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Hortiscope: Covering, rotating squash may curb nasty vine borer

Q: We have been having troubles with a worm that burrows through the stem of our vine plants about 2 inches above ground. The worm leaves a visible hole, especially on our winter squash. It killed our cucumbers and summer squash plants. I found one in the stem of a buttercup squash last fall. It was about an inch long and about the thickness of an earthworm. It had an off-white color. They seem to start doing their damage after the first of August. We do use Sevin to control the cucumber beetles, but it doesn't seem to affect this worm. Is there anything we could use at planting time, such as a seed or ground treatment? How about controlling it during the growing season?

A: This is squash vine borer causing your problem. It is an especially nasty pest because the borer, a grubby white caterpillar, hides inside the hollow vines of popular squash family plants, such as pumpkins and zucchini, as it does its dirty work.

Gardeners generally don't notice anything wrong until the whole plant starts wilting. By then, it's too late to save the plant. The trick will be to focus on prevention. The problem begins in late spring when a moth lays its eggs at the base of your squash plants.

Each female will lay about 200 eggs. The eggs are so small they are almost impossible to spot. The eggs hatch in a week or two. The grubs that emerge quickly tunnel into the hollow plant stems the eggs were attached to. These hungry youngsters feed, hidden from view, for a month or so and then drop down into the soil to pupate.

Rotate your planting of squash, cucumbers and pumpkins with a crop that is entirely different, such as beans, corn or tomatoes. Floating row covers will help prevent the moth from getting to the squash plants.

If you keep them covered until the first of July, all the egg laying activity should be finished and you can remove the covers. You could use a material, such as Dipel, which is an organic control that will stop the critter from eating too much of the vine before it expires. Whatever you do, don't use the floating row cover technique where you had squash vine borer activity the year before!

If you do that, the adult females will be in squash heaven because they will be protected from the elements. Depending on your powers of observation, you may have some success with deworming the vines. At the first signs of the sawdustlike frass, slit the vines lengthwise near where the damage is found and remove the borers. The stems should be covered immediately with soil. Sanitation also is important.

After harvest is complete, the vines should be removed from the garden and composted to prevent the remaining borers from completing larval development. Burying a few nodes along each vine will encourage rooting at these nodes. This will lessen the impact if squash vine borers girdle the base of the vine.

Q: Your answer to one of my e-mails about starting seeds indoors said to always use a pasteurized media. What exactly is that? Also, what is your opinion of pellet greenhouse kits?

A: Most potting soil or seed-starting media that you purchase in a garden center is pasteurized and contains inert material, such as vermiculite or perlite, which is sterile. I have nothing against pellet greenhouse kits for homeowners to use in getting things up and growing. If this is something that teases your interest, go for it!

To contact Ron Smith for answers to your questions, write to Ron Smith, NDSU Department of Plant Sciences, Dept. 7670, Box 6050, Fargo, ND 58108-6050 or e-mail ronald.smith