Squash Vine Borers - Signs of Damage and How to Control It.

Squash Vine Borer
Jim Jasinski, Ohio State University Extension, Bugwood.org

It's an all to common occurrence. Your squash plants looked fine yesterday. Today they’re wilting and no amount of watering has helped. What happened?

Sudden wilting of squash plants is a sure sign of the squash vine borer. The squash vine borer is the larvae of a black moth with orange-red markings. It has a wing span of about 1 - 1 ½ in. (25 to 37 mm). The moth lays its reddish-brown eggs on the squash leaves, often on the underside, where you can't see them.

When the eggs hatch, the larvae bores its way into the stem, usually in the lower 1 ft of the stem. That's what causes the plant to wilt. It looks bad, but it does not have to be fatal.

Signs of Squash Vine Borer Damage

Wilting is not the only sign that a squash vine borer has attacked your squash plant. You can often see a small hole and some frass that looks like sawdust. The injury can girdle the stem and prevent the plant from taking up water and nutrients, causing it to wilt and, if not corrected, ultimately to die. Multiple borers can be found in one stem.

Plants Affected by Squash Vine Borers

All squash plants can be susceptible to squash vine borers, but some of their favorite hosts include: Hubbard squash, all types of zucchini, pumpkins and gourds. Squash vine borers don’t usually attack cucumbers and melons, but if you see the tell-tale sign, take a look at the base of the stems.

Controlling Squash Vine Borer

Squash vine borers over winter in the soil as larva in cocoons, so your first line of defense should be removing the spent vines after harvesting. This will remove any borers that were lingering in the vines. Till the area to bring borers that have already made their way into the soil back up to the surface.

The birds will take it from there, swooping down and making a feast of the larvae.

Planting your squash later in the season, can help you to avoid squash vine borer infestations. If you hold off planting until after Memorial Day, the borers will have resurfaced from the soil and already moved on in search of a food supply.

However, if you do see signs of squash vine borer:

  • In the spring, the first mode of defense should be to monitor for eggs. Be sure to check the underside of leaves. The eggs are small, but since they are a bright orange color, they are fairly easy to spot. If you can remove the eggs when they appear, you're half way there.

     

  • The larvae usually bore into the stem where it meets the ground. Wrapping some foil around this area at planting time, before the borers are active, acts as a barrier.

     

  • If you do see a vine wilting or notice a hole at the base, it's still possible to save the plant by making a vertical slit into the stem and removing the larvae by hand. The plant will heal. You can cover the wound with moist soil to promote more roots.

     

  • And finally, you can pile some moist soil over the leaf joints near the in ground stem. They will root. So even if the stem is damaged, the plant won't die.