Post #G21-033: 1000 growing degree days and the squash vine borer

Posted on June 16, 2021


She’s back.

I would love to think of gardening as something that’s done by the calendar.  Plant your peas (and potatoes) on St. Patrick’s Day.  Don’t plant tomatoes before Mother’s Day.  Mind your mayflies and your June-bugs.

And similar folkloric claptrap.

In reality, it’s all chemistry.  Chemical reactions occur faster in warmer temperatures.  Insects emerge after a given number of “growing degree days”, like the little biots that they are.   The warmer the year, the sooner they arrive.

Any correlation with specific calendar dates is based on a) your local climate, and b) the stability of that local climate.  Of which, for b), not only do things vary from year to year, but we really can’t count on having a stable average from decade to decade, at least not for U.S. gardening hardiness zones.

All of the above is an arch way of saying that I’d been stupidly expecting to see the squash vine borer (SVB) in early July.  Because that’s when I saw her arrive last year. 

But surprise, she’s here now.  Showed up in my garden today.

If I’d been paying attention to cumulative growing degree-days, via Cornell University’s tracking, I would have known that we passed 1000 degree-days — the point at which the SVB emerges — this past week:

And so, like clockwork, she’s back.

You can see everything I learned about the SVB last year, in Post #G27.

Starting about five days from now, I’ll be spraying spinosad on the stems of my summer squash.  In addition to killing as may SVBs as I can via the “hand clap” technique.  All this, in the hopes of extending my summer squash season for a few more weeks, until the powdery mildew and other diseases and pests overwhelm my squash plants.

At any rate, the upshot of this is that if you are in Zone 7, and growing summer squash, pumpkins, some types of winter squash, or melons, you need to be aware that the SVB is up and about.  It takes maybe a week for the SVB eggs to hatch, maybe a week for the resulting larvae (borer) to start killing your plants.  There are plenty of remedies suggested on the internet.  I found that weekly spraying of the cucurbit stems with high-strength spinosad worked for me last year.  That’s what I’ll be doing again this year.