I have an evil nemesis. It is not the mean girl from church who told me during middle school that I must be stupid because I went to public school. It is not the smokers who seem to view the sidewalk in front of my house as their drive-by ashtray. It is not the folks who thought it was a good idea to let a chinaberry tree grow in my yard (this was not a good idea; chinaberries are quite invasive and should not be used in Southern yards on purpose). It is not even a person. My evil nemesis is an insect called the squash vine borer. I’m not alone—several readers have expressed concern about the squash vine borer, and I will try to answer your questions in this post.
The squash vine borer (Melittia satyriniformis or Melittia cucurbitae) wreaks havoc on squash and gourd plants. As Jessica Walliser notes in her excellent book entitled Good Bug, Bad Bug, “Unfortunately, most gardeners don’t notice borer damage until it’s too late.” In other words, if a squash vine borer attacks your garden, you have a beautiful zucchini plant one day and a wilted mess of sadness the next. To you, it may seem to happen overnight, but this horticultural murder is definitely premeditated. What happens is this: one day in late May, a black and orange moth that looks kind of like a wasp emerges from her cocoon. She meets a boy moth. One thing leads to another, and the girl moth lays some eggs on the vine of your squash plant. The eggs hatch, and some little white larvae emerge. Don’t be fooled by their diminutive size; the larvae are killers, and your squash plant is their all-you-can-eat buffet. The larvae bore their way into the stem and feast on the flesh, killing the plant from the inside. Your plant dies, you cry, and then you notice the tell-tale sawdust-like residue at the base of the vine, and you clench your fists and yell to the heavens, “why, why, why?” (At least that’s my reaction.) Then the larvae, finally finished with their gluttonous rampage, settle down into the soil as pupae. When spring arrives, they undergo a metamorphosis and turn into the aforementioned black and orange moth. And so the cycle continues.
Squash Vine Borer. Photo courtesy of Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org
For more photos, see http://bugguide.net/node/view/11810
How can you stop this evil insect? Everyone from Walliser to Walter Reeves says that prevention is key. Here are the universally acknowledged methods of preventing the heartbreak of a squash vine borer infestation.
* Get a Move On.
If it is possible, rotate your crops. Don’t plant squash in the same place for three or so years.
* Keep it Clean.
Well before you plant your first squash of the spring, make sure you have removed all of the old squash vines from your garden. That way, any larvae still in the vines will be removed from your garden. In late winter, till the area to expose any larvae/pupae that have settled down into the soil. Your friendly neighborhood birds should take it from there.
* Plant Early and Often.
Plant your squash as early as the weather allows (read: as soon as your soil hits 60° F and you think that frost is unlikely). The adult moths don’t emerge until early summer, so if you plant early enough, it’s possible that you’ll be sick of squash before the larvae launch their attack. And plant your squash throughout the season. Late plants may also miss the attack.
* Put Up Barriers.
There are lots and lots of recommendations, but the basic concept is the same: minimize how much space is available for the moth to lay her eggs. Some options:
- Mound soil over the vine to the lowest flower.
- Wrap aluminum foil around the plant base where the stem meets the ground (note: I’ve tried this one, but perhaps I did it wrong. Maybe I’ll try again this year. Mama read somewhere that plastic cup “collars” would work, but they didn’t. Perhaps the problem was in the execution.).
- Cover plants with floating row covers when they start to vine, and remember to anchor the fabric to the ground. Of course, you’ll have to remove the cover when the plants flower or you’ll have to hand pollinate.
* Search and Destroy.
Be on the lookout for the various stages of the squash vine borer. Show no mercy.
- If you see the orange and black moths flying around during the day, you’ll know it’s time to inspect the plants for eggs.
- Whether or not you see the adults hovering in your garden, you should inspect the plants for eggs and destroy them (just wipe ’em off and crush ’em). The eggs are, I’m told, reddish brown and are usually at the base of the stem. Note: while you’re looking for squash vine borer eggs, you could also look for squash bug eggs and destroy them too. You don’t want squash bugs, either—they are little squash vampires that suck the life right out of your squash plants. Well, they suck the sap, anyway. Squash bug eggs are usually on the underside of leaves.
- Take a look at the stem of your plants to see if there is evidence of borers. To me, it looks like sawdust on the vine. This is your chance for revenge: cut open the stem, dig out the borer, and kill it. Then cover your wounded squash vine with moist soil.
* Go Nuclear.
As a master gardener, I was taught to take an “integrated pest management” approach to insect control. That is because 95% of bugs are good or at least benign. We need bees and butterflies to pollinate our veggies. We need ladybugs to kill aphids. We need assassin bugs, praying mantises, and spiders to kill a whole mess of pests. Most insecticides kill the good guys along with the bad guys. And guess who bounces back first (hint: it’s not the good guys). So I try to use insecticides as a last resort. That said, if you can’t get the plants in early or if you always seem to be attacked by squash vine borers, you can try an insecticide. Walter Reeves suggests either a weekly application of carbaryl powder to the base of the stems or spraying with acetamiprid. Remember to read the directions! And note: once the borer has entered the vine, it’s too late for the insecticide to work. So take that into account when you’re devising your regimen.
Final Thoughts
One reader asked if she should consider removing an area of her soil and replacing it. This proposal has some appeal—as discussed above, the pupae of squash vine borers settle down in our soil for a long winter nap. In the spring, the pupae turn into adults and make their above-ground debut just in time for squash season. That said, removing and replacing soil seems like an awful lot of work, particularly given that it would only stop the reader’s homegrown grubs. In its adult form, a squash vine borer is a moth that could simply fly over to the reader’s yard and lay its eggs. So I’m reluctant to suggest the removal/replacement approach until she has exhausted the other, less dramatic alternatives, starting with crop rotation, tilling, and preventive barriers.
Now that we’re all armed with this information, I feel much better about our chances against the squash vine borer this year. I’ll keep you posted on my progress. Please keep me posted on yours!
Georgia Garden Girl 
I was told about a new product last year
(Captain Jack’s something) that you inject into the stalk of the squash early on to prevent the borers. It worked for my daughter as she had multitudes of squash well into August. We found it at Pike’s.
Thanks for the tip! I will add it to my arsenal.