ARS | Publication request: FALL SUBSURFACE INSECTICIDE TREATMENTS AGAINST EUROPEAN CHAFER GRUBS DAMAGING FIELD-GROWN ORNAMENTALS

Submitted to: Journal of Environmental Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 15, 2004
Publication Date: March 1, 2004
Repository URL: http://www.ars.usda.gov/sp2UserFiles/Place/36071000/Publications/Reding149041_2005_FallSub.pdf
Citation: Reding, M.E., Klein, M.G., Brazee, R.D., Krause, C.R. 2004. Fall subsurface insecticide treatments against european chafer grubs damaging field-grown ornamentals. Journal of Environmental Horticulture. 22(1):32-36.

Interpretive Summary: European chafer (EC) is an exotic invasive species of white grub, which is considered a pest primarily in turf. However, recent reports from growers and researchers suggest that EC is becoming a serious pest of field-grown ornamentals. During Fall 2001 and 2002, we were notified of damaging infestations of white grubs in two commercial nurseries in Lake county, Ohio. Surveys of these nurseries revealed that the grubs were EC. The grubs were feeding on the roots and killing the plants. The infestations in these nurseries were severe enough to require remedial action. Data from these surveys suggested that one or two grubs were able to kill a young plant. These infestations provided us with the opportunity to test some novel application equipment under 'real life' conditions. Each site was about two acres. We applied subsurface treatments of Dursban TNP against EC in 2001 and 2002. In 2001, we compared three novel subsurface applicators. In 2002, we compared subsurface treatments of insecticide with surface applied drenches. In 2001, all three applicator treatments reduced the numbers of grubs by about 95% compared to untreated plants. In 2002, the subsurface treatment of Dursban TNP reduced the numbers of grubs by about 95% compared to untreated trees and a surface applied drench of Dursban TNP. Both growers were satisfied that the effectiveness of the treatments offset the time required for application. This research shows that EC can be a serious pest in commercial nurseries. It also indicates that subsurface treatments of insecticides can be very effective against certain species of white grubs.

Technical Abstract: Third instar European chafer (EC), Rhizotrogus majalis (Razoumowsky), were found to be killing field-grown PJM rhododendrons and Eastern hemlocks in two commercial nurseries in northeastern Ohio. Subsurface applications of Dursban TNP were tested as rescue treatments against the grubs in these fields. Three novel 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. Apparently, 1 or 2 grubs per plant were sufficient to kill young plants. 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.