Orginally published in the N.E.P.G.A. Newsletter - March, 1996
There is no more evil insect in New England than the squash vine borer, dasher of dreams of pumpkin growers throughout the region. Absent a great amount of effort on your part, vine borers are almost certain to weaken or kill your pumpkin plant long before a championship pumpkin can be grown.
As an organic gardener, I have had to come up with my own techniques to ward off the borers. Organic gardeners come in all different stripes. I am a purist, and as such don't use any chemical pesticides, such as Sevin, or biological pesticides, such as Rotenone or Neem.
Nevertheless, I have found effective techniques for foiling the dreaded vine borers, and have even come up with an effective method for preventing powdery mildew.
The first stage of my plan unfolds in spring. Before the pumpkin plant is in the ground, I spray the patch with water in which beneficial nematodes are released. Nematodes are microscopic worms that eat the larvae of many nasty insects such as vine borers. In my garden, the jury is out on the effectiveness of this approach, but many other gardeners swear by them. If you are planting in the same patch as you have had infected plants in the previous year, I recommend giving it a try.
The most critical step in my plan is to cover the entire pumpkin plant during the vine borer's active season with a lightweight row cover. Row covers are polypropylene fabrics, which come in several different thicknesses. It is important to get the lightest weight available in order to avoid heat build-up and to allow for as much sun, air, and water as possible to pass through. Lightweight row covers allow 90% of sunlight to penetrate to the plant.
I purchase enough lightweight row covers to cover the plant from the beginning of June until the end of July. Since row covers come in any length, but only in six or eight foot widths, it is necessary to sew several strips together.
For my plant (I only have room for one), I construct a cover measuring about 18 feet by 30 feet. I then role up the ends, leaving enough to cover the entire plant in early June with enough play so that the plant can grow unimpeded for about a week. I then anchor it to the ground with earth staples, though heavy rocks will also do. You want to ensure that the cover will not blow off in strong winds. A week later, I unroll some more of the row cover and again anchor it down, continuing this process until the vine borer season is over at the end of July, when I remove the cover.
Lightweight row covers are permeable to water so you don't need to remove them for watering. Because mildew is a perennial problem for me and I want to water underneath the leaves, I often open a corner carefully and extend a hose under the cover to water during dry spells.
Naturally, you will want to keep a close eye on your plant so that you will know when the first flowers are about to blossom. With pollinators shielded from the plant you will have to hand pollinate your pumpkins.
Two problems I have encountered with the row cover method are aphids and mildew. Aphids are ubiquitous and find their way onto the plant despite the cover. With their natural predators shielded from the plant, the aphids multiply rapidly. This problem is easily solved by purchasing some ladybugs and releasing them under the row cover, where they will act as captive predators.
The second problem is powdery mildew, which is an annual problem on all my squash plants. The problem is exacerbated by the somewhat diminished airflow caused by the row cover. Last year, in early August, I began spraying the leaves on a weekly basis with a dilute kelp seaweed solution. For the first time, I didn't have any powdery mildew on my pumpkins, though all my unsprayed squash plants were affected as usual. Seaweed spraying is also reputed to be an excellent foliar feeding for the plant.
In the event that all these measures are unsuccessful and some area of my plant is showing damage by borers, I inject beneficial nematodes into the stem area wherever frass is showing. An injection of beneficial nematodes at three or four inch intervals seems to kill all the hardiest borers.
As you can see, it takes a lot of work to stay organic, but then giant pumpkin growers are used to hard work in their efforts to produce a half ton behemoth. Good luck.
- Lightweight row covers and earth staples can be purchased from Gardener's Supply Company, Burlington, VT, 1-800-863-1700.
- Beneficial nematodes, liquid kelp spray, and ladybugs can be purchased from Gardens Alive! of Lawrenceburg, IN 812-537-8650.