Ask the Master Gardeners
Q: Every year my zucchini plants start growing vigorously but by mid-July the leaves start wilting, the fruits show yellow soft tips and eventually rot. I think that the problem is squash vine borers. How do I control it?
A: The squash vine borer (Melitta cucurbitae) is an aggressive pest that attacks squashes, pumpkins, cucumbers and melons.
The symptoms of infestation are sudden wilting of sections of the vine, presence of yellow-green fecal deposits on the stems and soft pale tip on new fruits.
Your best defense against these pests comes from understanding their life cycle. The squash vine borer is a moth that overwinters as a mature larva in the soil.
By late June a moth emerges, which lays its eggs on the stems of squash and zucchini plants. The larvae bore into the plant stem where they feed and mature and become ready for reproduction the following year.
Ideally, you should start a new crop in soil that is not infested with larvae from the previous year. Skipping planting of susceptible plants for a year or moving crops to a new location far from the infested site would interrupt the borerâ€™s life cycle, while deep plowing or rototilling would break the larvae cocoons.
If not feasible, you can use traps and floating row covers. Yellow cups filled with water attract the moths, while tin foil collars around the stems create a barrier to egg-laying moths.
In spring, securely fastened floating row covers can be used to protect the plants until blooming time (remove the cover to allow for pollination).
If the plants become infested, carefully slit the stems and extract the larvae; burying the damaged part of the vine with soil may encourage rooting from the stem and help it recover. You may plant a second crop after the moths finish laying their eggs in mid-July.
While zucchini are more susceptible to the borer, the market now offers varieties of summer and winter squash that are resistant or less prone to infestation (i.e. Butternut, Green Striped Cushaw, Summer Crookneck).
â€” Cristina Malinverno, Blauvelt, master gardener, Cornell Cooperative Extension of Rockland County
Here’s a healthy zucchini plant in our food editor Liz Johnson’s garden.