Monday, May 16, 2016

Protecting Squash From Squash Vine Borers

Squash vine borers are one the banes of almost every gardener in the eastern U.S. who tries to grow zucchini and other members of the cucurbit family.  In this post, will talk about a few sustainable methods to prevent squash vine borers.

If you are new to gardening, you may not be familiar with squash borers.  However, you may have noticed your zucchini and spaghetti squash stopped producing all of a sudden last year, with a fine, saw dust like material at the base of their stem.  Within a few weeks the plant was completely dead - this is the result of the vine borer.  The vine borer affects most cucurbits east of the Rocky Mountains here in North America.

This pest, Melittia cucurbitae (also known as Melittia satyriniformis), is probably the greatest threat to all members of the squash family - whether that is summer squash (zucchini), winter squash (spaghetti, butternut, and acorn), and even cucumbers and melons.  Unless a gardener is vigilant, this pest can destroy a whole growing season of hard work.


Adult Squash Vine Borer; from By Pollinator at the English language Wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1350965

The first tip to decrease these insects is to rotate where you plant your squash and related (cucurbit) plants each year.  As squash vine borers overwinter in the soil, rotating your crop from one year to the next will dramatically decrease infestation rates.

Secondly, keeping the base of the plant stem hidden may have some effect on decreasing infestation.  As we here at the Arid Arborist and Gardener advocate planting with the Groasis Waterboxx, The Waterboxx shelters the stem in its central opening (all while providing water without electricity or continued manual watering).  This sheltering can decrease the chance that the adult vine borer will land on the stems.

In the north the vine borer tends to emerge around June or July; in the south May is more common.  In much of the south, two generations of vine borer are active at one time.  As the vine borer seems to infect zucchini more often, a change in what you plant in this region may increase success.  The tatuma squash (also called the tatume squash or calabacita, available here) seems to have very good natural squash vine borer resistance.

If you don't wish to change the species you are planting, we understand.  As the squash vine borer attacks the base of the plant, this part can be sprayed with a mixture of soap, water, and kaolin clay, a whitish substance that is thought to gum up the mouths of insects.  The recipe for a gallon of kaolin clay is 2 cups kaolin clay (Surround), 1 1/2 teaspoons of dish soap, and just under one gallon of water.  Apply the mixture (after shaking well) every 2 weeks through late July to the base of your plants using a spray bottle.

Kaolin clay spray being applied to the base of a zucchini plant growing in the Waterboxx.

Diatomaceous earth is another sustainable gardening product that can help control squash vine borers.  Diatomataceous earth is the remnant of a type of mineral based ocean plant (diatoms) which is quite sharp on the microscopic level.  This sharpness scratches insect exoskeletons and kills them.  If you do wish to apply this, make sure you get only garden or food grade diatomaceous earth and apply it when wearing goggles and a mask (as it is a fine dust that should not be inhaled).  Apply it to wet leaves or the stem and soil of the plant, preferably when rain is not soon in the forecast.

Companion planting can also help repel these pests.  Radishes (and in particular white icicle radishes) can repel squash vine borers.  Nasturtiums, which have edible blooms, are also said to keep vine borers away.  Finally, marigolds may attract ladybugs which eat soft body insects (like vine borer larvae).  You can buy lady bugs (as well as praying mantises) online to stock your garden.

One tip we do not agree with is covering your cucurbits with row covers.  Row covers block all flying insects from landing on your garden.  This will of course prevent the adult squash vine borer from laying eggs on your plant, but it will also prevent bees from pollinating your plant.  This hardly seems like a good deal - beautiful plants that produce no fruit!  Also, the row covers only come in certain shapes so prevent people from planting cucurbits in new structures like the Waterboxx Planting (Half) Pyramid.

With all of these tips, you should be able to control squash vine borers.  As squash are especially prolific when growing with the Groasis Waterboxx, our techniques can eliminate watering after planting for many gardeners.  One Waterboxx acorn squash grew 13 fruit last year, another 29 zucchini (from two plants in one Waterboxx).
A Waterboxx (hidden by the squash leaves) grew 13 extra large acorn squash in 2015

Another Waterboxx grew 29 zucchini from two plants - all without watering after transplanting.

You can learn more about Waterboxx growing at our main website, www.dewharvest.com

We would love to read your comments below.

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