Squash, pumpkins and zucchini can be killed by squash vine borers.

Tom Wallace, Star Tribune

Nancy Rose: Borers that can kill plants

  • Article by: Nancy Rose
  • June 22, 2004 - 11:00 PM

Q I've had problems with vine borers damaging or killing my zucchini plants. What can I do to prevent the problem?

A Squash vine borer is a common garden pest that can damage zucchini, winter squash and other summer squash and pumpkins. Squash vines that are infested with vine borers often collapse and die.

The adult squash vine borer is a type of moth. It has a slender, wasplike body with noticeable orange areas on the abdomen and clear wings. The adults emerge from the ground (where they've overwintered in cocoons) around late June, so start looking for them then.

The female moths deposit pinhead-sized brown eggs along the lower part of the squash stem, usually within several inches of the soil level. When the eggs hatch, the wormlike larvae burrow directly into the squash stem. They grow and feed within the stem. Their feeding ruins the plant's water transportation system, so one of the first indicators of borer damage is wilting leaves. Plants are often killed by squash borer larvae.

There are several methods for preventing squash vine borer damage. One is to use lightweight row cover fabric to keep the adult borers from reaching the plants. Drape the fabric (usually a spun polyester) over the plants and secure the edges with soil or sod staples. Keep the covering in place several weeks, until the adult borers are gone.

One problem with row covers is that they also prevent bees from pollinating flowers. (Male and female squash flowers grow separately and require a pollinator for proper fruit set.) This could be an issue with winter squash and pumpkins, because the fruit must set early to have time to mature before frost.

Theoretically, you could prevent squash vine borer damage by scraping off the eggs laid on the stems, but this would require daily monitoring. And if you missed even one egg you could still end up with a dead plant.

If you wish to use pesticides, apply one labeled for squash vine borers such as carbaryl (Sevin). Carefully dust or spray the lower stems with the pesticide in late June or when you see the first adult borer moths. Carbaryl is very toxic to bees, so avoid dusting or spraying it on or near the squash flowers.

Q What's the best way to grow black walnut trees from the nuts? The squirrels seem to do a good job of it, but I haven't had success when I've planted them.

A Black walnut (Juglans nigra) is a large native tree valued for its leafy shade, edible nuts and high-quality wood. It can be grown readily from seed by following a few basic steps.

Collect the seeds (nuts) of the black walnut when they drop off the tree in the fall. The leathery outer husk is usually brownish black when the seeds are mature. The husk encloses a hard nutshell, which in turn encloses the edible part of the nut.

Unhusked black walnuts are able to germinate when planted, but you'll probably have better success if you remove the husk before planting. This is easiest when the husks are firm but pliable. If the husk dries too much, it's harder to remove from the nut. Wear gloves and old clothes when husking black walnuts because the husks can leave stains.

The husked nuts can be planted directly into a garden. Plant them 1 to 2 inches deep. Water the area after planting, and continue to water until the ground freezes if there's not enough rain. The seeds should sprout in the spring.

You may need to place chicken wire or hardware cloth over the area to keep squirrels from digging back up the seeds and eating them.

Nancy Rose is a horticulturist, writer and photographer. To ask her a gardening question, call 612-673-9073 and leave a message. She will answer questions in this column only.

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