As summer begins to wind down, Montana homeowners, gardeners, landscapers, and nursery operators should keep an eye out for Japanese beetles (Popillia japonica). This invasive insect is a serious plant pest that can damage a wide variety of trees, shrubs, flowers, fruits, vegetables, and turfgrass. Japanese beetles have become established in the Billings area, but preventing their spread to new locations remains an important priority for Montana. Japanese beetles have a wide host range. Adults feed on numerous plant species, with roses, grapes, cherries, apples, raspberries, and lindens among their preferred hosts. Adults typically emerge from mid to late July and remain active through September. Their feeding creates a characteristic “skeletonized” appearance, where the tissue between leaf veins is consumed while the veins remain intact. Heavy feeding can cause significant defoliation and plant stress. Why Fall Is Important While the adult beetles may be disappearing by late September, the problem does not necessarily end. Female beetles lay eggs in the soil, particularly in lawns and other grassy areas. The eggs hatch and the developing grubs feed on plant roots throughout the late summer and fall. As temperatures drop, the larger grubs move deeper into the soil to overwinter. This makes late summer and early fall an important time to monitor turfgrass and take action when Japanese beetles are confirmed. Look for irregular patches of yellowing, thinning, or dying grass. A simple “tug test” can help identify possible grub damage—if sections of turf pull away easily from the soil, investigate beneath the sod for grubs. Keep in mind that several other Montana beetle species also produce white grubs, so proper identification is important. Prevention Starts with Movement One of the most important things Montana residents can do is avoid accidentally transporting Japanese beetles or their larvae. The beetle's soil-dwelling life stage creates particular concerns with nursery stock, potted plants, turf, and soil. When purchasing or moving plants, pay attention to where they originated and avoid transporting potentially infested soil or plant material from areas known to have Japanese beetle populations. Nurseries and landscapers should follow Montana Department of Agriculture requirements for regulated material and should take particular care when handling plants and growing media. Homeowners should also inspect plants for adult beetles during the summer and report suspected Japanese beetles. Managing an Infestation Management should be based on confirming the pest and determining whether treatment is warranted. Chemical controls are available for both adults and grubs in Montana, but products and application methods change, so always consult the current pesticide label, Montana State University Extension or the Montana Department of Agriculture before treating. Fall treatments targeting grubs are generally most effective before the larvae move deeper into the soil for winter. Japanese beetle traps can be useful for monitoring, but they should be used carefully. The pheromone used in traps can attract beetles from considerable distances and may actually increase beetle activity around plants if traps are placed incorrectly. Traps are therefore better considered a monitoring tool than a stand-alone solution. If You Find a Suspected Japanese Beetle If you find a beetle that you suspect is Japanese beetle, collect a specimen if possible and preserve it in rubbing alcohol. Record the location, date, host plant, and other relevant information. Suspected specimens can be submitted to the Montana State University Schutter Diagnostic Lab or the Montana Department of Agriculture for identification. You can also report through the iNaturalist app. Go to www.iNaturalist.org or scan the QR code! Japanese beetle may be small, but its potential impact is large. Early detection and preventing the movement of beetles and infested soil or plant material are among Montana's best tools for keeping this invasive pest from becoming more widespread. As fall approaches, take a few minutes to inspect your lawn, landscape plants, and nursery stock—and report anything suspicious.