This has been a particularly rough summer when it comes to our home garden vegetables. Excessive rainfall has prevented many plants from growing or ripening properly. To make things worse, we also have to deal with insect pests trying to devour the vegetables that did manage to grow. One pest we have to deal with every year is the squash vine borer.
Squash vine borers are insects that infest all members of the cucurbit family, including squash, pumpkins, cucumbers, and melons. Many gardeners will see strong, healthy vines one day, only to come back the next and observe a severely-wilted, dying plant. Squash vine borers can be difficult to detect and can kill a vine quickly.
Squash vine borers spend the winter as larvae or pupae in the soil where squash was previously planted. Adults emerge as moths in the late spring or early summer. They fly to surrounding squash vines and lay eggs on the stems. Squash vine borer moths are often mistaken for wasps. They have a ½- inch wingspan and are black in color. They normally fly during the day.
Eggs hatch in about a week, revealing pale-colored caterpillars. The grub-like larvae eat their way into the squash vine stems near the soil level. They then begin to tunnel up the stem, causing structural damage and restricting water flow. This will cause severe wilting in squash vines. Sawdust-like insect waste, called "frass," may also be observed around the base of a vine infested by a squash vine borer larva.
Squash vine borer infestations are often hard to control. The wilting symptoms often come without warning and appear to happen overnight. Most gardeners don't check the base of their squash vines for insect frass every day. Unfortunately there is no "silver bullet" method that will provide complete control of the squash vine borer. A combination of cultural controls and timed insecticides will help lessen the pest pressure.
Rotating the placement of your squash vines every year can help lessen the insect populations in different parts of your garden. Tilling up the soil in late winter will expose some of the overwintering insects to harsh conditions and predators. Because the vine borers don't emerge until late spring, planting your vines as early as possible will give them the best chance to survive a borer attack. Once your vines are planted set out yellow sticky traps and yellow bowls of soapy water to trap vine borer moths. These mimic the yellow flowers of squash plants.
Check your squash vines regularly for signs of frass. If observed, cut a vertical slit up the vine until you reach the larva. Remove the insect or kill it with a long needle. Next, mound soil up around the base of the vine to just above the point where the larva occupied. If you're lucky, the squash plant will sprout new roots above the borer damage.
Insecticides may also be used to help control newly-hatched vine borer activity. Bifenthrin and esfenvalerate are two products labeled for squash vine borer control in home gardens. Two sprays spaced seven days apart can help control new larvae if timed correctly.
Use www.georgiaweather.net to monitor degree days at surrounding weather stations. Squash vine borer adults normally begin emergence at 1,000 degree days, so start monitoring your vines when we reach 950 degree days. next year.
Clark MacAllister is the Dawson County extension agent. For more information, call (706)265-2442.