Starlings working dead patches of grass are searching for root-chewing grubs, which started the cycle of damage last fall and will continue feeding until they are ready to emerge as adult beetles in early summer.
Two culprits are to blame -- European chafer beetles and Japanese beetles. To determine if grubs are responsible for dead patches of turf, dig up a few shovels of soil at the edge of the dead spots and look for C-shaped grubs. If there are 10 or more grubs per square foot of turf, grubs are more than a nuisance.
European chafer beetles prefer dry soil, while Japanese beetles lay eggs in moist soil, notably irrigated lawns. Both damage turf roots, but adult Japanese beetles, identified by its metallic brown and green-colored body, also target landscape plants.
Spring feeding on turf roots wraps up in mid-May but resumes in fall and often with greater intensity, said Dave Smitley, an entomologist with Michigan State University.
“The peak time for grub feeding damage is usually in October, but you will see the damage any time in September or October when the soil is dry,’’ Smitley said. “It will only get worse through October as grubs grow larger and consume turf roots.’’
Strike Back At Grubs
There is still time to kill feeding grubs, but the window is closing. Feeding usually stops by mid-May as the white, C-shaped grubs get ready to emerge as adults.
Treat grub-infested lawns with products containing either carbaryl or trichlorfon, Smitley said. Products with carbaryl include Sevin, while trichlorfon is used in Dylox and Bayer Advanced 24 Hour Grub Control.
They can be used on spring feeding grubs between March and mid-May. The next opportunity to strike falls between Labor Day and Halloween.
This is a temporary solution, however, and does not work once grubs stop feeding. To get lasting control, apply a preventative product near the Fourth of July holiday when eggs are hatching or when grubs are small, Smitley said.
Preventative Treatments
Adult beetles start laying eggs in early-to-mid summer for the next generation of grubs. Eggs hatch in about two weeks and emerging grubs have voracious appetites. Products to control emerging grubs should contain imidacloprid or halofenozide, Smitley said.
Specific brands include Scotts Grub-Ex, Bayer Advanced Season Long Grub Control with Merit, Bayer Advanced Complete Insect Killer and Spectracide One Stop Once and Done.
“If applied in June or July and watered into the ground, these products will give 90 to 100 percent grub control,’’ Smitley said. Expect to spend between $35 and $62 to treat an average size lawn of about a quarter acre.
Natural Remedies
People not keen on chemical treatments should consider milky spore, a bacteria that destroys grubs by eating them from the inside. It primarily works on Japanese beetle larvae.
Milky spore is more expensive than conventional chemical treatments. Proponents say it provides long-term grub control and is safe for humans, pets and the environment.
Lawns with strong roots recover better from feeding damage. Turf experts recommend lawns be mowed at a height of 3-1/2 to 4 inches and properly fertilized to promote strong root development. Soils that are not compacted are more resistant to visible grub damage.
To lessen the presence of European chafer grubs, keep the lawn watered; about an inch per week through August, Smitley said. Females seek relatively dry lawns to lay eggs.
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