Squash bugs are a hassle for growers of zucchini, pumpkins and other cucurbits, but there are steps that can be taken to manage and control this challenging pest. My guest this week is entomologist and pest management expert Diane Alston, and she’s here to share strategies to reduce squash bug issues.
Diane is a professor and the head of the biology department at Utah State University, where she has worked for 32 years. She started there as the extension entomologist for the Utah Extension and later became the extension’s Integrated Pest Management (IPM) coordinator and also co-directs the Utah Plant Pest Diagnostic Laboratory.
Diane Alston is a professor and the head of the biology department at Utah State University, where she has worked for 32 years. (Photo Courtesy of Diane Alston)
Diane grew up in Southern California, about 30 miles east of Los Angeles, in a family that gardened. She was always interested in plants and that led to her interest in insects that feed on plants. Diane attended the University of California Riverside to study botany and then North Carolina State University, where she earned both a master’s degree and a doctorate.
The Difference Between a Bug and an Insect
Every bug is an insect but not every insect is a bug. Diane explains that there is a group of insects called “true bugs,” and the squash bug is one of them. These are insects that have piercing-sucking mouthparts. Most use their mouthparts to feed on plants, but there are predatory bugs as well, such as the assassin bug.
Bugs use their proboscis (an elongated sucking mouthpart) to pierce plant cells and feed in the phloem tissues. “They’re directly tapped into the vessels of the plant where the nutrients are flowing,” Diane says.
The plant takes up water and nutrients from the soil, photosynthesizes, and moves those nutrients around to produce its fruits. The squash bug taps into the plant and takes out high-quality nutrients from the sap.
Squash bugs are a type of true bugs because they have piercing-sucking mouthparts.(Photo Courtesy of Diane Alston)
How to Recognize Squash Bug Damage
Squash bug damage appears as little yellow lesions on leaves, stems and vines. Those spots will turn darker and grow in time. The edges of the leaves start to get crispy, especially as the days get hotter and the plants are stressed. The plants are trying to take up water for photosynthesis and respiration but struggle because of the damage.
Squash bugs will also feed on the fruits themselves, causing lesions. If the population of squash bugs is high enough and the plant is stressed enough, it may suddenly wilt as well.
It was previously thought that squash bugs inject a toxin as they feed, causing wilt, but Diana says rapid wilt is just a result of heavy feeding that breaks xylem tissues, disrupting water flow. “Basically, it’s like getting a puncture in your house,” she says.
Plants with squash bug damage may struggle to take up water and start to wilt. (Photo Courtesy of Diane Alston)
The Difference Between the Squash Bug and the Squash Vine Borer
The squash bug and the squash vine borer are much different pests, though they share a taste for squash. The squash vine borer is not a bug but a moth, and it’s the moth’s larva that does the damage.
The squash vine borer is not present west of the Rockies, though Diane was introduced to the pest during her time in North Carolina. She said that squash vine borer damage can cause sudden wilting of a plant the same way that squash bug damage does. The thing to look for to be able to tell the difference is a hole at the base of the plant on the main vine or stem. That is a bore where the squash vine borer larva, or caterpillar, entered the vine or stem to feed.
If the problem is squash bugs, the signs to look for are the bugs themselves. They often hang out at the base of the plant where the old leaves are touching the ground. Lift up the leaves and find brown-to-gray adult squash bugs.
Squash vine borer larvae bore into stems and continue to work their way through the plants, hollowing out stems and vines as they eat. Given enough time, squash vine borers can move several feet through vines.
Crops Squash Bugs Love to Feed On, and Crops They Are Less Likely to Attack
Squash bugs, as the name applies, are most commonly found on squash — but that’s not all.
Straightneck, crookneck and yellow squash are all targets, and zucchini and pumpkins are favorites. Squash bugs may also be found on cucumbers and winter squash, though the damage tends to be less extreme. Cantaloupe and watermelon may also be attacked, though that is even less common.
Black Zucchini is said to have fewer squash bug problems than traditional zucchini, and newer varieties tend to have fewer issues than older ones. Hubbard squash has a thick rind that resists squash bug damage.
Zucchini is a favorite of squash bugs, but some varieties are less susceptible than others.
Cucurbit Yellow Vine Disease
Cucurbit yellow vine disease is a bacterial disease found in the Midwest and the Eastern United States that squash bugs can spread as they feed. The bacteria will clog the plant’s vascular system, causing leaves to yellow and leaf edges to curl. The lower stem will turn yellow and the roots will rot. Affected plants should be removed and disposed of — not composted.
Remove Old Vines to Reduce Squash Bug Populations
Squash bugs are difficult to control because they overwinter as adults, Diane says. If old squash vines are left in place between growing seasons, the squash bug population will persist in the plant litter. She recommends pulling up all of the old vines and hot composting them to reduce the survival of the bugs. If your compost pile does not get hot, you should dispose of the vines off-site.
The Chemical Signals that Attract Squash Bugs
Cucurbits have certain plant chemicals that attract organisms that want to feed on them, such as squash bugs. Cucurbitacins are a group of volatile chemicals in cucurbits that squash bugs really hone in on.
Squash bugs are very well adapted to finding squash — they have evolved to do so.
IPM Strategies to Prevent Squash Bug Infestations
There are two planting strategies to outwit squash bugs. The first is to plant as early as possible so plants are up to a larger, more resilient size before squash bugs come along. Tiny seedlings will be much more sensitive to squash bug damage.
The second timing strategy is to put out plants later on, after squash that was planted elsewhere in the area has attracted the bulk of the squash bugs. The get the timing right either way, research when squash bugs are active in your area.
Using floating row cover will provide a physical barrier between plants and squash bugs, preventing the bugs from both feeding on plants and laying their eggs. The only issue with using a physical barrier is that the squash flowers need to be pollinated. If squash bugs can’t get in, neither can pollinating insects. One solution is to hand-pollinate, and the other is to remove the covers for a few hours in the warmest part of the morning when bees are most active. The squash bee is a widespread type of bee that is very effective at pollinating various squash.
Egg removal is another important proactive step to stopping a squash bug problem before it begins. Female squash bugs lay 220 to 250 eggs per season in clusters of 12 to 20 each. The slightly elongated copper to bronze eggs get even darker as they get closer to hatching. The eggs are commonly laid right up against the vein of a squash leaf, where the leaf is attached to the stem, and are well hidden to prevent predation from lady beetles and other insects. But if you know where to look, you’ll find them.
Diane recommends smashing those clusters with your garden gloves on. Another method is to remove the eggs with duct tape. Even a credit card can be used to scratch them off, or a lint brush can pull them off just like duct tape does.
Squash bug eggs are commonly laid right up against the vein of a squash leaf, where the leaf is attached to the stem, staying hidden from predatory insects. (Photo Courtesy of Diane Alston)
After the egg stage is the nymph stage, which progresses through five instars. The nymph stage looks fairly similar to the adults. When they are first hatched they have a red head and antennae. As they grow and molt, their legs become black and the body becomes grayer. Squash bug nymphs tend to stick together and are easy to squish.
Newly hatched squash bug nymphs are pale green and older nymphs are gray. (Photo Courtesy of Diane Alston)
The adult squash bugs are physically harder to kill. They can still be squished, but it takes more force. They are more spread out, they fly in short hops, and they scurry away. When you do catch and squish them, their scent glands leave a foul smell like a stink bug does.
Crop rotation is a strategy that Diane recommends for growers on a half-acre farm or larger. That means following a season of growing squash with a different crop that is not susceptible to squash bugs for the following few years. Crop rotation will reduce squash bug pressure and can also reduce disease pressure, such as Verticillium wilt.
Trap crops are another useful tool for commercial growers. If the grower is planting a crop that is sensitive to squash bugs but not a favorite, the grower can plant a trap crop that is very attractive to squash bugs. The primary crop will get relief from squash bug pressure, and the trap crop can be treated with insecticides to knock down the population.
Most commercial growers are using insecticides containing pyrethroids, which are man-made chemicals that are similar to pyrethrins derived from Chrysanthemums. Pyrethroids fortunately don’t last long, which is good news for pollinators.
Adult squash bugs can be hand-picked but are more difficult to kill because they fly and are harder to crush. (Photo Courtesy of Diane Alston)
Getting Some Help from Parasitoid Insects
Tachinid flies are parasitoid insects that lay their eggs around the thorax of squash bugs. When an egg hatches, the fly larva tunnels down into the body of the squash bug, slowly killing it in the process.
The most common natural enemies of squash bugs are parasitoids, which include the tachinid fly, Trichopoda pennipes. (Photo Courtesy of Diane Alston)
Squash bugs stop feeding soon after they are parasitized, so tachinid flies are an effective biological control as far as gardeners are concerned.
Tachinid flies lay eggs on squash bugs, then the flies’ larvae tunnel inside the bugs’ bodies. (Photo Courtesy of Diane Alston)
Squash Bug Controls Available to Home Gardeners
Kaolin clay is a hydrophobic fine clay that can be applied to plants to physically deter squash bugs. The same product is used by fruit growers to create a barrier film that stops insects.
Horticultural oil is a petroleum mineral oil that’s similar to dormant oil but highly refined. At a 1 percent concentration with water, horticultural oil can be used to suffocate squash bug eggs so they don’t hatch.
Pyrethrin is an organic product that is effective at controlling nymphs, but not adult squash bugs. The adults have essentially a coat of armor that makes it really hard to control them with sprays.
Diane works in the field to collect samples. (Photo Courtesy of Diane Alston)
I hope you enjoyed my conversation with Diane Alston. If you haven’t listened yet, you can do so now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
How have you overcome squash bug pressure? Let us know in the comments below.
Links & Resources
Some product links in this guide are affiliate links. See full disclosure below.
Episode 008: Organic Pest Control with Jeff Gillman
Episode 050: Organic Pest Control: Beneficial Insects And Beyond
Episode 067: Predatory Beneficial Insects: Feared Foes of Garden Pests, Pt. 1
Episode 068: Top Predatory Beneficial Insects and How to Attract Them
Episode 195: Identifying and Controlling Garden Pests Organically
joegardener blog: Squash Bug Prevention & Control
joegardener blog: Squash Vine Borer Prevention & Control
joegardener Online Gardening Academy™: Popular courses on gardening fundamentals; managing pests, diseases & weeds; seed starting and more.
joegardener Online Gardening Academy Master Pests, Diseases & Weeds: Learn the proactive steps to take to manage pests, diseases and weeds for a more successful garden with a lot less frustration. Just $47 for lifetime access!
joegardener Online Gardening Academy Perfect Soil Recipe Master Class: Learn how to create the perfect soil environment for thriving plants.
joegardener Online Gardening Academy Beginning Gardener Fundamentals: Essential principles to know to create a thriving garden.
joegardener Online Gardening Academy Growing Epic Tomatoes: Tomato expert Craig LeHoullier joins me in leading this course on how to grow healthier, productive tomato plants and how to overcome tomato-growing challenges.
GGW Episode 723: Natural Pest and Disease Control – Greener Solutions to Common Gardening Challenges
Utah State University Extension: Pest Advisories
Utah State University Extension: Utah Pests
Utah State University Extension: Squash Bugs
Utah Vegetable Production and Pest Management Guide
Soil3 – Our podcast episode sponsor and Brand Partner of joegardener.com
Milorganite® – Our podcast episode sponsor and Brand Partner of joegardener.com
Disclosure: Some product links in this guide are affiliate links, which means we get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us, and compensation is not an influencing factor on their inclusion here. The selection of all items featured in this post and podcast were based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Rain Bird, Corona Tools, Milorganite, Soil3, Exmark, Greenhouse Megastore, High Mowing Organic Seeds, Territorial Seed Company, Wild Alaskan Seafood Box and TerraThrive. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.
0 Responses to “218-Squash Bugs: How to Manage and Control This Challenging Pest”
The squash bugs we get here in NC are yellow as juveniles and they look like lady bugs when they are adults. What to do about this other than spending hours squishing them?
Very interesting. Learned a few new tricks. Didn’t know about the tachinid flies, or using kaolin clay (aka
Surround) for them – though I’ve been doing something similar with DE and I think it has similar affects. And LOVED the idea of smothering the eggs with horticultural oil, which I happen to have on hand. I had never heard that.The one thing I quibble with a bit is that they just said “squash bugs like pumpkins”. There are four genus/species of squash. Cucurbita pepo, C. moschata, C. maxima and C. mixta. ALL of them have varieties
referred to as “pumpkin”. In my experience, squash bugs will devastate C. maxima (things like Cinderella pumpkins.) But hubbard is also a C. maxima and they said those hold up so who knows – I never grow hubbard b/c I don’t want that big of a squash all at once! They will eventually do big damage to C pepo if unchecked, but most of those grow pretty quickly (zucchini, acorn, spaghetti and delicata squash, many of the smaller pie pumpkins etc.) and I can usually get a crop before the plants die. (SE Washington zone 7a). C. moschata (butternut) seem to be able to handle the pressure better, even though they take FOREVER to put on fruit and get ripe. I once grew 8 ball round zucchini and the squash bugs completely ignored the plant while eating the regular zucchini next to it. I’m growing Costata Romanesca zucchini this year, and I’ve not seen any on that one either (fingers crossed). Your mileage may vary.Secondly, they talked about just scraping off the eggs. I once removed squash bug eggs with duct tape and
put in a jar in my kitchen to see if they would still hatch. They did (I have a picture). I would NOT just rub the eggs off onto the ground. They are hard and difficult to squish. I’d either coat in oil as they suggested or remove with tape and then dispose of the tape (maybe with a blow torch, lol).I’m just now starting to see nymphs, but I’ve held them off for a good chunk of June/July using DE. I have 100 ft of squash, so what I can do by hand is limited.
That isn’t a squash bug. That’s some kind of beetle. Contact your local extension office for official identification. Spinosad (approved for organic use) works on beetle nymphs, but it takes a while b/c they have to eat it to die.
In NC. I’m in 7b zone and found a recipe online that seems to work along with being proactive by removing the eggs and the adult bugs themselves. The recipe is water, tea tree oil and liquid soap. I use Dr. Bronners Castile. And I keep a jar of water with same soap in the garden so when I find the eggs, spray the above spray on them, let it dry, then you may find it easy to remove the eggs. Also spraying the nymphs and adults with the same spray kills them, BUT be very careful not to hit your pollinators bc it will kill them. Also when I find the eggs and adults I scrape the eggs into the above water, and easily coax the adults into the water. I have a nice smelly jar of dead squash bugs. HA. I hope that helps!! We also just planted more Zucchini plants, so I hope to have better results. I hope this helps. Also the tea tree oil reacts with the sun, so when you run low on the spray add more oil- just a few drops, also try Neem oil, but tea tree is good for fungus which I saw on my poor buttercup squash plants. Make sure to add nourishing soil to your damaged plants and you may see new growth. I hope this helps. I’m just in my 2 ND year of planting.