Plant Pathology Infobytes

December 5, 1996
A Hot New Way to Control Garden Nematodes

Gardeners who've battled root-knot and other types of nematodes in past seasons know these pesky creatures can be tough to handle. These microscopic roundworms feed on the roots of susceptible varieties of tomatoes, peppers, lima and green beans, okra, sweetpotatoes, carrots, as well as other vegetables, and are often responsible for reduced yields and plant death.

To find out if nematodes have been zapping your vegetable crops, collect samples of garden soil for nematode analysis. Check with the County Extension Office for details on sample collection procedure.

If the sample analysis reveals a nematode problem, there are several control options which may be followed. These include crop rotation, treatment with soil nematicides, planting root-knot nematode resistant vegetable varieties, use of marigolds, and soil solarization, an increasingly popular technique for nematode control.

Soil solarization is a unique approach to nematode problems used by gardeners to replace chemical control. While solarization isn't something that can be done during the winter months, it works very effectively when practiced during the growing season. Gardeners with nematode problems might want to give this procedure a try next year.

Solarization, or solar heating, involves the process of trapping solar energy in the soil by covering the soil surface with a layer of polyethylene. There are several procedures that must be followed closely to insure the soil temperature is raised to the to the critical point where nematode control is obtained.

First, the soil should be moist and well-tilled before tarp installation. Also, solarization should be practiced during late spring months, or ideally at the hottest time of the year when the incidence of sunlight is greatest. Normally, four to six weeks is an adequate period of solarization. Six weeks is the preferred period if the technique is used in the late spring.

Selection of a plastic or polyethylene cover is probably the most important step in the process. The cover must be clear and no more than 2 millimeters thick. It should be strong and durable enough to allow for stretching.

Placement of the cover is also important. It should be stretched tight and in direct contact with the soil surface. Care must be taken to bury the edges of the tarp in the soil to a depth of at least six inches so as not to allow the wind to lift the tarp during the solarization period. Remember, the tarp has to remain in-place for a four to six week period.

When removing the tarp, avoid contamination of the treated area with untreated soil. This is also true at planting and best results are obtained when beds are prepared for planting before solarization and immediately planted after removing the tarp.

Solarization also controls other soilborne organisms such as fungi, insects, and certain weeds. However, the technique is probably most effective for reducing nematode populations in the top eight to ten inches of soil.

For additional information on soil solarization, or control advice on other garden pests, check with us at the County Extension Office.


Written by the late Dr. Frank Killebrew

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