Abstract

Third instar European chafer (EC), Rhizotrogus majalis (Razoumowsky), were found to be killing field-grown Rhododendrons ‘P.J.M.’ and Eastern hemlocks in two commercial nurseries in northeastern Ohio. Apparently, 1 or 2 grubs per plant were sufficient to severely damage young plants (rhododendrons). Subsurface applications of Dursban TNP were tested as rescue treatments against the grubs in these fields. Three novel single-point subsurface applicators were tested for delivery of Dursban in the rhododendron trial. A subsurface treatment of Dursban TNP was compared to surface applied drench treatments of Dursban TNP and Dylox 80 T & O in the hemlock trial. We found that EC grubs killed young plants of both species by removing most of the fibrous roots and/or girdling the stems. The subsurface treatments of Dursban TNP, significantly reduced (95%) the number of EC grubs compared to untreated hemlocks and rhododendrons when treatments were applied early or late fall, respectively. There were no differences in suppression of grubs among the applicators in the rhododendron trial.