The Problem with White Grubs
For months now I have been struggling to balance my love for nature with the damage that White Grubs cause to my lawn. The upside is that I get birds digging them out, and racoons and skunks searching for them and leaving telltale small holes and patches of exposed soil where they found their quarry. The downside is my lawn is a mess. I shy away from using insecticides to kill them because insecticides are indiscriminate in their effect and will kill all the good bugs as well as the bad. The offshoot of this is that the grasses in my lawn were so severely weakened by the grubs that crabgrass got a foothold and destroyed much of the rest of my lawn. The upside is that the grubs didn’t have any food so they’ve gone elsewhere. I won – I guess? So what are these little creatures and why can they be so devastating? White Grubs are the larval stage of a number of large beetles, such as Japanese Beetle, June Bug and Masked Chafer. They are a member of the Scarab beetle family, which includes the famous dung beetles – although ours don’t roll poop here like those other critters do. We really don’t see the larval (grub) stage because it lives and feeds underground for most of its life cycle, only emerging briefly in May and June as adults to breed and then lay eggs. The larvae start off as tiny inconspicuous white-bodied grubs with brown heads and legs that live, for much of the year, just under the root zone of a grassy lawn. As they mature, they slowly get bigger. Like other insects that go through this complete metamorphosis (i.e. egg, larva, pupa and adult), they shed their skin and then develop a new one slightly larger to accommodate their larger size. They will do this several times until finally they are ready to morph into an adult. To accomplish this, they enter a pupal stage, where the grub forms a hard case that surrounds it and inside the larva slowly changes structure and form and becomes a coppery-coloured beetle! Their life cycle can span one, two or even three years, depending on the species involved. In our area they have a 12 month life cycle that spans parts of two calendar years. Essentially, in June and July, the adults breed and the female lays her 10-30 eggs in the soil over a 1-4 week period. After 14-21 days, the eggs hatch, and for the rest of that season, the grubs develop as mentioned above. When conditions get cold in the late fall, they move deeper underground and stay there below the frost line until the following spring when conditions improve so they can move upwards through the soil column and resume feeding. In late May or early June they pupate and away we go again. So how do you know if you have these little critters? Well I mentioned one obvious clue – the small holes and torn up turf, which are usually most evident in August and September. Damaged lawns first show gradual thinning, yellowing and weakening of the turf, followed by the appearance of scattered, irregular dead patches that may increase in size over time. Apparently healthy turf areas may exhibit sudden wilting and weakening of the plants, and the turf may feel spongy as you walk over the infested area. The roots of sod that is heavily grub-damaged are often severed just below the surface so one can pull it loose from the soil as if lifting a carpet and in so doing you will likely see the grubs just below the root zone of the damaged grass. If your turf had a serious grub problem last year, the adult beetles are likely to return and reinfest the same areas this year. So what can you do? Well short of using pesticides there is no easy solution unfortunately. I will continue this dialogue next time as there is some hope but it will take a bit of effort on your part.
Geoff Carpentier is a published author, expedition guide and environmental consultant. Visit Geoff on-line at www.avocetnatureservices.com and on LinkedIn and Facebook.