The American rose chafer* (Macrodactylus subspinosus) is slender pale green to tan beetle with long orange legs. Although it is native to North America, its distribution is fairly irregular: you may have a major problem with it while a neighbor just down the road has never even seen it. It can be found anywhere east of the Rockies.
*The European rose chafer or green rose chafer (Cetonia aurata), metallic green in color, is a different species and is not found in North America.
Where it is present, the rose chafer can cause a lot of damage, devouring the leaves and flowers of roses. It may eat flowers entirely, while it can skeletonize foliage, leaving only the veins. Moreover, in spite of its name, the rose chafer is far from limited to roses, and will readily consume many other plants, including ivies, Japanese lilacs, hydrangeas, mountain ashes, Boston ivy, grapes, spireas, elderberries, peonies (flowers), brambles, cabbages, strawberries, apples, hollyhocks, cinquefoils, irises, elms, oaks, birches and hawthorns.
Stop Gap Measures
It is pretty much impossible to entirely eliminate chafers while the adults are already feeding on your plants, which will be in from late May to mid-July in most regions. The best you can expect is to reduce their numbers to the point where they cause little damage.
Probably the easiest way of controlling the adults is to knock them off the plant into a pail of soapy water or to suck them up with a handheld vacuum (then dump the prisoners into soapy water). For best results, do this in the morning when they are less active.
There are also traps designed specifically for rose chafers that give off a pheromone that attracts them. I have never seen these traps in stores, but you can obtain them from organic insect control specialists, like Nic Natural Insect Control. It is important to place these traps at least 30 feet (9 m) away from any plants the adults like to feed on, perhaps in the middle of a vast lawn or in a parking lot, because while they readily attract chafers into the vicinity of the trap, only a minority of them actually enter it. Then any chafers not caught will damage nearby plants that suit their diet.
For long-term control, you have to work on either reducing the chafer’s egg-laying ability or on reducing the number of larvae.
Rose chafers prefer to lay their eggs in sandy soil, preferably in dry, sunny spots covered in grass or weeds, especially lawns. They lay less abundantly in lawns that contain a significant proportion of clover. They dislike and will usually avoid rich, moist soils and shady spots.
To discourage them, you might want to redo your lawn by covering it with a good 6 inches (15 cm) of quality sand-free topsoil, then resowing with a mixture of lawn grasses and clover. Or grow a clover lawn. You can also try planting shrubs, trees, and tall perennials to shade the soil. Obviously, it would help if all your neighbors did the same, as the adults do fly, although they rarely travel far.
The larval stage of the beetle is a white C-shaped grub that lives in the soil. It is hard to distinguish from the grubs of Japanese beetles or May beetles (June beetles), which also live in lawns under much the same conditions. Nematodes designed to control white grubs will help control all types of white grub, including those of the rose chafer. Beneficial nematodes are readily available in most garden centers or can be ordered from various organic insect control specialists.
There is only one generation of rose chafer per year. After 3 to 6 weeks of damage, the infestation will end as suddenly as it began. Usually affected plants quickly recuperate, producing new leaves, and soon you can no longer see the damage. However, by then the chafers may have already ruined that summer’s blooms or fruit.
Curiously, rose chafers are said to be toxic to chickens, so you might want to keep your hens locked up when they are present!
No Host Plants, No Problem!
The most laidback way to control rose chafer? Every year, eliminate the 3 or 4 plants most seriously attacked, replacing them with species that are not affected (you’ll see which ones in your garden). In just a few years, your yard will no longer offer rose chafers anything interesting and they’ll go elsewhere!