Watching my summer squash’s leaves collapse just about overnight signals a problem. Further investigation proves worthwhile when I find a small, 1/8th hole on the plant’s stem. I cut the stem lengthwise, carefully splitting apart the vine to reveal the hollow vine filled with sawdust like frass. Frass is the excrement of an insect. About 12 inches away from the original hole lurks the offending caterpillar; the larval stage of the Squash Vine Borer. Not a pretty site from where I stand! Along with the insect chewing the inside of the vine, centipedes have also entered the vine feeding on the frass. All of the these insects introduce bacteria causing rot leaving a mushy trail in its wake. This plant is too far gone to save. It is pulled out after I kill the borer making sure I got them all, then tossed the plant in the compost.
The life cycle of the squash vine borer, Melittia satyriniformis, has one generation per year. The adult is a clear winged moth active during the day. There are orange and black rings on the abdomen. The front wings have greenish to black color while the hind wings are clear edged in brown. The eggs are laid at the base of the plant on the soil. Once the eggs hatch, they burrow into the vine to begin feeding. Adults are appear late June through July and into August. Signs of an infestation are small holes in the vine and piles of frass on the vine and below on the soil. The larva can reach 1″ in length. They mature after feeding for about four weeks at which time they will leave the vine to burrow into the soil. Once in the soil they will spin a cocoon in which to pupate. They spend the fall and winter in the pupa state until they emerge next summer as the adult moth.
Control measures are too late for my plant and should have been used much earlier in the season. Row covers made of Remay, a poly spun product reminiscent of mosquito netting, is an effective barrier, light-weight when applied over plants at the beginning of the season. The edges must be pinned down or buried in the soil to prevent the adult insects from crawling under the fabric. The idea is to exclude the adult moth from laying eggs at the base of the plant. Once the plant flowers, the Remay should be removed to ensure bees and other insects are able to reach the flowers for pollination. Turning over the soil at season’s end will expose overwintering pupae to the elements, and hopefully succumb to the cold. Another turn of the soil in the spring will further disrupt their protective site. Pull and destroy plants as soon as they finish producing to possible larvae from entering the soil. Chemical controls are either carbaryl (Sevin) or permethrin applied to the vines once per week starting the last week in June and continuing until the end of July.
If you do find frass and a hole in the vine, cut lengthwise splitting the vine until you find the boring caterpillar. Remove it then put the vine back together and mound soil on top of the damaged area. It might recover!