Do you have animals digging up your lawn, crows congregating and pecking in the grass or have you found shallow tunnels exposed after the snow melted?
These are all signs that your lawn is the home for a rather large community of grubs. After a mild winter with only shallow ground frost, grub damage is a predictable and unfortunate
Because lawns are actively growing when grubs do most of their damage, we typically don’t see problems in our lawns during the summer or the fall. The grubs end up weakening the plant enough that winter survival of the grass is compromised which is why we see all the damage in the spring.
On this chart, we really get a good idea of what’s happening with the grubs during the year. The life cycle of the grub begins with eggs laid in July by adult June Bugs, European Chafers or Japanese Beetles. Each species is slightly different, but for the purposes of control and management, they are all the same.
The grubs visible in the spring are at the largest larvae stage. When the soil warms in the spring, they come closer to the surface after the winter dormant period and do a little munching on fibrous grass roots. The damage seen in the spring, however, is the damage from the previous year. The appetite of the grubs in the spring is relatively minor and grass can typically survive this limited damage in April. The grubs then begin to pupate in the soil as plants start to grow. The adult beetle then emerges from the soil around June.
It is then that we need to brace ourselves for the sights and sounds of the rather heavy and ungainly insects bumping and attaching themselves to our window screens. At this point the adult beetle can become an annoyance in the garden, though its effects are less of a problem in our regions than the larvae is.
After feeding for a time, the adult beetle then lays her eggs back in the soil and those eggs hatch in June/July. This is the point where grubs are most susceptible to various control methods. The egg hatches and becomes a larva which feeds on grass roots. The larvae go through a few “growth spurts”, called instars, and become progressively bigger. For the rest of the summer, the larvae feed on grass roots and grow and then burrow down deep into the soil for the winter and thus the cycle repeats.
White grubs do the most damage at these times:
June beetle grub:
- Year 1 – August through September
- Year 2 – April through September
- Year 3 – April through May
European chafer grub:
- Year 1 – March through April
- Year 2 – September through November
Japanese beetle grub:
- Year 1 – April through June
- Year 2 – September through October
Prior to the Ontario Pesticide Ban in 2009, the time to control grubs was during their small larva stage when they reside close to the surface in late July until mid-August when the next generation of newly-hatched grubs has begun.
In Ontario, we have very few options left for grub control. Well, effectively one: Parasitic Nematodes – a microscopic worm that seeks out grubs and kills them. Products like GrubOut (water based Sevin) or commercial products (like Merit) were banned as of April 22, 2009. Control can be very difficult because the grubs are located beneath the thatch layer of the turf and the nematodes need to make their way through this layer to contact and kill the grub.
Also, nematodes are a fussy bunch of bugs. A small package can contain up to 50 million of these worms. They get diluted in water and are applied with a hose end sprayer. Their effectiveness is not 100% but it is typically effective enough to strike enough of a balance that the grub population is reduced to the point your lawn suffers little to no damage.
However, there are some rather specific conditions to nematodes. First, the soil needs to be 15 degrees Celsius or else they will die. Second, they travel in water so they need lots of water to get into the ground. Third, they are killed by ultra-violet light from the Sun. With all these conditions, it makes Nematodes sound rather difficult.
My suggestion with Nematodes: Stand out in the rain on a warm June day and water your lawn with Nematodes. You look like a dork, but it covers off all the conditions — the soil is warm, Mother Nature is providing water and you don’t often get sun and rain together. It’s not a perfect solution, but it seems to be the best option for the home-owner.
Your other option is to repair your lawn from grub damage by either re-seeding or laying sod. Your choice will depend upon the extent of the damage and the size of your wallet. Seeds will be slower to germinate in early spring because the soil is still cool and during the time of soil exposure, weed seeds will have the opportunity to invade and germinate so hand-pull weeds as you see them emerge.
The benefits of choosing seeding over sod, however, is the ability to select the type of grass (fescues, rye, Kentucky Bluegrass or a mixture of these), the low cost and the ease of handling. Choose any of Wright’s Feeds ‘N Needs grass seed mixes which contain an endophytic fungus that grubs find unappetizing and repels them.
Rake damaged area to remove the dead sod. Uniformly broadcast a good quality lawn seed. Ensure that the seed is in contact with the soil by raking it in. Spread topsoil or compost over the seeded area. A light rolling will help firm the seed bed and insure the seeds are in contact with the soil. The seedbed should be kept moist until the seeds have germinated and the seedlings are well established. This may require a light sprinkling several times a day. Once the seedlings are established, routine mowing and regular lawn maintenance can resume.
Sod will provide an immediate solution to the bare ground but it may contain a higher percentage of Kentucky Bluegrass which will only thrive in sunny locations plus it’s more expensive and requires a bit more handling. Prepare the soil as for seeding but allow for the thickness of the sod to be at the same level as the existing lawn. Maintain good moisture until the sod is well rooted.
Healthy, vigorously growing lawns can tolerate more grub feeding than stressed lawns because damage to one root is compensated for by others. Adequate leaf tissue also provides nutrients and energy to repair root damage. Remove excessive thatch, and aerate compacted soil areas to ensure proper drainage. A mechanized soil aerator with spikes or spiked sandals can also help kill some of the grubs.
Beetles prefer to lay eggs in closely cropped lawns, so raise your summer mowing height to 6 to 8 cm (2.5 to 3 inches). Leave lawn clippings after mowing because their slow release of nitrogen favours the decomposition of thatch by microorganisms. Use fertilizer with high potassium and adequate nitrogen.
If you detect grubs during the warm, dry periods of your lawn’s growing season, irrigate and fertilize your lawn to maintain the turf vigour and to compensate for the root feeding damage. Apply a top dressing of top soil, lawn dresser mix or triple mix and overseed with an endophyte-enhanced grass seed mix. Deep, infrequent irrigation encourages deep-rooted drought-tolerant lawns. Water no more than once per week and water until at least 2 cm (1 inch) of water collects in a container placed on your lawn or for about one hour.
Grub control is more preventative than anything. If there have been grub problems in your neighbourhood, I highly suggest the dorky Nematode application annually in June.
And one last bit of advice — a thick and healthy lawn attracts fewer bugs (and weeds don’t like the competition, for that matter, either). Keep your lawn thick and healthy — fertilize, overseed and water regularly — and you will have less chances of developing problems with grubs, pests and weeds.