ENVIRONMENT MANITOBA (1991). STATE OF THE ENVIRONMENT: REPORT FOR MANITOBA. MINISTER OF THE ENVIRONMENT MANITOBA. 191 PP.
Wildlife
Problem Plants and Animals.
Another source of stress on wildlife habitat and wildlife is the introduction of new plant species. If conditions are right, non-native plants can multiply without competition and may aggressively crowd out the native vegetation required by wildlife. If the new plants have no food or cover value, they can cut back on the wildlife production by eliminating habitat.
Purple loosestrife and leafy spurgetop the list of troublesome weeds in this category. They were introduced to North America from Europe in the 1860s. Purple loosestrife spread quickly, reaching Manitoba by 1896, with leafy spurge following in 1913. Within the last 3 years purple loosestrife has infested all the major waterways. Leafy spurge has taken over 47,000 hectares.
Purple loosestrife is a wetland plant found in pockets throughout southern Manitoba, especially along the Assiniboine River, and in the Cypress River and Rosendale areas. It can quickly take over open water and destroy feeding and nesting sites of waterfowl. Deer, muskrats, and other foragers ignore mature loosestrife because it is too tough and woody. As they eat around it, they effectively eat themselves out of their home range by clearing more room for loosestrife to take hold.
Leafy spurge had taken over waste lands, ditches, pastures, and grasslands in central Manitoba and added another threat to the survival of native prairie. It destroys wildlife habitat by outgrowing preferred food and cover plants.
Problem non-native plants are controlled under The Noxious Weeds Act (see Agriculture). Research to find inexpensive, long-term management techniques to control problem non-native plants are now being developed under laboratory and field conditions by Ducks Unlimited Canada, the University of Manitoba, Dow Chemicals, and the United States Department of Agriculture.
Water manipulation, herbicides, and biological control using insects are being examined as possible methods of managing loosestrife. The black dot flea beetle (Aphthona nigriscutis), imported from Europe, is being studied as a biological control for leafy spurge. Public educational programs that help people recognize leafy spurge and purple loosestrife, may be the biggest factor in halting the spread of these killer weeds.
HortScience 28(9):954. (1993)
FERTILITY OF 'MORDEN PINK' Lythrum virgatum L. TRANSPLANTED INTO WILD STANDS OF L. salicaria L. IN MANITOBA
Cory J. Lindgren
Manitoba Purple Loosestrife Project,
Oak Hammock Marsh,
Box 1160
Stonewall, Manitoba
R0C 2Z0, Canada
Robert T. Clay
Ducks Unlimited Canada
566 Welham Rd.
Barrie Ontario
L4M 6E7, Canada
Additional index words. hybridization, viable seeds, natural pollination, purple loosestrife
Abstract. Forty 'Morden Pink' Lythrum virgatum plants were transplanted into three wild stands of L. salicaria in June 1992. In Sept. 1992, seeds were collected and tested for viability and germination rates. Seed testing indicated that 83% of the collected seeds was viable (tetrazolium test) with a mean germination rate of 76%. We conclude that 'Morden Pink' will cross-pollinate and produce viable seeds when exposed to wild L. salicaria stands.
Wild purple loosestrife (Lythrum salicaria) is a herbaceous European perennial that has become an invasive wetland species in North America since its introduction in the mid-19th century. Its competitive ability and prolific seed production has resulted in its range's expanding across continental North America, thereby displacing much of the native wetland community in areas where it becomes established (Thompson, 1987).
Horticultural cultivars of purple loosestrife (Lythrum spp.) were developed in the mid- 1900s for use as a garden and landscape ornamentals (Harp and Collicutt, 1967). These cultivars initially were thought to be sterile and, thus, safe for horticultural use. Recently, Ottenbreit (1991) reported that artificial crosses between 'Morden Pink', 'Morden Gleam' (L. alatum Pursh x L. virgatum), and wild L. salicaria produced hybrid plants that were highly fertile. Further, Anderson and Ascher (1993) demonstrated that these cultivars are highly fertile when crossed with L. salicaria, L. alatum, or other cultivars. The authors of both of these papers concluded that purple loosestrife cultivars grown in gardens could serve as a pollen or seed source contributing to the spread of purple loosestrife in natural areas. Because both studies were conducted in greenhouses using artificial pollination, additional field work was required to determine if cultivars actually cross-pollinate in the field by natural pollination.
The purpose of our study was to investigate whether 'Morden Pink' would produce viable seeds under natural conditions. We chose 'Morden Pink' for this study because it is a common garden cultivar and because it was least likely to produce viable seeds (Ottenbreit, 1991).
Materials and Methods
In June 1992, 22 true stock 'Morden Pink' plants from the Agriculture Canada Field Station at Morden, Manitoba, and 18 'Morden Pink' plants purchased from garden centers in Winnipeg, Manitoba, were transplanted into three experimental sites: along the Red River north of Winnipeg (lat. 50o04'N, long. 96o55'W), along the La Salle River in Sanford (lat. 49o41'N, long. 97o26'W), and in a small wetland north of Cypress River (lat. 49o35'N, long. 99o04'W). Experimental plants were planted within or beside wild L. salicaria, except at the Red River site, where the nearest L. salicaria was 200 m upstream. Red flags were used to identify 'Morden Pink' transplants.
Seed capsules were collected from each transplant and wild L. salicaria plants in late Sept. 1992. Seed capsules then were assigned randomly to one of three seed-testing laboratories for germination and tetrazolium testing. Testing laboratories were Accu-Test Seed Laboratory (Rivers, Manitoba), Agriculture Canada (Saskatoon, Saskatchewan), and Newfield Seeds Co. (Nipawin, Saskatchewan). Tetrazolium testing consisted of presoaking the seeds in water for 24 h, piercing them, then soaking them in a 0.2% tetrazolium solution for 12 to 48 h. Germination testing was performed on seeds from the Cypress river site only. Such testing consisted of seeds planted on top of blotters, moistened with water, and exposed to an alternating cycle of 16 h of darkness at 20C and 8 h of light at 30C; no chemicals were used. Chi-square analysis was used to analyze the data.
Results and Discussion
Of the original 40 'Morden Pink' transplants, 11 were destroyed before seed capsules were collected. For statistical purposes, where more than one test per lot was performed by a testing laboratory, the mean was used. Lythrum salicaria produced significantly more viable seeds per lot (one lot = 200 seeds) when compared to 'Morden Pink' (x2 = 9.57, df = 1, P < 0.002). Analysis revealed significant differences (x2 = 36.64, df = 4, P < 0.001) between the number of viable seeds produced between sites; the reason for this difference is unknown. There were no significant differences (x2 = 3.38, df = 1, P > 0.05) between the mean number of viable seeds produced by 'Morden Pink' plants obtained from the Agriculture Canada Morden Field Station (87%) and those purchased from local Winnipeg greenhouses (77%). Further testing revealed a mean germination rate of 76% for 'Morden Pink' plants from the Cypress River site.
Our results indicate the 'Morden Pink' produced viable seeds within 4 months under natural conditions (Table 1). These results support Ottenbreit's (1991) and Anderson and Ascher's (1993) laboratory research indicating that purple loosestrife cultivars contribute viable seeds and pollen and, thus, contribute to the spread of purple loosestrife.
| Site | Plants (no.) |
Viabilityz (%) |
||
| Red River | ||||
| Morden Pink | 12 | 93 | ||
| Cypress River | ||||
| Morden Pink | 10 | 81 ±3.0y | ||
| L. salicaria | 2 | 95 ±1.4y | ||
| La Salle River | ||||
| Morden Pink | 7 | 77 | ||
| L. salicaria | 2 | 86 | ||
| z Each sample analyzed contained 200 seeds. | ||||
| y Mean of two samples. | ||||
Literature Cited
Anderson, N.O. and P.D. Ascher. 1993. Male and female fertility of loosestrife (Lythrum) cultivars. J. Amer. Soc. Hort. Sci. (In Press.)
Harp, H.F. and L. Collicutt. 1967. Lythrums for the home garden. Agriculture Canada, Ottawa.
Ottenbreit, K. 1991. The distribution, reproductive biology, and morphology of Lythrum species, hybrids and cultivars in Manitoba. MS Thesis, Univ. of Manitoba, Winnipeg.
Thompson, D.Q., R.L. Stuckey, and E.B. Thompson. 1987. Spread, impact and control of purple loosestrife (Lythrum salicaria) in North American Wetlands. U.S. Dept. of Interior, Fish and Wildlife Services, Washington, D.C.
Received for publication 21 June 1993. Accepted for publication 20 July 1993. We thank Henry Murkin for reviewing earlier drafts; Lynn Collicutt (Agriculture Canada) for supplying plants for this study; Ducks Unlimited Canada for providing funding for purchasing plants and testing seeds; Dave Gray, Ron Lyseng, and Eric Claeys for the use of their land; Canada Trusts Friends of the Environment for funding; and members of the Manitoba Purple Loosestrife Project Committee. The cost of publishing this paper was defrayed in part by the payment of page purchases. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact..
Kinnikinnick (1992) 7(8): 253-257
LYTHRUM: PLANTA NON GRATA
Roger Vick
The article "Lythrum: From Garden Delight to Monster of the Marsh" (Kinnikinnick May 1992) reflected the points of view of both the horticultural community and that of the environmentalist. On the basis of our further investigations concerning the Lythrum salicaria (purple loosestrife) complex, it is now time to review some of the good points that were made in that article.
The Good, the Bad and the Beautiful
Literature on this topic has supported the concept of "good" (garden type) lythrum, and "bad" (noxious weed ) lythrum. Our study of floral and vegetative characteristics now reveal that there is no consistent difference between the weed established in a wetland habitat, and garden lythrum offered for sale and grown in gardens. Examination of lythrums from a local infested wetland revealed a wide range of morphological characteristics, including size and color of petals, density of inflorescence, pubescence, alternate/opposite leaves, and so on. In other words, given the right conditions, any of the "garden type" lythrums could become established as a serious pest.
This conclusion is contrary to the entry on lythrum in Perennials for the Prairies (1991). However, co-author Professor Edgar Toop now says that he would be prepared to revise the lythrum entry in that publication , and entirely retract his support for "garden lythrum".
In Search of Safe Plants
Gardeners have been led to believe that L. virgatum (a species not specifically included in the Alberta Noxious Weeds Act) would provide a suitable alternative to L. salicaria. Unfortunately these two species hybridize readily, making L. virgatum a part of the problem. Neil Anderson and Peter Ascher (1) in their paper Male and Female fertility of loosestrife (Lythrum) cultivars, observe "...L. salicaria and L. virgatum...have both colonized wetland habitats, frequently becoming monospecific stands. These two species are considered by North American taxonomists to be the same, since they differ only by a few minor diagnostic characteristics and intercross freely." They go on to refer to naturalized populations of L. salicaria and L.virgatum as purple loosestrife.
Much of the loosestrife literature mentions the existence of sterile selections--specifically 'Morden Pink'--that presumably would not produce seed, and would therefore pose no threat to wetland habitats. None of the loosestrife complex, however, are "safe". 'Morden Pink' is not the sterile plant that it has been claimed to be, and is, in fact, a parent of numerous selections including 'Morden Gleam' and 'Morden Rose'.
It has been suggested that solitary plants in a garden situation would not proliferate by seed because of their need for cross-pollination by insects from another lythrum plant. On the contrary, isolated plants may not be safe form cross-pollination after all, as lythrum attracts honey bees, and bees are able to travel many miles, pollinating from plant to plant.
A recent cross-pollination study out of the University of Manitoba (2) concluded that lythrum cultivars "may contribute significantly to the problem of the naturalization of purple loosestrife in this continent."
In view of all this, it becomes evident that the vegetative propagation of a given selection is no guarantee of a sterile and innocuous clone.
No problem?
Alberta Agriculture's Crop Protection Branch (quoted in May 1992 issue of Kk) reported that Alberta wetland infestations of lythrum were far from severe. From personal observation of a wetland site some 5 kilometer west of the botanic garden, the situation is indeed severe. Covering several acres of wetland, complete eradication may be out of the question. Mr. Les Wetter, a representative of Ducks Unlimited, feels that the best that can be hoped for at that site is containment.
So what can we conclude? The so-called "good" lythrum become "bad" when they find a wetland habitat. We have serious infestations of wetlands that are far beyond mechanical removal.
Under the Noxious Weeds Act of Alberta it is illegal to grow or transport purple loosestrife. Problems associated with the enforcement of the Act, and recognition of the pest have yet to be properly addressed. Recognition of loosestrife is becoming easier as we appreciate the diverse morphology of the species. The complex population may be enriched by hybridization with the closely related L. virgatum and L. alatum, resulting in populations exhibiting hybrid vigor.
Controls?
Small outbreaks of a few plants may be controlled, or perhaps even eradicated, by diligent hand-digging. Floating seed readily establishes new colonies that may remain undetected for the first season or two until they flower; by which time they are firmly entrenched. European studies indicate that any control measure, including mowing, burning, water-level manipulation, and chemical applications, provide only short-term relief.
Entomologists in the United States are currently introducing a weevil and two beetles from Europe to start some biological control. Agriculture Canada has also approves the release of these three insect species in Canada. The weevil feeds on the central root parts, and the beetles feed on the leaves. The introduction of a new insect species into an ecosystem is not undertaken lightly, and the work must proceed slowly and with caution. Nevertheless, biological control through phytophagous insects will likely prove to be one of the best long-term controls.
The loosestrife invasion is not good news for gardeners who appreciate the horticultural value of lythrum selections, and is even more upsetting for commercial horticulturalists who will lose a lucrative commodity.
The sudden urgency surrounding the loosestrife question is puzzling
to many horticulaturalists who were, until recently, encouraged
to grow this plant as an attractive and reliable ornamental. The
unseemly haste in which this plant has been rejected is due to
what has been described as a situation reaching "critical
mass". The relatively slow build-up of loosestrife plants
in gardens, together with the appearance of a number of naturalized
colonies, has brought us to the point where cross pollinization
and the production of fertile seed is far more likely. With seed
production (a single flower stalk can produce 300,000 seeds) it
is only a matter of time before some seed finds its way to sensitive
habitats, creating a monoculture that provides little food or
shelter for native wildlife.
What now?
Meanwhile the Lythrum salicaria under cultivation at Devonian Botanic Garden, including selections and named cultivars, were all starting to set seed in the summer of 1992. To be on the safe side, therefore, the DBG collection has been removed and burned. The wetlands of Alberta are a precious natural resource, and there is no point in putting them at further risk for the sake of a garden ornamental.
Considering the rapidity with which this noxious weed is becoming established in wetlands, the nursery industry and municipalities should also be setting a good example for home gardeners, and carefully disposing of their loosestrife plantings.
When removing purple loosestrife, dig and burn (fire restrictions permitting) or bury deeply in the garden, or seal in a plastic bag for normal garbage disposal at a landfill site. Be aware that the clear bag garden waste system in use in Edmonton is for composting materials only, and not for the disposal of purple loosestrife.
References
(1) Anderson, Neil O., and Peter Ascher, Dept. of Horticultural Science, University of Minnesota, St. Paul MN 55108, Male and female fertility of loosestrife (Lythrum) cultivars, a paper submitted (1992) to the Journal of the American Society for Horticultural Science.
(2) Ottenbreit, Kimberly, and Richard Staniforth. Dept. of Botany, U of Manitoba, Winnipeg, MB. Dept. of Biology, U of Winnipeg, Winnipeg, MB. Crossability of cultivated and naturalized populations of purple loosestrife (Lythrum spp.) Canadian Botanical Association conference, Edmonton, AB (1991)
Invasive Plants of Natural Habitats in Canada
An Integrated Review of Wetland and Upland Species and Legislation Governing their control.
David J. White, Erich Haber and Cathy Keddy
Report prepared for the Canadian Wildlife Service, Environment Canada
In cooperation with the Canadian Museum of Nature
1993
PURPLE LOOSESTRIFE (Lythrum salicaria L.1)
ALTERNATE COMMON NAME
Spiked loosestrife, swamp loosestrife
TAXONOMIC OVERVIEW
The genus belongs to the loosestrife family (Lythraceae) and consists of about 30 species mostly of north temperate regions. The generic name comes from the Greek Luthron, blood, possibly in reference to the colour of the flowers or to one of its herbal uses, as an astringent to stop the flow of blood. Purple loosestrife was describe by Linnaeus in 1753.
DISTRIBUTION
Purple loosestrife is native to Eurasia. It was probably introduced to North America in ship ballast, on imported sheep, or in livestock feed and bedding in the early 1800s (Thompson et al., 1987; Hight and Drea, 1991). By 1830 purple loosestrife was well established along the New England seaboard (Thompson et al., 1987; Hight and Drea, 1991). In North America it now occurs in greatest concentrations primarily in northeastern United States and adjacent Canada where it is common to abundant (Figure 5). Keddy (1990) contains a detailed map of the distribution and abundance of purple loosestrife in Ontario. In lower densities it occurs across virtually the entire United States and the southern portion of Canada (Hight and Drea, 1991). Lee (1991) documents purple loosestrife in all Canadian provinces. A 1991 public survey extended the range as far north as The Pas, Manitoba (and in 1992 to Snow Lake, Manitoba), and confirmed it presence in salt marshes on both the Atlantic and Pacific coasts (G. Lee, pers. com., 1992). Although most of its spread in North America probably relates to the initial introductions from ship ballast etc., some populations may have spread from intentional introductions for herbal use of the plant, from home garden plantings, or from wildflower seed mixtures that often contain purple loosestrife seeds (Hanna, 1989; Thompson, 1991; Thompson et al., 1987).
1The treatment for purple loosestrife is limited to a general overview of the most recent information and is not intended to summarize the vast body of literature on the species.
BIOLOGY
Purple loosestrife is an herbaceous perennial. Its prolific seed production--up to 2.7 million per plant per year--enables the plant to establish dense stands within a few years (Hight and Drea, 1991; Thompson et al., 1987). It can also spread vegetatively by adventitious shoots and roots from clipped, trampled, or buried stems (Thompson et al., 1987). As well, ornamental-grown 'seedless' cultivars have been shown to produce large quantities of viable seed when fertilized with pollen from naturalized populations (Ottenbreit, 1991). The resulting hybrids from this cross are themselves highly interfertile (Ottenbreit, 1991).
ECOLOGY
The prolific seed production of purple loosestrife enables it to quickly develop a large seed bank at a site (Charvat and Stenlund, 1990). The seeds are able to live for several years and they can germinate across a wide range of environmental conditions (Welling and Becker, 1990). These factors have important implications for possible control of the species: removal of adult and/or seedling plants in an established population to re-establish itself from the seed bank.
The impact of purple loosestrife is seen in loss of native flora and fauna in infested wetlands, degradation of wetland pastures and wild hay meadows, clogging of irrigation systems, and the loss of natural habitats for recreational enjoyment (Hight and Drea, 1991). When purple loosestrife establishes dense stands it is able to displace native species (Thompson et al., 1987; Hanna, 1989; Balogh and Bookhout, 1989). Displaced species may include plants--rare or otherwise (Moore and Keddy, 1988), or they may include waterfowl and furbearers which are displaced because of the loss of foodplants or changes in cover values of the wetland (Thompson et al., 1987; Balogh and Bookhout, 1989; Heidorn and Anderson, 1991).
PRESENT STATUS AND POTENTIAL THREAT
At present, the area of greatest impact of purple loosestrife is the northeastern United States and adjacent Canada (Hight and Drea, 1991). Until recently, there has been only limited spread in central and western United States and Canada. In British Columbia, it is becoming increasingly invasive and is a fisherman's concern (G. Lee, pers. com., 1992). In Alberta, it is believed that there are only 15 locations (Ali, 1992). Infestations in prairie sloughs, which produce a large portion of many North American ducks, could have a major impact on waterfowl populations already under stress from other factors. Mosquin and Whiting (1992) regard purple loosestrife to be one of five invasive alien plants that have had a major impact on natural ecosystems in Canada. In The Plant Press survey it was regarded as a problem in southwestern, central, and eastern Ontario (Kaiser 1986). It is considered to be a high priority species for removal from Point Pelee National Park, Ontario (Dunster, 1990).
CONTROL MEASURES
Because purple loosestrife is so well-established, so widespread, and so prolific, it should be clear that it would be impossible to totally eliminate it from North America. It might be possible in the long term , however, to reduce its impact in large areas with and effective biological control program. In the short term at least, it might be possible to eliminate is from highly significant or sensitive areas, or areas where it was not well-established, by the use of physical and/or chemical control (Thompson et al., 1987). a recent workshop on the impact, spread, and control of purple loosestrife in Canada felt that no single control method would be sufficient but that an integrated approach with consideration of the particular site involved must be taken to control this alien (Lunam, 1992).
Effective control might consist of the use of physical and/or chemical measures, on an interim basis: (1) to eliminate the species from highly significant sites with a low population present; (2) to eliminate the species in geographical areas where it is just becoming established; and (3) to contain the plant in large sites with an extensive population in order to slow its spread (Thompson et al., 1987; Keddy, 1990). Such a program could minimize damage caused by the species and 'buy time' while development proceed on biological control efforts.
In Quebec, starting in 1941, Louis-Marie conducted a study to find suitable control methods (Thompson et al., 1987). The results showed that repeated mowing with continuous grazing, and deep discing and harrowing were effective in agricultural land (Thompson et al., 1987). More recently in Ontario there have been some preliminary study to identify effective control measures for natural areas (Keddy, 1990).
In the United States, there has been considerable research into possible control methods involving physical, chemical, and biological control (Thompson, 1991; Hight and Drea, 1991). Physical control, such as mowing or flooding, appears to be of limited usefulness (Crowder, 1991; Hanna, 1989); control using herbicide is a yearly operation due to the recruitment from the seed bank and is complicated by the need to control damage to other biota of the wetland (Crowder, 1991; Hanna, 1989); control using biological agents appears to be the most promising, however research into this control method is still in the field stage for several of the likeliest candidates (Hight and Drea, 1991; Thompson, 1991).
Studies on the seed bank dynamics of purple loosestrife have shown that to be effective, a control program would have to operate on a continuing basis. One-time control measures would have only a temporary effect due to new plants being recruited from the extensive seed bank which a population quickly establishes in a site (Welling and Becker, 1990). There is also evidence that a minority of established plants can remain dormant above-ground for a year and then resume growth the next season (Thompson et al., 1987). Control measures would also have to take that unusual plant behavior into account.
Physical control of purple loosestrife includes a range of options from hand-pulling and shearing, to inundation, mowing, cultivating, and fire (Thompson et al., 1987; Keddy, 1990; Hanna, 1989). Some of these, including mowing, cultivating, and probably inundation, are probably not suitable for the control of purple loosestrife in many natural areas because of the damage to native plant species. Hand-pulling and shearing are suitable only for very limited infestations due to its labor-intensive nature (Keddy 1990). Fire is ineffective because the root crown is well protected below the surface and little fuel accumulates on the surface to support the kind of hot fire which would be needed to affect the roots (Thompson et al., 1987). Flooding appears to take several years to have an appreciable effect in the reduction of purple loosestrife and the levels must be substantially higher than normal in order to be effective (Thompson et al., 1987). In many wetlands this flooding would probably have other profound effects on the native flora and fauna.
Chemical controls that have been used in the United States include 'Rodeo' and 'SEE 2,4-D' (Keddy 1990; Hemphill, 1991). Some reports consider these chemicals to be useful (Hemphill, 1991), however, others consider their use to be of limited benefit (Thompson, 1991) due to high cost and temporary effectiveness (Hight and Drea, 1991). Rodeo is not licensed for use in Canada, however, Roundup, which is closely related to Rodeo, could possibly be allowed in terrestrial habitats by permit since it can be used on a broad range of plants (Keddy, 1990). SEE 2,4-D can also be used on purple loosestrife in terrestrial habitats, however, no chemicals are registered in Canada for use against purple loosestrife in aquatic habitats, (Keddy, 1990). The problem of restricting the effects of the herbicide to the target plant, purple loosestrife, is one of the most difficult aspects of chemical control (Hanna, 1989; Keddy, 1990). Canadian herbicide trials are continuing in a number of provinces in search of formulations and applications that will satisfy Canadian environmental standards (G. Lee, pers. com., 1992).
Biological control agents for purple loosestrife were investigated initially by the International Institute of Biological Control (IIBC), Europe. The IIBC was contacted by the U.S.A. to so the initial survey fro biocontrol agents in Europe and to conduct the screening tests on candidate organisms (R. DeClerck-Floate, pers. com., 1992). Biological control tests were also conducted in the United States for a number of years (Thompson, 1991; Hight and Drea, 1991). Three beetles were approved for release in the United States on June 26, 1992-- Hylobius transversovittatus is a root-infesting weevil, and Galerucella calmariensis and G. pusilla are leaf-feeding beetles. Canada approved release of these threes insects on July 13, 1992. Feeding by these insects at high densities of attack resulted in defoliated mature plants, killed seedlings, and destruction of or prevention of formation of flower spikes (Hight and Drea, 1991). In addition to being effective, these insects are highly host-specific as has been confirmed during trials between 1988 and 1990. These trials involved the three insects and 50 plants that were either closely related to purple loosestrife , were commonly associated with purple loosestrife, were commonly associated with purple loosestrife in its wetland habitat, or were important agricultural crops (Hight and Drea, 1991). Supplies of these insects were acquired during the summer of 1991, quarantined first in the United States and then in Canada, and are presently being winter hardened in anticipation of initial releases and further propagation in 1993 (G. Less, pers. com., 1992). Several years of field trials will be necessary to determine whether or not these insects have real potential to effectively control purple loosestrife (Hight and Drea, 1991).
It seems clear that the only hope of achieving widespread and long-term control of purple loosestrife is with the development of an effective biological control program (Thompson et al., 1987). The plant is simply to well-established cross too wide an area for physical or chemical control methods to do more that achieve temporary and local relief.
SURVEY SUMMARY AND COMMENTS
The vast majority of the respondents to the survey rated purple loosestrife as a severe widespread problem that is spreading. Comments included: Purple loosestrife is the worst invasive alien of wetlands in Ontario. In British Columbia it is not yet very invasive. In Ontario it is perhaps the most invasive alien species. Along the Ottawa River in Quebec there has been a great increase in purple loosestrife in shoreline areas surveyed between 1979 and 1991. In Quebec it is the most aggressive competitor. One respondent felt that trying to control a well-established species like purple loosestrife is futile and wasteful. Purple loosestrife is one of the few alien species that presents a serious threat to the plant communities of natural habitats.
LITERATURE CITED
ALI, S. 1992. "Purple loosestrife in Alberta." Paper presented at National Workshop on Purple Loosestrife Management , March 2-5, 1992. Ottawa, Ontario. Unpublished.
BALOGH, G.R. and T.A. BOOKHOUT. 1989. Purple Loosestrife (Lythrum salicaria) in Ohio's Lake Erie marshes. The Ohio Journal of Science 89: 62-64.
CHARVAT, I. and D. STENLUND. 1990. Seed bank germination responses of Lythrum salicaria, Typha spp. and other species. American Journal of Botany 77 (Supplement) June 1990 abstracts, poster #168.
CROWDER, A. 1991. Purple Loosestrife. The Blue Bill 38: 46-50.
DUNSTEN, K. 1990. Exotic plant species management plan, Point Pelee National Park. Report prepared for Parks Canada, Ontario Region.
HANNA, J. 1989. Purple invader. Seasons 29(2): 20-22, 36.
HEIBORN, R and B. ANDERSON. 1991. Vegetation management guideline: purple loosestrife (Lythrum salicaria L.). Natural Areas Journal 11: 172-173.
HEMPHILL, D.R. 1991. A plague of perfect plants. Harrowsmith 96: 103-104.
HIGHT, S.D. and J.J. DREA, Jr. 1991. Prospects for a classical biological control project against purple loosestrife (Lythrum salicaria L.) Natural Areas Journal 11: 151-157.
KAISER, J. 1986. Exotic species of plants that are potential weeds of natural areas. In Proceedings of the Annual Meeting of the Ontario Chapter, Canadian Land Reclamation Association, May 5, 1986, Jordan Harbour, Ontario.
KEDDY, C. 1990. A protocol for purple loosestrife management. Draft report prepared for the Nature Conservancy of Canada, Wildlife Habitat Canada, and the Ontario Ministry of Natural Resources. 41 pp.
LEE, G. 1991. "Purple loosestrife (Lythrum salicaria) infestations in Canada: a national status report." Canadian Wildlife Service, Environment Canada. Ottawa, Ontario. Unpublished draft report.
LUNAM, B. 1992. A participant's assessment of the Purple Loosestrife Workshop. B.C. Naturalist 30(4): 8-9.
MOORE, D.R.J., and P.A. KEDDY. 1988. Conservation of infertile wetlands: priorities and management. Pp. 391 - 397 in M.J. Bardecki and N. Patterson, eds. Wetlands: inertia or momentum. Proceedings of conference, October 21-22, 1988, Ryerson Polytechnical Institute, Toronto, Ontario.
MOSQUIN, T. and P.G. WHITING. 1992. Canada Country Study of Biodiversity: taxonomic and ecological census, economic benefits, conservation costs, and unmet needs. Draft report for delegations to the International Convention on Biological Diversity, Brazil, 1992. Canadian Museum of Nature, Ottawa, Ontario.
OTTENBREIT, K.A. 1991. "The distribution, reproductive biology, and morphology of Lythrum species, hybrids, and cultivars in Manitoba." M.Sc. thesis, University of Manitoba, Winnipeg, Manitoba.
THOMPSON, D.Q. 1991. History of purple loosestrife (Lythrum salicaria L.) biological control efforts. Natural Areas Journal 11: 148-150.
THOMPSON, D.Q., R.L. STUCKEY, and E.B. THOMPSON. 1987. Spread, impact, and control of purple loosestrife (Lythrum salicaria) in North American wetlands. United States Fish and Wildlife Service, Fish and Wildlife Research No. 2. United States Department of the Interior, Washington, D.C. 55 pp.
WELLING, C.H. and R.L. BECKER. 1990. Seed bank dynamics of Lythrum salicaria L.: implications for control of this species in North America. Aquatic Botany 38:303-309.
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