Though I knew nematodes were my problem, I didn't know what to do about them. I had tried this spring to use beneficial nematodes to help counter the root-knot nematodes, but that turned out to be an expensive yet value-less investment. I went then to wise members of my local produce exchange—a font of local gardening knowledge—and the Internet for solutions, and I've learned, as is often the case with a difficult problem, there is no silver bullet. Instead, I'll have to incorporate additional strategies into the crop rotation, compost and manure amendment, and liquid seaweed fertilizer that are already my practice.
How I know I have root-knot nematodes:
- Ugly bumps. Last year, when I pulled out my tomatoes and a few other plants, I could see the heavily galled, deeply scarred roots. These weren't smooth main roots with lots of healthy, happy feeder roots, but instead a medusa-head of succulent-jointed ropes. I hung my hopes too heavily on what I thought a winter free of food would do to the root-knot communities. They, persistent suckers as they are, made it through the winter quite happily to hit this year's crop even harder.
- Weak plants. My tomatoes, squash, and melons really struggled this summer. They'd wilt after only a single day without water, when usually they'd need water only twice a week. If I looked at them wrong, they'd get sick. Most of the flowers on my tomatoes just fell off rather than setting fruit, and the majority of my squash and melons aborted fertilized fruit because they just didn't have the means to support the fruit to maturity. Beans, sweet potatoes, tomatillos, and peppers seem to be able to tolerate the nematodes better than tomatoes and cucurbits.
What I am doing as I clean out the beds now and into the future:
- Amend with more horse manure than ever. This will provide as rich as possible a medium to support struggling plants. As well, it will add more organic material to help ensure water retention, a deep challenge in our soil.
- Seed a winter cover crop of rye and mustard. I'll do this in half of my beds, those that will host next year's tomatoes and melons, come mid autumn. Root-knot nematodes are unlikely to feed on rye roots (apparently rye doesn't appeal to those buggers), so the plants will grow heartily over the winter, pulling up nutrients with their extensive root systems. While the nematodes may nibble on the mustard roots, the mustard will have its vengeance in the spring when I cut both the rye and mustard down and dig the plants into the soil. The mustard will gas the nematodes, and the rye will decompose quickly and feed the surface soil with the nutrients it pulled up from the deep.
- Add dried molasses to the soil. With every plant I plant, this fall, this winter, and next spring I'll be adding dried molasses. The molasses helps feed the microbes that both attack the nematodes and work symbiotically with the plants' root systems. This may be something I need to do forever.
- Plant French marigolds. Tagetes patula, when attacked by nematodes, interrupts their reproduction. I plant to start loads of French marigolds in the early spring so I can plant them thickly among my tomatoes and melons next year.
What I could but won't do:
- Solarize with black plastic. Yes, this would kill my mean root-knot nematodes, but it would also kill my lovely worms, happy microbes, red spiders, and other good guys.
- Mulch heavily in the vegetable garden. I'm a huge proponent of mulch in most places, but in my vegetable garden, I've found it makes it impossible to direct seed beans or squash or okra, or any of those other delicious vegetables that grow best when they stay where they started. Mulch provides a home for hoards of sowbugs that take out seedlings overnight. (And, don't join the chorus that sings "Sowbugs only eat decomposing matter"; I've watched them munch down a bean seedling. Sowbugs and seedlings do not mix. That chorus sings the wrong tune.)