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Gardening Articles: Care :: Pests & Problems

Beneficial Nematodes (page 3 of 4)

by Dan Hickey


Beneficial nematodes move in water-filled spaces between particles of soil. If the soil is too dry or too tight, they are not able to move and search out host insects. Commercial suppliers recommend watering the insect-infested area before applying nematodes. An additional sprinkling after releasing the nematodes will help rinse them off plants and grass into the soil.

Ultraviolet Light

Exposure to ultraviolet light or extreme temperatures can kill nematodes. During the warmer summer months, apply nematodes in the early evening, when the intensity of light is reduced and soil temperature is lower. Remember, watering your lawn before application will lower the soil temperature. Nematodes are either killed or less effective when soil temperatures are below 60oF or higher than 93° F.

For the typical garden, nematodes will take about two to three weeks to show results. You should see fewer of the targeted adult insects in your yard or garden. If you applied the nematodes in the fall, you should see results the following spring.

How can you make sure the nematodes have worked? If you want hard evidence, you'll have to do some digging.

"Look for insect activity," says Kaya. "If you dig up the soil you can usually find a dead insect. If the nematodes killed the insect, it should be brown or reddish orange, depending on what type of nematode was used. Secondly, it shouldn't have a putrid smell." Insects killed by Steinernema turn cream to dark brown, while Heterorhabditis turns insects orange-red. (They may even glow in the dark!) For most gardeners, nematodes must be reapplied each year.

Though be nematodes will overwinter in the soil, there will not be enough of them to effectively control pests for more than one season. Effective use of nematodes depends on a high enough number of the organisms to overwhelm your garden pests. Surprisingly, nematodes will work even when combined with some powerful pesticides. Farmers use nematodes in combination with diazinon, but home gardeners should check the package instructions before combining the two. On the other hand, the pesticide carbaryl will kill beneficial nematodes.

Because of its high nitrogen content, fertilizer can reduce nematode effectiveness. Manufacturers recommend that fertilizers not be used two weeks prior to and after nematode application. Again, check the package instructions.

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