Source: U Wisconsin Vegetable Entomology.
He was hanging out on my Waltham butternuts. Waiting for his ladyfriend to arrive, no doubt. Now terminated with extreme prejudice.
The squash vine borer (SVB) is back in town.
Just like clockwork. No sooner did I spot my first Japanese beetle (see just-prior post), when up pops my first SVB. Both driven by passing the 1000 growing-degree-day mark here in Northern Virginia,
It was a male. Not quite as flashy as the female shown above. But easily recognized from the general shape and the brilliant orange coloring. I have the vague notion that the males arrive first, followed a few days later by the females.
I found it surprisingly difficult to get the facts straight on this pest. So everything I learned about it is summarized in Post #G27. There’s a lot of folklore out there that, for one reason or another, either doesn’t work or does not apply to my climate zone.
My SVB strategy this year:
Let me quote the experts on which crops are at risk, and which are not:
Vine crops most susceptible to squash vine borer are jack-o-lantern pumpkins, summer squash, zucchini, acorn squash and Hubbard squash. They are not important pests of melons, cucumbers, watermelons, hard shell gourds, or squash and pumpkins cultivars from the Cucurbita moschata species, such as butternut squash, calabazas, neck pumpkins, French pumpkins or cheese pumpkins.
Source: Michigan State University extension service.
That matches what I observed in my Zone 7 garden. Of the plants I have grown, the SVB only seems to be able to kill hollow-stemmed summer squash. They did not appear to damage solid-stemmed squash. For example, last year’s butternut squash seemed completely unharmed by an intense infestation of SVBs.
The SVB was also unable to kill my cucumbers. But that’s because the cucumber beetles beat them to it.
If you grow summer squash or zucchini, you need to keep an eye out for the SVB. You won’t see the damage to your plants until long after the SVB has come and gone. Adult SVBs don’t cause any damage directly. They mate and lay eggs. A week or two later — depending on the temperature — those hatch. The resulting larvae bore into the stems of your squash plants. And some weeks after that, your squash plants suddenly die.
If you wait until you see damage, it’s much too late. In theory, you can sometimes rescue a plant after-the-fact by slitting the stem and removing the SVB larva. In practice, in the heat of a Virginia July, the elapsed time between “that zucchini looks it needs watering” and “that’s a dead zucchini plant” is maybe three days. And as a bonus, the SVB preferentially bores in from the underside of the stem, invisible for all practical purposes.
This means the first time you will note the SVB damage is when your summer squash plant keels over. If you’re like me, that’ll be a day or two after you gave it extra water, thinking it was just a bit too dry. And a day before you look at what’s left of it, tear it out, and plant something else.
Last year I defeated the SVB, but at considerable cost in time and effort. After looking at my options, I decided to spray the stems of my curcubits every five days with 0.008% spinosad solution. That was reasonably bee-safe (done in the evenings), reasonably well-targeted (e.g., I didn’t intentionally spray any leaves), and reasonably effective.
It just took a lot of effort, particularly because you have to keep it up for the better part of two months. That’s for the roughly seven-week SVB season in my zone, plus a week or so to allow time for the final eggs to hatch. During that entire time, the plants keep growing, which means the amount of stem you need to spray keeps getting larger.
If I had to pay myself minimum wage, I’d probably have been producing yellow summer squash and zucchini at $20 a pound. And as a bonus, even though spinosad is a very short-lived and reasonably innocuous pesticide, it’s still a pesticide. You still (e.g.) need to wait some time after spraying before you pick your zucchini. Do I really want to be spraying pesticide in my garden six times a month?
So this year, I’m punting. In keeping with a general theme of doing as little work as possible in the garden.
My strategy has two parts.
First, I’m growing a couple of varieties of solid-stemmed winter squash (butternut, and Dickinson pumpkin, which is actually a gigantic winter squash). In theory, the SVB shouldn’t be able to bother those. I’m just letting them grow, and we’ll see what happens.
Second, all my other curcurbits are parthenocarpic varieties, grown under insect-proof netting (Post G22-013). After one little hiccup (Post G22-019), that’s now proceeding according to plan. The plants are currently covered with floating row cover, and are getting big enough that I need to construct the insect-proof hoop houses that will cover them this season.
That choice was a case of killing two birds with one stone. If it works, it’ll keep the SVB off my zucchini and it’ll keep the cucumber beetles off my cucumbers. All without the use of pesticides.
But if you step back from it, the bottom line is that I punted. The SVB won. I’ve stopped growing cucurbits that are, by design, subject to attack from SVB and cucumber beetles. I’m only growing ones that should withstand attack (solid-stemmed winter squash), or that will produce fruit even if grown in an insect-proof cage (parthenocarpics).
I’m not sure either one of these will survive this summer’s onslaught. But I’m completely sure I’m not going to spend my evenings spraying insecticide around my garden this year. If I can’t get a decent crop of cucurbits this way, then I’ll just plant something else and move on.
