You’ve started your summer squash and zucchini. The plants look great! A couple of weeks later, the plants start to wilt and some die. What did I do wrong? After careful observation, you notice there is something that looks like wet sawdust at the base of the plant. Plus, you see small holes in the bottom stem. What is going on?
Your enemy is the Squash Vine Borer!! (SVB)
The female Squash Vine Borer moth (Melitta curcurbitae) lay brown eggs especially on the stems, just above the soil line.
Eggs hatch in 10 days. Once the eggs hatch, they immediately enter the stem, leaving a small hole at the place of entry surrounded by frass (moist sawdust like debris). The larvae (white caterpillars with brown heads) bore into the stem and remain until maturity before pupation (the transformation of the larvae to a pupa(in a cocoon)). They will now stay in the soil (usually 1″-2″) and over winter .
Squash Vine Borer moths emerge from the ground from early spring through mid-summer. The moth looks like a wasp and is a half inch long. The wings are clear and look like a windowpane. Unlike other moths, this one flies during the day and makes a buzzing sound.
Now that you have identified the enemy, what are your weapons of warfare?
- A preemptive strategy would be to use a floating row cover (sheer, light weight fabric that is placed over a crop to protect from insects). It is secured in place to prevent insects from damaging the crop. The row cover is put on at the time of planting until the plants begin to flower. Squash crops require insect pollination.
- Monitor by using a yellow colored bucket trap with water, placed near the newly planted squash plants. The yellow color attracts the moths. Traps must be checked daily. Once you’ve found moths in the traps, start looking for stem damage. This indicates the female moth is out laying eggs.
- Create a barrier on the lower stem by using materials such as aluminum foil. Wrap the foil around the lower stem to confuse and prevent the moth from laying eggs.
- Plant a trap crop of early planted Hubbard squash three (3) weeks prior to planting your preferred squash crop.
- Use succession planting (weather permitting). Have fresh transplants ready to go. A late crop planted after SVB pressure may offer a harvest. Do not plant your late crop where there has been previous pressure from the SVB. Rotate your planting to an unaffected area.
- SVB resistant varieties of squash, such as Waltham Butternut, offer a solid stemmed variety to thwart the penetration of the larvae. Cucurbita moschata are their least favorite, as they are solid stemmed. Cucurbita pepo are their most favorite, as they are hollow stemmed. Seed catalogs will list this information for each squash seed offered.
- When a squash plant has been attacked by the squash vine borer, find the borer by looking for the frass or small holes with frass. Carefully slit open the stem and remove the caterpillar. Cover the wound with fresh soil or compost to encourage the re-rooting of the plant.
- Remove and destroy any plants that are severely wilted or dead immediately. Do not compost these plants!!
- Sanitation is key! Immediately remove your squash vines after harvest. Do not compost!! Burn the vines or bag the vines and remove them from your property. The soil must be exposed to reveal the cocoons.
- Till or fluff the soil up to 2″ to expose SVB cocoons. Songbirds and poultry delight in eating the pupae (cocoons).
- Always rotate your squash crop to another space each year.
My strategy this year includes the Blue Hubbard trap crop and yellow trap buckets. Plus, I will preemptively spray the ground stems with a mixture of vegetable oil and Dipel (Bacillus thuringiensis). I’ll keep you updated throughout the summer.