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Battling Root-Knot Nematodes in the Summer Garden

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Lori L. Stalteri/Flickr

Photo by Lori L. Stalteri on Flickr

In the Sacramento region of California, where I live, my spring and summer garden started out growing at a remarkable rate. I planted the second week in April and started getting zucchini by the end of May. Not that everyone is thrilled with an over-production of zucchini, but my friends love my zucchini-pineapple bread and that’s a good enough reason to grow the squash.

I now garden in a raised bed, 14-by-14 feet, in a garden of raised beds with others in our apartment complex. For years, I only planted in-ground and have learned that gardening raised beds in my favorite these days. All gardening techniques apply to in-ground and raised beds alike. I find the raised bed easier to accommodate seniors.

Heat Wave and Nematodes Impacts in the Garden

Near the end of May, California started experiencing some hot spells. By June, we had triple digits temperatures for days on end. Triple digits right up until I took my summer garden out in August. Plants and people sweltered. Fires, ash, heat. Our poor gardens were spent.

There was an even bigger surprise when I uprooted still-producing, although barely, tomatoes: root knot nematodes! The butternut squash, the spaghetti squash, same thing. Those string of pearls had taken over one of my beds and just starting to take hold in the second bed. The zucchini plants escaped these parasites. In order to plant a fall and winter garden, I have to eliminate this problem.

First, I needed to understand this unseen robber.

Parasitic nematodes that attack plants are vigorous, slender, tiny roundworms. Most nematodes are harmless because they feed on decomposing organic material and other soil organisms. Nematodes that attack living vegetables suck the green color and cause stunting of vegetables, wilting, dieback, and similar signs.

The root-knot nematode causes galls to form on the roots of many vegetables, hence the term “string of pearls”. The first indication of nematode injury in a garden or field is often the appearance of small circular or irregular areas of stunted plants with yellow or bronzed foliage. This area gradually enlarges. I saw very few of these signs in my raised bed.

I did notice a lack of a second green bean production and tomatoes that didn’t seem to produce as well as they should. When my vertical crops of spaghetti squash and butternut squash were half, or even a quarter, of the size they should be, I thought I knew what was happening underground.

Nematodes are small microscopic roundworms in the soil.
Photo by U.S. Department of Agriculture

How to Get Rid of Root Knot Nematodes

First, after removing all vegetables, rototill or dig up the soil.

Then, there are products to help get rid of root-knot nematodes.

  • Growers Trust Nematode Control features geraniol (the oil of geraniums) and beneficial bacteria.
  • Eco Clear Stop Bugging Me! is geraniol (oil of geraniums) and cinnamon oils.
  • Aza Max which is pure azdirachtin neem oil extract.
  • Monterey Nematode Control use the saponins from the soap bark tree.

Prevent Nematodes

  1. Remove all plants and infected roots from your garden.  Root-knot nematodes can live in the root galls and will continue to multiply so remove everything.
  2. In the fall, till your bed several times (two or three). This breaks up the soil and nematodes die from sunlight exposure. If you have time between when you tilled your garden and between plantings you can solarize your soil by covering with clear plastic and put weights on the perimeter to hold plastic down. This clear plastic acts as a hot vapor bath and this too kills nematodes (good and bad nematodes). Let the sun work for you. If the sun is hot enough, a week or two should do the trick.

After your soil has been treated and you are ready to plant again, buy seeds or seedlings that have an N listed on the plant label. This means they are nematode-resistant. Be sure to check out seed catalogs to see which varieties would be best for your garden.

After I rototilled my beds I sprayed Monterey Nematode Control. I decided to only plant seeds in my fall garden and did so on September 11. In four days, I had seedlings popping out of the ground. We still have high temperatures here in the Sacramento Valley, so I watch the moisture content in my garden beds.  Only time will tell if I conquered the war on root-knot nematodes — and that will be for a future post.

Oh yes, and the zucchini variety I planted that escaped the disaster: ‘Black Beauty’.

Karen Newcomb has been writing vegetable gardening books since 1977 and is the author of The Postage Stamp Garden Book, The California Vegetable Patch, The Vegetable Gardener’s Sourcebook, and The Postage Stamp Kitchen Garden, co-authored with her late husband, Duane Newcomb. For more 30 years, she has practiced the intensive “postage stamp” gardening method in the Sierra Nevada rural area near the town of Grass Valley. She currently lives in Rocklin, California. Read all of Karen’s GRIT posts here.

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Updated on Sep 23, 2021  |  Originally Published on Sep 17, 2021

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