BIOLOGICAL CONTROL OF GARLIC MUSTARD (ALLIARIA PETIOLATA) AND BUCKTHORN: AN UPDATE

Laura Van Riper, Minnesota Department of Natural Resources
Luke Skinner, Minnesota Department of Natural Resources
Elizabeth Katovich, University of Minnesota
Roger Becker, University of Minnesota
David Ragsdale, University of Minnesota
Hariet Hinz, CABI Biosciences, Delemont, Switzerland
Esther Gerber, CABI Biosciences, Delemont, Switzerland
Andre Gassman, CABI Biosciences, Delemont, Switzerland
Bernd Blossey, Cornell University

Garlic mustard (Alliaria petiolata) and European/common buckthorn (Rhamnus cathartica) are non-native invasive plants that severely threaten native plant communities and degrade wildlife habitat. The LCCMR and MN DNR have supported research focused on development of biological control as a long-term management strategy for these species. This presentation will give an update on these research programs. Biocontrol could provide a long-term strategy for managing these invasive plants. Extensive host specificity testing on a potential biocontrol agent of garlic mustard, the stem and crown-boring weevil, Ceutorhynchus scrobicollis, has been completed at CABI Bioscience in Switzerland and at the University of Minnesota. Results of these tests indicate that C. scrobicollis is a highly specific herbivore. After completion of a series of vigorous host range tests, an application was submitted to the Technical Advisory Group (TAG) for Biocontrol of Weeds for approval for field release of C. scrobicollis and researchers are now testing some additional native mustards at reviewers' request.

In anticipation of biocontrol agents becoming available for garlic mustard, 12 long-term monitoring sites were established in MN, including one at Warner Nature Center. Garlic mustard monitoring data from 2005 to 2009 showed that garlic mustard populations can vary considerably from year to year. Garlic mustard plants are occurring at high population densities (mean densities up to 133 adult plants/m² and 720 seedlings/m²) and are currently experiencing very little herbivore attack in Minnesota. Buckthorn biocontrol research carried out in 2007–09 concentrated on a leaf-feeding moth, a leaf-margin gall psyllid, and a seed-feeding midge as potential biocontrol agents. The moth was found to lack enough host-specificity and was eliminated from consideration as a biocontrol agent. Host-specificity testing will continue for the leaf gall psyllid as larvae did not develop on the North American Rhamnus species tested. One complication is that the phytoplasma 'Candidatus Phytoplasma rhamni' has been detected in the leaf gall psyllid. Future work will explore the implications of this phytoplasma for using the leaf-gall psyllid as a biocontrol agent. Future work will concentrate on 3 promising potential biocontrol agents, 2 psyllids and the midge.

Suggestions for Reading

Email Laura Van Riper for PDF files

Van Riper, Laura C., Roger L. Becker, Luke C. Skinner. 2010. Population biology of garlic mustard (Alliaria petiolata) in Minnesota hardwood forests. Invasive Plant Science and Management 3: 48-59.

Gassmann, A., I. Tosevski, and L. Skinner. 2008. Use of native range surveys to determine the potential host range of arthropod herbivores for biological control of two related weed species, Rhamnus cathartica and Frangula alnus. Biological Control 45:11-20.