Parasitic nematodes are small round worms which live in the soil and feed on organic matter, insects, and plants. They are microscopic in size, and some are used by gardeners to destroy common garden pests without affecting the soil or health of the plants. Many different species are marketed and sold as biological control agents. They are considered benign to humans and pets, so there is no restriction on their use to control pests in gardens and farms. However, some types of nematodes may damage plants, and interfere with their ability to transfer nutrients from the roots to the above ground parts of the plant.
There are two primary types of parasitic nematodes – insect and plant. Insect parasitic nematodes, also known as beneficial or predator nematodes, live out at least part of their life cycle within a host insect. Many species also kill the host as part of this process, and are used as pest control in this way. This type of nematode will not harm the plants, but is beneficial to their health.
An insect parasitic nematode will move short distances through the soil to find a host insect, and then kill the host by releasing bacteria into its body. The host will die from blood poisoning within a few days. The nematode continues to grow by feeding on the bacteria and tissue of the dead host. The body of the host is used to reproduce, and up to two generations of parasitic nematodes can be born from a single host insect.
Plant parasitic nematodes attack the roots of plants and aren’t generally looked upon as favorably as their beneficial counterparts. The plant nematodes include two main subtypes – ectoparasitic and endoparasitic. The former lives outside the plant and feeds on the roots, moving up to three feet (0.9 meters) to find a suitable host. Endoparasitic nematodes instead penetrate the root and live inside it. Both types can cause serious damage to the plants on which they feed.
In general, plant parasitic nematodes do not kill plants, but can reduce vigor and resistance, making them more susceptible to outside diseases. It isn’t always easy to diagnose nematode problems of this kind. Often the symptoms are similar to traditional plant problems. Experts recommend checking your plants for proper irrigation, nutrients, and visible disease symptoms before suspecting that nematodes might be to blame.
Some common symptoms of parasitic infections by nematodes include wilting leaves during the warmest part of the day, stunted growth, curling or twisting of limbs and stems, delayed maturity, and lack of vigor. If these symptoms cannot be explained by other means, such as lack of water or food, nematodes may be to blame. The roots of one of the waning plants may be examined, and if there are knots or other deformities in the roots, a parasitic nematode infection is likely. Professional pest control may be necessary in this case, as nematodes are very difficult to remove once established in the soil.