The Oriental beetle, Anomala orientalis, is an invasive species and a significant pest of turfgrass and ornamental plants, particularly in the northeastern United States. Effectively eliminating this pest requires a targeted strategy addressing both the above-ground adult and the highly destructive subterranean larval stage. This information provides actionable methods for managing and controlling Oriental beetle populations in your landscape.
Recognizing Oriental Beetles and Their Damage
Damage caused by Oriental beetles is often confused with other pests or environmental stress. The adult beetle is small, measuring about one-half inch in length, with an oval shape characteristic of scarab beetles. Its coloration is highly variable, ranging from solid black or tan to a mottled pattern of black and brown patches on its wing covers.
The true source of turf damage is the grub, the cream-colored, C-shaped larva that lives beneath the soil surface. These grubs grow up to three-quarters of an inch long and are largely indistinguishable from other white grubs. Larvae feed voraciously on the fine rootlets of turfgrass, typically in the top two inches of the soil profile.
Infestations manifest as irregular brown patches of turf that wilt and yellow even when the soil contains adequate moisture. A defining symptom is the ability to easily lift or roll back the affected turf like a loose carpet, revealing the grubs underneath. Secondary damage often occurs when animals like raccoons, skunks, and birds tear up the lawn while foraging for the concentrated grub population.
Cultural and Physical Management Techniques
Simple changes to landscape maintenance can significantly reduce the attractiveness of your lawn to egg-laying females. Oriental beetle adults emerge from mid-June through July, and females prefer to deposit their eggs in moist, well-watered soil. Reducing or temporarily suspending irrigation during this peak adult activity period makes the soil less hospitable for egg development.
If possible, allowing the lawn to dry out during the three-to-four-week egg-laying period can lower the number of future grubs without relying on chemical treatments. Maintaining a taller mowing height also encourages deeper root growth, which allows the turf to better tolerate feeding damage from smaller grub populations.
Physical removal offers a non-chemical option for reducing the adult population, which is most active in the evening. A simple and effective trap involves suspending a light bulb over a pan of soapy water placed on the ground. The beetles are attracted to the light, fall into the water, and are drowned by the detergent, preventing them from mating and laying eggs.
Biological and Chemical Treatment Timing
Targeting the larval stage is the most effective way to eliminate Oriental beetles, and control depends on precise timing. The young grub, hatching in late July and early August, is the most vulnerable life stage. Treatments applied too early may degrade before the grubs are present, while treatments applied too late will encounter larger, less susceptible third-instar grubs that appear by late August.
Biologically, entomopathogenic nematodes, specifically Heterorhabditis bacteriophora (Hb), are a viable control option for the young grubs. These microscopic, parasitic roundworms actively seek out grubs in the soil and infect them. Nematodes should be applied when the soil is moist and temperatures are moderate, and they must be watered into the soil immediately after application to move them into the root zone.
Chemical control involves preventative and curative strategies. Preventative insecticides, such as products containing imidacloprid, are systemic and should be applied in June or early July to establish a barrier before the eggs hatch. Curative treatments, which are faster-acting contact insecticides, are best applied between late July and mid-August when feeding damage is first noticed and the grubs are still small. Both chemical and biological products require at least one-half to one inch of irrigation immediately following application to move the active ingredient down to the grubs in the root zone.
Preventing Future Infestations
Long-term management focuses on building a resilient turf ecosystem that is more tolerant of grub feeding. When establishing a new lawn or overseeding an existing one, selecting the right grass species is advantageous. Among cool-season grasses, tall fescue is the most tolerant species because its deeper root system helps it withstand damage better than susceptible varieties like perennial ryegrass.
Maintaining proper soil moisture is a significant preventative measure. Avoiding frequent, light watering that keeps the soil surface damp will deter females from laying eggs. Deep, infrequent watering encourages the development of a robust root system, which increases the lawn’s tolerance to any feeding that does occur.
Monitoring adult beetle activity helps predict the need for broad-spectrum treatments. Pheromone traps, which use a chemical lure to attract male beetles, can be used to gauge population levels and pinpoint the start of the mating and egg-laying season in mid-summer. Using these traps for monitoring, rather than mass trapping, provides an early warning that directs future cultural and treatment applications.