Garden Help: Avoiding the Squash Vine Borer

Your summer squash, zucchini, winter squash and pumpkin were looking so beautiful with wide expansive leaves… that is, until you kneeled down to pick a zuke and yellow squash for dinner. When down there on the ground, surrounded by ginormous leaves bigger than your head, you noticed that the vine has this ugly spot, sort of cracked, maybe oozing, with little ants gathering a meal of sappy lifeblood to take back to their nest.

Oh, no! What would cause such an ugly wound that you are sure will affect your ability to harvest more dinners and lunches for the summer and into the winter? What is this horrible creature that is stealing your summer squash and your winter pumpkins? It is Melittia cucurbitae,otherwise known as squash vine borer.

The squash vine borer overwinters as larvae or pupa an inch or two below the soil surface. For homesteaders, using a moveable chicken tractor using a rotational grazing method during fallow times will naturally stop the insect at this life stage. Once the insect has bored into the plant, things become much more difficult.

Adult squash vine borers usually start their flight in mid-June in climate zone 6. You can estimate your date by counting two weeks after this time for each growing zone north add two weeks after June, and two weeks earlier for each growing zone south.

A benefit to gardeners is that you have the option to try to deworm the vine. At the first sign of frass, which looks sort of like saw-dust, slit the vine length-wise near the damage, then remove the borer. Be sure to cover the vine completely with soil.  To help ensure that no other borers will survive in the vine throughout the winter, be sure to pull out all parts of squash and pumpkin vines and add to your compost pile.

Prevention includes pesticides to kill the adult moth (such use must not contaminate the flowers, as pollinators would be killed by poisoned nectar or pollen). Organic controls include wrapping the lower stem with nylon stockings or aluminum foil to prevent egg laying, which generally occurs within a couple inches from the point where the stem emerges from the soil. Row covers can be used up until bloom. An old gardener trick for vining squash and pumpkin cultivars is to cover the vine with earth at various points along its length, inducing rooting at several points, thereby continuing to feed the developing fruit despite the loss of the original stem. It may be noted that after the vine has taken root at multiple points, the infected portion of the plant can be cut off, along with another inch where the larvae is eating into healthy tissue, without significant damage to the plant.

But once the larvae are inside the plant, pesticides are ineffective. Gardeners find this a difficult pest to combat. Some try to avoid the pest by timing the production season to harvest before the pests can build up, or after they have peaked.  Once larvae are present within the stems control must be quick. Often the first noticed sign of the problem is wilting of the vine, and it is too late for control efforts at that point. Experienced gardeners watch the stems for signs of frass protruding from small holes, which is a giveaway to the presence of the larva inside. Some gardeners carefully cut the stem along its axis and remove the caterpillar before it does too much damage. Others use a stiff wire, a needle, or a toothpick to kill the borer without too much damage.