The Slowcook at Spydog Farm The Slowcook at Spydog Farm

Attack of the Squash Vine Borers

July 1st, 2010 · 2 Comments · Posted in garden

These will kill your zucchini

These will kill your zucchini

When you see the leaves of your zucchini plant suddenly wilt and fall to the ground, it’s a sure sign that somehting is drastically wrong. More likely than not, it’s a squash vine borer.

Lately we seem to be plagued with squash troubles. Last year it was too much rain and some kind of rot that ate up our favorite heirloom Italian zucchini. This year I planted our zucchini in a completely different bed at the other end of the garden. The seeds were started in a four-inch layer of new compost. Still, the other day one big, healthy plant simply collapsed and it took about 30 seconds to find the problem: a borer had eaten its way through the main stem.

Squash vine borers are the larvae of a moth that looks like a wasp. The moth lays her eggs on the squash plants and when the larvae emerge, they look for a squash plant to start feeding on. They bore right into the stem near the ground, potentially killing the entire plant. But rather than me digesting the scientific literature for you, I’ll just quote the pertinent intel from the University of Maryland’s Cooperative Extension Service site:

“Squash vine borer is a major pest of summer and winter squash and pumpkin, especially zucchini, acorn, hubbard and yellow squash. The main symptom is wilting of vines. Gardeners often watch plants die without discovering the reason. The adult squash vine borer is an orange and black, clear-winged moth that looks like a wasp. The forewings are coppery-colored and the wingspan is 1-1/2 inches. Adults can be observed beginning in late May in Central Maryland (depending on weather conditions). The female lays eggs singly on the vines of host plants. Eggs are usually laid around the crown or lower portion of main stems. Upon hatching, the larvae bore into the stem and may feed for up to 4 weeks. It is not uncommon to have more than one larva feeding inside a plant. The sawdust-like excrement (frass) that is pushed out of plant stems is the best indicator that larvae are feeding inside. The larvae are white and wrinkled with a brown head and reach 1 inch in length. The vine borer hibernates as a larva or a pupa in a cocoon, one inch deep in the soil. There are 1-2 generations per year.

“Management: The larvae can be excluded with collars made of aluminium foil wrapped around the lower stems or with a floating row cover placed over plants and secured to the ground. Be sure to remove the cover during bloom to allow for insect cross-pollination. If larvae are present, simply make a slit along the vine (halfway through the stem diameter) with a razor and remove them. Heap dirt over the damaged area of the vine to cover the wound and encourage new root growth. B.t. can be injected into infested stems with a hypodermic needle to kill larvae. (B.t. is Bacillus thuringiensis, a microbial insecticide that is classified as an organic pesticide. It is effective against all moth and butterfly larvae.)

“Start seeds indoors 4 weeks before the last expected frost. Planting out healthy transplants rather than direct seeding will ensure that plants are large and better able to withstand injury. One could also plant around the borer problem by sowing a late crop in mid-June.”

In other words, squash borer can be managed. But it still doesn’t answer my question: where the heck did it come from?

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  • trueepicure

    There has been discussion on Twitter about starting Zucchini in July to start after the Borer typically lays eggs. I’m going to try it this year. Here’s hoping.

  • Sylvie in Rappahannock

    and here it’s the onslaught of the Mexican Bean Beetle. I had no idea until now how nasty those things are. Beans defoliated.

    I think it’s spontaneous generation. How else to explain it?