Post #G08: Squash vine borer is here.

Posted on July 6, 2020


Source:  U Wisconsin Vegetable Entomology.

This is another in my occasional posts on gardening.  It’s short.  The squash vine borer has made its annual appearance in Vienna.  If you grow cucurbits, particularly summer squash, be on the lookout for this bug. 

She drops in.  Just for a week or so, each year.  She lays her eggs.  Two weeks later, all your squash plants wilt and die.   That’s the reputation, anyway.  You can read a more formal description at the Virginia Tech Cooperative Extension Service.

I’ve never had a problem with squash vine borer before.  On the other hand, I’ve never grown as many cucurbits as I am growing this year.  My squash-heavy plantings are the reason I was keeping an eye out for this pest.  And plausibly, extensive squash/pumpkin plantings made me a good target.  Or maybe the borer is just more prevalent this year.

So consider this a public service announcement.  These are easy to miss.  They aren’t around for very long, and they aren’t around in great numbers.  If not for the fact that I was watering my garden by hand yesterday, I would not have seen it.  But the brilliant coloring, plus the fact that it was digging around at the base of my zucchini, made for a pretty sure identification.  Another identifying factor is that the little @#$(# are fast, which means they are tough to kill by hand.

I only saw one.  Maybe two.  Can’t tell because I was too slow to get the first one.  And one is all it takes, anyway.

If you see one in your garden, act accordingly.  Apparently the pupae overwinter, so if you don’t stop them early, you can be stuck with them for years.

I looked over all the potential treatments that can be taken at this stage (my plants are grown, I’m harvesting summer squash already), and none of them seemed very attractive.  Many could not be done to mature plants.  Many looked like folklore.  Some seemed plausible, but experts said that they did not work.

With reluctance, early this morning, I went for what seemed like the minimal effective intervention.  I  sprayed spray the bases of the main stems of my summer squash with spinosad.

For the record, I don’t normally use insecticide.  I figure, if the bugs want to eat some plant that badly, I’ll eat something else.  E.g., this year, the cabbage moths got to my cabbage plants.  So I tore them out and re-planted with peppers.  Not worth spraying poisons around (even organic ones like BT) to try to preserve what might amount to $10 worth of dubious quality cabbages.

But I would like to keep my already-producing squash.

I got up early to avoid the bees — only to find that some of my local bees are early risers.  The theory being, once spinosad dries, it has little bee toxicity (per this reference, with the understanding that the sprays available to consumers are “low volume” sprays, under their definition).  I didn’t get near the blossoms.  I was really trying to avoid killing even one bee, purely out of self-interest.  I’ve been having such trouble with lack of fruit set that the bees are worth more to me than the squash plants.

I may or may not try putting Tanglefoot on the based of the main stems, in addition to that.  Apparently that’s bee-safe (because the bees have no reason to light there).  But that’s a treatment that may or may not be just a piece of folklore.

Give it two weeks, and we’ll have a one-way test of effectiveness.  If my summer squash plants die, I’ll know this didn’t work.  If they don’t die, I’m not sure what I’ll know.  There’ no way for me to know the extent to which the squash vine borer laid eggs.  (In theory, you can see them if laid directly on the plant.  But they’ll also lay them in the dirt around the plant.  In practice, the eggs  look like specs of dirt to me.)

Worst comes to worst, I’ll replant.  Apparently, cucurbits planted in a new spot, after the squash vine borer has made her appearance, are not at risk for squash vine borer infestation.  So I may end up with fall summer squash.