Today, (Sept. 24), I found a number of white grubs in an area of my lawn that was being resodded. Are the grubs eating at this time, and do they stay at this 3 cm depth until they are ready to emerge to mate, or, do they go deeper for the winter?
Thank you for your inquiry. The grub is the larvae stage of a variety of beetles. Japanese beetle, European chafer and June beetle are the most common three. Grubs feed on grass roots from mid-March to mid-May, and then develop into its pupal form. The adult beetle emerges in mid-June, mates over a two week span then re-enters the soil to lay its eggs. The eggs hatch and the grubs begin to feed in late July to August. The grubs will burrow below the frost line in the fall and stop feeding but if there is a thaw, they will resume feeding at any time, even during the winter. The grubs will continue to feed in the spring, constantly growing larger. You may wish to refer to the following website for an illustrated diagram on the life cycle of the grub: https://www.nysipm.cornell.edu/publications/grubs/life.asp
If a lawn is well maintained, well watered and well fertilized, there may be grub problems but because the lawn is so vigorous, it will grow more roots as they are destroyed. Please refer to the following website for information on promoting healthy lawn growth: https://omafra.gov.on.ca/english/crops/facts/08-017.htm
The nematode Steinernema carpocapsae is a parasite of white grubs. It is available from your local nursery as a biological control for white grub. The use of this nematode control agent requires that the soil be kept very moist to support the nematode growth. It is very important that the application instructions for this product be followed closely, as nematodes are living organisms that can be killed through improper handling, rendering the control ineffective. The following website contains detailed information on grubs: https://www.omafra.gov.on.ca/english/crops/facts/08-023w.htm