If your lawn is showing large patches of dead grass that seemed to appear overnight, it might be infected with grubs. To check for them, pull back some of the dead patch–if you find dozens, maybe even hundreds, of incredibly unattractive wormy things 2.5 to 4 cm long, and C shaped with brown heads and six small legs, that’s what you’ve got.

These little creatures can decimate a lawn in no time if left unchecked. You’ll have to act fast.

The white grub is the larval stage of the Japanese beetle, the June beetle or the European chafer beetle, and it lives just below the soil surface, feeding on the tender roots of grass. Grubs are most active in March and April, then they burrow into the soil for a dormant period, and become active again in late July into August. These months are the best times to get rid of an infestation.

It used to be that you could spray the lawn, killing every bug, good and bad, that lived there, but in these days of insecticide bans, you have one choice to deal with the grubs: insect parasitic nematodes, or Heterohabditis nematodes. These are microscopic, non-segmented roundworms that live in the soil and are harmless to all vertebrates, worms, plants and useful insects like ladybugs and bees. Nematodes are the only completely natural method of pest control currently available for getting rid of grubs.

The tiny creatures are sold under such trade names as BioSafe, Bio Vector, Scanmask, Exhibit, Oti-Nem and Guardian. Since they are living organisms they must be refrigerated until used. Exposure to extreme high or low temperatures can kill them, therefore it’s important to wait for a cool, cloudy day or evening to apply. The area should also be well watered before application, as nematodes need moisture to enable them to move through the soil.

The nematodes are packaged in a sponge that must be soaked for 30 minutes in about four litres of tepid water, preferably filtered or distilled, then applied with a clean hose-end sprayer with the filter removed.

For small areas, use a watering can or a hand-pump pressure sprayer. Whatever is used, it must not have held harsh insecticides or chemicals or the nematodes will be dead before they hit the ground.

Once in the soil, nematodes sense the temperature and carbon dioxide content of soil-borne insects. They hunt them down and enter the pests through body openings, releasing a bacterium that kills the host insect within 48 hours. The bacterium is harmless to humans and other organisms, and cannot live freely in nature.

Several generations of nematodes will live and breed within the dead pest before they move on to fresh prey.  The lawn must be kept moist for a few weeks after application while they’re at work.

A second application in the spring is recommended to kill grubs that may have got away.