Nematodes part two

Last week I opened up a can of “worms”-microscopic ones that is, with my first article dealing with those pesky little critters called nematodes. We began looking at ways to control these unwelcome garden intruders. Today we will explore several other approaches to nematode control, specifically with the root-knot nematode species in mind.

Recall that nematodes are microscopic, wormlike creatures which inhabit the soil and damage the roots of plants, impairing their ability to take up water and nutrients. Symptoms of this damage include stunting, yellowing of plant leaves, and loss of plant vitality. Although rarely killing plants, nematodes can drastically reduce plant growth and yields. Nematodes are usually found in certain areas of the garden and spread by movement of infested soil through cultivation, on soil clinging to garden tools and equipment, or on the roots of transplants introduced into the garden.

So far, we have noted that garden site selection, rotation of crops, and sanitation are important ways to discourage nematode populations. Fortunately, there are other strategies as well.

One of the easiest and most effective methods of controlling root knot nematodes in the home garden is the use of resistant varieties. Resistant varieties refuse to let nematodes feed on their roots, which results in the protection of the crop and the starving of the nematode population over time. Weeds, which may also serve as hosts for the nematodes, must also be eliminated for this to be successful, however.

To give an example of this resistance, recall that many tomato varieties are labelled as “VFN” or something similar. The “N” always stands for nematode resistance. Better Boy and Celebrity are just two of the most common tomato varieties with such resistance. There are many others. Look for the specific designation “nematode resistance” as you search for vegetable varieties to grace your gardens.

Following is another useful practice in the fight against nematodes. To lay fallow means to prevent any vegetation from growing in the garden soil over a period of time, thus starving the nematode population. The garden must be kept completely free of weeds in order to accomplish this. One year of fallowing will likely lower the nematode population enough to where a subsequent crop can be grown successfully. The longer an area is fallowed, the greater will be the decline in the nematode population. If possible, fallowed soil should be tilled every couple of weeks to expose nematodes to the sun and to reduce weeds.

Soil sterilization is yet another anti-nematode strategy. This is a simple, inexpensive, and safe method of nematode control. It preempts the need for lengthy crop rotations and provides other benefits such as control of soil insects and weeds. Soil sterilization consists of placing a clear polyethylene film over the soil in the subject area. The heat of the sun serves as a lethal agent, killing nematodes to a depth of about eight inches. Complete eradication will not be achieved, but the number of nematodes will be greatly reduced, allowing the chance for a successful crop to be grown in the treated area.

Unfortunately, some nematodes may survive at depths below the lethal temperature zone. Thus, following solarization, shallow-rooted crops will fare well while deep-rooted crops may see some damage.

The soil to be solarized must be thoroughly tilled, with all clods broken up to eliminate air pockets. Clear plastic must be used. White or black plastic will not transmit enough solar radiation to increase soil temperatures to required levels. A period of four to six weeks in the summer should be sufficient to kill nematodes and other soil borne pathogens. Six to eight weeks may be required in the spring and fall.

Next: final segment on nematode control.

Tim Lewis is a Georgia Green Industry Association Certified Plant Professional, gardening writer, former Perry High School horticulture instructor, and former horticulturalist at Henderson Village and Houston Springs. He and his wife, Susan, own and operate Lewis Farms Nursery located on Hwy 26 two miles east of Elko, where he was born and raised. He can be reached at (478)954-1507 or timlewis1@windstream.net.