Biology
- These generally become a problem when skunks and birds try to eat them. To get at the grubs, these animals will pull up chunks of grass, exposing the soil underneath and damaging the lawn.
- White grubs are the larval form of the common June beetle and, and two other invasive beetle species, the European Chafer and the Japanese Beetle. They are a part of the Scarab family.
- They are whitish yellow and possess fleshy, wrinkled c-shaped bodies. They have tan or brown heads and six spiny legs. They usually reach lengths up to 2-4 cm.
- Adults are usually a shiny reddish brown and can reach lengths of up to 2.5 cm. They feed on the leaves of many trees and shrubs. Females lay their eggs either 5-10 cm deep in the soil, or directly on the blades of grass depending on the species. The grubs hatch 2-3 weeks later.
- For the first summer, the grubs feed mostly on decaying vegetation in the soil. In fall, they burrow deeper in the soil to overwinter. The following spring, the grubs will start eating grass roots and causing lawn damage. They will hibernate once again and then, in June, will form a cell in which they will pupate. The adults will emerge within a month but will remain within the cell until the following spring.
- The European Chafer and Japanese Beetle have a simillar lifecycle, however they only remain in the soil for one winter before emerging as adults in the summer. The Common June Beetle has a three year lifecycle as described above. Although it pays to know which exact species is in your lawn, generally in Quebec we have a problem with the European Chafer primarily, and the Common June Beetle secondarily. The Japanese Beetle is mainly a problem on the west coast in Canada.
How to Control
It has been found that excessive watering and mowing the grass too short (less then 7.5cm) are some things that attract white grubs. Grubs eats your roots, and they prefer shallow fiberous roots. Mowing your lawn frequently, mowing it very short, watering frequently and for short period of times, and using quick release fertilizers all encourage short roots in your lawn. The past ways of dealing with this pest often included the use of pesticides that kill beneficial insects such as predators like wasps, nematodes, and ants who eat your white grubs. Ironically, chemical dependance attracts the white grubs since they are provided an environment with no predators.
- Water deeply and infrequently: this discourages females from laying eggs beacuse the soil surface dries between watering. Deep infrequent irrigation also encourages deep-rooted, drought tolerant lawns.
- Aerate the soil: in June, the beetles lay their eggs in compacted soil. Ways of aerating soil include poking holes with a pitchfork or garden fork, renting an aeration instrument from one of the numerous rental companies or calling a lawn care contractor. It's also healthier for your grass in general. This can be about $89 for 2500 feet.
- Mow higher then 7.5 cm: beetles prefer to lay eggs in closely cropped lawns. Raise the summer mowing height to as high as possbile, around 7.5 cm (3 inches). This will also improve root growth.
- Remove adult beetles: vacuum or handpick them in the early morning when they are still sluggish. They can then be killed by immersion in soapy water. One evening try attracting the adults in a trap to be killed before they lay their larva. This is done using a light attached 30 cm above a pail of water. The light can be a 25-watt light bulb mounted on an aluminium plate. Place a funnel above the pail so that when beetles are attracted to the light they will run into it and fall through the funnel into the water, unable to escape. Place the pail anywhere you can plug the light in.
- Install birdhouses: birds are natural predators that will eat grubs.
- Fertilize: high-potassium encourages strong leaf blades and nitrogen encourages fast, succulent growth. Slow release fertilizer also encourages deep root growth. Overseed with white-dutch clover if possible. The type of beetles that procreate the white grub do not lay eggs in clover. Add a top dressing of lime, rock powder (e.g. Botanix) and composted manure. Spread the mixture all over the lawn and rake it. Make sure to rake off the dead grass on the yellow parts. In the fall, a high potassium fertilizer like seaweed can be applied.
- Fall garden clean up will help reduce the number of grubs that overwinter. Removing old plants and weeds as well as cultivating the soil thoroughly will help as well.
- Beneficial nematodes: these seem to be the best bet. They are most effective if applied from mid-August to early September. The finicky part is that they need to be refrigerated and the lawn must be kept wet before and after applying the whole area with the nematodes. Also, do not apply to a specific spot; nematodes need to be put everywhere otherwise the grubs will emigrate elsewhere.
- Entomopathogenic nematods of the Steinernema type are living organisms that enter into the body of the larvae and excrete bacteria that attacks the body of the grub. It is used in August and September and their application requires very specific conditions and procedures. If this is something that interests you please call us here at U.N.I.S. during our summer hours or your local nursery or garden shop.
- Other methods will likely require buying a product and consulting with vendor or contracting out a professional. One example is to treat your lawn with "Milky spore Disease" not really a disease, it is two types of bacteria that kill the grubs of Japanese beetles and several other beetles, but are harmless to other organisms.
- Infected grubs are filled with an opaque, milky-white liquid full of bacterial spores, which will remain in the soil after the grub dies.
- Treat lawn when not frozen and over the entire area of lawn, NOT only the infected patches (They will move into good patches if the entire lawn is not treated).
- 7-10 pounds of spore dust per acre, or 10 ounces per 2,500 square feet. Apply dust in spots about 4 feet apart, and about 1 tbsp per spot.