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Entomopathogenic nematodes : fighting against white grubs

White grubs populations can be reduced with entomopathogenic nematodes. Here is when and how to apply them for an effective treatment.
Photo: Jardin botanique de Montréal (Édith Smeesters)
Festuca arundinacea

Is your lawn heavily damaged by white grubs? Applying entomopathogenic nematodes, along with good lawn-care practices can reduce their population. In order for the treatment against white grubs to be effective, however, it is important to follow the instructions on the label carefully.

What are entomopathogenic nematodes?

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.

The two main species of entomopathogenic nematodes commercialised in Québec are: Heterorhabditis bacteriophora and Steinernema 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.

Where to buy them?

Products available on the market contain one or many nematode species. They can be purchased from some garden centres and nurseries, department stores and specialized biological control companies.

Note that entomopathogenic nematodes pose absolutely no health risk for humans, animals, plants or the environment.

When and how to apply them

It is important to follow the manufacturer's recommendations as to when to apply nematodes.

The best time to apply nematodes is generally from the end of July to mid-September, depending on the product used. For optimum nematode activity, the soil temparature should be around 20°C, but it may somewhat vary depending on the species of nematodes inthe product. In addition, white grubs are relatively small and most vulnerable at the end of the summer.

Springtime treatments are generally not effective, because the soil is often toot cold and white grubs are more mature (larger and more difficult to parasite).

Choosing a product

Different products are available on the market. In order to know which species of nematodes are in the formulation, read the label carefully. Note that not all nematode species can parasitize all types of white grubs since they are larvae of different insect species (June beetle, European chafer and Japanese beetle).

A tip : choose the product according to the insect that was predominantly present the previous year or opt for a formulation that contains several nematode species in order to broaden the action spectrum.

Application guidelines*

  • Check the expiry date on the package before buying any product. After that date, the survival rate of nematodes may have an impact on the effectiveness of the treatment.
  • If the product needs to be refrigerated, 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. Nematodes disperse in the soil with water, hence the importance of keeping the soil moist, but not soggy.
  • 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.
  • Remove any fine-meshed filters if you are using a sprayer.
  • 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 if a temporary lawn-watering permit is 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.

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