Insecticidal nematodes are microscopic roundworms that live in the soil. Although there are many types of nematodes, only insecticidal nematodes in two genera, steinernema and heterorhabditis, are used as biological controls for horticultural purposes. These beneficial organisms will eat the various insects that can plague a garden. All you have to do is let them loose, and they will move through the soil beneath your lawn, seeking insects and larvae to feast upon. You can purchase nematodes that specifically target lawn pests on the Internet and at some nurseries.
This nematode is the most studied and, therefore, most available nematode for the home gardener. It is most effective against turf pests such as armyworm, cutworm, sod webworm and termites. Known as an "ambush forager," it will stand upright on the soil and wait for a host to wander by, then attach itself to it. If you live in one of the warmer areas of the country, this is the nematode you should consider as it prefers soil temperatures from 70 to 80 degrees F.
According to scientists at Cornell University, H. bacteriophora is incredibly versatile in the number of lawn insect species it will attack, but has been shown to be very effective against white grub (U of Delaware). Not one to sit around and wait, it will seek out its host. Like S. carpocapsae, this nematode likes warmth in the soil. Not a particularly hardy species, it will be rather sluggish and inefficient if temperatures drop below 68 degrees, F. Keep your lawn very moist both before and after nematode application, as they need a lot of water.
If you live in a cooler climate, S. feltiae may be the nematode for you. It does best when soil temperatures are below 50 degrees F. It is also more effective in sandy soils and prefers immature insects and larvae. S. feltiae will feast on cutworm, sod webworm, termites and more.