Susceptibility of Purple-Versus Greenleaved Cultivars of Woody Landscape Plants to the Japanese Beetle

Abstract

Twenty-six purple- or green-leaved cultivars representing 12 species of woody landscape plants were evaluated in the field for defoliation by Japanese beetles (Popillia japonica Newman) over three growing seasons. We further evaluated the hypothesis that, within closely-related plants, purple cultivars generally are preferred over green ones by comparing beetles' consumption of foliage in laboratory choice tests and their orientation to painted silk tree models baited with Japanese beetle lures. Cultivars of Prunus cerasifera Ehrh. and hybrids of that species [e.g., Prunus ×cistena (Hansen) Koehne, Prunus ×blireiana André] were more heavily damaged than nearly all other plants tested. Among maples, Acer palmatum Thunb. `Bloodgood' and A. platanoides L. `Deborah' and `Fairview' were especially susceptible. None of the cultivars of Berberis thunbergii DC, Cercis canadensis L., Cotinus coggygria Scop., or Fagus sylvatica L. were heavily damaged, regardless of foliage color. In the choice tests, purple Norway maples were preferred over green ones in three of four comparisons, but preference varied within the other plant genera. In fact, more beetles oriented to green-leaved tree models than to purple ones. Our results indicate that within a genus, purple-leaved plants do not necessarily sustain more damage than green-leaved ones. Widespread use of certain purple-leaved cultivars of generally susceptible plant species probably contributes to the perception that purpleleaved plants, overall, are preferred. Purple-leaved cultivars of redbud, European beech, smoketree, and barberry, or the purple-leaved Prunus virginiana L. `Canada Red' or Malus ×hybrida Lemoine `Jomarie' may be suitable substitutes for more susceptible purple-leaved plants in landscapes where Japanese beetles are a concern.