Post #G18: She’s baaack!

Source:  U Wisconsin Vegetable Entomology.

I killed a squash vine borer (SVB) moth in my garden yesterday.  (See Post #G09 for more than you want to know about this pest.)  That’s the first one I’ve seen since 7/25/2020.

It’s like my brain is now hard-wired — I was reaching out to kill it about half a second after it entered my field of vision.  Vine borer must die! Got it with the hand-slap technique — one hand under the leaf its sitting on, then clap your hands.

I thought the vine borer season was over, lasting roughly three weeks.  I was wrong.  So the traditional talk about a “week long” SVB moth season in this area is bad folklore, and in all likelihood, we have a long, ill-defined season similar to that documented for New Hampshire (below).

Source:  Managing Squash Vine Borer in New Hampshire (.pdf).

I’m far from the only gardener in the area to be bothered by this pest.  That’s based on the comments in yesterday’s garden column in the Washington Post, and chatter that showed up on the Vienna plant exchange FacBook group.

This recurrence is particularly galling for two reasons.  First, I had declared victory in my last post (Post #G17).  Spraying all my cucurbit stems with 0.008% spinosad solution every five days (for “the length of the season” plus time for egg hatch-out) seems to have prevented nearly all vine borer damage.  This, despite seeing multiple borer months daily for three weeks (5/5/2020 – 5/25/2020).  Second, my summer squash have finally gone back to setting fruit, after taking a break during the last heat wave.

I’m not going to go back to spraying spinosad on every vine.  For one thing, the area I’d need to cover has literally grown.  I must have at least a hundred yards of pumpkin vines trailing around/through/over/ various parts of my garden and back yard.  For another,  there’s a good chance the powdery mildew will kill most of those before the squash borer gets a chance to.

From this point forward, I’m going with a two-part strategy. 

First, monitor.  I bought a couple of the pheromone-based SVB traps.  I thought they arrived too late to do any good.  Now I have a reason to put those up.  As I understand it, those aren’t sold as a “control” measure because they only attract the males.  They are sold to professional farmers as a way to monitor the extent of infestation.  By counting the number of dead male months each day, you have an idea of how many are visiting your garden.  The traps look like they should be pretty good at avoiding by-catch — they aren’t yellow, and the sticky part is pretty fully enclosed.  Seem to be worth a try.

(By contrast, lure-based sticky traps for cucumber beetles were a one-day crash and burn, due to the by-catch.  They were big yellow traps with a large volume of stick surface covering the entire outside of the trap.  And, unsurprisingly, they caught everything.  They went up one evening, they came down the next morning.  And I’m back to squishing beetles every AM as they eat the pollen in my squash blossoms.)

Second, spray critical parts of high-production plants (only).  Contrast two plants.  One is a nice, compact yellow squash that has half-a dozen fruit set and powdery mildew under control.  The other is one of many rambling pumpkin vines that has yet to set fruit.  And is or will be beset by powdery mildew.  I’ll take two minutes, every five days, to try to save the first one.  The second one is expendable.  If I find borer damage, I’ll cut the plant down and solarize it to kill the larvae.  (If you see a black trash bag sitting in my driveway, that’s what I’m doing.)  And replant with something that’s less trouble to grow.