Fall subsurface insecticide treatments control European chafer grubs damaging field-grown nursery crops.
Third instar European chafer (EC), Rhizotrogus majalis [Amphimallon majalis], were found killing field-grown rhododendron P.J.M. (hybrid of Rhododendron carolinianum × Rhododendron dauricum var. sempervirens) and Eastern hemlocks (Tsuga canadensis) in two commercial nurseries in northeastern Ohio, USA. Apparently, 1 or 2 grubs per plant were sufficient to severely damage young plants (rhododendrons). Subsurface applications of Dursban TNP (chlorpyrifos) were evaluated as rescue treatments against the grubs in these fields. Three novel single-point subsurface applicators were also evaluated for the 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 and O (trichlorfon) in the hemlock trial. The 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 autumn, respectively. There were no differences in the suppression of grubs among the applicators in the rhododendron trial.