Drought-damage aside, if your lawn is looking torn-up lately with holes everywhere, it’s likely infested with beetle grubs.
Grubs are fat, creamy-white, worm-like larvae that curl up in a C-shape while they feed on grass roots an inch or so below the lawn surface.
While they can kill whole sections of turfgrass by eating the roots out from underneath, what’s making the holes now are assorted critters trying to feast on the grubs.
Grubs make nutritious (and apparently tasty) snacks to three other species in particular — skunks, raccoons, and birds.
All three can scratch, burrow, and peck into the soil during grub-hunting excursions, sometimes causing significant lawn damage in their own right.
Grubs are in peak season now, although they’re likely not going to be as widespread in this year’s dry lawns as in wetter-summer years. (Eggs and newly hatched grubs don’t survive as well in bone-dry soil.)
Eggs laid in late summer — primarily by Japanese beetles and masked chafer beetles — spend September and most of October feeding on grass and plant roots.
As the weather cools, they burrow deeper into the soil, where they overwinter in a mostly dormant stage.
When enough grubs are present, patches of lawn begin to brown and die in early fall. The telltale sign is when these brown patches pull up easily like loose pieces of carpet since the anchoring roots underneath are now in grub stomachs.
Grubs feed on plant roots in garden beds, too, but they favor sunny lawns and do most of their damage there.
To solve the current lawn-hole problem, Ohio State University entomologist emeritus Dr. Dave Shetlar recommends Dylox (trichlorfon) as an insecticide that quickly kills grubs. (Carbaryl is an alternative.)
With the grubs dead, critter feeding will taper off.
Shetlar says one option is to rake off any dead grass and hope the damaged areas will fill in well enough for your liking.
However, weeds often beat grass to the punch, so a second option is overseeding damaged areas with fresh grass seed. October still allows enough time for seed to germinate and develop at least some roots before the ground freezes.
Perennial ryegrass is the fastest of our cool-season grass species to germinate, especially if you keep seed damp and we get an extended warm fall.
To nail down a diagnosis of grubs, poke around the soil a few inches down where you’re seeing damage and to just outside the perimeter of the damage. Since grubs are active now, you’ll probably see colonies of them slowly squiggling around as you unearth them.
A few here and there are normal and not destructive, but if you’re seeing six or more per square foot, that’s enough to kill lawn patches.
If you have a grub problem, here are four options other than the kill-now insecticide approach:
1.) Pacifist approach. Pull up the dead turf pieces, plant grass seed (or sod), and hope next year isn’t as good of a year for grub life. Violent variation: smash as many grubs as you can before reseeding.
2.) Go with the flow. Now that the lawn’s gone anyway, dig up the ground, and turn it into a garden. Thank the grubs for doing some of the lawn-removing work for you.
3.) Organic approaches. Milky disease is a grub-sickening bacterium sold in granular or powder form. Spread it one to six times over two years (depending on the version), and it’s supposed to be effective for 10 to 20 years without hurting pets, people, earthworms, fish, etc. Down sides: it only works against Japanese beetle grubs, and research has shown variable effectiveness against even them.
A newer bacteria-based granular product is grubGone, which uses a different bacterium (Bacillus thuringiensis galleriae) to disrupt the digestive ability of a variety of beetle grubs without harming off-target beneficials such as bees and birds.
GrubGone is best applied in mid-summer to kill just-hatched grubs, but the maker (Phyllom BioProducts) says it’s also effective against larger feeding grubs in early fall.
A third organic option for early fall is scattering granular, microscopic grub-eating organisms called “nematodes” over infested lawns. Once the nematodes are watered into the lawn, they feed on grubs without harming birds, bees, butterflies, and most anything else other than grubs. They’re effective for one season.
Look for nematodes that go by the name of Heterohabditis or Steinernema.
4.) Procrastinator special. Go watch a football game and worry about fixing the dead lawn next spring.
If you run into grub trouble regularly and/or would just rather head them off each year rather than react to damage, the other grub-control route is applying grub-preventer products.
These are granular products that are timed to go on the lawn just before eggs hatch. That’s because the chemicals in them are most effective against young grubs — not the bigger and more mature stage that’s active now and again for a few weeks in late spring before the grubs pupate into the next generation of adult beetles.
Grub-preventers are effective mainly only into mid-July, so timing is important.
These products usually contain one of four active ingredients: imidacloprid, thiamethoxam, clothianidin or chlorantraniliprole. They’re sold under a variety of brand names, usually in granular form.
For the first three above, ideal timing application in central Pennsylvania is mid-June to mid-July, while application in May is better for chlorantraniliprole, according to research at Michigan State University.
Michigan State also says that chlorantraniliprole is the only one of the four that’s not very toxic to bees.
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