Description
Introduction
The rapid spread of invasive plants threatens natural resources across the United States, and the Pacific Northwest is no exception. Invasive species displace natural plant communities and have the following impacts:
- Degraded and destroyed wildlife habitat
- Reduced plant and animal diversity
- Impaired land productivity
- Obstructed waterways and reduced water levels
- Erosion
- Fire hazards
- Restricted recreational activities
- Reduced land values
- Need for costly restoration
Prevention is by far the most effective approach in dealing with invasive plants. For best results, incorporate as many preventive practices as feasible into your land management strategy:
- Monitor property for invasive plant species.
- Avoid introduction of invasive species:
- Do not plant known invasive species or use wildflower mixes in gardens or landscaping.
- Avoid driving through infested areas.
- Clean equipment, vehicles, and materials before leaving infested sites.
- Use only weed-free seed, soil, and feed.
- Limit soil disturbances and revegetate disturbed ground with desirable species.
- Contain animals that have fed on weed-infested forage for at least 3 days to allow pass-through of weed seeds.
- Dispose of aquarium plants away from natural waterways.
- Monitor beneath bird feeders for invasive plants.
- Contain established weed populations by treating perimeter plants.
- Restore and maintain healthy native plant communities.
The control of any weed begins with early detection. The objective of this guide is to aid in the identification and control of invasive weeds found in eastern Washington. For further information about noxious weed identification, control options, and control requirements under state law, please contact your county’s noxious weed coordinator or a Washington State University Extension educator.
Always wear protective clothing, including gloves, when pulling weeds. Many weed species contain toxins that may cause mild to severe dermatitis. If using herbicides, it is important to take additional precautions.
Use Herbicides With Caution!
- Before using any chemical, always read the label carefully and closely follow the instructions. Warnings include wearing protective clothing and safety devices when storing, handling, and applying herbicides.
- Some chemicals may not be registered in your area or may have restricted use, so beware of usage restrictions.
- Be aware of your legal responsibilities as a pesticide applicator. You may be liable for injury or damage resulting from herbicide use.
- This handbook is not intended as a complete guide to herbicide use.
Washington State University and its employees are in no way responsible for the misuse of any products or damages caused by any products mentioned in this publication to control the specified weeds.
Index of Invasive Plants by Flower Color
White| Common Name | Scientific Name |
|---|---|
| Diffuse knapweed | Centaurea diffusa Lam. |
| Hoary cress | Cardaria draba (L.) Desv.; Lepidium draba L. |
| Japanese knotweed; giant knotweed; Bohemian knotweed | Polygonum cuspidatum Siebold & Zucc.; Fallopia sachalinensis (F. Schmidt ex Maxim.) Ronse Decr.; Polygonum x bohemicum (J. Chrtek & Chrtkovß) Zika & Jacobson |
| Oxeye daisy | Leucanthemum vulgare Lam. |
| Perennial pepperweed | Lepidium latifolium L. |
| Poison hemlock | Conium maculatum L. |
| Common Name | Scientific Name |
|---|---|
| Black henbane | Hyoscyamus niger L. |
| Common groundsel | Senecio vulgaris L. |
| Common tansy | Tanecetum vulgare L. |
| Dalmatian toadflax | Linaria dalmatica (L.) Mill. |
| Leafy spurge | Euphorbia esula L. |
| Meadow hawkweed | Hieracium caespitosum Dumort |
| Puncturevine | Tribulus terrestris L. |
| Rush skeletonweed | Chondrilla juncea L. |
| Scotch broom | Cytisus scoparius (L.) Link |
| St. Johnswort | Hypericum perforatum L. |
| Sulfur cinquefoil | Potentilla recta L. |
| White bryony | Bryonia alba L. |
| Yellow starthistle | Centaurea solstitialis L. |
| Yellow toadflax | Linaria vulgaris P. Miller |
| Common Name | Scientific Name |
|---|---|
| Orange hawkweed | Hieracium aurantiacum L. |
| Common Name | Scientific Name |
|---|---|
| Musk thistle | Carduus nutans L. |
| Plumeless thistle | Carduus acanthoides L. |
| Russian knapweed | Acroptilon repens (L.) DC.; Centaurea repens L. |
| Saltcedar/tamarisk | Tamarix ramosissima Ledeb. |
| Spotted knapweed | Centaurea bierbersteinii DC.; Centaurea maculosa Lam.; Centaurea stoebe L. ssp. micranthos (Gugler) Hayek |
| Common Name | Scientific Name |
|---|---|
| Canada thistle | Cirsium arvense (L.) Scop. |
| Houndstongue | Cynoglossum officinale L. |
| Purple loosetrife | Lythrum salicaria L. |
| Scotch thistle | Onopordum acanthium L. |
| Common Name | Scientific Name |
|---|---|
| Common bugloss | Anchusa officinalis L. |
| Viper’s bugloss | Echium vulgare L. |
| Common Name | Scientific Name |
|---|---|
| Kochia | Kochia scoparia (L.) Schrad |
| Russian thistle | Salsola tragus L.; Salsola kali L.; Salsola iberica Sennen & Pau |
Black Henbane
Hyoscyamus Niger L.
Solanaceae
Nightshade
Common Names: insane root, stinking nightshade, fetid nightshade, hog’s beam, hogbean, hogbane, poison tobacco
Origin: Europe
Description
Historically, black henbane has been used medicinally and as an ornamental. It is an annual or biennial plant that reproduces solely by seed. The plant forms large rosettes with alternate, serrated leaves, and develops a fleshy taproot. Mature plants grow up to 3 feet tall. The stems of a mature plant are erect, thick, coarse to tough, and widely branched. Black henbane has abundant, foul-smelling foliage that is covered with fine, sticky hairs. The leaves are alternate, oblong to ovate, and coarsely toothed to shallowly lobed. Flowers can be seen from spring to early fall. The flowers are funnel-shaped, 5-lobed, yellowish with deep purple veins and throats, and arranged in spike-like clusters. The fruit is pineapple-shaped, approximately 1 inch long, with capsules that contain hundreds of tiny, dark seeds. A single plant can produce up to a half million seeds that are highly germinable and remain viable in the soil for several years. Black henbane is commonly found in rangeland, pastures, roadsides, and waste areas. The plant contains alkaloids that can cause livestock poisoning, although it is unpalatable and therefore seldom grazed. It is largely considered poisonous to humans, but some people still value it for medicinal properties.
Management
Efforts to control black henbane should be timed to precede seed production. Small infestations of black henbane plants can be pulled, cut, or dug. Moist soil helps to remove the entire tap root system. Any seedpods should be bagged and removed from the site to avoid further seed dispersal. Mechanical methods, such as mowing, can be difficult if the plant is mature because of its thick, coarse stem. Herbicides can provide excellent control and should be applied at the rosette to bolt stage, but before flowering. No biological insect agents are currently available for control of black henbane.
Seedlings. Jan Samanek, State Phytosanitary Administration, Bugwood.org
Rosette. Jan Samanek, State Phytosanitary Administration, Bugwood.org
Flowers and seed capsules. Steve Dewey, Utah State University, Bugwood.org
Canada Thistle
Cirsium arvense (L.) Scop.
Asteraceae
Sunflower
Common Names: Canadian thistle, creeping thistle, field thistle, small-flower thistle
Origin: Europe and Asia
Description
Canada thistle is a dioecious herbaceous perennial that spreads primarily by an extensive, rhizomatous root system that gives rise to numerous aerial shoots. Mature plants can grow up to 5 feet tall. The stems are slender, ridged, branched, and somewhat hairy at maturity. The leaves are alternate, lance-shaped, and irregularly lobed with spiny, toothed margins. Purple to white flowers surrounded by spineless bracts appear between June and October and occur in clusters at branch ends. The small, slightly tapered fruit (achene) has a feathery pappus that enables wind dispersal. The seeds are abundant and can remain viable in the soil for 20 years. Canada thistle is an aggressive invader of a variety of open habitats and can form dense stands that shade out and displace desirable vegetation. Canada thistle can result in reduced forage, as its spiny leaves render it unpalatable to most livestock.
Management
Because many thistle species exist in North America, Canada thistle should be accurately identified before control is attempted. In managing the plant, control practices are most effective when combined. Regular tillage and planting of competitive crops can keep Canada thistle in check, although tillage also produces root fragments, giving rise to new plants. Repetitive mowing before seed set—preferably at early bud stage when food reserves are at their lowest—will weaken the plants and prevent seed production. Several herbicides are available for either targeted or broad application, depending on the presence of desirable vegetation. Repeated applications are often necessary. Biological control agents include the stem-boring weevil Ceutorhynchus litura and the thistle stem gall fly Urophora cardui. Though neither insect will kill plants outright, both can reduce Canada thistle populations over time, particularly in conjunction with good plant competition. Sheep, goats, and some cattle have been known to graze Canada thistle and provide some control; however, other control measures should also be used.
Seedling (young rosette). Phil Westra, Colorado State University, Bugwood.org
Foliage. Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
Infestation. Steve Dewey, Utah State University, Bugwood.org
Ceutorhynchus litura adult and larvae. Noah Poritz, Bio-control.com
Urophora cardui. Norman E. Rees, USDA Agricultural Research Service, Bugwood.org
Common bugloss
Anchusa officinalis L.
Boraginaceae
Borage
Common Names: common anchusa, alkanet, blue bugloss
Origin: Europe
Description
Common bugloss is a deep-rooted perennial that spreads by seed. A rosette appears the first year, followed by a flowering stalk the second year. Mature plants can have multiple flower stalks. The stems are robust, hairy, and grow to 2 feet tall at maturity. Leaves are lance-shaped, fleshy, and covered with stiff hairs. Basal leaves have a leaf stalk (petiole) that becomes progressively smaller up the stem to a point where the upper leaves are sessile (no petiole). The flower stems start out coiled like a fiddleneck, but unfold and straighten out as each flower bud opens. Purplish-blue, 5-lobed flowers appear from straight tubes rather than the curved tubes of annual bugloss. The fruit is a 4-chambered nutlet, with 1 seed per nutlet. A mature plant can produce up to 1,000 seeds in a single season. Common bugloss invades alfalfa fields, pastures, rangeland, and disturbed areas. Its succulent leaves and stalks can cause mold in baled hay.
Management
Cultural control will not eliminate common bugloss populations. To gain control of common bugloss, seed production must be prevented, so pulling, digging, or cultivating should take place before flowering. Removing most of the taproot improves the effectiveness of these methods. Herbicides can be used and are most effective when applied early, particularly before bud stage, and should include a surfactant to help penetrate the hairy leaf surface. Biological control agents are not available for common bugloss.
Rosette. Richard Old, XID Services, Inc., Bugwood.org
Common groundsel
Senecio vulgaris L.
Asteraceae
Sunflower
Common Names: old-man-in-the-spring, ragwort, grimsel
Origin: Europe
Description
Common groundsel is usually a winter annual, but can also be biennial and grow in all seasons depending on climate. The plant has a taproot with a fibrous root system, and grows upright, branched, and up to 18 inches tall. Basal leaves are usually purplish on the underside, somewhat fleshy, and attach to the stem with a short stalk. The stem leaves clasp at the base and are alternate, mostly hairless, and pinnately divided or irregularly toothed. Flower heads composed of small yellow disk flowers but no ray flowers (petals) occur in clusters at stem ends and have distinct black-tipped bracts around the base. The seeds are abundant, long, slender, ridged, and when mature, are tipped with a tuft of silky white hairs (pappus) that aid wind dispersal. The plant contains 4 pyrrolizidine alkaloids, which can cause irreversible liver damage in livestock if consumed in sufficient quantity. Common groundsel is found in disturbed sites along roadsides, waste areas, cultivated fields, and gardens.
Management
Good management practices that promote competitive plant growth can reduce groundsel. Because of the plant’s prolific seed production, common groundsel is best controlled by eliminating it before it has a chance to flower. Monitoring for seedlings should begin in early fall. Shallow tilling or hoeing of young plants will control the plant if done before seed set. While herbicides are not very effective for common groundsel infestations in alfalfa and other legumes, they can be effectively used in other crops. Despite the plant’s toxicity, sheep and goats are sometimes used to graze it since they have rumen bacteria that detoxify the alkaloids. Larvae of the cinnabar moth Tyria jacobaeae will eat groundsel, but are not around long enough to provide control. The rust fungus Puccinia lagenophorae is showing promise as a biological control agent, and is being further researched.
Rosette. Lynn Sosnoskie, University of Georgia, Bugwood.org
Flower. Steve Dewey, Utah State University, Bugwood.org
Common tansy
Tanecetum vulgare L.
Asteraceae
Sunflower
Common Names: garden tansy, golden buttons
Origin: Eurasia
Description
Common tansy, a pungent-smelling perennial herb, was brought to the United States for horticultural and medicinal purposes. The plant reproduces both by seed and creeping roots. Stems are erect, brown or purplish-red, and dotted with glands. Mature plants grow from 2–6 feet tall. Fern-like leaves are alternate and deeply divided into numerous, individual leaflets with toothed margins. Flowering occurs from July to the fall, varying by location. The yellow and button-like flowers without ray florets appear in dense, flat-topped clusters at the top of the plant. The seeds are yellowish-brown, 5-angled achenes, with no pappus. Common tansy is distinguishable from tansy ragwort (Senecio jacobaea), which is non-aromatic and has ray florets and seeds with pappus. Common tansy plants invade disturbed areas, pastures, ditch banks, and riparian areas. This prolific plant contains alkaloids and is potentially toxic to humans and most animals. Cattle and horses seldom graze the pungent plant, allowing common tansy to outcompete desirable pasture plants.
Management
As with other rhizomatous perennials, a combination of control measures is most effective in managing common tansy. Small infestations of common tansy can be hand-dug, but the entire root system must be removed since plants can resprout from severed roots. Gloves and other protective clothing should be worn to prevent absorption of toxins through the skin. Although tillage can produce root pieces that result in new plants, common tansy does not persist in regularly cultivated lands. Repetitive mowing before the flowering stage can prevent seed production, but other measures (such as chemicals) should also be used to achieve control. Numerous herbicides are available to manage common tansy. Applications made between the bud and bloom stages tend to provide the best results. No insect biological control agents are currently available, although research is ongoing. Sheep and goats can be used to graze common tansy.
Plant. Richard Old, XID Services, Inc., Bugwood.org
Flower. Steve Dewey, Utah State University, Bugwood.org
Infestation. Steve Dewey, Utah State University, Bugwood.org
Dalmatian toadflax
Linaria dalmatica (L.) Mill.
Scrophulariaceae
Figwort
Common Names: broadleaf toadflax, wild snapdragon, butter and eggs
Origin: Mediterranean regions of Europe to Central Asia
Description
Dalmatian toadflax is an attractive herbaceous plant that was likely introduced to North America as an ornamental. It is a short-lived perennial that reproduces both by seed and rootstocks. Dalmatian toadflax has taproots and a creeping root system, reaching depths up to 10 feet and extending laterally up to 10 feet from the parent plant. New plants can form vegetatively from adventitious buds on the horizontal roots, as well as from root fragments as small as ½ inch. The plant grows 1–3 feet tall. The stems are woody at the base, but become smooth, waxy, and often branching toward the top. Waxy, light green to bluish-green leaves are broad, ovate to heart-shaped, and clasp the stem. Dalmatian toadflax flowers, resembling those of a snapdragon, are bright yellow and 2-lipped, with an orange-bearded throat and long spur. The flowers occur individually in a long, dense, terminal cluster and mature from the lower part of the stem upwards. During a single season, a plant can produce half a million seeds that can remain viable for 10 years. The seeds, produced in a 2-celled capsule, are irregularly-shaped, sharply angular, slightly winged, and dark-colored. Dalmatian toadflax contains a poisonous glucoside, but reports of livestock poisoning are rare because the plant is unpalatable. Dalmatian toadflax is an aggressive colonizer that invades disturbed sites, including roadsides, clear cuts, rangelands, and croplands. It can outcompete desirable species and significantly reduce forage.
Management
Control strategies should be aimed at preventing seed production, depleting root reserves, and eliminating seedlings before they can propagate vegetatively. Cultural control, including seeding of desirable competitive species, should be integrated into a management strategy. Physical and mechanical control measures can be used to effectively prevent seed production and exhaust root reserves if done repeatedly and/or combined with other control methods. Hand-pulling small infestations of Dalmatian toadflax can be effective if all root fragments are bagged and removed from the site. Another control technique sometimes used is intensive cultivation, which extends over a 2-year period beginning in early June and is repeated so that there are never more than 10 days of green growth. To prevent the spread of root fragments, tillage equipment should be cleaned on site. Although herbicide efficacy can vary, herbicides are often the most successful control method available for toadflax. In general, herbicide labels recommend that toadflax plants be sprayed at the flowering stage, although treatments may have to be repeated. Herbicides should be rotated annually to prevent resistance. Several insect biological controls are available, including the defoliating moth Calophasia lunula, flower-feeding beetle Brachypterolus pulicarius, and seed capsule-feeding weevils Gymnetron antirrhini and G. netum. While these agents may be beneficial, the stem-mining weevil Mecinus janthinus is the recommended first choice because it has demonstrated excellent control of toadflax across Washington and throughout the western region according to WSU integrated weed management expert Jennifer Andreas. Sheep grazing may also help suppress stands of Dalmatian toadflax and limit seed production.
Flower. Bob Nowierski, Montana State University, Bugwood.org
Nonflowering, prostrate Dalmatian toadflax shoots produced mid- to late summer. Linda Wilson, University of Idaho, Bugwood.org
Infestation. Steve Dewey, Utah State University, Bugwood.org
Mecinus janthinus adult. Noah Poritz, Bio-control.com
Calophasia lunula adult. Bob Richard, USDA APHIS PPQ, Bugwood.org
Brachypterolus pulicarius adult. Susan Turner, British Columbia Ministry of Forests, Bugwood.org
Gymnetron antirrhini adult. Eric Coombs, Oregon Department of Agriculture, Bugwood.org
Diffuse knapweed
Centaurea diffusa Lam.
Asteraceae
Sunflower
Common Names: spreading knapweed, tumble knapweed, white knapweed
Origin: Eastern Mediterranean and Western Asia
Description
Diffuse knapweed is normally a biennial, but may live for several years as a rosette before flowering. The low-lying rosette is made up of deeply lobed basal leaves more finely divided than those of spotted knapweed and similar to carrot leaves. When diffuse knapweed bolts, it puts up a single upright stem, typically 1–3 feet tall with numerous upward-spreading branches, giving the plant a bushy appearance. Stem leaves are alternate, stalkless, and progressively smaller and less divided up the stem. Flowers are generally white, occasionally pink-purple, urn-shaped, and appear alone or in small clusters at the ends of branches. Bracts on flower heads are stiff, spiny, and crab-like. Seeds are oblong, dark brown to gray, and remain viable for up to 10 years; they are spread when mature plants become windborne and tumble. Diffuse knapweed is a highly competitive and aggressive plant that grows under a wide range of conditions, but prefers arid and semiarid conditions, and can quickly infest large areas.
Management
Whichever control method is used, a revegetation plan must be implemented to prevent reinvasion of diffuse knapweed. Small infestations of diffuse knapweed can be hand-pulled (using gloves), but efficacy depends on removal of the entire crown before seed production. Removing the rosette and cutting 2–4 inches of the taproot is also effective. While mowing reportedly reduces seed production, it may merely delay it, so mowing should be followed with herbicide treatments. Deep cultivation can reduce knapweed. Accounts of livestock grazing knapweed vary; nevertheless, grazing alone does not provide control. More than a dozen biological control agents have been released in North America. The seed-feeding weevil Larinus minutus has caused widespread reductions of diffuse knapweed in Washington, Montana, and Oregon, particularly in conjunction with drought conditions. The root-mining beetles Cyphocleonus achates and Sphenoptera jugoslavica compoundthis impact. Some success has also been found with 2 ubiquitous seed-head flies, Urphora affinis and U. quadrifasciata, and the seed-head weevil Bangasternus fausti.
Rosette. Richard Old, XID Services, Inc., Bugwood.org
Flower. Cindy Roche, Bugwood.org
Larinus minutis. Dan Fagerlie, WSU Extension Tribal Relations Liason
Cyphocleonus achates. Laura Parsons, University of Idaho, Bugwood.org
Sphenoptera jugoslavica. Laura Parsons, University of Idaho, Bugwood.org
Hoary cress
Cardaria draba (L.) Desv., Lepidium draba L. or Cardaria Pubescens (C.A. Mey.) Jarmolenko
Brassicaceae
Mustard
Common Names: whitetop, globed-podded hoarycress, heart-podded hoarycress, pepperwort, peppergrass, whiteweed, pepperweed
Origin: Central Europe and Western Asia
Description
Hoary cress is a single-stemmed, deep-rooted perennial forb that grows up to 2 feet tall. The stems are generally erect, but can bend or lodge with age. Stems and leaves are grayish-green. The leaves are alternate, lance-shaped, and slightly irregular; lower leaves are stalked, while upper leaves clasp the stem with 2 ear-like lobes. Numerous flower branches and compact clusters of small, white, 4-petaled flowers give the plant a white, flat-topped appearance. The fruits are pods that are shaped somewhat like an inverted heart, which helps distinguish this species from other Cardaria species. Each fruit-pod usually contains 2 dark reddish-brown seeds that are rounded at one end and narrowed to a blunt point at the other. Hoary cress reproduces by seed but primarily spreads vegetatively by root segments. Even very small root fragments are capable of growth. The plant’s extensive root system consists of vertical and lateral roots, both of which produce adventitious buds that develop into rhizomes and new shoots. Within a 3-month period, roots can extend a foot from the stem and add nearly 50 new shoots and over 80 buds. Depending upon fall precipitation, plants may emerge in mid to late fall, but generally wait until early spring. Flowering occurs in late spring and seeds are set by mid-summer. Hoary cress is common in disturbed ground; disturbances such as cultivation and irrigation promote the plant’s spread and density. It prefers alkaline soils, but can grow in a variety of soil conditions.
Management
Preventative measures involve keeping machinery, hay, and crop seed free of contaminants (seeds and plant fragments). Because livestock can spread the plant, grazing should not occur during flowering and seed set. Mechanical control is effective only if the plant’s entire root system is removed. Because cultivation is a common cause of the plant’s spread, its effectiveness as a control measure depends on timing and persistence. Cultivation should start when the plant is at the bud or flowering stage and be repeated frequently throughout the growing season for several years to destroy the root system and deplete the seedbank. Mowing offers limited results. If mowing occurs before hoary cress sets seed, it can reduce plant biomass and seed production and slow the plant’s spread, but it does not provide long-term control and should be combined with other control methods (herbicides) to increase efficacy. Hoary cress can be effectively controlled with herbicides, often recommended to be applied at bud or bloom stage. Repeat treatments are often necessary. No biological control agents are currently available, although the stem gall-mining weevil Ceutorhynchus cardaria has demonstrated excellent host specificity at screenings and may be available within several years. Several other insects are also being investigated. Sheep and goats will readily graze hoary cress, but several years of grazing—each prior to seed set—may be needed for control.
Rosette. Steve Dewey, Utah State University, Bugwood.org
Plant. Chris Evans, River to River CWMA, Bugwood.org
Ceutorhynchus cardaria. Mark Schwarzländer, University of Idaho
