Nematode-infected plants are not only weakened, but their root systems are more susceptible to secondary infections by fungi or bacteria. For example, nematode-infested okra plantings are often attacked by Fusarium wilt. Not all nematodes are plant pathogens, however. The majority of nematode species live in the soil on decaying plant material where they are active in decomposition and nutrient recycling. Some species parasitize other nematodes or insects.
Correct identification is the first step when a nematode problem is suspected.
The second step is to determine whether populations are high enough to threaten the crop. Most state soil testing services can analyze for nematodes. Soil samples taken during warm weather and when plants are growing are more useful in revealing nematode problems than samples taken in winter or from fallow land. In the south, broadleaf plants growing in warm sandy soils are the most vulnerable to nematode damage. Root knot nematodes, the most common pathogenic nematodes in vegetables, cannot penetrate roots when soil temperatures are below 50 degrees F, and will not reproduce when soil temperatures are below 58 degrees F. Their reproductive rate is slower at cooler tempera tures, so populations build up more slowly.