Relative Resistance or Susceptibility of Landscape-suitable
Elms (Ulmus spp.) to Multiple Insect Pests
Daniel A. Potter and Carl T. Redmond
Abstract: The National Elm Trial is a cooperative project to assess landscape suitability of Dutch elm disease-resistant elms (Ulmus spp.) in various regions of the United States. Researchers evaluated 20 cultivars of American, Asian, and hybrid elms for relative resistance or susceptibility to multiple insect pests in central Kentucky over seven years. Ratings for Japanese beetle, European elm flea weevil (EEFW), and several other pests were previously published. This paper reports data for seven additional pests, including honeydew-excreting scale insects (Parthenolecanium corni, Eriococcus spuria, and Pulvinaria innumerabilis), leaf-distorting woolly elm and woolly apple aphids (Eriosoma spp.), elm cockscomb gall aphid (Colopha ulmicola), and an invasive weevil (Oedophrys hilleri) not previously known to damage elms. Rankings for all 12 of the monitored pests are summarized. Most U. americana cultivars were relatively susceptible to the scale insects and likewise, Eriosoma spp. and C. ulmicola only infested the American elms. O. hilleri is a new state record for Kentucky. Its adults, active in mid- to late summer, chewed notches in edges of leaves. Cultivars of the Asian species U. parvifolia and U. propinqua, including ‘Athena Classic Lacebark’, ‘Everclear Lacebark’, ‘Emer II Allee’, and ‘Emerald Sunshine’ were top-rated for insect resistance. They were nearly pest-free except for foliar damage by EEFW, to which nearly all elms were susceptible. Insect resistance should be considered when re-introducing elms to urban landscapes. The data may help city foresters, landscapers, and others re-introducing elms to urban landscapes to select relatively pest-free cultivars requiring minimal inputs for insect control.
Keywords: Cockscomb gall Aphid; Dutch Elm Disease; Eriococcus spuria; Eriosoma spp.; European Elm Flea Weevil; National Elm Trial;
Oedophrys hilleri; Parthenolecanium corni; Ulmus spp.