Common Name: Squash Vine Borer
Scientific Name: Melittia cucurbitae
Squash vine borers are one of the most common pests encountered when growing pumpkins or squash. They are a native American insect and are rarely seen west of the Rocky Mountains, but are extremely common in the east. They are diurnal, which means that they are active during the day and are known to prefer laying eggs at sunset.
Adults: Narrow-winged, olive-brown, 1-1 ½ inch moths, with fringed hind legs, clear hind wings, and reddish orange abdomens with black rings. The squash vine borer moth can possibly be mistaken for a bee or wasp because of its movements and bright orange hind-leg scales.
Eggs: Brown, flat, oval. Laid generally singly on the basal stems.
Larvae: Start out as tiny white caterpillars with brown heads. Feed for 4-6 weeks.
Pupae: Silk-lined, black cocoon, ¾inch long. Generally 1-2 inches below the soil surface.
Vines of squash, pumpkin, cucumbers, melons and gourds.
Larvae or squash vine borers chew the inner plant tissue near the base causing vines to wilt, girdle and die off. You can often see a small hole and some frass that looks like sawdust at the base stems.
Organic Control and Prevention of Squash Vine Borers:
Good organic control should involve a combo of several different methods.
1. Cultural practices: Since squash vine borers overwinter in the soil as cocoons, removing spent vines and crop debris after harvesting is a good idea. Till your grow area to destroy any larvae or pupae still present and expose them to natural predators. Avoid planting squash in the same location in the garden season after season.
2. Row covers: Early in the growing season, use floating row covers to keep adult squash vine borer moths from laying eggs. Later when vines start flowering, uncover for pollinators or hand-pollinate. After removing the row covers, use pieces of tulle (wedding net) or aluminum foil to cover any exposed lower sections.
3. Monitoring and handpicking: Keep a close eye on your plants, especially check the stems near the ground. Seek and destroy vine borer eggs. If you see vine borer holes in the stems, one of the only things to do is surgically cut them out. Use a knife to make a slit along the stem (not across!) until you find the culprit or culprits. Remove and kill the caterpillar and cover the cut area of the stem right away with soil or compost to promote rooting.
4. Grow resistant varieties: Butternut squash and other varieties classified as Cucurbita moschata are naturally resistant to squash vine borers. Hubbard type winter squash varieties, yellow summer squash and zucchini, i.e. Cucurbita pepo varieties on the other hand are highly preferred by squash vine borers, and can be used as a trap crop. Another general rule of thumb is that wide hollow stems are preferred to narrow or more solid stems.
5. Color traps: The adult moths are attracted to the color yellow. Surround the garden with small yellow pails half filled with water.
6. Encourage secondary rooting: Heap soil or compost along stems of the plant at several points along the vine choosing nodes where new leaves and sprouts are occurring. This encourages the plant to send more roots into the ground giving rise to a healthy and strong plant that even if attacked by vine borers will not suffer too much damage.
7. Organic insecticides: Spray plants with Bt (Bacillus thuringiensis), concentrating on the stem area to tackle squash vine borers. You can also inject Bt or beneficial nematodes into the stalk where infection is present. These are commercially available, but always seek advice from a local expert to ensure its necessity.
8. Strategic timing: If you have a long growing season, set out transplants as late as possible to avoid the initial swarm of squash vine borers. If the weather permits, try to beat the vine borers by getting a very early crop out before the vine borers emerge.
9. Grow healthy organic plants: Strong, healthy squash plants can manage to give good yields even after taking some damage from vine borers. Ensure that your plants are in a sunny location, in loose, well-drained rich soil with plenty of nutrients and compost.
10. For those who keep chickens or other poultry, allow them to clean up garden patches before the season (after tilling the soil) and at the end of the season.