United States Department of Agriculture BIOLOGY AND BIOLOGICAL CONTROL OF COMMON GORSE AND SCOTCH BROOM Forest Forest Health Technology FHTET-2017-01 Service Enterprise Team September 2017 The Forest Health Technology Enterprise Team (FHTET) was created in 1995 by the Deputy Chief for State and Private Forestry, USDA Forest Service, to develop and deliver technologies to protect and improve the health of American forests. This book was published by FHTET as part of the technology transfer series. This publication is available online at: http://bugwoodcloud.org/resource/pdf/commongorse.pdf How to cite this publication: Andreas, J.E., R.L. Winston, E.M. Coombs, T.W. Miller, M.J. Pitcairn, C.B. Randall, S. Turner, and W. Williams. 2017. Biology and Biological Control of Scotch Broom and Gorse. USDA Forest Service, Forest Health Technology Enterprise Team, Morgantown, West Virginia. FHTET-2017-01. Cover Photo Credits Top: Common gorse (Forest and Kim Starr, Starr Environmental, bugwood.org). Left of common gorse, top to bottom: Agonopterix umbellana (Janet Graham); Exapion ulicis (Janet Graham); Sericothrips staphylinus (Fritzi Grevstad, Oregon State University); Tetranychus lintearius (Eric Coombs, Oregon Department of Agriculture, bugwood.org). Bottom: Scotch broom (����������������������������������������������Eric Coombs, Oregon Department of Agriculture, bugwood.org). Right of Scotch broom, ��������������top to bottom: Bruchidius villosus (Jennifer Andreas, Washington State University Extension); Exapion fuscirostre (Laura Parsons, University of Idaho, bugwood.org); Leucoptera spartifoliella (Eric Coombs, Oregon Department of Agriculture, bugwood.org). References to pesticides appear in this publication. Publication of these statements does not constitute endorsement or CAUTION: PESTICIDES recommendation of them by the U.S. Department of Agriculture, nor does it imply that uses discussed have been registered. Use of most pesticides is regulated by state and federal laws. Applicable regulations must be obtained from the appropriate regulatory agency prior to their use. CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish and other wildlife if they are not handled and applied properly. Use all pesticides selectively and carefully. Follow recommended practices given on the label for use and disposal of pesticides and pesticide containers. The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. 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Persons with disabilities who require alternative means of communication for program information (e.g., Braille, large print, audiotape, American Sign Language, etc.) should contact the responsible Agency or USDA’s TARGET Center at (202) 720-2600 (voice and TTY) or contact USDA through the Federal Relay Service at (800) 877-8339. Additionally, program information may be made available in languages other than English. To file a program discrimination complaint, complete the USDA Program Discrimination Complaint Form, AD-3027, found online at http://www.ascr.usda.gov/complaint_filing_cust.html and at any USDA office or write a letter addressed to USDA and provide in the letter all of the information requested in the form. To request a copy of the complaint form, call (866) 632-9992. Submit your completed form or letter to USDA by: (1) mail: U.S. Department of Agriculture, Office of the Assistant Secretary for Civil Rights, 1400 Independence Avenue, SW, Washington, D.C. 20250- 9410; (2) fax: (202) 690-7442; or (3) email: [email protected] . Federal Recycling Program Printed on recycled paper BIOLOGY AND BIOLOGICAL CONTROL OF COMMON GORSE AND SCOTCH BROOM Jennifer E. Andreas, Rachel L. Winston, Eric M. Coombs, Timothy W. Miller, Michael J. Pitcairn, Carol Bell Randall, Susan Turner, and Wyatt Williams For additional copies of this publication, contact: Jennifer E. Andreas Richard Reardon Integrated Weed Control Program U.S. Forest Service Washington State University Extension Forest Health Technology Enterprise Team 2606 W. Pioneer 180 Canfield Street Puyallup WA 98371 Morgantown, WV 26505 253-445-4657 304-285-1566 [email protected] [email protected] This publication is available online at http://bugwoodcloud.org/resource/pdf/commongorse.pdf Authors Jennifer E. Andreas, Invasive Plant Biocontrol Specialist, Integrated Weed Control Project, Washington State University Extension, Puyallup, WA; [email protected]; www.invasives.wsu.edu Rachel L. Winston, Environmental Consultant, MIA Consulting LLC, Sandpoint, ID; [email protected] Eric M. Coombs, Biological Control Entomologist (retired), Oregon Department of Agriculture Plant Division, Salem, OR; [email protected] Timothy W. Miller, Extension Weed Scientist, Washington State University Extension, Mount Vernon, WA; [email protected] Michael J. Pitcairn, Senior Environmental Scientist, Pest Detection/ Emergency Projects Branch, California Department of Food & Agriculture, Sacramento, CA; [email protected] Carol Bell Randall, Entomologist, USDA Forest Service, Forest Health Protection, Coeur d’Alene, ID; [email protected] Susan Turner, Invasive Plant Biocontrol Specialist, Ministry of Forests, Lands and Natural Resource Operations, Kamloops, British Columbia; [email protected] Wyatt Williams, Invasive Species Specialist, Oregon Department of Forestry Private Forests Division, Salem, OR; [email protected]; http://tinyurl.com/ODF-ForestHealth Acknowledgments We are very grateful to Fritzi Grevstad (Oregon State University), Richard Hill (Landcare Research), Todd Neel (USDA FS), and Paul Pratt (USDA ARS WRRC) for help with specific sections of this manual, and to Janis Matsunaga (Hawaii Department of Agriculture) and Pat Conant (Hawaii Department of Agriculture, retired) for help gathering information. We would like to thank all of the county weed coordinators and land managers that we have worked with through the years for encouraging us to develop our series of “Biology and Biological Control ” manuals. Some of the material in this manual was adapted from past manuals in the series; we wish to acknowledge the authors of the original material. The layout of this manual was designed by Wendy W. Harding. We appreciate all of the photographers who granted permission for the use of photos. We also extend our gratitude to Richard Reardon (Forest Service-Forest Health Technology Enterprise Team or FHTET) for producing this guide. Contents Chapter 1: Introduction . 1 Overview . 1 Responding to the Threat of Gorse and Scotch Broom . 3 The Invasion Curve . 4 Management of Gorse and Scotch Broom Infestations . 6 Classical Biological Control of Weeds . 7 Code of Best Practices for Classical Biological Control of Weeds . 9 Biological Control of Gorse and Scotch Broom . 10 Is Biological Control of Gorse and Scotch Broom Right for You? . 11 About This Manual . 12 Chapter 2: Getting to Know Gorse and Broom . 14 Taxonomy and Related Species . 14 Gorse . 15 Classification . 15 History . 15 Description . 15 Biology and Ecology . 19 Habitat . 19 Distribution . 20 Comments . 20 Commonly Confused Species . 22 Scotch Broom . 23 Classification . 23 History . 23 Description . 23 Biology and Ecology . 28 Habitat . 28 Distribution . 28 Comments . 30 Commonly Confused Species . 30 Broom and Gorse Comparison Tables . 31-32 Chapter 3: Biology of Gorse and Scotch Broom Biological Control Agents . 33 Insects . 33 Beetles . 35 Butterflies and Moths . 35 Thrips . 35 True Bugs . 35 Mites . 36 Fungi . 36 Gorse and Scotch Broom Biological Control Agents (General) . 37 Contents Gorse Biological Control Agents (North America and Hawaii) . 37 (continued) Exapion ulicis . 37 Gorse seed weevil Tetranychus lintearius . 40 Gorse spider mite Gorse Biological Control Agents (Hawaii Only) . 42 Agonopterix umbellana . 42 Gorse soft shoot moth Apion sp. 44 Gorse seed weevil Pempelia genistella . 45 Gorse colonial hard shoot moth Sericothrips staphylinus . 45 Gorse thrips Stenopteriapion scutellare . 47 Gorse stem-mining weevil Uromyces pisi f. sp. europaei . 48 Gorse rust Scotch Broom Biological Control Agents . 48 Bruchidius villosus . 48 Broom seed beetle Exapion fuscirostre . 54 Scotch broom seed weevil Leucoptera spartifoliella . 57 Scotch broom twig miner Unapproved Natural Enemies of Gorse and Scotch Broom . 60 Aceria genistae . 60 Agonopterix nervosa . 62 Arytainilla spartiophila . 63 Comparison Tables . 65-69 Chapter 4: Elements of a Gorse and Scotch Broom Biological Control Program . 70 Before You Begin . 70 Determining the Scope of the Problem . 71 Defining Goals and Objectives