squash bugs and other squash problems, with diane alston of utah state
WHEN READERS SAY, “I can’t grow cucurbits,” or, “Forget squash—I surrender,” I take notice. An incredibly helpful report on controlling squash bugs (above) sent me in search of its author, Diane Alston, an entomologist and professor in the Department of Biology at Utah State, who I figured knew the other cucurbit opponents, too: vine borers, powdery mildew, and more.
Diane, who creates the popular “Bug Bytes” segments on Utah Public Radio’s garden show and serves as the Utah Extension’s Integrated Pest Management Coordinator, joined me on the radio and podcast. It included tactics for preventing and controlling diseases and insect pests of squash—and how a gardener’s toolbox that includes resistant seed varieties, Reemay fabric, kaolin clay, and even a roll of duct tape can help you succeed.
squash success, with utah state’s diane alston
Q. Many web readers comment whenever I mention cucurbits—sentiments like, “I have given up” and “I can’t grow them any more.” Shall we start with a tour of the potential of unwanted visitors in the squash plot?
A. Those in the East do have some additional challenges than we do in the West—so I do feel for you. In particular the pest that does not occur West of the Rockies is the squash vine borer. When I was a graduate student at NC State, my husband and I were growing gardens, and it was my first experience with the vine borer. It was not a good experience.
Q. It’s pretty shocking.
A. They can kill the plant quite quickly. [More on controls below.]
The second pest is the squash bug—and we do have that in the West, too; it’s often our most severe pest.
Q. Anasa tristis, yes?
Q. What cracks me up is that the tristis part means sad in Latin, I believe—and it does make gardeners really sad when it appears.
A. It’s a tough one, too—there is a disease it can vector, and it can cause a wilt of the plant, but typically, it’s more of just a stubborn pest that you have to keep working against.
Q. Other insects?
A. Spider mites, which are relatives of insects, can be problems here in the West and elsewhere—especially in hot, dry conditions. They can flare up really quickly and make our squash plants sad, too. But you can manage them with a lot of around-the-home techniques, like washing them off with the hose-end sprayer, or applying soaps or oils, so they’re not so bad.
With diseases, here in the West we have powdery mildew, just as in the East, which typically comes on at the middle to late age of the plant, and can cause it not to produce as heavily as you’d like—especially for winter squash and pumpkins, which you want to get all the way matured, it can be particularly problematic.
The one disease we don’t have in the West because it requires more humidity is the downy mildew…
When I began gardening, Diane, the wisdom was that the squash bug didn’t spread disease the way, say, a cucumber beetle does while feeding, but as you alluded, evidence now says otherwise.
A. The particular disease that the squash bug has shown to vector doesn’t show up here in the West., but what is seen in other areas is the cucurbit yellow vine disease, CYVD, a bacterium found only recently. The squash bug can vector it, or carry it, on its mouthparts—causing the vines to yellow and eventually decline. It can happen in a week or two weeks, but it’s not an overnight wilt like with vine borer. You notice the plants not looking as healthy, and will typically see a spreading pattern—one or two plants at first, and then moving to adjacent plants.
Q. Backing up a minute: You are Utah Extension Integrated Pest Management Coordinator, so can you explain IPM briefly? Is the philosophy to use the least-toxic method at any time–starting with choosing the most disease- or pest-resistant varieties of seed?
A. Yes. We’re trying to be as sustainable as possible, and plan ahead with preventive measures—using all the tools in our toolbox, so you can think of it as a comprehensive approach. In some ways it’s using good old-fashioned approaches to farming and gardening, but also incorporate new technologies: things like taking advantage of insect pheromones, or newly discovered bacterial insecticides. We look for opportunities and options—to make it as holistic as possible, so each individual grower or gardener can pick the one that work best for them.
Q. With that approach in mind, let’s grow some squash. What’s key?
A. On the home-gardener scale, trying to reduce overwintering success is the first and foremost thing to do. Squash bugs actually overwinter in the adult stage. They go into a state of quiescence or diapause, where they’re not very active over the winter; they’re not feeding. But they can on a warm day or if they get disturbed, they can move to another protected spot. But what they love is debris in the garden.
If you do not clean up after you are finished in the fall, and leave squash vines and other kinds of plant debris there, that is the perfect overwintering habitat for them.
Q. And clean up long before the vines lie there collapsing under increasing powdery mildew, and are no longer producing prolific fruits, right? Get it out of there! I suppose it’s a subject of debate, but do you compost the debris?
A. It depends on what you consider composting. If you have an active, hot pile and you’re regularly turning and working it–then you can add most garden debris to it. If you’re just piling it up at the edge of your garden and letting it sit there, that doesn’t count.
Q. So good sanitation is our biggest opportunity. I confess I also take great pleasure in hand-picking squash bugs, when they’re quieter early in the morning, and squishing them or knocking them into a can of water. Is that part of IPM?
A. That’s a great time of day to do it, and anything you can do mechanically, physically is great. On the garden scale, where it’s not so overwhelming, it’s a great tool. Another tool we’ve been trying: taking some duct tape, and making a roll of it, then sticking your fingers through it. You turn over the squash leaves and you see the eggs or young nymphs just hatching out—put that piece of duct tape on it to pull them right off that leaf.
Q. And that’s really important: Look under the leaves—because that’s where many insects are, not out in the open all the time. So the squash bug has three stages: eggs, nymphs and adults. When does the cycle begin? [Utah State photo of eggs and nymphs, above.]
A. As soon as they pick up the odor of your squash seedlings, that will start attracting them, and of course it’s timed with temperature and daylength—but generally all those come together at the time the squash bug is seeking out new plants to lay eggs on.
So the time to start looking for insects or eggs is as soon as you put out plants, and they are getting established and putting on new leaves. As soon as you see squash bugs active, you want to start doing this checking early in the morning, when things are cool. Do a good walkthrough and check the undersides of all the leaves.
A. Makes it a little easier. They lay the eggs between the midribs, or veins, of the leaf undersides—so with the tape you can really get at them.
Q. What about barriers, like Reemay or Agribon or other agricultural fabrics?
A. You have to be a little careful with any kind of mulch—that’s the general term we use with any kind of barrier, whether artificial or biological living materials. It can provide protection and hiding habitat for the insects. If you are using black plastic to get earlier plants, keep that plastic down tightly against the ground. Black plastic won’t reduce the squash bugs, but will get the plants growing faster to maybe outgrow some of the big damage.
Q. I know people who cover their melons, cucumbers, and squash with Reemay at transplant time, for the extra heat and also some pest control. What do you think?
A. Row covers will provide some help—and this is also true for the vine borers. I’m not saying it will be a cure-all or 100 percent, but when the squash are younger, before they start to bloom, you can use those lightweight fabrics and cover the plants up. This will help keep the squash bug and vine borers from finding them and laying eggs.
Once they start to bloom, you do have to open them.
Q. So we’re practicing good sanitation; monitoring frequently; using some mechanical methods as barriers or for removal of pests. Are there some other safe products we can use as organic home gardeners?
A. For squash bug [and cucumber beetle]—not the vine borer, unfortunately—we’ve had some success with kaolin clay, usually sold as the brand name Surround.
It works in a physical way. It’s a hydrophobic. The squash bugs or any insects don’t really like to crawl across it; they’re repelled by it. It makes them move away.
The challenging thing with the kaolin clay is to get it on to the parts of the plants where it needs to be: the undersides of the leaves, down at the base, on the main vine—the lower plants of the plant. You kind of have to hold the leaves up or get the wand of your sprayer down underneath to get good coverage there.
Q. I know farmers who sow their squash indoors, so that they can turn the seedlings (even whole flats) upside down and dip them in the Surround solution before transplanting. I know it sounds crazy—but it’s true.
Any other least-toxic sprays, like soaps or oils, that are applied against squash bugs?
A. There is azadirachtin (an extract from neem oil), which is a good product against squash bug, too. It doesn’t last very long—and requires reapplication fairly frequently. Also insecticidal soaps work when they contact the egg or insect, and break down the waxy barrier they have as an outside protection to prevent them from drying out, or desiccation. The eggs or insects dry out and die. You can use summer-weight or horticultural mineral oils—at 1 to 2 percent, too.
THOUGH THERE ARE natural and chemical fungicides that can be applied to plants to try to try to stay ahead of powdery mildew, the best tactic is prevention. Your top tools: Plant resistant varieties, and grow vigorous plants—avoiding setbacks from too little heat, water, or fertility that can make them weak and vulnerable. More on how at this link, from organic seed farmer Tom Stearns.
about squash vine borers
A FORMIDABLE pest East of the Rockies is the squash vine borer (above, Minnesota Extension image of adult moths). Once larvae bore into vines, control becomes difficult or impossible. Better to try prevention by growing butternut types, ‘Green-Striped Cushaw,’ cucumbers, melons, and watermelons, which seem to resist the borer better. Hubbard type winter squash are among its favorites.
Other IPM tactics include floating row cover (removed or opened once vines are flowering), unless there were borers last season who could be in the soil beneath the tents.
Watch for and destroy the adult moth, which lay eggs that become this season’s damaging larvae–or lure them into yellow bowls or pails filled partway with water. Adult moths buzz, and are large and distinctive, emerging in early summer (and flying till August in some areas). They are wasplike, orange and black, about ¾ to an inch long with a wingspan of about an inch to an inch and a half. In flight, one pair of its wings is revealed to be clear.
Prompt cleanup of infested areas to destroy larvae can reduce future populations. A late-sown crop may fare better, so stagger plantings. More on vine-borer IPM from the University of Minnesota Extension and Illinois Extension.
more from diane alston (including her radio show)
- Diane’s Utah State fact sheet on squash bugs
- Utah Public Radio’s “The Zesty Garden” show features Diane’s “Bug Bytes” segments
- Utah State offers regular IPM email advisories for to alert gardeners when and how to control pests and disease
prefer the podcast?
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