(Raymond Cloyd, KSU Entomology)
As many of you are well aware, Japanese beetle adults are out in full-force feeding on one of their favorite host plants…roses. The means of dealing with the adult stage of this insect pest are limited, however, and have been for many years, primarily relying on the use of insecticides. Japanese beetle, Popillia japonica is native to Japan and was first reported in the United States in 1916 in the state of New Jersey. Since then, it has spread throughout the country from Maine to Georgia becoming permanently established in nearly every state east of the Mississippi River and several states westward. Japanese beetles have been established in eastern Kansas. The adult is one of the most destructive insect pests of horticultural plants in both landscapes and gardens. The larvae or grub stage is a major turfgrass pest in home lawns, commercial settings, and golf courses.
Adult Japanese beetles emerge from the soil and live from 30 to 45 days feeding on plants over a four to six week period. They feed on many ornamental plants including trees, shrubs, vines, herbaceous annual and perennials, and of course—roses. Placement of plants in the landscape and volatiles emitted by plants are factors that may influence adult acceptance for feeding. Japanese beetle adults produce aggregation pheromones that attract individuals (both males and females) to the same feeding location. Adults may fly up to five miles to locate a feeding site; however, they tend to fly only short distances to feeding and egg-laying sites.
Japanese beetle adults feed through the upper leaf surface (epidermis) and leaf center (mesophyll), leaving the lower epidermis intact. They typically avoid feeding on tissue between leaf veins, which results in leaves appearing lacelike or skeletonized.
Adults are most active during warm days, feeding on plants that are exposed to sunlight throughout the day. This is likely why roses, which require at least six hours of direct sunlight, are such a susceptible host plant. They also tend to initiate feeding at the top of plants, migrating downward after depleting food sources. Japanese beetle adults congregate in large numbers on rose flowers. Although adult beetles feed primarily on flowers, they will also feed on leaves. Japanese beetle adults chew holes in flower buds, which prevent flowers from opening or cause petals to fall prematurely. In addition, adults will consume entire rose petals, and feed on the pollen of fully-opened flowers.
The management of Japanese beetle adults involves implementing a variety of cultural, physical, and chemical strategies.
Cultural: maintaining healthy roses through proper irrigation, fertility, mulching, and pruning is allows important in minimizing any type of “stress,: which may decrease susceptibility. Also, removing weeds such as smartweed (Polygonum spp.) that are attractive to Japanese beetle will at least alleviate infestations of adults.
Physical: Japanese beetle adults may be removed from roses by hand-picking or collecting prior to populations becoming extensive. The appropriate time to hand-pick or collect adult beetles is in the morning when ambient air temperatures are typically “cool.” Adults can be easily collected by placing a wide-mouthed jar or bucket containing rubbing alcohol (70% isopropyl alcohol) or soapy water underneath each adult, and then touching them. When adults are disturbed, they will fold their legs perpendicular to the body, and fall into the liquid and be killed. This procedure, when conducted daily or every-other-day, particularly after adults emerge, may significantly reduce plant damage. The use of Japanese beetle traps is not recommended since the floral lure and synthetically-derived sex pheromone tend to attract more adult beetles into an area than would “normally” occur. In addition, adult beetles may feed on roses before reaching the traps, which increases potential damage.
Chemical: contact insecticides are commonly used to kill Japanese beetle adults, and repeat applications are required; especially when populations are excessive. Thorough coverage of all plant parts will increase effectiveness of the application. The insecticide carbaryl (Sevin) and several pyrethroid-based insecticides including those containing bifenthrin or cyfluthrin as the active ingredient may be used to suppress populations of Japanese beetle adults. However, since most of these types of insecticides are harmful to many natural enemies (parasitoids and predators) their continual use may lead to secondary pest outbreaks (such as twospotted spider mite). Systemic insecticides, in general, are less effective because Japanese beetle adults have to feed on leaves and consume lethal concentrations of the active ingredient. If extensive populations are present then this may still result in damage to rose plants.
So, not much has changed over the past 20 years in regards to managing Japanese beetle adults on roses. Therefore, diligence is required in order to prevent adults from causing substantial damage to roses…and still make growing roses a favorite past-time.
Raymond A. Cloyd
Professor and Extension Specialist in Horticultural Entomology/Integrated Pest
Department of Entomology
Kansas State University
123 Waters Hall
Manhattan, KS 66506-4004
Phone: (785) 532-4750