Those Famous White Grubs

12 STEPS SOLUTION

White grubs are ravaging many Deux-Montagnes lawns. Although municipal bylaws prohibit pesticide use in Deux-Montagnes, there are ways to reduce the presence of white grubs and the following tasks can be performed to solve the problem in the long run.

In spring:

1. Remove the patches of grass that have been damaged.

2. Aerate the lawn to mechanically kill certain specimens and to discourage egg development.

3. Apply compost: 50 to 100Kg/100m2 (in a single application).

4. Re-sow: Mixture of gramineae (hay, ryegrass, meadowgrass) + 10% white clover to protect the damaged patches. White clover is toxic for white grubs. Then, moisten the seeds once or twice a day to promote lawn growth (light watering).

5. Fertilize with natural fertilizer that is low in nitrogen, but rich in phosphorous and potassium

IMPORTANT! ALL OF THE WHITE GRUBS PRESENT IN SPRING WILL COME OUT OF THE SOIL AS ADULTS IN JUNE. SPRING IS THEREFORE NOT THE BEST TIME TO APPLY PESTICIDES, AS THE INSECTICIDE WILL REACH ONLY 15% OF THE WHITE GRUB POPULATION.

IN OTHER WORDS, IT IS PREFERABLE TO CONCENTRATE YOUR EFFORTS ON PREVENTING THE ADULT FROM LAYING ITS EGGS IN JUNE-JULY AND FOCUS ON DESTROYING THE WHITE GRUBS DURING THE MID-AUGUST TO MID-SEPTEMBER PERIOD BY INTRODUCING NEMATODES ONTO THE LAWN.

During the summer:

6. Always mow the lawn to 3” to discourage the June beetles from laying their eggs.

7. Turn out the outdoor lights in June and July, as the June bugs are attracted to light.

8. Apply a repulsive agent prepared with eucalyptus essential oil; here is the recipe:

Mix from one third to half a bottle of eucalyptus essential oil (5 to 10 ml) and water in a liquid fertilizer applicator (pump model) and spray the lawn with this mixture once every 7 days.  This mixture will cover about 5,000 square feet. The eucalyptus odour will be too strong for the June beetles and they will not lay their eggs on your lawn. This operation should be repeated 5 times throughout the summer, between June 18 and July 22.

9. Try diversifying the vegetation to attract natural predators.

10. Avoid watering the soil too much in June and July, as the soil should remain dry during the egg-laying period.

11. Do not use chemical pesticides that eliminate natural predators.  For example, the ant feeds on white grub eggs.

Autumn (mid-August to mid-September) :

12. Introduce Heterorhabditis Bacteriophora (HB) nematodes, also called and sold as Terranem. In order for the treatment to be effective, it is very important to follow the manufacturer’s recommendations, as described on the product label. Also, during the car ride from the store to your home, you must keep the product in a cool environment, as nematodes are very sensitive to heat.  Afterwards, you must store them in the refrigerator until you are ready to use them.

iMPORTANT ! These steps must be repeated each year to make sure the white grubs stay away from your lawn and, in any case, these treatments are good practices for healthy lawn maintenance.

For additional information, please call 450-473-4688.

To know more about the white grub...

GENERAL INFORMATION

The devastation of lawns by “white grubs” is a relatively new problem in Quebec. Though it seems to be more prevalent in cities where soils are very sandy, it has also spread to Rosemere, even though a large proportion of the soil on our territory is rather argillaceous.

The insect causing such devastation is, in fact, the larva of the European June beetle, commonly referred to as “white grub”, as is the larva of the common beetle (indigenous in Quebec, often called “beetle”) and the larva of the Japanese beetle (introduced species). A magnifying glass or binoculars are required to tell the types of white grub apart. However, it has already been determined, through observation, that the one causing so much damage in the Greater Montreal Area is in fact the European June bug. Generally speaking, the white grub feeds off the roots of various species of plants (herbaceous plants, leafy trees and conifers) but has a net preference for the gramineae roots. As a result of its feeding habits, the grass dies, sometimes in large patches. The number of grubs per square meter is not directly proportional to the damage observed on the lawn. In fact, the type of soil, le initial length of the roots, the presence of predators and the diversity of species present in the soil can greatly affect the intensity of the symptoms observed.

The Insect’s Life Cycle

In Quebec, the adult European June beetle comes out of the ground around mid-June, which means to say just a few days before the province’s National Holiday, or just as the Catalpas come into bloom. It then mates during nuptial flights, between 8 and 10 in the evening, and the female lays her eggs in the grass - between 20 and 50 eggs that she lays about 10 cm below the soil’s surface. The eggs will hatch during the month of July and the larvae (typically “C-shaped”) will slowly develop by feeding on the gramineae roots present onsite. The larvae will go from Stage 1 to 2 around the end of August and from Stage 2 to 3 in October.

Stage 3 is when they begin to cause the most damage. Before the first frosts occur, they dig deeper into the ground to hibernate. When the following spring comes around and the soil warms up, the larvae (Stage 3) will move back up towards the surface and become active once again. At that point, they are very big and particularly attractive for skunks, racoons and crows, for whom they are quite the delicacy. Around mid-May, they once again dig deeper into the soil to become pupas (this intermediate transformation nymph stage lasts about 1 month), which represents the ultimate transformation into its adult form. The cycle will start again when the adult comes out of the ground to mate.

What to do?

If you discover your lawn has been damaged by white grubs, in late fall or early spring, you should know that no products should be applied at that time to get rid of the grubs. On the other hand, using an animal repellent like “Scent-a-gone”, which basically consists of black pepper oil, could be very efficient against skunks as they can make even more damage than the grubs themselves.

You will have to be patient and wait until mid-May to resow new grass, as soon as the temperature allows. It is important not to wait too long, because as of the end of May, there are lots of weed seeds in the air searching to fill in your patches of bare soil. To repair damaged lawns, the ideal mix to use would be an ecological grass seed mixture containing different types of gramineae (e.g.: hard fescue, chewing fescue, red fescue, Kentucky meadowgrass, perennial ryegrass, etc.) to increase the biodiversity of your lawn. Some mixtures also contain small quantities of white clover seeds; others contain “endophytes”, toxic symbiotic fungi for certain destructive insects such as the chinch bug. Adding good compost (forest, vegetable, etc.) to your soil and seeds mix is also very beneficial for establishing new grass. Ask for advice at your neighbourhood nursery.

If white grubs have been damaging your lawn for several years or if you have good reason to believe that June bugs have laid eggs on your property, you can detect the presence of larvae as early as the beginning of August. All you have to do is lift patches of grass in different areas of the lawn and stir up the soil around the roots looking for white grubs. Be careful! Don’t look for large grubs; at that time of year, they only measure a few millimetres.

If you find several per square foot, you can choose to use a nematode-based biological treatment. Sold in nurseries, you can either apply this type of treatment yourself from the beginning of August to mid-September, or you can call a contractor to have it done.  Applying nematodes must however be done according to procedures for the results to be satisfactory. Here are a few important tips:

  • Nematodes must be stored in a cool area (do not leave the box in the sunlight or in a warm place);
  • The treatment should be applied at the end of the day or during a cool, cloudy day;
  • It is important to use the right type of spray (without filter, with right size tip);
  • Shake the watering can or spray bottle throughout the application, in order to oxygenize the solution (hydrated nematodes powder);
  • Watering the soil 24 hours before and for 10 consecutive days after the application is of primary importance. Get a temporary watering permit from City Hall by presenting proof of purchase of your nematodes.

Be careful! Nematodes are efficient when all application conditions have been filled, including, namely, watering for 10 days, a ground temperature ranging between 15 and 22°C, and adequate soil type (not too packed). The efficiency can be drastically reduced if you omit one of these conditions. No matter what you choose, be sure to follow the instructions to the letter and if you have any doubts whatsoever, you can obtain a nematodes application guide from the Public Works Department.

The best solution remains prevention, through the adoption of good cultivation techniques, as June bugs prefer to lay their eggs in short, sparse grass. Moreover, if the lawn is healthy, its roots are longer and will be able to support a greater quantity of white grubs.

What about Pesticides?

The only chemical pesticide against white grub used in Quebec is a synthetic insecticide called “Merit”, which is applied by contractors. Authorized in only a few provinces as it is still under study, this new insecticide is very controversial. “Merit” must be applied between the beginning and the end of July, as a preventative treatment when the grubs are not yet visible, which goes against the principle of integrated pest control.

As “Merit” is systemic, it is absorbed by the plants (the plants targeted here are the grass gramineae), which then become toxic for all insects or animals that feed off it, no matter what species that may be. As the June beetle larva grows, it eats more toxic roots and dies a few weeks after hatching. If the treatment is applied too late in the season (after July), there is a risk that it will not be as effective as the larger larvae will be harder to kill. For example, the efficiency of the product can go from 83% in July to 40% in August, which does not justify using this pesticide for such low results, considering the product remains in the lawn for 120 days.

Finally, please take note that, if you are still considering this option, you must first contact the City’s eco-counsellor at Public Works so that he can assess the damages to your lawn, either in the fall or early spring, and, if applicable, issue a permit for pesticide application. You must also be able to provide proof (example: supporting invoices) that the adoption of good cultivation techniques and/or the application of nematodes were attempted but were unsuccessful.

References: 
© 2007 Ville de Deux-Montagnes : Legal Notice : Credits