Plant Pathology Infobytes
June 8, 1999
Nematode Control in the Garden Through Solarization
Home vegetable gardeners who've battled root-knot and other types of nematodes in past seasons know these pesky creatures can be tough to handle. The plant parasitic types of nematodes are microscopic roundworms which feed on the roots of susceptible varieties of tomatoes, peppers, lima and green beans, okra, sweetpotatoes, carrots, as well as other vegetables.
When parasitic nematode populations reach high levels within root systems, the end result is reduced yield and occasionally 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, planting root-knot nematode resistant vegetable varieties, and the use of marigolds to suppress nematode populations.
The hottest technique for controlling root-knot nematodes is through the use of solarization. The technique is a simple and easy way to clean up your garden soil to grow nematode-free garden plants and boost yields. Early summer is a great time to use solarization to clean up nematode "hot spots."
Soil solarization is a unique approach to handling nematode problems and is often used by gardeners to replace chemical control. The technique utilizes the sun's heat to zap nematodes by trapping solar energy in the soil with a layer of polyethylene. There are several procedures that must be followed closely to insure the soil temperature is raised to the level 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 your county Extension office.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.