“How can I determine if a squash plant in my raised bed is just “doing bad,” or if it’s “doing bad because a squash vine borer might have gotten it?” And does one bad squash plant ruin all the rest in the same bed? Nothing seems to be bearing fruit now.” Question from Cat of Horse Shoe, North Carolina.”
Answer: You are in luck! Most of these common questions for squash growers have already been answered for Ask a Garden Expert inquirers. The answers are below. But, you also ask a question has not been addressed. This is about the idea of one squash plant damaging another.
One squash plant can only damage another if it is carrying a disease that can easily be spread. Do you see badly wilting leaves without the evidence of holes or damage on the stems (see the vine borer piece, which shows stem borer images.). Do you see white, dusty mold (powdery nildew) on the leaves or brown or yellow spots? If so, your plants likely have a disease. There are many that attack squash. Some, like powdery mildew, can be managed, while others are deadly. (Click here for a detailed article on all squash diseases.)
“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.
