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Squash Vine Borer

Borers cause Zucchini wilt

By: Sandy Feather ©2010
Penn State Extension


Q. I had two productive zucchini plants that seemed to decline very suddenly. They were doing fine, then I noticed they started to wilt during the hot weather.  Now both zucchinis look pretty sad. Any thoughts on what happened?

A. Squash vine borers could cause the symptoms you are seeing. Adult squash vine borers are clearwing moths that grow about one-half inch long. They have orange abdomens with a line of black dots down the middle. They could easily be mistaken for a wasp of some kind. While most moths are active at night, squash vine borer adults are active during the day.


EGG LAYING

Borers lay their eggs on summer squash, winter squash and pumpkins as soon as the vines start to run from late June in to July. They rarely attack other members of the cucurbit family such as cucumbers or melons. The larvae that hatch out of those eggs tunnel into the stem as soon as possible and begin feeding. Their feeding damage cuts off the supply of water and nutrients, resulting in the wilting you have noticed. The larvae feed inside the stems for four to six weeks, then leave the stems to pupate in the soil around host plants. They remain there until hatching out as adults the following summer. There is one generation of squash vine borers yearly.

squash

On close examination, you can see sawdust-like frass coming from holes along the portion of stem near the ground where the larvae have tunneled into it. The stem may be soft and mushy from their tunneling and feeding. If you slit the stem open, you can often find the larvae inside. Squash vine borer larvae are white, worm-like insects with brown heads and legs. They are one to one-and-a-half inches long, and about as big around as your little finger. It is common for more than one larva to infest a single stem. If you find them, remove them from the stem and kill them or seal them tightly in a plastic bag. Re-bury the damaged portion of the stem in garden soil and keep that area moist. Squash are often vigorous enough to outgrow the damage if you catch it early enough.

 


BORER CONTROL OPTIONS

Other control options focus on keeping the larvae from burrowing into the stems because once they are inside the plant they are almost impossible to control.  You may consider planting a more resistant crop such as butternut squash, or you can wait to plant zucchini until early July when the adults are done laying eggs.

You can also cover zucchini seedlings with floating row covers (Garden Blanket or Reemay) to exclude egg-laying by squash vine borer adults. Floating row covers are lightweight and do not interfere with the plants' growth, and they allow sunshine, air and water to pass through freely. To use floating row covers, plant zucchini as you normally would. Lay the floating row cover over the transplants or seeds, making sure to leave plenty of excess fabric in the middle so the plants have lots of room to grow. Seal the edges with soil. Once the adults' egg-laying time has past in early-mid July, squash vine borers should not be a problem. You must remove the floating row covers once the vines have grown and come into full bloom so that bees can pollinate the separate male and female flowers in order for the fruits to form.


INSECTICIDES

Finally, you can make insecticide applications to the base of zucchini stems while the adults are laying eggs to control the small larvae when they hatch. Organic gardeners can use products that contain spinosad as the active ingredient such as Captain Jack’s Dead Bug Brew. Conventional gardeners can obtain control with Sevin (carbaryl).


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