Don’t Let the Size of Green June Beetles Intimidate You

Green June beetles Cotinus nitida have been flying in many areas across the Midwest and although they are harmless, their sheer size can be very intimidating to folks who don’t recognize them. These large, attractive, emerald and copper colored beetles are one of several species of scarab beetles whose larvae are known as annual white grubs. Of the insects belonging to this group Green June Beetles may be one of the most interesting, not only because of their charisma, but also because of their peculiar biology and behavior, reports Dr. Doug Richmond in the July 31 Turf Tips from Purdue Extension. Richmond is Associate Professor and Turfgrass Entomology Extension Specialist at Purdue.

Adults typically emerge from the soil during July and heavily infested areas may appear to swarm with activity as the beetles fly about during the day. Adults feed on a variety of ripe fruits and vegetables and may also be attracted to the sap oozing from wounded trees. They can also become turfgrass pests, especially the larvae, which feed on turfgrass roots.

Because green June beetle adults are attracted to high organic matter soils, thatch layers should be managed and kept at a minimum. Reduced use of compost topdressings and manure based-fertilizers may reduce the attractiveness of turf areas to egg-laying females.

If insecticides must be used, early instar grubs that are present in late July and early August are the best target because they are relatively easy to control. Any soil insecticide labeled for white grubs will be effective if the application is followed by enough irrigation to move the material into the thatch where the larvae are feeding.

Applications targeting later instar larvae should be left on the surface and not irrigated since these larvae come to the surface to feed at night. However, pre-treatment irrigation can encourage these larger larvae to come to the surface where the insecticide is deposited. A larvae can be 2 inches long. Neonicotinoid insecticides are sometimes not effective for controlling late instar green June beetle larvae. Carbaryl (Sevin) or trichlorfon (Dylox) are recommended in such cases.

It should be noted that insecticides applications targeting late instar larvae will often result in larvae dying on the surface. Mortality of large numbers of these larvae may create a problematic stench when conditions are conducive – take my word on this, reports Dr. Richmond.

Dr. Richmond’s post, which contains additional information about the Green June beetle along with some excellent images and a fascinating video taken by Dr. Cliff Sadof, can be accessed here.