Conditions throughout Illinois continue to favor heavy infestations and resulting damage of Japanese beetle grubs and annual white grubs in irrigated turf areas. The majority of these eggs will have hatched in central and southern Illinois within the first few days of August. Hatch should be completed in northern Illinois by about August 10.
Applications of imidacloprid (Merit) or halofeno-zide (Mach 2) made during July or earlier should provide control. These insecticides can still be used until about August 10. After that, grub injury may be possible before the insecticide provides control. Because these insecticides take about 3 weeks to kill the grubs, clientele may discover live grubs. Once grubs have hatched, trichlorfon (Dylox) is usually the insecticide of choice, providing control in about 3 days. Because it is a short-lived insecticide, grubs should have hatched before it is applied.
We are receiving some reports of large white grubs being found during tree planting and other soil work. These are probably 3-year white grubs, May beetle larvae, in their second year. They pupate in late summer, emerge as adults, and stay underground through the winter to emerge next spring. Usually there are not enough to cause serious damage. Marginally damaging numbers can be managed by watering the plants--helping them grow roots faster than the grubs can eat them. In general, insecticides are not very effective against large white grubs. Dylox may be the best choice of the three listed here.
Adult grub beetles are being seen, sometimes in large numbers, in scattered areas in Illinois. These beetles look like masked chafers (annual white grub) about 1/2-inch, tan June beetles. They are probably a species of May beetle (Phyllophaga), but identification has not been confirmed. Masked chafer emergence this late in the summer is unlikely. The genus Phyllophaga contains many species, with a variety of beetle appearances and life cycles.