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Question of the Week © 2017 Mike McGrath
Note: Hundreds of Mike's informative articles are available (in alphabetical order!) right here at the Gardens Alive website. To find Mike's answers to your specific garden problem, Click here and find your topic (like Weeds, Worms, Rhododendrons...) in our complete alphabetical archive of Questions of the Week.
Your 'Wilting' Squash Plants May be Bored to Death
Q. Over the past few years I've heard you talk to many callers about the squash vine borer moth and the damage it causes to squash and zucchini plants. I can attest to how frustrating these pests can be; second only to cucumber beetles in my garden. This year I'm trying your suggestion of wrapping the lower part of the vine in medical gauze. I have seen a lot of the moths this year so this tactic will certainly be put to the test.
My reason for writing is that you have recently referred to this pest as 'a night flying moth'. Perhaps they also fly at night, but they seem to be out in force during the day in my garden. I'm an amateur "wannabe" entomologist who loves to study and photograph the insects in my yard. The squash vine borer moths are highly attracted to my Common Milkweed plants and I see them out during the day feeding on the flowers alongside flies, bees, wasps and butterflies.
I have attached a photo to ensure we are talking about the same insect. (Note: I now have better camera equipment, but I don't take the time to photograph them anymore; I'm focused on "squashing" them before they can make it to my zucchini plants!)
---Jonathan, who listens "via podcast in Kearney, Nebraska (along the Platte River, home of the annual Sandhill and Whooping Crane great bird migration)"
A. This was one of the most polite corrections I have ever received. And Jonathan is correct. Although I have been saying they fly by night lately, I did get it right and call them day-flying moths in our previous articles on this pest. I guess I forgot and/or got lazy and started grouping them in with the vast majority of garden-destroying moths that do fly by night.
Jonathan's (excellent) photo shows a 'clear winged' insect that looks more like some kind of bee or wasp. The long orange body is the opposite of what gardeners think of as 'moth shaped'; which is why we're posting the photo with this question of the week; so people will realize that their squash and pumpkin plants are under attack when they see this very distinctive wasp-like insect.
Specifically, the female moth will lay an egg at the base of a squash vine near where it enters the soil. The egg will hatch out a very tiny caterpillar that will quickly eat its way into the hollow vine, where it can feed undetected—at least until you notice your plants wilting and see the sawdust-like frass (a $20 word for 'bug poop') at the base of what is now probably an almost completely-severed vine.
If you go out and see that this is happening right now, pull the plants up and squish the nasty little caterpillars inside. Otherwise they'll drop into the soil and pupate, emerging as flying adults—next Spring in cooler portions of the country, but later this summer in warmer climates, where this pest has two generations a season.
Now, before you say, "either way, no zucchini or pumpkins this year…."
It may be too late in most regions to replant and ripen up a crop of pumpkins, but there's still time to plant a new run of zucchini and other summer squash in most places and get a nice harvest. The seeds will germinate fast in the warm soil, and the plants will produce more quickly than their listed 'days to maturity' might suggest. And there aren't any egg-laying moths active now in the North and mid-Atlantic, so those gardeners don't need to protect their late-season vines.
And in warmer climes, where second generation moths may be buzzing around?
Pull out any damaged plants and squish the hidden pests. If there aren't any caterpillars inside, dig around in the soil under the plants until you find their pupal stage and squish that.
(Yes, we're doing an awful lot of squishing today, but almost everyone who gardens has lost plants to these pests, myself included—so no prisoners!)
Then plant fresh seed and put yellow sticky traps out around the emerging plants; these moths are attracted to the color yellow. Some websites suggest placing yellow-colored bowls of water around the plants; apparently the moths will drown themselves in the water and alert you that they're out and about. I think that yellow sticky traps—which are widely available; they work on numerous plant pests—might work better.
Or do both. Can't hurt. Either way, if and when you catch your first moth, start spraying the vine with insecticidal soap to smother any eggs or with the old original form of Bt to kill the caterpillar when it takes its first bite of the vine. Or just gently wipe the vine down with a damp cloth twice a week to physically remove the eggs.
Then next season, use traps to detect the adults' emergence time and delay planting until after they're gone. Or plant good sized starts and wrap the vines with medical gauze or aluminum foil at planting time to create a physical barrier against the pests.