Beating Squash Vine Borers

“The last couple of years that we have planted zucchini, a worm of some sort has eaten to roots and caused the plants to die. We try to use as little chemicals as possible but don’t know what else to do. We have tried 7 dust, diatomaceous earth and this year we even tilled several times before planting but yet our plants still died because of this insect. It doesn’t bother other plants just the zucchini.” Question from Michelle of Copperas Cove, Texas

Answer: You have squash vine borers! These moth pests lay their eggs at the base of zucchini and squash vines. Then their larvae hatch and bore into the base of the squash, eating away at the stem interiors until the vines wilt and die due to lack of food and water. Bush zucchini and squash are most susceptible because they have just one stem supporting the whole plant.

There are several things you can do to keep borers and bay, and none require pesticides.

Tackle Borers Early

The key is getting to the borers before they get to your squash. The half-inch-long moths are gray with orange-red bodies dotted with black. They buzz like wasps and reproduce just once a year. Look for them early in the summer, when they are ready to lay clusters of tiny, flat, brown eggs at the base of squash stems or lower leaves. The eggs take just one week to hatch.

Keep a lookout for adults and egg clusters after you plant your squash. If you find the eggs, gently scrape them away. Continuous checking and egg removal will keep the borers at bay. The moths are also attracted to the color yellow, so another method is laying yellow sticky traps at the base of the stems.

Some gardeners also find success placing floating row covers over squash up until midsummer. You just have to secure the row cover edges to keep insects from getting inside until the borer threat has passed. Then remove the covers to ensure your zucchini flowers get pollinated.

Remove Borers

Here’s what an active borer looks like in a squash stem (cross-wise cut). Look for the tan, gravelly frass at the stem base!

If borers do infiltrate your zucchini stems, you can actually remove them! Look for holes filled with tan, gravelly frass (insect droppings) at the stem base. As soon as you see these borer signs, gently slice open the stem lengthwise, doing as little damage as possible, and remove the yucky borers. This process is a lot easier than you might think.

Plant Zucchini Later in the Season

Lots of bush zucchini will produce fruit in as little as 45 to 50 harvest days. So, if you plant new plants in midsummer, after the squash borers have stopped reproducing, you can worry less about borers.

Plant Borer-Resistant Zucchini

Vining squash and zucchini types require more space, but their stems root along the ground, making them resistant to borers. If one stem is attacked, the others will support the growing vine. Two great resistant varieties to try include ‘Cocozella Di Napoli‘ and ‘Costata Romanesco‘.

I hope this information helps!

Happy zucchini growing,

Jessie Keith

Squash vine borer drawing by author Mary Foley Benson.



Plants are the lens Jessie views the world through because they’re all-sustaining. (“They feed, clothe, house and heal us. They produce the air we breathe and even make us smell pretty.”) She’s a garden writer and photographer with degrees in both horticulture and plant biology from Purdue and Michigan State Universities. Her degrees were bolstered by internships at Longwood Gardens and the American Horticultural Society. She has since worked for many horticultural institutions and companies and now manages communications for Sun Gro Horticulture, the parent company of Black Gold. Her joy is sharing all things green and lovely with her two daughters.

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