Berks County Cooperative Extension -

GRUB CONTROL

What and when.

Several species of grubs damage turf, Japanese beetles being by far the most common. Merit (commonly sold as Grub-Ex®) is an effective agent for grub control. It should be applied from mid-May to mid-August for control of Japanese beetle and masked chafer grubs. If Merit is applied earlier, it will likely run out of steam by the time the new crop of grubs arrives in late July to early August. Merit is not effective against the overwintered grubs that surface in April and May.

Control of other pests.

If Merit is applied to lawns from mid-May to early June, it will help control several pests and thus eliminate the need for any other surface insecticide application (such as Dursban found in the third step of four-step programs). This early application will eliminate billbugs, take out the first generation of chinch bugs and knock out the first generation of sod webworms. It also appears to suppress the June generation of black cutworms.

Source: Penn State Home Gardener Headlines (Berks County), Summer 1999 citing Shetlar, The Pest Newsletter, May 1999