Oregon Department of Agriculture Pest Risk Assessment for Iris pseudacorus February 2005

Transcription

1 Oregon Department of Agriculture Pest Risk Assessment for Iris pseudacorus February 2005 Yellow Flag Iris (Iris pseudacorus L.) Synonym: water flag, yellow flag, pale yellow iris Family: Iridaceae Findings of this review and assessment: Iris pseudacorus, yellow flag iris has been determined to be an invasive plant within the criteria of a B listed noxious weed as defined by the ODA Noxious Weed Policy and Classification System. This determination is based on two independent risk assessments and a review of the literature. Using a rating system adapted from the USDA-APHIS Weed Risk Assessment Guidelines, Iris pseudacorus received a score of 23 out of a potential score of 29. Using the ODA Noxious Weed Rating System, yellow flag received a score of 15 supporting a B listing. Summary: Yellow flag iris is a popular ornamental in North America that is planted in natural and artificial wet areas within urban and rural landscapes. It is particularly popular as a large and colorful flowering element in ponds and has been planted in wastewater ponds where it is used to remove heavy metals. Unfortunately, I. pseudacorus commonly escapes from cultivation. The species has naturalized extensively and is currently distributed across the United States. Once established, it is an aggressive invader in most wet habitats. Along the Pacific, Atlantic and Gulf Coasts it has invaded estuarine and wetland habitats. Inland, I. psuedacorus has invaded riparian, open water features and irrigation ditches. In these habitats it has displaced native plants, disrupted ecological relationships and interfered with water movement. Growth characteristics: Yellow flag is a very showy species growing 3-4 feet in height with the most vigorous growth attained in the wettest environments. The leaves are long, flattened and sword-like, typical of most iris. Large plant clumps are formed from the lateral growth of rhizomes sometimes attaining 20 feet in width. Flowers are produced on Final 2/23/05-1 -

2 erect plant stalks with multiple flowers produced on each. Fruit capsules are large, 3- angled and up to 4 inches in length. Disk-like seeds are shed from the capsules throughout the fall and winter. Floating mats of seed can be observed in backwaters and marshes aiding dispersal. Reproduction can occur asexually through rhizome fragmentation or by seed production. Food storage in this species is unique. Fructan is the main storage compound held in the cells as opposed to starch. This allows the plants to metabolize energy under very low oxygen conditions and may provide cells with a natural anti-freeze for the winter. Considerations and impacts: An infestation of yellow flag iris presents a dual impact on both human interests and native environments. Irrigation canals and flood control ditches can be severely restricted by the physical nature of the plant clumps. Removal can be costly requiring large excavation equipment or herbicides. Control of heavily infested waterways can be cost prohibitive due to the huge volume of plant material needing to be removed. Any rhizome fragments that remain quickly reestablish a population. Invaded marshes in some eastern states are experiencing a significant displacement of native sedges and rushes with monocultures of iris. Many over-wintering waterfowl species are dependent on sedge and rush seeds as a high-energy food source. Replacement of this food source with yellow flag iris would reduce the carrying capacity of these marshes to sustain waterfowl populations. A small volume of yellow flag still exists in the nursery trade. A variegated variety is popular with aquatic gardeners and can be found in several catalogs and web sites. The ease with which this plant can be established using rhizome fragments has led to extensive trading among gardeners and aquatic plant enthusiasts. Native range: Yellow flag is native to most European countries with the exception of Iceland. It is also known from North Africa and the Mediterranean regions. It has significant freeze tolerance and can be found in Scandinavia to 68 degrees North. Weedy populations: It is reported weedy in New Zealand and Canada. Most states in the U.S. report escaped populations but the extent of these populations are not well documented. In Oregon, significant populations can be found in the Willamette valley, in costal lakes and streams, in the Columbia River and in Central Oregon on irrigation canals. Smaller populations are also known to exist in northeast Oregon. Final 2/23/05-2 -

3 U.S. Distribution of Yellow flag Iris Assessing Pest Risk: Two weed rating systems were used to assess pest status for this weed risk assessment. The first is a rating system adapted and modified from the Weed Risk Assessment Guidelines for Qualitative Assessment developed by the U.S. Department of Agriculture Animal and Plant Health Inspection Services, Plant Protection and Quarantine (USDA-APHIS 2002). A second system, Oregon Department of Agriculture Noxious Weed Rating System, developed by the ODA weed staff was also used for the assessment process. Final 2/23/05-3 -

4 Assessing Pest Risk USDA-APHIS Qualitative Assessment 1. Habitat Suitability Explanation: Suitable climate and habitats (and availability of host plants, if organism is a parasitic plant) would permit the weed to survive and establish. Scoring: High (5) Can thrive and reproduce in most or all of the potential habitat and potential habitat is enormous or extremely limited. Plant acreage is currently severely limited <10 acres net Medium (2) can grow and reproduce in approximately one-third to two-thirds of potential habitats or plant acreage is >10 but < 100 acres net Low (1) Can thrive and reproduce in approximately one-third or less of potential habitats. Plant acreage is greater than 100 acres net. Rating Numerical Score Explanation Medium 2 Establish in most potential habitat Explanation Oregon contains significant acres of suitable riparian and marsh/wetland habitat available for invasion. Plant establishment is very dependent on stable, moist environments found typically in the lower reaches of large river systems, in canals and permanent ditches and wetlands subjected to river flooding during major storm events. 2. Spread potential after establishment: dispersal potential Ratings and definitions: Ratings: High (3) Weed has potential for rapid natural spread throughout its potential range. Weed has high reproductive potential and highly mobile propagules. Seeds are wind dispersed. Medium (2) Weed has potential for natural spread with either high reproductive potential or highly mobile propagules. Propagules spread by moving water, humans or animals. Movement possible through long distance commerce. Low (1) Weed has potential for local spread within a year. Moderate reproductive potential or some mobility of propagules. Propagules may be moved locally by animals, wave action in lakes. Negligible (0) Weed has no potential for natural spread in the analysis area Scoring Rating Numerical score Explanation Medium 2 High reproduction, not wind dispersed Final 2/23/05-4 -

5 Explanation Extensive selling and trading of plants by gardeners has lead to this plants introduction into most waterways in central and western Oregon. Rapid downstream movement of seeds and root fragments enables this plant to reach most sections of a waterway especially during flood events. 3. Economic Impact Ratings and definitions: Ratings: High (3) Weed causes impacts in reduced crop yield, lowered commodity value, increased cost of production or a loss of markets due to contamination or weed also may cause significant impacts to recreation, fishing and hunting and property values. Control costs to manage infestations would become significant. Medium (2) Weed causes two of the above economic impacts or a single impact over a wide range (over 5 types) of economic plants, recreation, products or livestock. Low (1) Weed causes one of the above impacts. Negligible (0) Weed causes none of the above impacts. Scoring Rating Numerical Score Explanation Low 1 Weed causes limited economic impacts in one category Explanation Economic impacts are limited to the increased costs of irrigation canal maintenance and vegetation control via herbicides or by physical removal. Some drainage systems may experience reductions in function and flow due to sediment entrapment by vegetation. This may result in damage to the system or surrounding areas during flood events. 4. Environmental impact Descriptions of environmental harm: - Causes impacts on ecosystem processes (fire, sedimentation, hydrology, growth, others) - Causes impacts on natural community composition (biodiversity losses, threaten T&E species, alter native fauna etc.) - Causes impacts in community structure (cover canopies, alter layers alter habitat) - Impacts human health negatively - Indirect impacts measured by a reduction in aesthetic value, reduced opportunities for recreation and reductions in other non-monetary values. - Stimulate control programs for control where non-target impacts could be significant (e.g. aquatic weed treatments, non-target affects from pesticide applications). Ratings: High (3) Three or more of the above categories. Medium (2) Two of the above categories. Final 2/23/05-5 -

6 Low (1) One of the above categories unless weed has potential to reduce population of T&E species with only limited impact on the environment. T&E threats are ranked higher. Negligible (0) None of the above effects probable. Rating Numerical Score Explanation Medium 2 Weed causes impact in two categories Weed causes impacts to plant diversity and species composition in streamside, wetland and marsh habitat. Waterfowl nesting and over-wintering potential is reduced due to displacement of food species. Large iris infestations may increase mosquito populations locally due to decreased predation of larvae in dense protected iris stands. 5. Likelihood of Introduction/Spread Entry Potential: The likelihood that an exotic weed will be introduced and spread depends on the number of associated factors, some physical, some biological, some social/economic. For this analysis, consider these 5 factors: 1. Weed is pest in similar climactic zones. 2. Proximity to State. 3. Probability of early detection. 4. Probability of introduction to an environment suitable. 5. Come into contact with suitable growing substrate or host material Factors of Introduction, Establishment and Spread: Scoring: 5 or 3=High, 3 or 2=Medium, 1=Low 1. Weed is a pest in similar climactic zones. 5=Weed is known to be a significant pest in similar climactic zones at place of origin or weed demonstrates significant adaptation to multiple climactic zones wherever it is found. 3=Plant demonstrates weedy characteristics in non-place of origin areas only. Plant limited to a few climactic zones 1=Weed is strictly limited to one minor climactic area or zone. Plant exhibits little adaptability to new environments. Score: 5 Final 2/23/05-6 -

7 2. Proximity to State: 5= Weedy populations found in state or adjacent to Oregon border. 2=Weedy populations found in Western US regions but not adjacent to Oregon border. 1=Weedy populations found in Eastern US regions or foreign country only. Score: 5 3. Probability of detection at introduction point. 3=high probability of no initial detection, weed shape and form obscure/not showy, introduction probable on lands remote or offlimits to weed professionals 2=Weed easy to identify by weed professionals, land managers, botanists, some survey and detection infrastructure in place. 1=probability of rapid detection high, plants showy, public easily recognizes weed, access not limited. Score: 1 4. Probability of weed imported or moved to suitable habitat. 3= high probability that weed will be introduced yearly via agriculture, commerce, commodities. 2=moderate probability of introduction. Generally non-agricultural commerce, vehicles, equipment. 1=low probability of introduction either naturally or by humans. Low probability of humans or animals contacting weed at point of origin. Score: 2 5. Weed already established. Probability of further expansion in state. 3=Weed found in highly disturbed areas. Weed found in rangeland or in areas that are hayed, grazed, logged. Infested area possesses ideal growing conditions for reproduction and spread. 2=Weed found in State outside of ideal growing environment. Reproduction occurring but limited or weed growing in stable environment or subjected to significant competition from native plants. Final 2/23/05-7 -

8 1= Weed is at edge of growing range. While demonstrating significant impacts in other climates, local infestation is limited by weather, temperatures, freezing, biocontrol, or lack of reproductive ability. Score 3 Category 5 total= 16 Total score for Iris pseudacorus: 23 out of a possible 29, derived from the sum of all 9 categories. Grading scale: is an "A" score; is a"b"score. Exceptions may be made for certain weeds of very limited distribution in the state. Total risk score for Iris pseudacorus: 23 (moderate) out of a possible 29, derived from the sum of all 9 categories. This analysis determines that Iris pseuacorus can potentially disperse and become invasive over large areas of aquatic habitat in slower moving streams and in lakes, ponds, and canals. In certain habitats it may displace native shoreline vegetation significantly. Economically it may increase the cost of irrigation canal maintenance or obstruct drainage canals. It does not invade agricultural land. Its widespread distribution makes containment impossible. Iris pseudacorus is rated a "B" weed. Final 2/23/05-8 -

9 OREGON DEPARTMENT OF AGRICULTURE NOXIOUS WEED RATING SYSTEM Yellow flag iris Iris pseudacorus Common Name Scientific Name Points Category 1. 2 Detrimental Effects: Circle all that apply, enter number of circles 1. Health: Causes poisoning or injury to humans or animals 2. Competition: strongly competitive with crops, forage, native flora 3. Host: host of pathogens and/or pests of crops or forage 4. Contamination: causes economic loss as a contaminate in seeds and/or feeds 5. Interference: interferes with recreation, transportation, harvest, land value, or wildlife and livestock movement 2. 4 Reproduction and Capacity for spread Circle the number that best describes 1. Few seeds, not wind blown, spreads slowly 2. Many seeds, slow spread 3. Many seeds, spreads quickly by vehicles or animals 4. Windblown seed, or spreading rhizomes, or water borne 5. Many wind-blown seeds, high seed longevity, spreading rhizomes, perennials 3. 3 Difficulty to Control Circle the number that best describes, enter 1. Easily controlled with tillage or by competitive plants 2. Requires moderate control, tillage, competition or herbicides 3. Herbicides generally required, or intensive management practices 4. Intensive management generally gives marginal control 6. No management works well, spreading out of control 4. 2 Distribution Circle the number that best describes, enter 1. Widely distributed throughout the state in susceptible habitat 2. Regionally abundant in a part of the state, 5 or more counties, more than 1/2 of a county 3. Abundant throughout 1-4 counties, or 1/4 of a county, or several watersheds 4. Contained in only 1 watershed, or less than 5 square miles gross infestation 5. Isolated infestation less than 640 acres, more than 10 acres 6. Occurs in less than 10 acres, or not present, but imminent from adjacent state 5. 4 Ecological Impact Circle the number that best describes, enter 1. Occurs in most disturbed habitats with little competition 2. Occurs in disturbed habitats with competition 4. Invades undisturbed habitats and crowds out native species 5. Invades restricted habitats (i.e., riparian) and crowds out native species 15 TOTAL POINTS (Note: Noxious weeds are those non-native plants with total scores of 11 points or higher. Any plants in 4.1, 4.2, 4.3 should not be classified as A rated weeds. Ratings: 16+ = A, 15 11= B) Final 2/23/05-9 -

10 References: Iris pseudacorus: Non-Native Invasive Plants in the United States. Web page publication of the Center for Aquatic and Invasive Plants, University of Florida and Sea Grant Iris pseudacorus; Invasive plant profile. Varigated yellow flag iris. (Detailed description of plant and cultivar) Sutherland WJ Biological flora of the British Isles. Iris pseudacorus L. J. of Ecology 78(3): Pfauth M research proposal submitted to USDA-ARS for funding to conduct studies on the reproductive biology, growth and allocation of resources of Iris pseudacorus. USDA-APHIS, U.S. Department of Agriculture, Animal and Plant Health Inspection Services, Plant Protection and Quarantine, Weed-Initiated Pest Risk Assessment: Guidelines for Qualitative Assessments. USDA-NRCS, Plants National Database, Final 2/23/