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Glen Buschmann Slightly Wild Service P.O. Box 11464 Olympia, 98508

Weeds of South Puget Sound Prairies by Glen Buschmann

Abstract

While Scotch Broom may be the most apparent weed threat to the prairies of South Puget Sound, it is far from the only meance. Several non-native and grasses have invaded the prairies, or threaten to do so, in numbers large enough to constitute an ecological threat. This paper looks at five common weeds well established in the prairies of South Puget Sound and at four weeds common elsewhere, but presently limited in distribution in the Puget prairies. Consideration is given to growth habits, tolerances, propagative methods, pests, and other characteristics which both makes these weeds plats of concern and which potentially limits their spread. The paper first discusses two common invasive grasses, colonial bentgrass (Agrostis tenuis), and velvet-grass (Holcus lanatus), and three common invasive forbs, St. Johnswort (Hypericum perforatum), hairy cat’s ear (Hypochaeris radicata), and ox-eye daisy (Chrysanthemum leucanthemum). This is followed with discussion of four threatening wees, (gorse (Ulex europaeus), leafy spurge (Euphorbia esula), spotted knapweed (Centurea maculosa), and mouse-eared hawkweed (Hieracium pilosella), and some near relatives. The paper also looks at government noxious weed programs and how their work can affect prairie conservation, and concludes with a brief look at some issues prairie managers may face.

Introduction presented is based on research and interviews, some of the material is This paper is an examination of a few anecdotal in nature, based on my pest plants of the Puget Prairie. It is observations. Many of those undertaken with the belief that a better observations were made during 1995 and understanding of pest plants can assist in 1996 while employed by The Nature their control. This paper looks at both Conservancy as a member of its prairie weed already common to the Puget restoration team. Other observations are Prairies, and at invasive plants common based upon many years experience as a elsewhere which have the capacity to professional gardener. become pests on the Puget Prairies. While weeds often share common The prairies of Puget Sound are a characteristics, and their control may relatively small , facing share common solutions, each weed here double threats from invading human is examined independently. Presenting development and invasive plant species. consistent comments about each plant It is generally agreed that the most has proven difficult, and research gaps blatant prairie invaders are Douglas-fir, are present. While much of the material (Psuedotsuga menziesii), a very large

Prairie Weeds G. Buschmann 163 native conifer historically excluded from widespread, but is uncontrolled and Puget prairies by grass fires, and Scotch looks to be rapidly increasing. broom (Cytisus scoparius) and similar European relatives (C. striatus, C. Colonial Bentgrass- Argostis tenuis mospessulanus). But Douglas-fir and Sibth. Scotch broom are only the two most dramatically observable weeds of the One of the most outstanding nuisances to prairie. This paper examines some of the the prairie is Agrostis tenuis, commonly other prairie weeds whose presence pose known as Colonial bentgrass. The significant – possibly even greater – common and scientific names are both ecological threats to the Puget prairies. descriptive of this plant’s nature. “Tenuis” shares the same as First of all, what is a prairie weed? In “tenacious”, a very apt description, and native a weed is a non-native Colonial refers to the (large) colonies it plant which is able to thrive in a foreign forms as it grows. Pojar and MacKinnon ecosystem. In this paper attention is (1994) contend that A. capillaries is the given to those weeds which either proper name for this weed, but that name overwhelm native plants and /or animals is ignored by Hitchcock and Cronquist of the existing prairie , or (1973) and rejected by Hortus III (1976). appear to have that potential. The weeds These disagreements greatly confuse the discussed in this paper are but a few of research. The thin leaves and relatively the many weeds which grow in the short size of bentgraass cloaks its prairies. Most of the prairie weeds grow aggressive nature. Bentgrass is a sod comfortably alongside their established forming grass. In a bunch-grass prairie native cousins in a tame and unobtrusive such as southern Puget Prairies, sod manner: they will not be discussed in excludes many plants which depend on this paper. open for reproduction and survival, making bentgrass a very unwelcome Five Well-Established Invading pest. Weeds Also present on the Puget prairies is The five plant species singled out in this Agrostis diegoensis, a native Agrostis. section of this paper are among the most Similar in appearance to and easy to significant of the many weeds found on confuse with Colonial bentgrass, A. the Puget prairies. The two grasses, diegoensis is less competitive, and tends colonial bentgrass (Agrostis tenuis) and to grow in distinct and contained velvet grass (Holcus lanatus), are both patches. On Puget prairies, with practice very invasive but have distinctly the two species can be readily different growth habits. Of the three distinguished in the , even at a forbs, hairy cat’s ear (Hypochaeris distance. A good field guide and a good radicata) is already very wide-spread, hand lens will aid in differentiating the and uncontrolled; St. Johnswort two. (Hypericum perforatum) is also very widespread, but is contained with Bentgrass’s running root system is biological controls; and ox-eye daisy supplemented by its prodigious (Chrysanthemum leucanthemum) is less production of small, light-weight seed

Prairie Weeds G. Buschmann 164 which can be wind-blown considerable stunt bentgrass; conclusions on this distances. The seed of bentgrass appears dilemma are left to the reader. to have an extended ripening which continues into late summer. Some Velvet Grass- Holcus lanatus L. seed germinates almost immediately with the fall , while other seed does Holcus lanatus, (velvet grass, or in its not germinate until the following spring, native England, Yorkshire fog), is a or even later. My research did not turn large, coarse, easily recognized perennial up any information on long-term seed grass, with bulky seeds, a loosely viability, although grass seed in general clumping , and a large fast growing is short-lived. fibrous root system. The seed is light enough to disperse on the wind and also An effective means of controlling Scotch spreads by adhering to fur and clothing. broom may encourage the spread of Velvet grass is generally a grass of poor bentgrass when bentgrass is producing and infertile soil, and tolerant of widely seed. When chopping down Scotch ranging environmental conditions. It has broom with a tractor and heavy duty a remarkable ability to tolerate salts and mowing deck, at Fort Lewis the first heavy metals and to alter its root system week of October 1996, I observed that a in the presence or absence of water, thick layer of grass chaff and seed had nutrients, salts and metals (Thompson accumulated on the mower deck at the and Turkington 1988; Pilcher and Russo end of the day. In all likelihood seed 1988). It is a vigorous competitor and its tumbled onto and was broadcast from ability to absorb nutrients in essence the mower deck all day. Roads through robs other weaker plants. Furthermore, the prairies appear to have denser stands in lab studies Newman and Rovira of bentgrass, presumably because of (1975) found that velvet grass increased seed movement. In October alleopathically inhibits competition. 1995 at Thurston County’s Glacial While velvet grass does spread by Heritage Park a wide swath of dense vegetative means, it mostly spreads by Scotch broom was mowed, including an seed, which it produces prodigiously. old railway bed. The following spring Thompson and Turkington (1988) write the old rail bed showed up distinctly in that Watt (1976) found that plants grown the cleared prairie, a thriving straight from seed sown the previous spring line of bentgrass. produced as many as 240,000 seed for each plant. Some herbicides will damage bentgrass, as is recurrently mentioned in manuals While velvet grass is an inarguably on lawn management and confirmed by important graminoid pest of Puget Richard Robohm (1996) in his recent prairies, its roles as an invader in studies on Idaho fescue. However, it is undisturbed prairie remains unclear. unclear as to how much herbicide would Based on two years of undocumented be needed to successfully and observations made while undertaking significantly reduce bentgrass over the at Fort Lewis, velvet long-term. Ho (1964, in Aarssen 1981) grass seems to grow most strongly in found Hypochaeris radicata (hairy cat’s prairie altered by Scotch broom and ear) to have alleopathic qualities which Douglas-fir infestations. It does not

Prairie Weeds G. Buschmann 165 appear to spread as easily through “ …reduce[ed] the relative abundance of undisturbed prairie as does bentgrass. H. lanatus in ” (Thompson and Studies on Scotch broom and associated Turkington, 1988). In barren restoration plants found that bentgrass was a sites potentially infested with velvet common invader everywhere and velvet grass, it may be possible to manipulate grass quite uncommon. In broom condition and stimulate germination, and infested prairies the likelihood of finding then treat the germinated area with velvet grass increased, but not herbicide or heat treatments such as significantly (Parker, unpub. data). flaming or steam. While these techniques may have been tried on Regardless of the role velvet grass plays velvet grass, I did not uncover any in disrupting pristine prairies, the published research. Velvet grass has a disruptive role it plays in restoration number of biological pests and merits equal or greater concern. It pathogens, but except for rabbits none appears to outcompete prairie plants in appear to be significantly destructive. severely disturbed prairie and to overwhelm native prairie plants being Klamath Weed- Hypericum replanted. Based on both research and perforatum L. personal experience, it is clear that restoration must be conducted in ways Few invasive prairie forbs have received which ensure that in infested areas, more press than Klamath weed germination of the enormous seed bank (Hypericum perforatum). Long valued in does not defeat the restoration. Velvet Europe as both a valuable medicine and grass seed does not exhibit much an aid favoring good fortune and dormancy, does not typically sprout countering evil spirits, this plant when buried, and once buried looses continues to be regarded with great viability. The trick is to get the surface interest. In the old world it has been seed to sprout, destroy seedlings, and called St. Johnswort after John the minimize future soil disturbance. Baptist, as well as Aaron’s beard, Tipton Vigilance is still needed until the weed, and goat weed. With its restoration is more established, as some introduction to came a new seed displays delayed germination, and name – Klamath weed. Not only did gophers and earth worms, if present, Klamath weed spread rapidly and thickly continually bring seed to the surface. in the New World, its potent pharmacological properties proved A number of herbicides effectively poisonous to grazing livestock. control velvet grass, although whether any are selective enough to use safely in Efforts to control Klamath weed have the presence of desirable plants is been written about in virtually every unclear. Hand pulling plants is difficult book on weed control published in the and labor intensive, requiring past 50 years. Unlike many efforts at considerable effort and causing weed control, biological control of significant soil disruption. It was found Klamath weed was achieved when a that ‘lack of irrication (Morrison and species of Chrysolina beetle, Chrysolina Idle 1972; Watt and Haggar 1980), quadrigemina Suffr., was successfully [and} burning (Grime and Lloyd 1973), introduced in the 1940’s into California.

Prairie Weeds G. Buschmann 166 Within a short span of time the beetle leading to speculation about its effect on spread, defoliating vast acres of Klamath HIV” and Ernst (1995) found it to be an weed first in California, then Oregon, herbal antidepressant possibly superior Washington and Idaho. While Klamath to synthetic ones. weed continues to be found in the Puget Prairie landscape, Chrysolina has Hairy cat’s ear – Hypochaeris radicata reduced the plant population so greatly L. as to make the presence of the plant mostly just interesting (Holloway 1964; While sometimes mistaken for common Crompton et al 1988). dandelion, (Taraxicum offinale), hairy cat’s ear, (Hypochaeris radicata) is Still one cannot expect Klamath weed to distinctly different. Like dandelion, cat’s completely go away, for some factors ear’s flower is a yellow composite which favor it. Fluctuations in the predator and matures to a puffball of seeds. But the weed population are observable in the flower heads are born several to a stem, field. Briese (1996) writes of problems the stem frequently stands 18 inches with biological controls in Australia, high, and the leaves grow flat to the problems which seem to apply to ground in a smothering rosette. Unlike conditions in Puget Sound. Klamath dandelions, which relish fertile gardern weed grows well in partial shade, which soils, cat’s ear thrives in neglected lawns Chrysolina avoids. In Australia a great and the poor dry soils characteristic of deal of infested land is shaded and our Puget prairies. It is less distinctly control of Klamath weed is less different from another composite, effectively achieved by Aphis chloris, as autumn hawkbit (Leontodon shade-tolerant aphid. This suggests that autumnalis); in all likelihood the two are the understory of the Puget prairies confused, including perhaps on our remain at risk. Briese also found that Puget prairies. See Hitchcock, et al after fire Klamath weed flourishes, (1955), Aarssen (1981), and Mulligan increasing production of both seed and (1988) for distinctions. vegetative top growth. Fire also impacts predator populations, although Briese’s While cat’s ear thrives in poor soil it has study suggests that after an initial drop, been found growing in almost any soil – the predator populations rebuild from the wet, dry, clay, sand, peat, - and probably additional nutrients introduced by fire. on every continent of the world. With origins in Europe, Asia, and North Klamath weed’s potent medicinal Africa, it has traveled worldwide. It is properties also continue to attract recorded form the Aleutian Islands to attention. While its pharmacological Central America and the subject of value may seem to be of little scientific papers in places as distant as importance in prairie management, the Tasmania, Croatia, Holland, New resulting demand seems to assure that Zealand, and British Columbia. Cat’s ear full eradication, even if were possible, is not as common in the intermountain will not happen. For example, Pojar and prairies of and is MacKinnon (1994) note that “two designated a “noxious” weed in Eastern compounds isoleated form this species Washington (Aarssen 1981; WAC16- strongly inhibit a variety of retroviruses, 750 1996).

Prairie Weeds G. Buschmann 167 Cat’s ear’s cosmopolitan nature is Or a few individuals in a group, but not apparent by its many names. Not only as patches or pure stands.” Aarssen also does it have a multitude of common wrote that Ho (1964) found cat’s ear to names, the scientific community cannot possess allopathic qualities, which agree as to whether its name is properly significantly stunted bent grass. Sheldon spelled Hypochaeris or Hypochoeris and Burroughs (1973) studied seed (Turkington and Aarssen, 1983). Among dispersal in the lab and found that cat’s its common names it is called false ear seed on average does not disperse as dandelion, hairy cat’s ear, cat’s ear, far on the wind as one might expect. In a spotted cat’s ear, gosmore, flatweed, 16.4 kph (10+ mph) wind, seed disperse dandelion, hairy dandelion, and in only an average of 2 meters; lesser some of Europe, pigweed, (Ferkelkraut winds result in a proportionately shorter and Saukraut in German, Biggkruid in spread. Dutch and Salade de Porc in French, which all translates as “pigweed”) Controls for cat’s ear seem to be limited. (Jacobson, 1987). Although susceptible to herbicides, in a prairie this plant is almost always It is clear that cat’s ear impacts prairie growing in the presence of native forbs, significantly, if for no other reason which are also susceptible. Fall herbicide than sheer numbers. When conducting application would seem to be safer in surveys at Fort Lewis, the limited situations, when most native few times we did not find cat’s ear in our forbs have died back. However, fall study plots always elicited a remark of germination and growth is not exclusive surprise. Beyond cat’s ear ever-presence, to cat’s ear. Even if a safe time for its growth habit, with leaves hugging the spraying can be determine, the frequency ground to the exclusion of any other of spraying needed to control this vegetation, places this plant high on the invader may exceed the ecological list of obnoxious invaders. benefit. Cat’s ear also seems well adapted to fire regimes. In New Zealand Salisbury (1942) found each cat’s ear Guthrie-Smith (1969, in Turkington and plant produces on average 970 seeds Aarssen 1983) reports it as one of the with an average germination rate of 60 first invaders after fires. to 70%. After flowering most flowering Frequent fires may slow its spread rosettes of cat’s ear dies. After summer (Wolfe and Horton 1959, in Turkington dormancy side (non-flowering) rosettes and Aarssen 1983), but other studies begin to regrow and most of the seed show that frequent fires slow the spread germinates; juvenile and side rosettes of native prairie plants as well, thus overwinter (H. de Kroon 1987). accomplishing little. Newman & Rovira (1975) found cat’s ear to be autotoxic, that is, to inhibits Biological controls – the introduction of growth of other plants of its own species. some exclusive predator or disease – are In his article on cat’s ear, Aarssen (1981) highly expensive and highly unlikely hypothesizes that “this may explain why prospect. While Torrington and Aarssen plants of Hypochaeris radicata are list a number of predators and some normally found as isolated individuals, diseases, none seem to cause cat’s ear

Prairie Weeds G. Buschmann 168 any noticeable harm. Besides, in most plant produces an average of over 2700 settings it is a minor pest. Cultivation seed, with a 94% seed viability. Howarth virtually eliminates cat’s ear from farms and Williams (1968) report that ox-eye and . Its susceptibility to daisy’s seed matures in late summer; the herbicides quickly eliminates it from seed germinates mostly as soon as it is chemically maintained lawns, and just shed, and the seedlings then establish supplemental food and water and a themselves the next spring. This is greater mowing height will reduce the based on conditions in Great Britain, population. While it is listed as a where summers can be wet; undoubtedly “noxious” weed in Eastern Washington, germination in the Puget Sound region and is regarded as poisonous to (some) waits until the fall rains come, While livestock, herbicide is generally seed tends to germinate immediately, considered to be adequate control in Toole and Brown’s concluding report pastures. Wile animals such as black (1942) on “the Duvel experiment” found bear eat cat’s ear with relish (Poelker 82% of seed was still viable after 6 years and Hartwell 1973) as do some (summarized by Howarth and Williams domesticated animals (Turkington and 1968). Several studies, including most Aarssen 1983). recently O.M. Heide (1995) found it to be constant in its requirements for Ox-eye Daisy – Chrysanthemum flowering: short days and cold leucanthemum L. temperatures followed by longer days are needed to ensure flowering. Chrysanthemum leucanthemum L., (Syn. Leucanthemum vulgare Lam), Although the tall weak (floppy) stems commonly called ox-eye daisy, is a help to strew the seed, animal and sentimental favorite in the bouquets of mechanical means play a large role in many and an invasive noxious weed. Its the spread of this plant. Well adapted to dual identity is displayed by the variety the dry Puget prairies, once establish ox- of common names given this weed. E.R. eye daisy forms dense colonies which Spencer (1957), recounts some of them: spread by both seed and surface “White week, Dog daisy, Bull daisy, rhizomes and fully out competes its Poorland daisy, Maudlin daisy, Butter native neighbors. Other factors also daisy (meaning it spoiled the butter), contribute to how this plant spreads. For Poverty weed, Dog blow, and Moon one, people like this flower. It is a tough penny”. Native through much of Eurasia, job convincing people that this charming it is now well established in North flower is a wicked weed. Restricted America and New Zealand among other “Noxious Weed” laws in Washington places. It is not as widespread in the State, (see next section); the flower seed prairies of Western Washington as is remains a popular component of cat’s ear, but it is present in large enough “wildflower mixes” in many parts of the numbers to cause concern, and it appears U.S. to be spreading. Some techniques might t help contain Ox-eye daisy flowers on weak stems, the spread of ox-eye daisy. In infested which can reach close to one meter in areas managers should be cautious about height. Salisbury (1942) found that each using a deck mower (‘brush- hog”) when

Prairie Weeds G. Buschmann 169 this weed is dropping seed. Manual Noxious Weeds and Weeds Which containment and removal, while not a Pose A Threat to Puget Prairies simple option, may be a necessary step to at least ensure that entire prairies are Most state, and all four northwest states not completely overwhelmed by this (Washington, Oregon, Idaho and plant. Ox-eye daisy is easier to manually ) have Noxious Weed Control remove than some weeds. First of all, the Boards. Because the weed boards serve plant is very conspicuous and distinctive as a sort of guardian at the gate, I have in flower, making filed observation and turned to them to discover which weeds removal easier by people with limited could be a source of future trouble in the training in plant i.d. And it grows in Puget prairies. A digression here shallow-rooted mates, which are describing the weed board is appropriate. relatively easy to manually remove. In areas of Puget prairies where this plant is not yet thickly established these methods The Washington State Noxious Weed may be appropriate. Board was created by legislative act in 1969 in response to concerns of the No biological control is listed for ox-eye agricultural community that certain daisy in the PNW weed control weedy invaders were so noxious as to handbook, (1996). Howarth and threaten livestock, crops, and even the Edwards (1968) list with little comment livelihood of Washington State farmers. a number of presumably European As defined by the Washington State law, insects, which feed upon ox-eye daisy. a noxious weed is “any plant which Guillet et al (1994) studied in a lab a when established is highly destructive, moth, not mentioned by Howarth and competitive, or difficult to control by Edwards, which eats ox-eye daisy. That cultural or chemical practices” (RCW moth tries to only feed and reproduce on 17.10). Presumably other states have plants growing in shade, because of ox- similar laws and definitions. eye daisy’s phototoxic qualities. Although some human cultures eat the The intent of Washington State’s distinctive semi-sweet leaves as a green, noxious weed control act is to prevent and some livestock will eat it, both cattle establishment of certain weeds. Weeds and pigs try to avoid it. Indeed one already well established in an area reason for ox-eye daisy’s noxious weed usually escape inclusion on the weed status is due to the off-flavor it imparts list, the primary purpose being to limit to cow’s milk. Herbicidal control of those weeds not already established broadleafed weeds in a prairie mosaic is (RCW 17.10). The state divides its inherently difficult, for usually target noxious weeds list into three classes: plants are present in a mix with desirable “A”, “B”, and “C”. Class A and B weeds vegetation; herbicidal control of ox-eye are never native to the state. Noxious daisy is constrained further because this weeds not established in a region of the weed show resistance to most of the state are Class B; the state is divided into common broadleafed herbicides ten regions. Scotch broom, cat’s ear, and (Howarth and Edwards, 1968; PNW ox-eye daisy are all Class B weeds in weed control handbook, 1996). Eastern Washington regions. Class C is a catchall for any noxious weeds not in

Prairie Weeds G. Buschmann 170 Class A or Class B, and tends to include its weed board only after vehicle radiator widespread weeds, which are grills and horse digestive tracks shed agricultural pests. Klamath weed is a millions of weed seed from Eastern Class C weed. Washington along the I-90 corridor through Snoqualmie Pass. AS will be The noxious weeds of concern in this discussed, Knapweeds, firmly establish section of the paper are mostly Class B in King County, now pose a big threat to weeds for the Puget prairie regions, the prairies of southern Puget Sound. established elsewhere in the state. Mouse-eared hawkweed, is a Class A Gorse- Ulex europaeus L. weed, not established anywhere in the state. In 1996 23 weeds are listed as Some noxious weeds are obviously Class A, 47 weeds as Class B, and undesirable. Of those weeds with the another 31 weeds as Class C, a total of potential of establishing themselves as a 101 plants species defined as “Noxious” major prairie nuisance, top on the list of in Washington State (WAC 16-750 blatant undesirables is Ulex europaeus, (1996)). commonly known as gorse, also called furze and whin, and humorously referred The state weed board and its director are to as “Scotch broom, armed and responsible for designating plants as dangerous”. With thorns 3 cm in length, “Noxious” and to see to their control. seedlings from a single plant can grown Each county, however, is responsible for into impenetrable more than 3 its own weed board, including board meters tall. While gorse is a more activation, funding, weed control, and common pest in the coastal counties of requested listings. There is also a Washington and Oregon, it is establish Federal Noxious weed program, and in both Thurston and Pierce counties, although the legal obligations are and in places uncomfortably near the limited, the State and County weed prairies. One site in Thurston County is boards are influenced by the Federal the Nisqually Wildlife Refugee. Another board. The federal weed board works site extends from a Thurston County closely with Customs to prevent the gravel pit a few hundred meters south of unintended (mis-intended) importation the Upper Weir prairie of Fort Lewis all of noxious weeds. along the county road almost to Upper Weir. County autonomy for the most part has worked very well. Each county sets its Apparently Thurston County is seriously own priorities, arranges for its own concerned. At the instigation of the funding, designates its target weeds. But county weed board, Thurston County a county board is inactive until the recently imposed construction conditions county governance; the citizenry, the in one section of the county near the neighboring counties, or the State weed Nisqually Refuge, specifically to contain board feels that it is necessary to activate the further spread of gorse. Those the county board. Until a call arises to conditions require all construction activate it, the county board rests in equipment to be thoroughly cleaned of unobtrusive slumber. In on regard this all weed seed and subsequently failed miserably. King County activated inspected by a member of the weed

Prairie Weeds G. Buschmann 171 board staff before leaving a work site – Distinctly different from gorse, but conditions any prairie land managers obnoxious and tenacious in its own way, might chose to voluntarily adopt in the is leafy spurge, (Euphorbia esula). presence of any invasive weed problems. Individual plants up can grow to 3 feet And the county has stepped up its efforts tall and send taproots down more than 8 at controlling gorse county-wide feet. The exude a chemical, which (Thurston Co Weed Board staff). None- inhibits the growth of other neighboring the-less, a fully concerted effort to stop it plants, and its milky latex sap bears a from invading Fort Lewis seems very irritating alkaloid. Where urgently important, for military practices established it can form dense stands could lead to a rapid spread if it ever which exclude all other plants. The very gets a start on Fort Lewis’s prairies. small yellow flowers are partially If there is good news, it is that gorse is surrounded by larger yellow-green slower to spread than Scotch broom. bracts, which from a distance appear to Thurston County Weed Board personnel be the flowers. The seed of leafy spurge estimate that gorse was planted matures in capsules which when ripe pop (deliberately!) in the county at least 50 explosively, propelling the seed up to 20 years ago, and the largest infestation is feet away (Callihan 1990). still confined to that general area, near the Refuge. It is most quickly spread A rhizomatious perennial, leafy spurge through construction activities. The bad creeps in inconspicuously. Often it news is that once established it is spreads unnoticed through seed and root devilishly difficult to control. Large fragments introduced by standard Scotch broom plants when cut construction practices. It grows easily in dependably dies; large gorse plants gravelly conditions, so it is natural that dependably resprouts. It yanked out by one vector is gravel pits. Livestock are the roots; gorse roots left behind can another vector; in grazing, the sprout. Its highly flammable nature is indigestible seed is eaten, excreted credited for spreading the flames, which unharmed, and thus spread (Callihan et left the coastal Oregon town of Bandon al, 1990). Because the remaining prairies in ashes in 1935, and yet after burning it of South Puget Sound usually exclude tends to resprout from the base. Some livestock and construction, it might seem herbicides are effective in controlling it, unlikely that leafy spurge would which is fortunate because cultural represent a threat. But the habitat is ideal practices, as already state, seem and once established this is a very ineffective. Some biological controls difficult plant to control. Both also have been found: a seed-feeding cultivation and herbicide are limited in weevil introduced into California and their effectiveness, requiring annual Oregon in mind 1950 may be slowing it treatments for several years to achieve spread (J.K. Holloway 1964, Issacson, more than just suppression (Lym et al, 1994), and Hoshovsky, (1988) and PNW 1993). Weed control handbook mention other predators as well. One of the sites where it is presently found in Western Washington is a prairie Leafy Spurge – Euphorbia esula L. in the central portion of Fort Lewis. There are attempts to control leafy

Prairie Weeds G. Buschmann 172 spurge have been actively under way for doubtless one of the best known. several years. While it is contained to Literature about knapweed is broadly one site, as to eradication there is no available: both the State University immediate end in sight (Thurston Co. Cooperative Extension Service and most Weed Board, 1996). county weed boards maintain sizable files of literature available for little or no Leafy spurge is not a significant weed in cost. It is highly recommended that its native Europe, which suggests the people concerned with weed control and presence of natural pests. In North identification in the Puget Prairie avail America biological controls such as themselves of these resources, (a insects and pathogens have been comment which extends to all the introduced: in 1994, the Animal and noxious weeds discussed here). While Plant Health Inspection Service section this paper singles out the two most of the U.S. Department of worrisome knapweed species, several “mass-produced” and then released eight others are potential invaders and many biological pests of leafy spurge, in 127 seemingly specific comments are counties in 16 States (Bridges, 1995). generally applicable. In addition, tow These controls are somewhat containing knapweed species – one perennial, (C. leafy spurge, but they are slow to montana), another annual (C. cyanus), establish and are not yet significantly are grown as “Bachelor Buttons” in reducing the plant population. For states flower gardens and usually not such as Montana and with considered a threat. (The State of hundreds of thousands of acres infested, Washington lists 6 Centurea species as this is unfortunate. Sheep may be the “Class B” weeds, and 4 as “Class A”.) most effective means of reducing large stands in pastures, as sheep can eat leafy Several knapweeds are found in Western spurge without apparent harm (Lamp, Washington, but in the opinion of 1995). With all the recently introduced Thurston County’s Weed Board, spotted biological controls, it is not surprising knapweed (Centurea maculosa), and that leafy spurge continues to be heavily knapweed, (C. nigra X jacea), studied. An average of 5 scientific probably pose the most serious threat to journal articles appear each year, with at the Puget Prairies. In Western least half a dozen insects and pathogens Washington, spotted knapweed is the being researched. The results, and lack most common, and meadow knapweed is thereof, of this research seems to the most vigorous. Both of these confirm that for now the most certain knapweeds are “class B designate” and effective controls in the Puget weeds in the counties of southern Puget Prairies are awareness, avoidance, and Sound, meaning that they are beyond immediate action. control elsewhere in the state, (Eastern Washington), but designated for control Spotted Knapweed – Centurea in the Puget Prairies. maculosa Lam. – and Other Knapweeds Most knapweeds differ markedly in ther juvenile and reproductive stages. The Of those noxious weeds gaining press juvenile state of spotted knapweed forms and notoriety, the knapweed complex is basal clumps of foliage, which originates

Prairie Weeds G. Buschmann 173 from a strong taproot. Plant clumps knapweed indicates that knapweed seed nearly a foot across and 6” tall are eaten by sheep and deer can be excreted possible, although half that size seem in viable condition for a week or more more common. At this stage the plant after ingestion (Wallander, 1995). foliage can completely screen the Horses, in tandem with mobile and ground. In its reproductive stage much inattentive humans, regularly increase of the lower growth withers as the main the spread of this weed through both body of the plant grows to typically droppings and trailer sweepings. At Fort about 2 feet in height, sometimes twice Lewis spotted knapweed is found that tall. At this stage, in the summer, regularly along roads of those prairies plants flower profusely and then produce used by recreational horse riders; other seed. While spotted knapweed at this prairies with horse riding presumably stage do not typically shade out other have similar experiences. plants, they never-the-less can grow so close together as to completely alter the Spotted knapweed spreads physical (and visual) character of the rhizomatiously as well as by seed. landscape. Additionally, knapweed Because spotted knapweed is a short- flowers seem to be so favored by bees lived perennial, which relies on seed that in large establish patches, native reproduction (Lacey, 1986), repeated plants dependent upon bees for mowing might reduce this weeds long- pollination may experience a drastic term survival. But in general spotted drop in fertile seed production. knapweed seems well adapted to a mowed life, altering its shape to a more Like all knapweeds, spotted knapweed prostrate from of low-lying rhizomes spreads along travel corridors, the seed and flower stems until it grows beyond being easily caught on vehicles. With the reach of a mower. A 3-year study on King County’s utter failure to organize sheep grazing spotted knapweed at and enable a noxious weed board years Montana State U. (Olson and Wallender, ago, the I-90 corridor between Eastern 1995) found that “shoot and toot and Western Washington became a of spotted knapweed was not perfect growth medium for an appalling affected by repeated grazing, [but] Idaho infestation. Had it not been ignored for fescue was negatively affected by many years it would not be the invasive repeated grazing. threat to Western Washington, which today it is. To be fair, highways are not Biological controls for different the only vectors for this weed. An knapweed species have been tried, infestation of spotted knapweed is achieving mixed results. Several pests slowly creeping into an and diseases are currently being adjacent to the McCord Air Force Base. researched and discussed. APHIS Likely delivered by air, its success is a reports that as of September 1995, 12 tribute to a different complex insects ere cleared for release in the US bureaucracy. by the USDA for control of some knapweed species. Like most biological Animals are another vector for the pests, different ones attack seeds, stems, spread of knapweed. A Montana State and roots (Bridges, 1995). Two gall University study conducted on spotted flies, (Urophora affnis and U.

Prairie Weeds G. Buschmann 174 quadrifasciata); infest the seed heads of Beyond the knapweeds, the other spotted knapweed, the larvae feeding on grouping of closely related invasives are and around the seed head. The damage the hawkweeds. This general are causes seed production to be reduced, composites, mostly yellow flowered and but the fly does not seriously damage in the Chichorieae tribe. Seeds have existing plants and only slightly reduces pappus (tuft), allowing the seed to the plant’s spread (Roche, Piper, and disperse on the wind. Thurston County Talbot, 1986). An intriguing project with Weed Board agents are most concerned promise has been the development of a about mouse-eared hawkweed discovered in the field. (Hieracium pilosella), which has been Maculosin is a host-specific phytotoxin, found in one site. At Rocky Prairie is produced by the fungus Alternaria south Thurston County efforts to alternata, which can seriously damage eradicate it have been going on for spotted knapweed (Strobel, 1991). nearly ten years. When first discovered Finally, not to be overlooked is manual the infestation was one patch of a few removal, which over several years is square meters. At this point the main very effective, although initially labor infestation has been eliminated through intensive (Thurston Co. Weed Board). judicious use of the herbicides Clopyralid and 2-4-D. Unfortunately, the Meadow knapweed, (Centurea nigra X plant when young is inconspicuous, the jacea) is a naturally occurring hybrid flowers are small and short lived, seed between black knapweed (C. nigra) and development is rapid and seed dispersal brown knapweed (C. jacea). At this time is airborne. When mouse-eared its distribution in Western Washington is hawkweed was first discovered at the more limited, but it is found in all site, the plants had already gone to seed counties of the Puget Prairies. Some and dispersed throughout the site. While counties are experiencing rapid increases the ongoing control methods are fairly and in Pierce County it is considered the effective and the total population is most commonly occurring knapweed. shrinking, new plants continue to be While I have not encountered it in the found. An established infestation nest to course of my prairie work, that Thurston the prairie preserve has recently been County Weed Board staff believe that located; hopefully, its control will aid both its rapidity of increase and manner the preserve (Davenport, 1997). of growth pose a real threat to Puget Prairies. Meadow knapweed is a Dalmatian Toadflax – Lineria vigorous perennial with large coarse dalmatica [L.] Mil. leaves growing in a broad basal clump. Apparently gaining the stronger One more noxious weed, added as a characteristics of each of its parents. It footnote, is Lineria dalmatica. was originally introduced into Oregon as Commonly called Dalmatian toadflax, winter forage, although it appears this weed has an extensive horizontal intolerant of heavy grazing (Roche et al and vertical root system, and grows 2 to 1986). 4 feet tall (Parker and Peabody, 1983). Thurston County Weed Board staff also Mouse-eared Hawkweed – Hieracium considers this to be a threat to prairies. pilosella L. – and Other Hawkweeds In the spring of 1997 I easily observed it

Prairie Weeds G. Buschmann 175 in flower along the I-5 freeway corridor education. As prairie managers and in Pierce and King Counties, and it has restoration biologist look to the future reportedly been seen is some of our care of the Puget Prairies, a powerful prairies. I have not researched it, ally in our work might be found in the however, and it will not be discussed in County Noxious Weed Boards. this paper beyond this note. Some materials are available from Cooperative The Nature Conservancy, The Evergreen Extension Service offices. State College in Olympia, Washington, The Center for Urban Horticulture at the Conclusions University of Washington, and other educational facilities including the State It is clear that there are many complex Universities will also make valuable issues in the management of Puget contributions to research and Prairie weeds. In this paper I have conservation. There may be other allies explored different control measures: to be found in business, government, or biological controls, controlled by fire, environmental groups. Certainly there is herbicides, manual removal. Typically need for an umbrella organization, which the solutions are far from perfect. regularly exchanges research and ideas, Control measures that curb one weed although the organization may already may benefit another. Or control exist in another form. Together we can measures may seem very effective, but work together to define problem plants arouse public ire – “air pollution”, in prairies and support research into “groundwater pollution”, and “misuse of appropriate control plans. Working public funds”. And, each managing together, we can move forward into a agency has different priorities and deeper understanding of prairie ecology, resources to bring controls into action. so as to preserve our Puget Prairies for Some weeds are well researched, but the generations to come. control measures still have not been found. For other weeds, only limited Literature Cited research can be found in the literature, so we are faced with the problem of Aarssen, L. W. 1981. The Biology of learning about the plant in order to Canadian Weeds, 50. Hypochoeris control it. radicata L. Canadian Journal of Plant While these issues may present a Science. 61: 365-381. daunting task, we do have some resources at hand that may be useful. Bridges, V. 1995. Protecting U.S. Noxious Weed Boards are already in Agriculture from Noxious place in Thurston. Lewis, and Pierce Weeds. Plant Protection & Counties, where the majority of the Quarantine Fact sheet. USDA. Puget Prairies are found. Their staff are already knowledgeable about the general Briese, D.T. 1996. Biological Control of issues around problem plants and indeed Weeds and Fire Management in provided much material for some of this Protected Natural Areas: Are paper; of recent years they have become There Compatible Strategies? much more oriented to community

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