Duration: 10/01/2007 to 09/30/2012

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Statement of Issues and Justification

Lawns, parks, golf courses and other cultivated turf areas comprise one of the most important crops in the U.S., both in acres planted and in economic value. At an estimated 40+ million acres (Milesi et al., 2005), managed turf acreage rivals that of total U.S. corn (74 million), soybean (71 million) and wheat (50 million) acreage harvested in 2005 (NASS). The production and management of turf areas is estimated at $60-65 billion in annual sales, a significant portion of the estimated national green industry total of $147 billion (Hall et al., 2005). The economic importance of the national turf industry is evident when compared with the estimated national total farm market prices of corn at $22 billion (11 million harvested bushels, at $2/bushel) and soybeans at $75 billion (15 billion harvested bushels, at $5/bushel) (NASS).

On 3 Feb., 1999, former President Clinton signed Executive Order 13112, which sought to prevent the introduction of invasive species and provide for their control (USDA, 2005). Two of the most popular turfgrasses, Kentucky bluegrass (Poa pratensis) and creeping bentgrass (Agrostis stolonifera), were introduced to the U.S. as long ago as the 1600s. Both species have become naturalized and are now identified as invasive species by national and state groups/agencies (Plant Conservation Alliance, 2005; Stubbendieck et al., 1994; The Nature Conservancy, 2005; USDA, 2005, Wisc. Dept. Nat. Res., 2003). A number of subspecies and varieties exist, however, with major differences in growth, development, stress tolerance and perhaps invasiveness (Murphy et al., 1997; NTEP, 2005). Many states are carefully winnowing and sifting their lists for accuracy; for example, in 2004 Connecticut banned the import and sale of 80 ornamental plants excluding certain cultivars pending research results on invasiveness. States such as Massachusetts, however, are planning to ban 140 species regardless of varietal differences (Anonymous, 2005). The Midwest turf industry is an important component of agriculture; in Wisconsin, for example, the Agricultural Statistics Service estimates the annual value of the Wisconsin turf industry at nearly $1 billion, with $25 million just from sod farms (WASS, 2001; WASS, 2005). Most of the 10,500 acres of Wisconsin sod production is P. pratensis, with a small but increasing amount of A. stolonifera. This is comparable to most states in the Midwest and central Great Plains. Sod farms are typically surrounded by natural areas of fields and forests. Continuous influx of seed into the area at planting time and grass production of vegetative propagules (rhizomes, stolons) could facilitate spread into surrounding areas, but data are lacking to determine the extent to which this occurs.

The turfgrass species sold and planted (via sod, seed or sprigs) on the vast majority of cultivated turf areas are not native to the United States. Kentucky bluegrass (Poa pratensis) and bermudagrass (Cynodon spp.) are the most widely used turf species on northern and southern (respectively) lawns. Other non-native species used less commonly in lawns  but commonly on golf courses  include bentgrasses (Agrostis species) and perennial ryegrass (Lolium perenne). Several different non-native fescues (Festuca species) are used on both lawn and golf courses. In recent years concern has been expressed by a number of private groups with interests in preserving ecologically sensitive or unique areas, as well as by some municipal, state and federal agencies, that commonly used turf species may prove to be invasive species under certain geographic, ecological or environmental conditions. Numerous invasive species lists designate bluegrasses, bentgrasses, bermudagrass and other turf species as invasive. Many turf industry professionals and university researchers believe that inclusion of turf species on some of these lists has occurred because of misidentification. Grass species are difficult for even the most experienced scientists to identify. Further, there are many native species of bluegrasses (Poa species), bentgrasses (Agrostis species) and fescues (Festuca species), which could be easily confused with the cultivated, non-native turf species. Finally, it is not uncommon for these lists to be copied or cloned by groups and some agencies  without any collection of valid data to support the inclusion of species on the lists.

The proposed research is important because inclusion of commonly used turf species on invasive species lists may lead to prohibition of their propagation, sale or planting. Any restriction on the production, sale or planting of these turf species would cause immeasurable economic harm to both the U.S. sod production industry (over 2,100 farms covering over 386,500 acres, with $1 billion in annual sales in 2004) and the U.S. turf seed production industry (over 650,000 acres, with sales exceeding $750 million in 2004).

The proposed research is suitable for Hatch funding because turfgrass production and management are considered urban agriculture. Both sod and turf seed production are real farm production enterprises, often providing farmers with new markets and substantial profits. The USDA has a 100-year history of hiring turfgrass researchers, and a $32.5 million annual initiative is currently being developed with ARS to expand turf research at the federal level.

While turfgrass positively affects quality of life by providing recreational areas, preventing erosion, enhancing groundwater recharge in urban areas and filtering runoff, and providing cooling in the urban environment, any potential for cultivated turf species to become an aggressive, damaging invasive species in natural and ecologically sensitive areas must be identified.

The proposed project suggests the use of multiple locations throughout the central U.S.. The inclusion of diverse environments is critical to developing a comprehensive understanding of invasiveness of targeted species. No single state offers the breadth of environments prominent in the region. By crossing state lines, precipitation, edaphic and existing vegetation variability will be significantly enhanced and offer better possibilities for project success.

Related, Current and Previous Work

Accurate identification and measurement of potentially invasive species is vital to protecting our natural resources. However, scientific data on the invasiveness of amenity grasses are nearly nonexistent. Nearly 70 Poa spp. and 40 Agrostis spp. exist in the U.S. (Hitchcock, 1950), with species designations usually dependent upon minor, often plastic, morphological characteristics. The Nature Conservancy lists numerous natural areas where P. pratensis and Agrostis spp. exist. However, clear species designation must be made. A report of a monostand of A. stolonifera at Theodore Roosevelt Park on Long Island, NY, turned out to be the closely related and morphologically similar A. capillaris (Eric Nelson,O.M. Scotts, Marysville, OH, personnel communication, 2005). Reports of invasive P. pratensis in forests of northern Wisconsin may be either P. trivialis or P. annua, both relatively shade tolerant compared to the sun-loving P. pratensis. Swards of suspected P. pratensis at the University of Wisconsin-Milwaukee field station were in fact a mixture of brome (Bromus spp.), Poa compressa, and P. pratensis (John Stier, Univ. Wisc. Madison, personal observation, Oct. 2004). Sod farms grow improved elite types with better turf quality than wild or common types, while common types are better adapted to grow without mowing, fertilizing and irrigation (Murphy et al., 1997). Distinguishing among varieties of P. pratensis and Agrostis spp. based solely on morphological traits has historically been difficult and prone to error. Molecular marker techniques developed at the University of Wisconsin now allows us to distinguish among species and varieties of Agrostis and Poa (Casler et al., 2003; Curley and Jung, 2004; Hollman et al., 2005; Scheef et al., 2003, Stier et al., 2005).

It is difficult to find any research-based documentation that turf species are acting as invasive species in any natural habitat. However, there has been enough anecdotal evidence collected by private (The Nature Conservancy, 2005) and state or federal agencies (USDA, 2005) to merit investigation of turf species as possibly invasive under certain circumstances. Work with other grasses (not turf-types) is only beginning to explain why some grass species become invasive, while others do not (Lavergne and Molofsky, 2004). It is apparent that invasiveness is governed by both abiotic factors (disturbance, nutrient availability, hydrological conditions), as well as by plant growth characteristics (periods of active growth, potential to spread vegetatively, seed production potential, growth rate, and degree of architectural plasticity) and genetics (degree of genetic diversity, phenotypic plasticity, and response to ecological conditions).

Objectives

1. Determine the potential for turf-type species of Kentucky bluegrass and creeping bentgrass to become invasive in landscapes by a) surveying lesser disturbed or native areas adjacent to existing sod farms and golf courses for populations of escaped bluegrass and bentgrass (or other turf-type species), and b) surveying abandoned sod farms and golf courses for the occurrence and persistence of turf species that had been planted at establishment.
   
2. If turf-type grasses are found growing in areas where not originally planted (have spread), or are persisting on abandoned (not maintained) sites, develop a measure of invasiveness for that species, at that site.
   
3. If turf-type grasses are found growing in areas where not originally planted (have spread), or are persisting on abandoned (not maintained) sites, determine what conditions are allowing them to persist.
   
4. Measure the potential for establishment and propagation/spread of bluegrass and bentgrass introduced (both vegetatively and via seed) into native shortgrass prairie.
   
5. Visit locations where turf species have been identified as exotic and/or invasive to identify the plant species in question and to determine its level of invasiveness.
   
6. Objective 6. From preceding objectives, develop and evaluate cultural modifications which will limit or eliminate the identified invasive species. Objective 7. All cooperating states will field test results and hypotheses from objectives 1-6, as appropriate, to evaluate edaphic, meteorological and geographical similarities or differences of observed and measured responses.
   

Methods

Species identification. Grass samples collected during surveys and when visiting suspected invasive populations will be identified (initially) using morphologic characteristics and grass identification keys (Hitchcock, 1950). Plant samples collected from participating states will be identified initially based on morphological characteristics, then verified using DNA markers. Poa spp. will be identified as P. pratensis, P. annua, P. trivialis, or other. P. pratensis plants will then be identified as common or elite types. Agrostis plants will be identified to the species level. Clonally-propagated plants will be grown under greenhouse conditions to provide fresh plant material for DNA extraction. Genomic DNA will be extracted by macerating fresh, individual leaves in potassium ethyl xanthogenate (PEX) DNA extraction buffer using a FastPrep FP120 machine (BIO 101 Inc., Carlsbad, CA) (Scheef et al., 2003). The rest of the DNA extraction procedure will follow Scheef et al. (2003). Polymerase chain reaction cycling parameters will follow the procedure of Johns et al. (1997). Reactions for RAPD analysis will be performed in 10 µl volumes in 96-well plates in an MJ PTC-100 (MJ Research, Watertown, MA). Four RAPD primers (M14, P8, Y9, and AG14) previously shown to identify over 120 P. pratensis varieties will be used to distinguish between common and elite types (Curley and Jung, 2004; Stier et al., 2005). Suitable primers to identify P. annua and P. trivialis, the other most common types of Poa spp. associated with human activity, will be selected from a larger pool of RAPDs useful for identifying grasses (Operon Technologies, Alameda, CA). Agrostis spp. will be distinguished using 5 RAPD primers (A-13, G-19, O-6, P-8, and Y-5) as described in Casler et al. (2003) and Hollman et al. (2005). All RAPD reaction products will be electrophoresed on 1.5% agarose gels as described by Scheef et al. (2003). Gels will be run for 1 hr 40 min. at 300 V, stained with ethidium bromide, illuminated by UV light and photographed. Distinct DNA bands will be manually scored with scoring tracked using GeneTools software (Syngne Inc., Frederick, MD) then compared for uniqueness to each species (or cultivar type for P. pratensis) and counted. When no molecular technique exists, grasses with unsure identification will be grown out (to form flowers and seeds) in the field and/or greenhouse. Species surveys. The researchers will work with plant ecologists from NREL and National Institute of Invasive Species Science (NIISS) to identify the most appropriate method of surveying land surrounding sod farms and golf courses, as well as on abandoned sod farms and golf courses. The following sites within each participating state will be surveyed for the presence of cultivated turf species: - All participating states will identify native or naturalized prairies in cooperation with state and federal entities. Presence of either Poa pratensis or Agrostis stolonifera will be confirmed by sampling. - Areas surrounding golf courses located in prairie areas will be surveyed. A diverse sampling of golf courses of varying management inputs will insure a better understanding of conditions favorable for invasiveness of identified turfgrasses. - Golf courses located adjacent to Bureau of Land Management or USDA Forest Service land will be surveyed for potential movement of cultivated species into native surrounding areas. - Other areas as identified through collaboration with the NIISS. Within the sites described above, locations and cooperators will be identified to evaluate potential for establishment and propagation/spread of bluegrass and bentgrass introduced (both vegetative and via seed) into native (or naturalized) prairie; both elite and common cultivars of P. pratensis will be used while Agrostis stolonifera cultivars will be chosen based on local/regional Extension recommendations. Sod of both species will be grown on turfgrass research facilities in participating states or obtained from local growers. The sod will be harvested and reestablished into the identified native/naturalized areas. During the course of this project, the rate of vegetative spread and seed transfer/establishment will be evaluated. Seed survival. Data on survival of turfgrass seed in the soil is almost nonexistent except for work conducted by Dr. Bruce Branham at University of Illinois on P. annua seed survival (personal communication, 2003). Seeds of three common and three elite types of P. pratensis will be compared for in situ survival relative to each other, three varieties of P. trivialis, and six biotypes of P. annua representing both P. annua var. annua and P. annua var. reptans. Seed survival of three varieties each of four Agrostis spp. (A. stolonifera, A. alba, A. capillaris, and A. canina) will be compared within and between species, and pooled Agrostis spp. will be compared with pooled Poa spp. The experimental design will be a split-split plot, randomized incomplete block with four replications. Main plots will be Poa and Agrostis. Sub-plots will be individual species of the two genera. Sub-sub plots will be biotypes of P. pratensis (common vs. elite) and P. annua (P. annua var. annua vs. P. annua var. reptans). Experimental sites will be determined based on facility availability within cooperating states. Seed representing common and elite P. pratensis and P. trivialis will be obtained from commercial sources. Poa annua var. reptans seed will consist of a commercial variety TruPutt and two types from Dr. David Huff at the Pennsylvania State University. Poa annua var. annua seed will be obtained from collections made region and the U.S. Germplasm Resources Information Network (GRIN). All Agrostis spp. seed will be obtained from commercial sources. The in situ portion of the experiment will be conducted at the UW-ARS OJ Noer Turfgrass Research and Educational Facility in Madison, WI. A prairie area, established in 2000, will be used as the in situ environment. Sufficient soil silt loam will be autoclaved to devitalize existing weed seed; preliminary trials for longevity of autoclaving requirements will be conducted until no existing weed seed is found to germinate. If successful autoclaving cannot be achieved, a sterile synthetic soil will be used instead. Sterile soil (approximately 1 cm3) will be mixed with 50 seeds of a given grass type and constitute one experimental unit (replicate). The soil:seed mixture will be placed in a nylon mesh bag (pore size approximately 300 µm) to allow passage of air and water while retaining seed and preventing other grass seed from entering. Bags will be buried approximately 7.5 cm below the soil surface, allowing exposure to freeze/thaw and wet/dry conditions, yet deep enough to prevent incidental light from stimulating germination. A steel plate will be placed at the soil surface near each bag to allow bags to be found with a metal detector, if necessary. Germination tests will be conducted at 0, 6, 12, 24 and 36 months. Bags will be exhumed from the plot area and the soil:seed mixture will be spread on a flat containing synthetic sterilized potting media. Soil in the flat will be thoroughly moistened, then the flat will be covered by a transparent layer of plastic wrap containing air holes. Flats will be incubated in the greenhouse for up to three weeks to allow seed. Typically, seed germination will be expected in five to seven days, but the additional time will allow any recalcitrant but viable seed to germinate. Seedlings will be counted and removed from the flat as they germinate. Viability will be measured based on the percentage of seeds that germinate in each of the four replicates. The time to reach 50% death (LT50) and 100% death will be determined for each grass type. Control and mitigation development and implementation. Principle investigators are well published in research and extension venues on (integrated pest management) IPM strategies and selective herbicide technologies. Sites and scenarios described in the preceding method sections will be used to implement and evaluate, using results from previous objectives, IPM approaches to eliminate or deter encroachment of those species and/or varieties found to be invasive. Field survey data analysis. The amount of cover and frequency (compared to other vegetation) of turfgrasses at distances from sod fields will be tested for significant differences using Kruskal-Wallis non-parametric one-way analysis of variance (ANOVA). A second series of analyses will be used to test for differences between common and elite types of P. pratensis, P. pratensis vs. other Poa spp., and A. stolonifera (the only species planted for sod) vs. other Agrostis spp. Multiple regression will be used to determine the impact of soil type and site type (forest, meadow, riparian area) on the distribution of Agrostis and Poa spp. Soil and site types will be used as independent variables. Cover and frequency of turfgrasses will be used as dependent variables. Data transformation will be used if appropriate to achieve required statistical assumptions (normality, additivity, variance stability, etc.) (Steel and Torrie, 1980). Species identification data analysis. A multidimensional scaling procedure (MDS) will be used to group unknowns with known controls for species identification by fitting the genetic distance matrix into two-dimensional coordinates (SAS PROC MDS; SAS Institute, 1990). Species information will be used as described under Field data (above) to determine the relative abundance of species and, in the case of P. pratensis, also biotypes. Analysis of molecular variance (AMOVA) will be used to partition variation among species, among populations within species, and among individuals within populations as in Hollman et al., 2005. Seed survival data analysis. Analysis of variance will be conducted on survival rates at each time period using replicates, blocks, genus, species, and varieties as factors. Replicates and blocks will be considered as random effects, while other factors will be considered as fixed. Contrasts will be used to compare Poa vs. Agrostis spp., P. pratensis vs. other Poa spp., P. pratensis vs. P. trivialis, P. pratensis vs. P. annua, P. annua vs. P. trivialis, elite vs. common P. pratensis, and P. annua var. annua vs. P. annua var. reptans. All four Agrostis spp. will be compared with one another, and varieties within each Agrostis spp. will be compared to determine varietal differences within a species. Control and mitigation development and implementation data analysis. Conventional and appropriate field plot design will be used for this objective. It is anticipated that a factorial arrangement of treatments will be the most statistically powerful and efficient. When possible locations will be replicated across the region to substantiate results and strengthen recommendations for mitigation and control. Expected results. It is expected that multiple types of Poa spp. will be found in natural areas, including a few species other than P. pratensis, P. annua, and P. trivialis. P. annua and P. pratensis will most likely be found at greatest densities in transects closest to sod fields and other disturbed sites (e.g., dirt lanes), while P. trivialis and Agrostis spp. will most likely be found in riparian areas, in areas moistened by irrigation, or in areas with high water table. The extent of P. pratensis is unknown, as is the extent and variability of Agrostis spp., as this will be among the first known targeted assessment of such species distribution in the U.S. Seed germination of P. pratensis may slightly increase from 0 to 12 months as inherent dormancy factors dissipate (D. Brede, personal communication 2001), after which survival should decline. Seed survival of other species is expected to decline with an increasingly negative trajectory over time. It is unknown what proportion, if any, of the seed will survive by 36 months. Van Clef and Stiles (2001) showed seed viability of native and non-native woody perennial species declined rapidly, often to zero, after 12 months, though approximately 33% of seed from one non-native invasive species (Polygonum perfoliatum) survived at 36 months. Development of field tested, efficient and successful mitigation approaches will help alleviate increased invasion and potentially eradicate existing compromised native areas.

Measurement of Progress and Results

Outputs

• Workshops with interested private and public entities to teach identification of turf species of concern.
• Participation in regional and national invasive species workshops, meetings and conferences to provide education regarding turf species and their potential to be an invasive species, and to report research results as they become available.
• Presention of a minimum of one paper annually at American Society of Agronomy meetings, Weed Science of Society meetings and/or other meetings as appropriate.
• Web site devoted to the subject of turf species as potential invasive species, with the intent of providing education on proper identification of species, as well as answering questions on management (cultural and chemical) of species growing in situations where they are not desired.
• Minimum of one paper submitted annually to a refereed journal, beginning in the second year of the project.

Outcomes or Projected Impacts

• Ability to determine the potential for turf species to become invasive, and identify those combinations of species and environments that may result in the development of an invasiveness problem.
• Ability to work with the sod production and seed industries (and their professional organizations) to address the issue of invasiveness and its potential effects on their respective industries.
• Establishment of a productive working relationship with the National Institute of Invasive Species Science, headquartered at the USGS Fort Collins (CO) office; the NIISS provides a hub for invasive species science collaboration, coordination, and integration across agencies and disciplines.
• Establishment of professional and productive working relationships with private groups (such as The Nature Conservancy) to ensure proper identification of species and instances of suspected invasiveness.
• Should instances of invasiveness by turf species be positively and critically identified, work with local agencies to develop management programs to limit or or eradicate the invasive species.

Milestones

(2009): Oct. 2007-September 2009: Survey sites and collect plant samples.

(2008): Jan. 2008-May 2008: Acquire seed for longevity project.

(2008): July 2008: Plant seed and conduct base germination tests.

(2011): August 2008-July 2011: Determine seed viability at 6, 12, 24, and 36 months after burial.

(2012): October 2009-March 2012: Field testing of mitigation strategies.

(12):ctober 2009-March 2012: Analyze and present survey data at appropriate venues. 2011: June 2011-Sept. 2011: Submit scientific manuscripts for publication in appropriate journals. 2012: October 2009-March 2012: Share results with state and federal agencies (USDA-APHIS, USDA-NRCS) and organizations (Nature Conservancy, Plant Conservation Alliance etc.) for invasive species listings.

Projected Participation

View Appendix E: Participation

Outreach Plan

Development and promotion of a web site on turf species as invasive species.

Development of fact sheets on turf species identification for private and public agencies to assist them in proper identification of turf species.

Results will be shared at local, state (turf conference, sod producer, golf superintendent) and national industry meetings (Turf Producers International, Golf Course Superintendents Association of America).

Results will be shared with other research and Extension colleagues at annual professional meetings (ASA-CSSA-SSSA).

Organization/Governance

The project will be governed by two officers: a chair and a secretary. Project participants will initially elect the two officers who will serve the first year. For each succeeding year, the secretary will become the chair for the following year and a new secretary will be elected. Terms for each will start at the end of the annual meeting. The chair and secretary will be responsible for conducting necessary business in close coordination with the administrative advisor. The duties of the secretary will be to take meeting minutes, prepare the approved minutes and the annual report, and other duties as assigned by the chair. The chair will conduct the annual meeting, and with the help of the secretary, coordinate any other reports or proposals as required. The chair will appoint subcommittees for each project objective. Subcommittees will be responsible for drafting uniform research procedures for each objective, subject to approval by project members and preparation of materials and meetings for technology transfer.

Literature Cited

Anonymous. 2005. Its official: Massachusetts will propose banning 140 invasive plants. Green Side Up. 28(9):16.

Beard J.B. and R. Green, 1994. The role of turfgrasses in environmental protection and their benefits to humans. J. Envir. Quality 23:452-460.

Casler, M.D., Y. Rangel, J.C. Stier, and G. Jung. 2003. RAPD marker diversity among creeping bentgrass clones. Crop Sci. 43:688-693.

Curley, J., and G. Jung. 2004. RAPD-based genetic relationships in Kentucky bluegrass: Comparison of cultivars, interspecific hybrids, and plant introductions. Crop Sci. 44:1299-1306.

Hall, C.R., A.W. Hodges and J.J. Haydu. 2005. Economic impacts of the green industry in the United States. Final Report to the National Urban and Community Forestry Advisory Committee. Univ. of Tennessee Coop. Ext. 90 pp. www.utextension.utk.edu/hbin/greenimpact.html

Hitchcock, A.S. 1950. Manual of the grasses of the United States. USDA Misc. Publ. No. 200. U.S. Govt. Print., Washington, D.C.

Hoffman, R., and K. Kearns (eds). 1997. Wisconsin manual of control recommendations for ecologically invasive plants. Wisconsin Dept. Natural Resources, Madison, WI. 102 pp.

Hollman, A., M.D. Casler, J.C. Stier, G. Jung, and L. Brilman. 2005. Identification of putative velvet bentgrass clones using RAPD markers. Crop Sci. 45:923-930.

Johns, M.A., P.W. Skroch, J. Nienhuis, P. Hinrichsen, G. Bascur, and C. Muñoz-Schick. 1997. Gene pool classification of common bean landraces from Chile based on RAPD and morphological data. Crop Sci. 37:605-613.

Lavergne, S. and J. Molofsky. 2004. Reed canary grass (Phalaris arundinacea) as a biological model in the study of plant invasions. Critical Rev. in Plt. Sci. 23(5):415-429.

Lundgren, M.R., C.J. Small, and G.D. Dreyer. 2004. Influence of land use and site characteristics on invasive plant abundance in the Quinebaug Highlands of southern New England. Northeast Naturalist 11:313-332.

Milesi, C., S.W. Running, C.D. Elvidge, J.B. Dietz, B.T. Tuttle, R.R. Nemani. 2005. Mapping and modeling the biogeochemical cycling of turf grasses in the United States. Env. Management. 36:426-438.

Murphy, J.A., S. Bonos, and P. Perdomo. 1997. Classification of Poa pratensis genotypes. Int. Turf. Soc. Res. J. 8:1176-1183.

NASS (National Agricultural Statistics Service). 2005. Web-based commodity data and statistics. http://www.nass.usda.gov/

National Turfgrass Evaluation Program. 2005. 2003 National bentgrass (fairway/tee) test. Progress Rpt. NTEP No. 05-1.

Plant Conservation Alliance (PCA). 2005. www.inps.gov/plants/alien/list/a.htm

SAS Institute. 1990. SAS/STAT users guide. Ver. 6, 4th ed., Vol. 2. SAS Inst., Inc., Cary, NC.

Scheef, E.A., M.D. Casler, and G. Jung. 2003. Development of species-specific SCAR markers in bentgrass. Crop Sci. 43:345-349.

Steel, R.G.D., and J.H. Torrie. 1980. Principles and procedures of statistics: a biometric approach. McGraw-Hill Book Co., New York, NY.

Stier, J.C., J. Bae, and G. Jung. 2005. Composition of Kentucky bluegrass and perennial ryegrass mixtures subjected to traffic. J. Intl. Turfgrass Res. Soc. 10:645-653.

Stubbendieck, J., G.Y. Friisoe, and M.R. Bollick. 1994. Weeds of Nebraska and the Great Plains. Nebraska Dept. of Agriculture, Bureau of Plant Industry. Lincoln, Nebraska. 589 pp.

The Nature Conservancy (TNC). 2005. Invasive plant listings. http://tncweeds.ucdavis.edu/photos.html (verified 10 Sept. 2005)

United States Department of Agriculture (USDA). 2005. http://plants.usda.gov (verified 10 Sept. 2005)

Van Clef, M., and E.W. Stiles. 2001. Seed longevity in three pairs of native and non-native congeners: assessing invasive potential. Northeastern Naturalist 8:301-310.

Wisconsin Agricultural Statistics Service (WASS). 2001. 1999 Wisconsin turfgrass survey. 16 p.

Wisconsin Agricultural Statistics Service (WASS). 2005. Sod sales total $25 million. www.nass.usda.gov/wi/misc/sod_2004.pdf. (verified 10 Sept. 2005)

Attachments

Land Grant Participating States/Institutions

CO, IA, NE, OR

Non Land Grant Participating States/Institutions

USDA-ARS/MT