Organic Pest Control for Your Lawn: All About Nematodes

Nematodes live naturally everywhere. A handful of garden soil contains thousands of them, some beneficial and some not. More than 20,000 species of nematodes are classified in the phylum Nemata. They range in size from microscopic to 9 feet long (a parasitic nematode found in a whale's intestine). Heartworms in dogs are nematodes. So are roundworms. Some live near the surface of the soil, within the first couple of inches; others are deeper dwellers and live 6 or 7 inches deep. There are harmful nematodes, such as tomato nematodes that can ravage tomato plants, damaging the roots so that the above ground portions die. Beneficial nematodes feed on insect larvae and other nematodes, and these are the ones that are used to treat insect problems in lawns.

Purchase beneficial nematodes at organic gardening supply stores or from garden catalogs. Different species are used to target different pests. A blend of nematodes will control a variety of soil pests with one application.

• Japanese Beetles, June beetles, several types of weevils, chafers, and midges are some species that can be controlled by nematodes. The larvae (grubs) of these are considered deep soil dwellers, since they live several inches down in the soil. Hb nematodes (Heterorhabditis bacteriophora) will take care of these deep dwellers.

• Closer to the soil surface is where black cutworms, other weevils, billbugs, army worms, mole crickets, and flea larvae live. Sc nematodes (Steinernema carpocapsae) live in this level of soil and attack the undesirables.

• Many species of fly larvae live in the top 3" of soil. They are the favorite food of Sf nematodes (Steinernema feltiae).

Nematodes must be handled properly so they stay alive. UV rays will kill them, and so will too much heat. If you order from a catalog, place your order before hot weather arrives. They will not survive transport in a hot truck. A pack of nematodes can be kept in the refrigerator for up to one month, so you can order early and then wait for the right conditions to apply them.

Nematodes are packaged in a carrier of some sort, usually clay, granules, or a sponge that will dissolve and release millions of the little guys when mixed with water. Remember, these are tiny, and you won't really see them. The soil should be moist when applying nematodes. They move into the soil by "sliding" along on the infinitely tiny layer of water that is between soil particles. If the soil is dry, they cannot work their way in. Water the area before and after applying them, and they will have the best chance of making their way into the soil. Evening is a good time to apply nematodes, because the UV risk is low, and the temperature is lower and won't increase again for several hours. This also means that the moisture will not evaporate quickly.

To apply nematodes, simply mix them in water and use a watering can, irrigation system, or a sprayer with the screen removed. Shake or stir the mixture every so often during application because they may settle to the bottom of the container. Spring and fall are the seasons when larval activity is highest. They are the seasons when nematode release will be most effective.

Nematodes find their prey by either lurking among the soil particles waiting for larvae to pass by so they can latch on, or by actively seeking a host. The seekers can detect minute changes in CO2 levels and temperature which are signals that a victim is near. Some nematodes follow trails of excrement left by larvae in the soil. Once a host is located, a nematode enters through the skin or a body opening. Then it releases bacteria from its digestive tract that quickly kills the host. Bacteria also convert the host's insides into usable food for the nematodes. The Steinernema require two nematodes to reproduce; one Heterorhabditis will reproduce on its own. In a little over a week there will be several generations of nematodes in the host, and when it has been devoured, they move on to locate another victim.

As vicious as they sound, beneficial nematodes are harmless to humans. They can make a big difference in your lawn in only a few weeks. They are also effective against termites, German cockroaches, and ants in the soil. They will not harm earthworms. No mask or protective gear is needed when applying nematodes, and children and pets can safely play on treated areas. They can safely be applied in the garden right before harvest.

Sources: http://www.organiclawncare101.com/pests.html#pest-control
Personal experience