Relative resistance to defoliation by Japanese beetles (Popillia japonica Newman) was compared among 28 cultivars of flowering crabapples (Malus spp.), 8 species and cultivars of lindens (Tilia spp.), and 53 cultivars of hybrid tea, floribunda, and grandiflora roses (Rosa spp.) in multi-year field evaluations in central Kentucky. Defoliation of crabapples ranged from >95% to <10% among cultivars at the same site, with cultivars ‘Jewelberry’, ‘Louisa’, Malus baccata ‘Jackii’, and ‘Harvest Gold’ having greatest resistance. All lindens were severely damaged in years with heavy beetle flight, but Tilia americana ‘Legend’ and T. tomentosa ‘Sterling’ were less damaged than the others in years with moderate beetle pressure. When beetles were abundant, all rose cultivars were severely defoliated regardless of bloom color. Under more moderate beetle pressure, however, ‘Milestone’, ‘Dynasty’, and ‘Headliner’ hybrid tea roses sustained less damage than others. Damage among individual plants within cultivars often varied widely on a given date, reflecting the beetles' tendency to aggregate on foliage with prior feeding damage.
This research was supported in part by grants from The Horticultural Research Institute, 1250 I. Street, N.W., Suite 500, Washington DC 20005, and by USDA SRIPM grant 96-34103-3346. Technical assistance of C. Harper, B. Kreuger, J. Scannell, L. Terry, and A. Walston, and donation of plant materials by Bear Creek Gardens (Medford, OR), Conard-Pyle Co. (West Grove, PA), Lake County Nursery (Perry, OH), Mollers Nursery (Gresham, OR), and J.F. Schmidt & Son Co. (Boring, OR) is gratefully acknowledged.
2To whom all correspondence should be sent.
3Department of Horticulture and Landscape Architecture, University of Kentucky.