Cooperative Extension Service
The University of Georgia College of Agricultural and Environmental Sciences
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Plant Susceptibility to Major Nematodes in Georgia

Use this guide to select rotation crops that are non-hosts to damaging populations as one part of a nematode control program. Ideally, the rotation crop should reduce specific nematode populations levels in the soil and not sustain reduced yield or quality because of nematodes present. In order to do this, you need to properly identify the nematodes present in the field through a soil assay, and you need to know which crops are non-hosts to nematodes present in the field.

Nematodes can be correctly identified in the Extension Nematology Laboratory if a soil sample is carefully taken and properly handled. Take soil samples for nematode assay in the root zone to a depth of about 8 inches. Take 25 to 30 cores from each 4 to 5 acres and thoroughly mix the cores together. Place 11/2 to 2 pints of the soil in a plastic bag immediately and keep the soil cool. Send the soil with a completed information form to the Extension Nematology Laboratory through your county extension office. Your county extension agent can provide further information on sampling.

After receiving the nematode assay report, use this guide to select rotation crops that are non-hosts to specific nematodes identified as present in each field. Host crops and weeds for each nematode are given in the following tables along with known non-host crops. Lists are incomplete in many cases because information is incomplete. Table 1 lists the host status of several major crops to the most important nematode pests in Georgia.

Remember that although crops are listed as hosts for specific nematodes, there may be varieties or cultivars that are resistant or tolerant to certain types of nematodes. This is particularly true for soybean cyst nematodes and for some species of root-knot nematodes. Consult your county extension agent or the appropriate crop specialists to obtain the latest information on resistance.

How Non-Host Crops Reduce Nematodes

Nematodes that damage crops must have living plant tissue to feed on in order to mature and reproduce. Thus, if a non-host plant is grown, nematode populations will be reduced through starvation and lack of reproductive capabilities. The length of time nematodes will live without a suitable host plant to feed on varies with the kind of nematode and the prevalent environmental conditions.

For example, the soybean cyst nematode can live several years protected in its cyst in the absence of a host plant; most nematode populations, however, can be reduced below threshold levels in one or, at the most, two years if a suitable host plant is not available for feeding. At lower temperatures in late fall, winter and early spring, nematodes survive well as eggs, larvae and even adults in the absence of a host plant. With warmer soil temperatures, many nematode eggs hatch and nematodes become more active, use up food reserves, and die if they cannot feed on a suitable plant.

Problems Using Rotations

Although crop rotation is a major part of the total program necessary to minimize losses from nematode pests, the practice is not always totally effective. Some reasons why rotations fail include:

Mixed nematode populations often occur in a field. It is not difficult to select a non-host crop when only one major nematode occurs in a field, but usually more than one kind is present. A crop that is a non-host to one kind of nematode may be a host to another in the same field. So while reducing one kind of nematode, the rotation crop maintains or builds up another kind that will damage the crop or crops grown the following year.

A species of root-knot nematode that has not been identified occurs. As you study this guide, note that four different species of root-knot nematodes are present in Georgia, each with a different host range. Of these, southern, peanut and Javanese are the most important. The Extension Nematology Laboratory will identify root-knot nematode species upon request -- provided fresh, heavily-galled roots are sent in and a complete cropping history is furnished for the field in question.

Uncontrolled grasses and broad-leaf weeds may support nematode populations even though a non-host crop is being grown. Although the crop selected for rotation is not affected by the nematodes, infestation of grass- or weed-hosts may cause the buildup of nematodes capable of attacking subsequent crops. Weed-hosts for each nematode are included in Table 2. Good weed control is important with rotation as part of an effective nematode control program.

This guide and the Guide to Interpreting Nematode Assays (available from your county extension office) can be used to develop a total nematode control program for most nematode problems in major field crops grown in Georgia.

How to Use This Guide

Look first at Table 1 to determine which nematodes affect each major field crop. A non-host crop may be selected from this table.

If additional study of host plants or non-host plants is desirable, turn to the page on the specific kind of nematode that has been identified on your farm. Select a non-host crop that will best fit your farming operation but will not build up nematode populations identified as present in the field to damaging levels. Although information is not available for all nematodes on all plants, remember that each of the more economically important crops grown in Georgia is damaged more by some nematodes than by others. Maintain close communication with your county extension agent or specialist in order to make the appropriate decision on crop rotation for your specific situation.

Study weed-hosts of major nematodes as given in Table 2. Remember that good weed control can be an important part of a nematode control program.

Kinds of Nematodes