Updated: April 9, 2010
Stopping squash vine borers on my zucchini may be my biggest gardening challenge. These pests have made it a lot more difficult to grow zucchini organically. Normally zucchini is one of the easiest vegetables you can grow in the backyard garden.
A lot of people feel my pain. Not only does squash vine borer kill zucchini plants, it kills almost all types of summer and winter squash.
But, for me, it is zucchini that’s important because it’s one of the few vegetables that everyone in the family enjoys. When my kids were young, it was one of the few vegetables they would eat without me having to sit on them first 🙂 .
What are squash vine borers?
Since you are reading this article, you probably already know something about the dreaded SVB (SVB … doesn’t it sound like a venereal disease).
Squash borer is the larva of the moth shown in the photo below. The moth has a wing span of about one inch. It lays reddish-brown eggs on the host plant.
Let’s take a sec to get the legal words out of the way. This article may contain affiliate links. That means if you click and buy from my partners, I will make a tiny amount of money at no cost to you. This in no way affects my recommendations.
The single most successful strategy is to wait until the second week of July to transplant zucchini in the garden.— Suburban Hobby Farmer
When an egg hatches, a one-inch, white lava with a brown head emerges. The larva bores its way into the stem of the squash plant. Typically, this in the first inch or two above the ground, and it leaves a saw dust like material called frass nearby.
After that, the plant wilts and then dies.
Does this sound like your situation?
How I stop squash vine borer on zucchini
After years of trial an error I’ve found a way to stop SVB. Here’s how I do it:
1. Start plants late.
If you live where the last frost date is in May, the single most successful strategy is to wait until the second week of July to transplant zucchini in the garden.
Why then? Because this is after the SVB has laid eggs, but early enough so that you will get ripe zucchini before the end of the growing season.
If, on the other hand, you live where the last frost date is earlier than May 1, you will likely have a second generation of squash vine borers.
In this case, SVB will kill your plants before the end of the growing season.
I have found SVBs in my backyard hoop house. They must get in while the door is open.— Suburban Hobby Farmer
Zucchini growers who live where there is no frost, can’t wait out the SVB because there will be one generation after another.
Besides having a last frost date in May, there is also two other factors to consider for the “waiting” strategy to work:
First, you must grow your own zucchini seedlings indoors or in a screened in hoop house (the windows and the door have screens). This is because if you buy seedlings they could already have SVB eggs on them.
In fact, this is how many neighborhoods get introduced to the pest. One gardener brings eggs home from the garden center and the whole neighborhood can no longer grow zucchini.
Take note, however, I have found SVBs in my backyard hoop house. They must get in while the door is open. So keep an eye out for moth in your hoop house, too.
Second, you won’t have zucchini until at least the second week of August. So you’ll have to buy zucchini until then. This is not ideal for zucchini-loving families.
Let’s take a sec to get the legal words out of the way. This article may contain affiliate links. That means if you click and buy from my partners, I will make a tiny amount of money. This in no way affects my recommendations.
2. Floating row covers
Another option is to go ahead and plant soon after the last frost date and immediately cover transplanted seedlings with floating row covers. This will work sometimes.
It also provides some protection against other types of pests, e.g., squash bugs (not the same as squash vine borers).
Still, this is not ideal. Floating row covers do not prevent squash vine borers that are already in the dirt. So if you’re unlucky enough to have them there already, this strategy won’t help.
The other issue is that floating row covers don’t just keep out SVBs. They also prevent pollinators from doing their job.
Some floating row cover users open the row covers in the middle of July when the SVB threat has passed. This allows pollinators to do their thing when zucchini flowers are plentiful.
Others hand pollinate their zucchini flowers, which can have good results.
3. Spray with bacillus thuringiensis var kurstaki
Bacillus thuringiensis var kurstaki (Bt) is an OMRI-listed caterpillar killing spray with seemingly no environmental concerns or harmful effects on beneficial insects. It’s made with a naturally occurring bacterium that kills caterpillars and SVBs.
It must be on the stems (main vine and leaf stem) when the eggs hatch. This means you must spray it after every rain and weekly until there are no SVBs around.
This can be tricky. If you miss just one time after a rain, and it’s the wrong time, a squash vine borer could get through.
Also, although it’s not supposed to have an impact on pollinators and other beneficial insects, but I wouldn’t spray it on flowers because who knows?
Combing methods for stopping squash vine borers
Probably the best way to make sure that you are able to harvest zucchini from your backyard garden is to combine all three of the above methods. But you might consider this too much work.
I’ve tried a number of other methods that haven’t been consistently successful. These include:
- Wrapping stems in toilet paper rolls or tin foil
- Putting panty hose around the vines
- Covering the stems with mulch
I’m hoping that I won’t need to use any of these additional methods in the future.
If you have an organic method that prevents squash vine borer from eating your cucurbits alive, let us know in the comment section below.
Related articles that might interest you:
- A Hoop House is a Tomato Growing Machine
- Get Rid of Gnats on Seedlings Indoors
- Wildflowers for Beneficial Insects
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