Emory University’s Oxford College Organic Farm this morning putting out insect traps in the zucchini patch for an upcoming field day. When you’re stringing up sticky traps in the canopy of big zucchini leaves and digging holes for pitfall traps, you are really up close and personal with the plants…and everything else that lives on them.
As I was crouched there, I began to notice small clusters of rusty, golden eggs stuck to the tops of the leaves. Being the curious naturalist I am, I started turning over leaves and noticed more egg clusters on the leaf undersides, too.
Squash bug eggs on the underside of a zucchini leaf.
I knew what these were immediately. While teaching the Journeyman Farmer class on pest management last year, I led a whole activity on identifying insects in vegetable crops using this exact pest as an example! The culprit: squash bugs. Squash bugs (Anasa tristis) are one of the most ubiquitous pests in cucurbit crops, like squash, zucchini, and pumpkin, and definitely one you should be familiar with.
Squash bugs are “true bugs” in the suborder Heteroptera, a group which also includes stink bugs, kudzu bugs, leaf-footed bugs, and bedbugs. And like other true bugs, squash bugs have mouthparts that are shaped like a needle, called a stylet. They use this stylet to pierce leaves and other plant parts and suck out the nutrients, carbohydrates, proteins, and water held within the cells of plant tissues. This type of feeding often results in a stippled or mottled appearance on leaves or fruit, the result of the bugs piercing and sucking out chlorophyll and other pigments.
As you can imagine, with chlorophyll being sucked out by the bugs, plants can’t produce as many carbohydrates through photosynthesis. This means the plant can’t produce as many squash. When the squash bug feeds, it is also injecting toxins from its saliva into the leaves. These toxins can cause leaves to wilt, turn black, end eventually die—a condition called “anasa wilt.” All in all, squash bugs = stressed plants, leaf dieback, and lower yields.
Squash bug populations can explode in a patch of summer squash once all those egg masses begin to hatch. Squash bugs have “gradual” metamorphosis, meaning they don’t have a true larval or pupal stage like beetles or butterflies do. Rather, immature squash bugs are called nymphs, and their features gradually get more adult-like at each molt.
Once they hatch from their rusty-gold eggs, they go through five molts as nymphs, getting larger and looking more like adult squash bugs following each molt. The young nymphs are about the size of a grain of rice with light green, pear-shaped bodies and black legs. They turn light gray as they get older.
You will often see lots of young nymphs hanging out in a group together. They tend to spread out over time: they need more space to forage and can move around a lot quicker as they get bigger, and many become lunch for predatory insects.
At their last molt they become adults, complete with wings and the ability to reproduce. Adults are about a half-inch long. They are gray-brown with tan flecks all over and horizontal tan stripes down their sides.
Squash bugs can live for up to eight weeks and have 2-3 generations per year in Georgia. In the fall, any adults that remain will ride out the winter under leaves, clods of soil, rocks, wood piles, and other sheltered locations. It’s important to clean up and remove your dead squash plants at the end of the season so the bugs have fewer places to hide.
What You Can Do About Squash Bugs
You’re probably wondering what you can do should these bugs colonize your cucurbit crops. The first step is to grow strong, healthy plants. I like to say, “a healthy plant is a resistant plant.” Have your soil tested early and fertilize appropriately before planting. Make sure you have soil with good drainage and plenty of organic matter and start with clean seeds or transplants from a reputable source. Make sure your site has full sun, water regularly (deeply and less frequently is the mantra), and water at the base of the plants or with drip irrigation if possible to reduce diseases.
The second step to success is to inspect your plants early and often. Crouch down and get into the leaf canopy, like I did at Oxford Organic Farm. Look for signs of feeding, and make sure to flip the leaves over! Reach out to your local Extension office if you need help identifying the insects you see.
One of the most effective ways to head off an infestation is to squash the eggs as soon as you see them. If you’re squeamish, you can fold the leaf over and squash them with the other side, or you can wear a pair of latex or nitrile gloves. A paper towel will work, too. Hand-squishing (not a real term) the young nymphs as you see them will also help prevent an unmanageable horde of older, more damaging bugs from wreaking havoc in your garden.
University of Minnesota Extension recommends an interesting tactic:
“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.”
Squash Bugs in Home Gardens, UMN Extension
A great way to protect young plants is to cover them with a floating row cover. A fine mesh will prevent insects from getting in and laying eggs or feeding on your plants. Install your row covers at planting and leave them on for about three weeks or until plants start to flower—you’ll need to let pollinators in at that point or you won’t get any fruit! By that time, plants have grown out of their most vulnerable stage and have started developing more robust chemical defense systems. With better chemical defenses, mature plants can withstand feeding by insects and still produce good yields.
There is evidence that planting a trap crop, such as the squash variety ‘Blue Hubbard’, is effective for attracting bugs to a specific area. Then you can focus your management activities on those plants rather than the whole patch. I wouldn’t rely on this as your only strategy, but it can be a useful part of your overall integrated pest management plan.
Lots of insects like to feed on squash in Georgia, so I generally recommend folks adopt a succession planting approach when growing squash. The UGA publication, Controlling Insects on Summer Squash in the Home Garden, said it better than I can:
“Instead of planting all your squash seed at one time, plant a few new [plants] every two weeks to allow a new crop to continually develop…By planting a succession of squash every few weeks throughout the growing season, you have a greater chance of having a good crop throughout the summer. As older vines become inundated by borers or pests, they should be eliminated from the garden and placed in a compost pile.”
Controlling Insects on Summer Squash in the Home Garden, UGA Extension
Adult squash bugs have a thick exoskeleton and are difficult to kill with insecticides. Products containing bifenthrin, carbaryl, cyfluthrin, and permethrin are labeled for squash bug management, but you should target the nymphs rather than the adults when you apply these insecticides. Remember, always read the label in full and follow all instructions, including application rate, what plants you can apply the product to, personal protective equipment, and ways to reduce risks to pollinators and other animals. See the Georgia Pest Management Handbook for the most up-to-date insecticide recommendations.
Although squash bugs can throw a wrench in the perfect, productive summer garden, they offer a great opportunity to get to know the insects that call our landscapes home! I encourage you to take a minute to observe them, find out what they’re doing, and then use that wisdom to outsmart them.
