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Squash Vine Borer

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Here are tips on how to identify, eliminate, and control the squash vine borer.

What are Squash Vine Borers?

Squash vine borers are very difficult to control.  If your plants suddenly wilt because larvae may be boring within the lower part of the stems. Look for holes and green to orange-yellow sawdust-like frass (droppings).

They attack squash, zucchini, pumpkins, and gourds. They prefer Hubbard squash and are not as fond of butternut squash. Cucumbers and melons are not usually an issue.

The borers overwinter in soil as pupae in cocoons. When the adult clearwing moths emerge in early to midsummer, they lay eggs singly or in small groups at the base of stems. The eggs will hatch within 1 to 2 weeks after being laid. The larvae will then bore into stems to feed for about 2 to 4 weeks; sometimes they may also bore into the fruit. In northern areas, there is one generation per year; in southern areas, there may be 2 generations.

If caught early, it's possible to save the plant. If caught after the eggs hatch, it may be too late. Controlling the squash vine borer is mainly about prevention.

How to Identify Squash Vine Borers

The eggs are tiny, flat, oval, and brown. If you slit open a stem lengthwise with a fine, sharp knife, you will see the borer larva, which has a fat, white, wrinkled body and brown head; it can grow to about an inch long.

The adult is a moth about 1/2 inch long that looks a bit like a wasp with a black body, marked with orange-red. The hind wings are transparent and the front wings are metallic green.

How to Control Squash Vine Borers

  • Slit the lower stem lengthwise with a fine, sharp knife to remove the larva by hand.
  • Or, if you spot entrace holes and "sawdust," try inserting a wire and thread through the stem for some distance to kill the inside larvae.
  • Then cover the slit stem section with moist soil about the point of injury to promote formation of secondary roots.
  • Also, extra rich soil near the vines helps rerooting.
  • If possible, catch and destroy the moths at twilight or in early morning when they are resting on the upper side of leaf bases.
  • There are insecticides, too, but timing is critical; they are effective when applied at the time that eggs are hatching. The biological insecticide B.t. (Dipel) is not usually effective. Many find carbaryl (Sevin) to work. See your local garden store for advice on appropriate chemical controls.
  • Preventative measures include covering the stems with a barrier, such as strips of nylon stockings, to prevent egg laying. 
  • Cover crops with floating row covers to prevent egg laying (but only if you are sure there aren't pupae overwintering in the soil).
  • Importing parasitic wasps prior to the egg stage can be helpful as these wasps are the borers' natural enemy.
  • A trap crop of very early-planted Hubbard squash can be used to alleviate pest pressure on other squash.
  • As soon as the squash is harvested, get rid of the vines. Till the soil in the fall and spring to get rid of overwintering pupae.

See our Squash & Zucchini page for more plant care tips.

 

 

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Comments

This is the first year that I

By Hank Puphal

This is the first year that I didn't see a sign of Squash Vine Borers in my zucchini or acorn squash. I tried something different this year.
After they started to vine out pretty good I injected the stems with a Thuricide mixture. Then I started spraying the stems with Liquid Sevin, especially the lower stem where it comes out of the ground. As the vines got longer, I sprayed the main stem further away from the ground too. I sprayed every time after a good rain as well as once a week.
I figured, when the egg hatches and it starts to bore into the stem, it had to go through the Sevin, therefore, it would die before it got in the stem. Maybe it was just coincidence but I never saw a sign of borers. After the end of August I stopped spraying.
Don't spray the flowers with Sevin! It will kill the bees and other pollinators. I use Thuricide if I want to spray the whole plant to prevent bugs from eating the leaves.

My pumpkin leaves began

By Krisd

My pumpkin leaves began wilting and fruit stopped growing. I saw the orange stuff coming out at the base of the stems, by the roots and saw holes so I figured bores. I took a blade to them this morning and cut out long, vertical sections out and found bores in every vine. All but one looks like it has been infected. I covered them with soil and watered heavily. We'll see what happens. I figured I either saved the plants or more likely killed them faster than they were already dying.

Well, we are going to get a

By Krisd on September 29

Well, we are going to get a total of 9 pumpkins from our 8 seeds planted. The borers definitely hurt our crop. After I cut them out, the vines kept growing for a while, producing a female here-and-there. They eventually starting dying, turning yellow and brown. They don't look pretty right now, but we did get some results. Most are pretty small though. I also had to deal with cucumber beetles and a lot of mildew due to the wet summer. All three problems occurred for our first year of growing. Hopefully next year will be easier.

this year I decided to try

By cornpatchguy

this year I decided to try giant pumpkins again, not for competition just local fun. but when I was looking for something to spray or drench the pumpkins, they miss informed me about their product killing vine borers. wiped out one plant, finally tried some Malathion 57%. it actually says it kills vine borer. I had some success with injecting the spray with cattle syringe and large needles, it does kill the worm fore sure, but no way on knowing how many I missed. I will try the nematodes next spring. I use to use this professional spray called WARRIOR T OR Z, but unless u know a commercial friend sprayer its almost impossible to buy. its deadly and all the giant pumpkin growers use this. very pricy, but hey it works. just have to be carefull when u spray. in my area , we've had no bees for a few years because of aerial crop sprayers, this is the first year I've seen some in my patch. after my pumpkins are set that I want to keep, I cut off all the flowers to help keep the bees away.

IS there one source of

By cornpatchguy

IS there one source of nematodes better than another? this will be a new and hopefully have great results using nematodes.

I have not had any problems

By Jenn Benham

I have not had any problems with squash vine borers since I started using beneficial nematodes in the spring. Garden's Alive is the source I've used. They are called 'Grub Away Nematodes' - they are pricey but they work & should control the cornworms too. Unfortunately they do nothing for cucumber beetles!

Any good solid total kill

By Jim Grim

Any good solid total kill methods would be great to know, even if I need to wait till next year to replant. These pests (all 3 together) are killing everything I have growing!

The article is inaccurate.

By Pete Walrath

The article is inaccurate. The eggs are laid on the OUTSIDE of the stem, singly, by the adult moth. They then hatch and burrow into the stem, where the larva grows. There are no egg masses in the stem, as larvae don't lay eggs. The larva later crawls out of the plant and into the ground where it builds a cocoon and emerges the following year as an adult moth.

Thank you for your feedback!

By Almanac Staff

Thank you for your feedback! We have updated the copy.

VERY well put Pete Walrath! I

By Jim Grim

VERY well put Pete Walrath! I am having a bugger of a time and my whole crop is being taken down from 3 directions at once. Flea Beetles, Vine Borer, and Armyworms/cornworms. They took my greens, took my squash, and are working on my tomatoes and peas now. About the only thing unaffected is my strawberry crop which was extra small because of a large Spring seedling crop of tomatoes.

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