I’ve gotten a few calls recently asking when I should treat for grub worms to avoid having so many Japanese beetles next year. The answer is – you can’t.

Apparently most folks are fully aware that Japanese beetles, green June beetles, and a few similar beetles spend most of their lives in the soil feeding on the roots of plants or just feeding on organic matter (green June beetles). We call these things white grubs most of the year. The Japanese beetle grub will feed extensively on the roots of grass. Sometimes there are enough of them (5-10 per square foot) to justify use of an insecticide to protect the lawn. But not often.

If you need to protect the lawn there are two strategies:

1) For areas with a history of grub infestations and damage to the lawn, a preventive

approach is justified. In these cases a product like Merit or Advanced Lawn Grub Control should be applied before eggs are laid, i.e. Now.

2) For other areas, a lawn inspection in September is more appropriate. Cut a

one-foot square of lawn, fold it back, and examine the root zone. If you find 5-10 grubs per square foot, then you can use an insecticide such as Sevin. You can use the biological Milky Spore, or you can introduce an entomogenous (insect feeding) nematode (Heterorhabditis spp.) These strategies are most effective in the early fall before the grubs have eaten your lawn rather than after.

But – here’s Catch-22 – neither approach is likely to reduce the number of adult Japanese beetles you’ll encounter next year. They fly. They fly from a mile away just to feed on your delicious roses. Nice of you to provide them.

And I don’t have any really good strategy for dealing with adult Japanese beetles. No matter what you spray, or how many you handpick and drown, there are usually more tomorrow until they finish mating and die. They are legion. Resistance seems futile. Even if you spray your rose buds this morning, they can be feeding undeterred inside the open blossom this afternoon.

Most people seem to have found by now that traps are more effective at attracting beetles than at catching them. Place them far away from susceptible plants. Neem and spinosad products offer little protection. Insecticides that may kill some of the pests include Sevin, malathion, and Merit. Fine netting may help keep them off.

Fortunately, the onslaught should be over soon.

If Al Cooke
Extension Agent - Agriculture
Chatham County Center
North Carolina Cooperative Extension Service
N C State University
PO Box 279
Pittsboro, NC 27312
919.542.8202, FAX 919.542.8246
al_cooke@ncsu.edu http://chatham.ces.ncsu.edu/staff/acooke/home.html