White grub populations can be reduced by applying entomopathogenic nematodes, along with good lawn-care practices. In order for the treatment to be effective, however, it is important to follow the instructions on the label carefully.
Entomopathogenic nematodes are microscopic worms that are parasitic on white grubs. After penetrating the grubs’ body cavities through natural openings, they release bacteria. The bacteria then multiply and quickly kill the white grubs, which turn from creamy white to reddish brown. The nematodes feed on the nutrients provided by the bacteria and the decomposing tissues of the white grubs. They reproduce inside these carcasses, and the juveniles then attack new white grubs.
Two species of entomopathogenic nematodes are commercially available in Quebec: Heterorhabditis bacteriophora and Steinerma carpocapsae. The first species burrows up to 20 cm underground, while the second stays closer to the surface, at depths of about 7 to 8 cm.
Products available on the market contain one or both of these two nematode species. They can be purchased from some garden centres and nurseries, department stores and specialized biological control companies.
Research is being conducted to come up with nematode species that are more aggressive and better suited to our climate.
Note that entomopathogenic nematodes pose absolutely no health risk for humans, animals, plants or the environment.
When to apply them
The best time to apply nematodes is from mid-August to mid-September, when the soil temperature is optimal (14° to 30°C) for nematode activity. In addition, white grubs are relatively small and most vulnerable at that time of year. Springtime treatments are not effective, because the soil is too cold and white grubs are more mature (larger and more difficult to parasite).
How to apply them *
- Check the expiry date on the package before buying any nematodes. Too many of them may have died off after that date for the treatment to be effective.
- Nematodes must be kept cool until you are ready to use them. Make sure that they have been kept refrigerated by the seller. Take them home in a cooler and then store them in the refrigerator.
- Water your lawn deeply before treating it, or apply nematodes after a heavy rain. The soil must be thoroughly moist, but not waterlogged.
- Apply the treatment in the evening or on a cloudy or rainy day, because nematodes are sensitive to ultraviolet rays.
- Nematodes are usually sold in concentrated form on a damp sponge or in powdered clay. Before application, they must be mixed with tepid water. Follow the instructions on the label to prepare the mixture.
- If you are using a sprayer, remove any fine-meshed filters.
- Shake the watering can or sprayer frequently while applying nematodes in order to keep them in suspension.
- Water your lawn deeply after the treatment and then keep the soil moist for at least a week. Contact your municipality or borough to obtain a temporary lawn-watering permit, if necessary.
NB: Nematodes are not very effective in compact soil. If your soil is hard-packed, it should be aerated and top-dressed (ideally in spring) before you apply any nematodes.
* This information is intended only as a guide. Always read product labels carefully. Various factors may affect the efficacy of any treatment. The Jardin botanique does not assume any responsibility in this regard.