Controlling Squash Vine Borers (Melittia cucurbitae)

A squash vine borer moth in Patty Leander's garden. Photo by Bruce Leander

In my mind, squash vine borers are kind of the nut sedge of the insect world. They reproduce like crazy and they are very difficult to control. Very few pests in the garden are as dreaded and damaging as the squash vine borer.  While aphids make your leaves look ugly, squash vine borers make your whole plant die!

A close up of the grub like larvae of the squash vine borer. Photo by Bruce Leander

Since we have had such an unusually mild winter, many people have planted early.  Because of this, their squash is now at a perfect state of maturity to be attacked by these  pests.  So, I thought I would take this opportunity to give a few tips on controlling them.  While there are both organic and commercial pesticides out there , the best way to control these pests (in my opinion) are your growing practices.

Squash Nine Borer eggs. Photo by Bruce Leander

First, if you want to stop the problem before it begins, grow your squash under floating row cover. If you put row cover around your plants when they start to vine, you can prevent the borer from laying its eggs on your vine.  Cut a fairly large piece of row cover so it can expand as the plant grows.  Anchor the edges in the soil with dirt, boards or bricks; anything that will create a seal and prevent the moth from getting to the base of your plant. Be aware that if you put row cover over your plants before they pollinate, you will have to pollinate by hand.

Squash being grown by under row cover in Patty Leander's garden. Photo by Bruce Leander

If row cover and hand pollination are more than you want to deal with, watch for the adult borers in your garden. You can hear them buzzing if you are close. However, if you can’t be outside, you can place yellow sticky traps around your plant. Since they are attracted to the yellow (like the squash flowers) the moths will get trapped and let you know they are in the area. Once you know they are there, look for their eggs on the stems and under the leaves that are close to the base of your plant. They are pretty small and reddish brown in color. Once you find them, pull or scrape them off with your fingernail or a sharp knife.

A healthy zucchini. Photo by Bruce Leander

If you see little bumps forming on the base of your vines, you have an infestation.  You can take a razor blade and cut into the infected area. If this doesn’t kill the larvae, remove it and then tape the cut with floral tape or pack with soil. If done soon enough, the plant will recover and produce as normal.


If your squash wilts and does not recover in the morning, there is a very good chance you have the squash vine borer. Photo by Bruce Leander

Because effective control of this pest is so hard to do, try planting squash varities that are not as affected by the borer. I grow tatume’ squash and it has no problems with the bugs. Also, do not plant in the same place year after year. They larva pupate in the soil under the plant they killed so every year move your squash as far as possible from where it was grown last year.

Some squash varieties like "Tatume" are not bothered by the squash vine borer.

If you are not of the organic mindset, there are a few chemicals out there that do a pretty good job of controlling borers.  The most common and readily available is Sevin Dust.  Sevin works pretty well against the moth.  However, it has a very short effective period so if using it, apply weekly.  Also, the chemical Methoxychlor (trade name include Marlate, Chemform and Methoxy-DDT) is very effective and relatively safe.  Methoxychlor is very popular in greenhouse applications because of its relatively low level of toxicity.

Nothing is more disappointing than seeing your beautiful squash reduced to a pile of shriveled of green stuff in two or three days.  Squash vine borers have broken more hearts than any other bug I know.  Because these pests are so destructive it is important to be alert and stay on top of them.   The best way to control an attack is to stop it before it starts.  So, go to garden regularly and watch for any sign of the pest.  With a little diligence you can keep this bug from depriving you of all of the wonderful summer squash.