If your zucchini, squash, pumpkins or other vining crops (Cucurbits) wilt in mid to late July, an insect called the squash vine borer may be feeding on your plants. Look at the base of the plant for a hole or brown sawdust like insect droppings called “frass”.  If you see this, split the base of the stems open with a very sharp knife or razor blade and you can see a plump, cream colored caterpillar with a dark brown head.  You may also see frass inside the hollowed vines.  Or, you may see brown “frass” pushed out from the stem by this feeding larva that looks like a small grub.

          Squash vine borers overwinter in the soil and will emerge through July as day flying, wasp like moths. They lay brownish-red eggs at the base of young plants near the soil line and undersides of vining stems from June through August.  In about a week, larvae hatch from eggs and immediately bore into stems to disrupt water and nutrient flow.  Infested plants lack fruit, wilt and die. Damage occurs from July through August.    

          If it is early in the season you may keep the moth from laying eggs  on the plant by covering the vines with some type of floating row cover. Remove the row cover when the plants begin to blossom so other insects can pollinate the blooms.

          If you use chemicals in your garden, insecticides with Permethrin (Eight), Carbaryl (Sevin), Malathion, Bifenthrin, or Rotenone can be used if applied early in the season and reapplied every seven to 10 days. Bt (Dipel) works only if injected into the stem with a syringe as the worm does not eat on the outside of the stem. CAUTION: Some insecticides, applied under conditions of high temperatures (above 80 degrees) and high humidity, may injure or burn plant foliage.  Also it is best to avoid dust formulations on plants that are in bloom as the dusts are more toxic to beneficial insects that are needed to pollinate the plant, especially bees.  Spraying in late evening after the beneficial insects have gone to bed will reduce injury to pollinators.

          Once you discover the borer problem and the plant starts to wilt, insecticides will not work.  Sometimes, you can save the plant by splitting the stem with a razor blade starting where the borer entered and working up. Then remove or destroy the worm by hand, and then cover the vine with moist soil and water well. You might be able to save the plant this way.    

          For butternut squash, acorn squash, and vine crops such as pumpkins, and watermelons where the fruit sets on the end of a long vine, cover the vine and leaves with soil about every 3 or 4 feet.  New roots will grow under the mound and if a borer gets in at the base of the plant, you might be able to save the rest of the plant by cutting off the damaged section. I water my squash with soaker hose and try to lay the vine along the hose.

          If your plants are wilting, and you cannot find any squash vine borer activity, there may be other causes.  A disease called bacterial wilt often affects vine crops, especially cucumbers.  This disease is carried by the cucumber beetle so pick off the insect, destroy any eggs on the top or underside of the leaves, and spray with Permethrin (Eight), Malathion, Carbaryl (Sevin), Bifenthrin, or Rotenone. Use a sticker-spreader such as Turbo so the insecticide sticks to the leaf and does not wash off easy. It is best to spray in the evening about sundown, after the beneficial insects have gone to bed.          

                    For more information contact your local County Extension Office or go on the internet to: In the top box scroll down to Extension. In the bottom box type in “squash vine borer” (use quotation marks), or the number of the publication, or the disease or the insect you want information about. These NebGuides or NebFacts, or other publications can be printed from your computer. 

          (This article was developed from InfoSource material prepared by the University of Wisconsin-Extension, and from publications of the University of Nebraska-Lincoln, Department of Entomology, and the University of Nebraska-Lincoln Extension Service.)                     

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