What are Nematodes?
Broadly, nematodes or “roundworms” describe a very large and diverse group of organisms found all over the world in nearly every ecosystem. There are over 25,000 described species, but it is speculated there may be as many as over a million species worldwide. Most are very small organisms, many are microscopic. Some species feed on living plant tissue and can be harmful to your garden, others feed harmlessly on fungi and decaying plant matter, and some feed only on harmful insects and their larvae. It is this last group of nematode that can be very useful in combating pests that damage our lawns and gardens.
These beneficial nematodes are very useful in controlling grubs in particular. Grubs are the larval stage of insects in the beetle family, such as June bugs and black vine weevil. During this stage of a beetle’s life cycle, it lives in the soil and eats away at the roots of plants; usually grasses, but vegetable and ornamental plants can be effected as well. In lawns the damage is usually seen as patches of grass that grow poorly, and quickly brown in dry weather (see image below). In other plants the damage can manifest in stunted leaf growth, early leaf drop and frequent wilting. Depending on the species, grubs remain in their larval stage and feed on the roots of plants unseen for months or even years. A bad infestation can be especially detrimental to the overall health of your lawn and gardens.
Because these insects live and feed in secrecy beneath the soil, it can be difficult to diagnose the problem, and even more difficult to remedy with traditional pesticides. This is where beneficial nematodes are exceptionally useful. The nematodes you can buy to apply to your lawn or garden are predatory parasites of grubs as well as some other harmful pests (such as caterpillar, crane fly and fungus gnat). These nematodes will actively seek out a host insect to feed on, moving through the soil (usually at a speed of 2.5 cm an hour). They can detect the presence of host insects by temperature fluctuations in the soil as well as the presence of methane gas. Nematodes can survive in the root zone of plants without a host for 2-3 months.
Upon finding a host insect, the nematodes will infect it with a bacteria that will kill it within 48 hours. The nematodes will then reproduce, using the dead insect as a food source for its offspring. This results in even more nematodes in your lawn seeking out harmful insects. Perhaps the best part of nematode application is that it solves the pest problem without the use of harmful chemical pesticides. Unlike chemical pesticides, beneficial nematodes pose no harm to people, pets, plants or beneficial insects. As you can see, the nature of beneficial nematodes make them especially useful in dealing with these troublesome, soil dwelling pests.
Nematodes can be applied to the soil May through June, but ensure the soil is at least 10 degrees Celsius. They can also be applied August through October to kill grubs that have hatched in the summer. It’s recommended to pre-water the area before applying nematodes. The area should also be watered after application. As much as 2-3 inches of water may be necessary to ensure the nematodes are able to penetrate down into the soil. It is a good idea to keep the area watered for 3-4 days after application. It is important to keep the lawn moist at and after application because the nematodes are more mobile in moist environments.
Nematodes are typically sold as a small, sealed sponge or gel pack that contains millions of the tiny organisms. Nematodes can be applied with a hose sprayer, back pack sprayer, or even a watering can. (In the case of the watering can and back pack sprayer, the container of water should be agitated regularly to mix the nematodes evenly through the water. Nematodes are heavy and tend to settle to the bottom, limiting their equal dispersal if left undisturbed.) Once added to water, nematodes should be applied within 2 hours. When applying nematodes always follow the directions on the product labels.
Keep in mind when purchasing nematodes that they are living organisms. They have been kept refrigerated, and should continue to be kept cool until they are used. Exposure to extreme heat can be detrimental to their effectiveness. It is best to use them immediately after purchasing, as even when refrigerated, they have a limited shelf life.