Nematodes
Nematodes themselves are described earlier in this entry. Symptoms of nematode invasion include reduced growth, wilting, and lack of vigor.
Some nematodes cause excessive branching of roots, rotted roots, and enlarged lumps on roots. Other nematodes attack leaves, causing triangular wedges of dead tissue.
Root knot nematodes attack a variety of plant root systems, including most vegetable and ornamental crops. Carrot plants will be stunted, with yellowed leaves, and roots may be distorted. Roots of other plants will have swollen areas. Remember that legumes are supposed to have swellings on their roots that are caused by nitrogen-fixing bacteria.
Prevent nematodes from invading your plants by maintaining your soil organic matter. Plant resistant varieties when possible. Take care not to spread soil from nematode-infested areas to other parts of your garden or yard. Reduce nematode populations by solarizing soil. Use a marigold (Tagetes patula or T. erecta) cover crop to reduce nematodes. Rotate susceptible crops. Adding products containing chitin to the soil can help reduce problems.
Hot-water dips can eradicate nematodes from within roots, bulbs, and the soil on them.