About the Squash Borer Rule

Dear Gardeners,

There’s a new rule this year which says:

All types of squash, zucchini, watermelon, pumpkin and cucumber are NOT permitted to be planted in plots due to an invasive pest that spreads from plant to plant.

So, simple rule, don’t plant anything that can harbor the squash borer, but why? First off, read up on this insect, here’s a good page describing it. Check out the life cycle details, and the various methods to protect plants from the borer.

OK, but what about the squash borer in our garden? Strange but true, but there are gardeners who are not aware that the squash borer is well-established in our garden, and it’s been here for as long as many of our long-time gardeners have been here. Every year we’ve observed our plants, waiting for those weeks in late July when the borer damage appears, and the plants collapse and die, usually very quickly, sometimes overnight. In 2019, for example, I planted 2 different varieties of summer squash (2 Pantheon, and 1 Black Beauty) and all 3 plants were killed by the end of July.

Some gardeners will say “But I grew summer squash last year!” That’s right! A handful of plants survive every year, sometimes very weakened, but sometimes doing pretty well. But if you observe our garden every year over the years like we’ve been doing you’d conclude that somewhere around 3 out of 4 plants are killed each year, and the larvae leave the dead plant, burrow down, pupate, and wait in the soil for the warm weather of the following year, when they emerge as adults to mate and lay eggs on the plant stems, year after year.

Back to the treatment methods, and the real world of our garden. Pesticides are out, many gardeners in our garden would absolutely refuse to use them. Plus this would involve spraying all plants in the garden every week for multiple weeks. This won’t happen. What about row covers? I tried this myself a few years ago, it did not work, presumably because the borer was in the soil right where I’d planted. As the article says:

…because squash vine borers spend the winter in the soil near their host plants. When the adults emerge the following summer, they may be trapped under the row cover instead of being kept out.

There are also other methods discussed on other pages online, diatomaceous earth, coffee grounds, wrapping stems in foil, etc. For every one of these methods there’s a person who says “did not work for me”, these methods are partially effective, at best. I tried the diatomaceous earth one season, it did nothing.

What is the most effective method, without using pesticides? From the article:

Practice rotation to minimize this issue by planting cucurbits in different areas of your garden (if possible) or alternate seasons when you grow cucurbits.

Here’s the same advice, from Managing Squash Vine Borers in New Hampshire:

Rotation can help reduce problems with this pest. Moving cucurbits to different fields year-to-year can reduce problems, especially if the fields are far apart. In a backyard situation, the space is so small, moving the crop a few feet doesn’t help prevent damage next year. One option is to skip a year: don’t grow any (susceptible types of ) squash or pumpkins next year if you had significant damage this year. If your neighbor grows them just a few feet away, that defeats the purpose of this technique.

This method works, this is what an organic farmer would do. For example, they might have 2 separate fields, and plant summer squash in one of them in alternate years.

So what will happen in our garden this year because of this new rule is that the borer adults will emerge in late spring, they will look for squash plants or other cucurbits, they won’t find any plants to lay eggs on, there will be no larva growing, and no larva overwintering. Then next year, in 2021, there will be no squash borers in our garden, and everyone will be able to grow fantastic summer squash, for the first time in many years.

Brian O.