Nematodes and grubs are two very different pests that live and feed in the soil beneath your lawn and garden. Nematodes are parasites generally classified by what they eat. Grubs are the larvae of the Japanese beetle. Both can inflict considerable damage to your treasured lawn or ornamental flowers; the activity of some types of nematodes, however, is beneficial to your garden.
Types of Nematodes
Nematodes are tiny (1/500th-inch-long) nonsegmented worms that are abundant in almost every habitat, including woodlands, salt and fresh water bodies and the soil. Some are parastic on humans and other vertebrates. Within the phylum Nematoda are at least 20 orders of nematode, about 10 of which inhabit the soil.
There are four major groups of soil nematodes, often grouped by their food of choice. Herbivore nematodes make their way into the roots of plants and feed exclusively on them. They can cause serious damage, making it impossible for nutrients and water to get to the plant. Bacteriavores strictly eat bacteria and help the soil by assisting in the decomposition of organic matter. This also helps the recycling of nutrients in the soil. Fungivores eat strictly the various types of fungi in soil, which also helps decompose organic matter and recycle nutrients. Predators eat other nematodes and protozoa in the soil. Omnivores eat roots of plants, other nematodes, fungi and bacteria, insects and algae.
General Nematode Information
One square yard of agricultural soil can contain several million of the various types of nematodes. The microscopic worms live deep in the soil during the cold months as well as the hottest summer months, remaining dormant until conditions improve. Nematodes need moisture in the soil, as the moisture is their means of transportation.
Bacteriavores and fungivores are actually beneficial to the soil as they recycle nutrients and do not eat or harm plants. The problem is attracting these helpful worms without attracting the harmful ones.
Escaping Nematode Destruction
There is no "nematicide" to effectively eliminate nematodes from your garden. These worms simply move on until the effect of the chemical has worn off and return to eat again. Your best bet in ridding your garden of these pests is to pull up the affected plants and burn them; till the soil frequently where the plant grew to discourage nematodes from reclaiming the spot.
Japanese beetle and their larvae--grubs--can both be very destructive to your garden, so it is important to identify them and entice them to leave your plants (and lawn) alone.
Japanese beetles can frequently be seen on golf courses, since they enjoy feeding on grass roots. Many greens keepers will put out bright plastic bags that attract and trap the beetle, hopefully before its eggs have been lain. The larvae overwinter beneath the soil, burrowing up just in time for the first green shoots of grass. They can decimate the roots. You know they've been feasting beneath your lawn if you can lift the grass as though it were a carpet--the roots are gone. Grubs also cut ornamental plants at the soil line, killing the plant.
Escaping Grub Destruction
While it may be tedious, you trap and kill beetles whenever you see them to ensure that you'll have fewer grubs to deal with the following year. Or you can handpick the beetles and place them into soapy water. Beetle traps, which are commonly seen on golf courses, have phenomes that attract the beetles; however, warns the Department of Entomology at the University of Kentucky, many more beetles are attracted than are actually trapped. There are effective pesticides available to kill Japanese beetles, but many can be harmful to animals and the environment. Beetles tend to group, so killing those you see may prevent many more from coming.