Field Guide for the Biological Control of Weeds in the Northwest

This guide focuses on the most problematic weeds in western North America for which there are at least some biocontrol agents established and/or available. Multiple photos and descriptions of each weed included in this guide emphasize key identification traits and plant ecology. For each weed included in this guide, all biocontrol agents released or currently found in North America are described individually. Photos highlighting key identification features and damage are included. The release history, current status, and recommended use of each biocontrol agent are described in detail. Because current impact and recommendations often vary between the US and Canada, information is presented separately.

Efficacy Quick Reference Guide 4

Introduction 8

About This Field Guide. 8

Biological Control of Weeds 10

Selected Plant Features 12

Life Cycle 12

Duration 12

Typical Leaf Arrangement and Margination 13

Flower Heads 13

Biological Control Agent Life Cycles 14

Insects 14

Mites 16

Nematodes 16

Fungi  16

Scientific Name Changes  17

Collection Methods 18

Transport Considerations 20

Releasing Biocontrol Agents 22

Monitoring Biocontrol Agents  24

Additional Considerations  27

Weed Biocontrol Systems 28 Weed species are arranged first by flower color, then grouped by related species and listed alphabetically. All biocontrol agents introduced or established on each weed are included in that weed’s section, listed according to efficacy on the target weed. To look up a particular biocontrol agent or weed, refer to the index at the back of this guide.

Pinkish-Purple Flowers  28

Knapweeds 28

Diffuse knapweed, Centaurea diffusa 30

Spotted knapweed, Centaurea stoebe  32

Purple loosestrife, Lythrum salicariam 62

Eurasian watermilfoil, Myriophyllum spicatum 70

Swallow-worts 74

Black swallow-wort, Vincetoxicum nigrum 74

Pale swallow-wort, Vincetoxicum rossicum 76

Thistles 80

Bull thistle, Cirsium vulgare 82

Canada thistle, Cirsium arvense 84

Musk thistle, Carduus nutans 86

Waterhyacinth, Eichhornia crassipes 108

Yellow Flowers 118

Table of Contents Tansy ragwort, Jacobaea vulgaris 118

Common St. Johnswort, Hypericum perforatum130

Toadflaxes142

Dalmatian toadflax, Linaria dalmatica 142

Yellow toadflax, Linaria vulgaris 144

Green Flowers160

Mile-a-minute weed, Persicaria perfoliata 160

Spurges 164

Cypress spurge, Euphorbia crassipes 164

Leafy spurge, Euphorbia esula 166

Tree-of-heaven, Ailanthus altissima 190

White Flowers 194

Alligatorweed, Alternanthera philoxeroides 194

Scentless chamomile, Tripleurospermum inodorum 202

Poison hemlock, Conium maculatum 210

Hydrilla, Hydrilla verticillata 214

Knotweeds 222

Bohemian knotweed, Fallopia xbohemica 222

Giant knotweed, Fallopia sachalinensis 224

Japanese knotweed, Fallopia japonica 226

Melaleuca, Melaleuca quinquenervia 230

Multiflora rose, Rosa multiflora  240

Brazilian peppertree, Schinus terebinthifolius 244

Tropical soda apple, Solanum viarum 248

Waterlettuce, Pistia stratiotes  254

Does not or Rarely Flowers 260

Air-potato, Dioscorea bulbifera 260

Old World climbing fern, Lygodium microphyllum 264

Salvinias 272

Common salvinia, Salvinia minima 272

Giant salvinia, Salvinia molesta 274

Current Studies in Weed Biocontrol 278

Glossary 282

Selected References 288

Appendix 324

Biocontrol Agent Monitoring Form 324

Vegetation Monitoring Form 325

Species Index 326

Farmers, conservationists, agriculture experts and consultants, agriculture colleges and universities, agriculture professors and instructors, agriculture students, weed control experts and manufacturers,