Squash Vine Borer: Best Effective Organic Control of a Devastating Pumpkin, Zucchini, and Squash Pest

Squash Vine Borer: Best Effective Organic Control of a Devastating Pumpkin, Zucchini, and Squash Pest That I've Ever Implemented

When left unchecked, the squash vine borer is capable of decimating an entire crop of squash, whether that be pumpkins, zucchini, summer squash, or other winter squashes. If you've ever walked outside to your squash plants only to find one of your plants completely wilted over and dying, when it was doing so well the day before, you've likely experienced the wrath of the squash vine borer. There are a lot of ways that people have tried to manage this pest, but there's only one organic method that truly seems to work; the rest of the methods involve conventional, inorganic pesticides. Let's talk about it. (Oh, and I've included my video at the end of this post, where I demonstrate the process and repeat most of this; this passage is a supportive post for my video, but it also goes far more in depth than the video does. Product links are in the pinned comments on Youtube.)

Life Cycle of the Squash Vine Borer Moth, Detection

The squash vine borer moth emerges from a cocoon underground in late Spring and early summer. You can use a pheromone trap to detect when moths are actively reproducing, alerting you that females are beginning to lay eggs on plants. These are the same traps that people assume will help to control squash vine borers- However, they simply attract the males. So, while they can catch a number of adult males, they will not capture egg laying females. Very important note about that control method.

When the females lay eggs, they typically lay them one at a time, usually on a stem. However I find these eggs all over the plants; leaves, leaf stems, and all along the main vine. Sometimes you'll find more than one egg nearby, but usually the moth will lay the eggs one at a time on different stems. It takes about 10 days for the eggs to hatch, and they immediately burrow into the squash vines. It takes 25 to 27 days for the larvae to complete the larval stage, at which point they exit the plant, burrow into the soil, and pupate. They will then appear the following spring or summer.

Supposedly we have two generations in my area. Vines seem to get attacked no matter where we are in the growing season, though. In cooler climates, there is usually one generation. It's important to know the behaviors and the life cycle of the vine borer, So that you can modify your pest control program based upon their behavior in your area.

"It's important to know the behaviors and the life cycle of the vine borer, So that you can modify your pest control program based upon their behavior in your garden."

My DIY homemade squash trellis this year.

Laundry bags covering squash plants in order to prevent the squash vine borer moth from laying eggs.

Physical Barriers: Keeping Borer Larvae Out of Squash Vines Physically

Physical barriers can be an important part of your squash management program. I'm not talking about vet wrap, nylon pantyhose, or foil on the vines, as they don't keep moths from laying eggs on leaves or leaf stems. I'm more so referring to row covers. If you keep your squash vines under cover until they begin blooming, you can avoid the borers for the first 4 to 6 weeks of growth. You could also keep your vines under cover permanently, but you will have to hand pollinate female flowers every morning. Another option is to release pollinators into your row cover. I hear that blue bottle flies are supposed to be great for this purpose- but I haven't had an opportunity to put them to the test. The biggest issue with keeping squash vines covered is that they do not produce fruit if they are not pollinated. If you're excluding squash vine borer moths, then most other pollinators will be excluded as well. If row cover seems expensive for your application, let's say you're only growing 2-3 plants, there's another option: mesh laundry bags. I got them at the dollar store, and they did VERY well! That's a budget friendly option that makes more sense for those who are growing a handful of plants over a $15 section of bug netting.

In the end, it comes down to one of three options for physical barrier methods:

Cover the plants permanently, and hand pollinate or use isolated populations of pollinators, such as flies.
Cover the plants until maturity, then remove covers allowing pollinators to have access to the blooms (as well as pests.)
Not covering the plants at all, risking early borers (or late borers, with a late season crop.)

Laundry bags covering squash plants in order to prevent the squash vine borer moth from laying eggs.

Why Most Organic Control Methods Don't Work for the Squash Vine Borer Larvae

Most methods of SVB control involve spraying the affected plant with different chemicals, whether conventional pesticide or organic. Conventional pesticides will work for the borers; however, many home gardeners, like myself, put an emphasis on natural gardening and organic gardening. When it comes to organic solutions, most of them simply don't work. I know, I know- "Tell us something we DON'T already know." Hang in there for just a bit longer, we're getting to it!

The ineffectiveness of organic products is due to the fact that the pest doesn't live on the exterior of the plant. The adult moth visits to lay eggs. The pupae remain underground over winter. Eggs are laid on the exterior of the plant, but the hatched larvae immediately bore into the plant, protecting them from most exterior applications of organic pesticides. The plant shields its most problematic pest within its stem; the borer slowly eats away at the plant's vascular system, slowly cutting the plant off from its root system- which is eventually what leads to the plant collapsing. You have to administer a product inside of the plant in order to access the squash vine borer larvae- but you won't want to do this with most products, and if you do, it's all off label anyways. This is where Bacillus Thuringiensis enters the chat- even though this is still an off label method.

Squash vine borer frass is the most obvious sign of this pest, ahead of vine collapse. If you catch this symptom early enough, you can save the plant.

Bacillus Thuringiensis: The Most Effective Way to Control SVB Larvae with Organic Pesticides

Now I realize that Bacillus Thuringiensis is a mouthful, so we're just going to call it BT from here on out. This is the name of a naturally occurring bacteria species, commonly used as an organic pesticide. It's found under many brand names, but the product is simple: it's a live, concentrated bacterial culture. It's found in the environment naturally, but in much lower numbers- this is a concentration. Once ingested by the vine borer, the toxins cause the larvae to quit eating, immediately stopping any further damage from occurring. They will live for a few more days, but the damage is halted and your plant can begin to recover.

So why is this stuff so effective, you ask? How's it different for us? Well, we go off label with its use. We're not applying it to the exterior of the plant like you're supposed to on the directions, like how you would with every other product. Instead, we use it in our garden by injecting it straight into the plant! There's some controversy around it, sure. But in my opinion, with my research, I believe it to be the safest option for my garden. This isn't the method for everyone, it's not everyone's cup of tea. For those people, there are other search results that may provide alternative insight regarding squash vine borers. However, it's our garden, and it has served us very well, so I'm sharing my experience.

Injecting squash (Dickinson Pumpkin) with BT for squash vine borer larvae after identifying frass.

How I'm Injecting Squash Vines in My Garden: BT for Larvae Control

Before I proceed, again, this is an off-label usage. This is what I do in my garden. My bottle says that it's safe to use up until the day of harvest. I typically harvest any squash that I plan to harvest in the next two days BEFORE I do a round of injections.

These are the items I use for this procedure:

BT pesticide (I use Safer Brand usually, but there are other brands!)
Syringes (I use 3-6 CC)
Needles that fit syringes (3/4- 1 1/2", 18-22 gauge is typically what I have.)
A vessel for mixing the BT solution/transporting to my garden (quart jars.)
Tool for poking holes before injecting (I'm using a hook tool. Nails work when I can't find it. Not necessary, but it prevents needle clogs.)

Here are the steps I follow, but I will elaborate momentarily:

I mix my BT solution in my quart jar, and it's carried to the garden with me.
I place the needle on the syringe.
At the vine, I'll take my hook tool or nail and poke holes along the vine, then I'll inject 1-3 CC of BT solution into the hole. If I don't have something to poke the vine, I just inject. However, plant material tends to clog the needle, making it hard to depress the plunger, it gets messy, it's just a pain overall.
I inject every 3-9", closer together at the base, further apart towards the growing tip.
I inject every leaf stem.

Now, I'll elaborate. BT is only effective for about 48 hours after mixing. I inject vines every 5-10 days. 5 being the safest (borers won't stand a chance, BT is active 40% of the time) and 10 days apart being the most risky (allows 8 days for borers to munch on my squash vines.) We have extreme borer pressure here. EXTREME. Populations cannot get much worse than they do here! With that being said, I've had a great experience with going to 10 days. I try to spray the plant's exterior vine when I do injections, just to catch any newly hatched larvae. However, it's not necessary, and it gets skipped frequently.

I'm going to work on simplifying my process next year, as an experiment. I'll explain further in the next section. It's a lot of work injecting one vine 10+ times; 30+ times when it's a 12'-15' pumpkin vine! This is one of the reasons that I frequently go to 10 days between injections; it just takes a very long time during the height of the harvest season. All of these injections serve to ensure complete coverage along the squash vine. The goal for me is to interrupt the life cycle of the vine borer larvae, and prevent large larvae from taking my plants down. Smaller larvae don't do anywhere near the amount of damage that larger borers do; therefore, I'm not as concerned with small larvae getting inside of the vine during their first week of life. They'll do minimal damage, and the next wave of BT will take care of them.

Next Year's Experimental Project: Can I Get Away with 1-2 Injection Sites Per Plant?

Even though I've been avoiding susceptible varieties for the last couple of years, I've had this question lingering in the back of my mind. I didn't want to risk the plants previously. This year, my squash seedlings that I'd planted for this project perished due to unrelated circumstances. So next year, I want to FINALLY answer my own question. Can I get away with only 1 or 2 injection sites per plant?

Someone once asked if the BT gets into the fruits and, well, I don't have an answer for that. I do know that the bacteria is harmless for humans, though. So once I received this question from a commenter on the original YouTube video, it sparked my curiosity: Does it? Does it make its way into the fruits? Does the BT travel through the circulatory system of the plant? If I'm being honest, I'm hoping that it does circulate throughout the plant. If it does, that means 1-2 injections should be sufficient to protect the plant. It would only take less than 5 minutes to inject 6-10 plants, which is a fairly typical number for the average family. It's not a bad process if I could combine minimal injections with an extended time between injections; 30 minutes per month (3x per month, including prep work) dedicated to vine borer control isn't terrible!

This is the experiment that I'm planning:

15 susceptible squash plants: yellow squash & zucchini, 5 each for treatment, and the last 5 will simply be controls that will go down fairly quickly due to borers.
Seedlings will be covered for the first 3-4 weeks ONLY. Just to keep squash bugs and cucumber beetles away from tender seedlings, rather than vine borers. I will need robust plants going into this experiment.
The day that I remove the covers, I will attempt to inject all of the plants depending on stem size. If the stems are too small, I will try again 5 days later.
I will then inject every 10 days, once into the main vine close to the roots, and once into the oldest, healthiest leaf stem. Leaf stems are hollow, and it'll allow me to inject a significant amount of solution.
When possible, I'll inject during a dry period, or in the morning when the day is expected to be very hot (when leaves wilt down.) My reasoning being that the injected fluid may be taken up more readily by the vine when the root system is not handling the high rate of transpiration very well.
If the plants remain alive for 6-8 weeks after being uncovered, without obvious signs of frass that generally accompany larger borer larvae, I'll consider this experiment a success.
I may wind up pulling all of the plants and cutting them along the stem to see if there is any significant borer damage that may have gone undetected, and document it on my channel. Uprooting 10 heathy, productive plants is hard to do for me, so we'll see. It's in the name of science, though!

How I Primarily Deal With Squash Vine Borers Now (and Have)

Now, I want to discuss the two ways that I primarily manage squash vine borer issues now, and how I have for the last couple of years. Spoiler: I don't! The more unconventional method that I've been using since last year is chaos gardening in a goat pasture. I go in, I throw summer squash seeds everywhere, and I allow my goats to graze heavily, getting the forage under control. While grazing, the goats are stomping the seeds into the soil. After several days, the goats are removed. Two to three weeks later, they're reintroduced to “weed” around the squash vines, as they don't eat them. This results in lots of plants in a small area, with a huge initial harvest, and I do not have to weed them! I also do not inject them, I let the plants go down as they will. I trade labor in weeding and injecting for an increase in seed cost. To be honest though, I can buy large packs of squash seed at our local co-op for about 2 to $3 on clearance in the fall. For a mere six bucks, I have about a thousand squash seeds that I can chaos garden with. And let me tell you, the yields are incredibly high with this method.

** Note: This method failed me this year. The plants were growing great, but we had an abnormally high amount of rainfall this year. This meant that the weeds and grass grew very fast, especially since the soil was rich. When I released the goats into the high grass to take care of it, I learned that the squash plants had actually grown quite leggy, as they couldn't keep up. This became obvious as the grass height declined, which was supporting the leggy leave stalks and stems. As the goats ate, they significantly damaged the plants while walking around them, due to the leginess. Generally, these varieties form a bush; these had stretched over 24" as juvenile plants, and were getting ripped apart as the goats grazed and walked. So while it worked great last year, it did not this year. Will I stop using this method? No. But I will make sure that I do a little site prep next time, just to get a head start on the weeds if it's shaping up to be a wet season. Mind you, we had most of our annual average rainfall by June- so not a typical growing season.

The second method that I use is growing resistant varieties. I've been doing this for several years now. I grow a lot of resistance squash plants so that I do not have to inject my squash vines all the time. Most resistant varieties are winter squash varieties, but they are harvested while they are green. Lots of winter squash varieties can be harvested green and used just like summer squash. Even green pumpkins can be used this way! Rampicante Squash and Tatume squash have been my favorites. Tatume is excellent on the grill, too!

** Note: Resistant doesn't mean the plants are borer-proof. I've had the rare plant go down due to borers, but we're talking 1 out 25 maybe. The bigger concern is that I've occasionally noticed borers in the actual fruits when there is a lack of susceptible varieties. This isn't a really big deal if you are processing the squash in its green state, because green winter squashes will not keep. This is more of a concern for the squashes that you intend to store whole, for long term winter storage. Carefully inspect winter squash a few weeks after harvest for borer holes. If you find borer holes, I highly recommend processing that squash before it rots. It can be frozen in chunks, or cooked and pureed. The puree can be frozen, pressure canned, or it can be dehydrated for pumpkin puree powder.

Above, you'll find the YouTube video that goes along with this post. You will see how I do my injection procedure, and there may be some content in the video that I may have missed here; and vice versa. You'll also find links to the products that I used pinned in the comments. This video was posted over six weeks before this blog post was, so I didn't have another update for my goat pasture chaos garden at that time. Perhaps it's a good thing that this post was delayed, so that I had that information fresh on my mind!

The Aberrant Garden

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