Fighting Nematode Colonies in Gardens

Last summer as I pulled up old squash, cucumber and string bean plants in my garden, I was horrified at what I found – the one thing that gardeners do not want: nematodes.

I garden in seven raised beds, and four of the seven beds had nematodes in them. Nematodes are tiny, microscopic, wormlike creatures that live in the water that is found between soil particles. There are beneficial nematodes that attack insects and other nematodes, but I have root-knot nematodes, which is one of the nematodes that feed on plant roots..

Root-knot nematodes bore into the root and form galls. The galls block water and nutrient flow to the plant, stunting growth, impairing fruit production and causing foliage to yellow and wilt. Plants can die from nematodes, which attack a wide host of plants from turf grass to shrubs, flowers and trees.

Why was I so horrified when I discovered them? Well, there are no chemical control products that can be used around homes to control them. Farmers have some chemical products that will reduce the numbers, but as homeowners we have to try other methods.

The first and most important method is prevention. Nematodes can move two to three feet a year in the soil. However, we spread them faster by our actions. When you dig, till or move soil from an infested area to another area, you are spreading them faster. When you use equipment in an infested area, you need to thoroughly clean the tool before using it in another area. This includes tires.

Also, you need to buy good quality plants that are free of nematodes and diseases. Pull up vegetable plants as soon as they finish producing. This removes the feeding site for the nematodes. Weeds can host nematodes as well. Weeds such as crabgrass and ragweed are used for development of nematode populations.

Another management practice that you can use is to add large amounts of organic matter to the soil. Organic matter such as compost and animal manures are full of fungi and bacteria that will attack and consume the nematodes. Another benefit is that the added organic matter improves the rooting conditions and the plants will outgrow the damage of the nematodes.

There are plants that you can use in your garden to help reduce the numbers of nematodes. Some of these plants are not host plants, so the nematodes have nothing to feed on and they cannot reproduce. The population will decrease. Other plants have allelopathic compounds in them that kill nematodes. Some of these compounds are released by the roots during the growing season and some are released after the crop is tilled into the soil. Some of the plants that have these chemicals are marigolds, castor beans, cereal rye (not ryegrass), sorghum-sudan grass, chrysanthemum and plants in the brassica family. The brassica family includes mustard, turnips, cabbage, kale, and broccoli. The brassicas need to be tilled into the soil for them to reduce the number of nematodes.

If you use the other plants that I listed, you will need to plant the whole area that is infested with the nematodes. Planting a plant here and there will not work. I planted one of my beds solid with marigolds.

Another option is solarization, a method of pasteurization. For solarization to be effective, you will need to till the area with the nematodes and moisten the soil. Take clear plastic and cover the area, then seal the edges of the plastic so the heat can not escape. The plastic needs to stay on the area for six to eight weeks during the hottest part of the year. You will have better results with solarization if you use the practice in conjunction with a cover crop. Research in other states has shown that if you till in the brassicas and cover the area with plastic, results will be better than with plastic alone.

Another option is to use resistance varieties of vegetable plants. There are numerous tomato and bell pepper varieties that are resistant. If the tomato has VFN beside the name, the N stands for nematode resistant. Also, rotate the vegetables in your garden. Rotating the plants helps reduce the number of nematodes and diseases.

I will discuss more options on controlling nematodes next week.

Columbia County Extension Agent Charles Phillips can be reached at (706) 868-3413 or by e-mail at charlesp@uga.edu. The Extension Web address is www.ugaextension.com/columbia.

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