Invasive plants continue to spread in riparian ecosystems, causing both ecological and economic damage. This research investigated the impacts of common reed, purple loosestrife, riparian shrubland, and riparian woodlands on the quality and quantity of sandhill crane roosting habitat in the central Platte River, Nebraska, using a discrete choice model. A more detailed investigation of the impacts of common reed on sandhill crane roosting habitat was performed by forecasting a spread or contraction of this invasive plant. The discrete choice model indicates that riparian woodlands had the largest negative impact on sandhill crane roosting habitat. The forecasting results predict that a contraction of common reed could increase sandhill crane habitat availability by 50%, whereas an expansion could reduce the availability by as much as 250%. This suggests that if the distribution of common reed continues to expand in the central Platte River the availability of sandhill crane roosting habitat would likely be greatly reduced.

Nomenclature: Common reed, Phragmites australis (Cav.) Trin. ex Steud.; purple loosestrife, Lythrum salicaria L.

Interpretive Summary: This research demonstrates the suitability of discrete choice modeling for quantifying the impacts of invasive plants on sandhill crane roosting habitat. Moreover, this research successfully applied a discrete choice model to forecast the implications that a spread (unsuccessful management) or contraction (successful management) of the invasive plant common reed (Phragmites australis) could have on the distribution and abundance of sandhill crane roosting habitat. The methods presented in this research could easily be adopted to provide managers with useful information that aids in the management of invasive plants for the benefit of native species' habitat.

For example, managers could use the modeling and forecasting methods developed in this project to quantify the degree to which invasive species impact native species' habitat, prioritize the location of invasive plant management, and forecast which invasive species are most likely to impact native species. In addition, the discrete choice model forecasting methods described in this research allow the user to quantify the change in abundance and distribution of native species habitat as a result of invasive species spread or contraction. As the availability of digital land cover data grows and knowledge of invasive species' impacts expands, discrete choice modeling and forecasting simulations based on discrete choice models could be instrumental in aiding a field practitioner's management of invasive plants.

A survey of the Maine landscape and nursery industry was conducted to identify industry views on invasive plant issues, attitudes towards potential regulation, and to estimate the potential economic costs of banning the sale of specific invasive plant species in Maine. Analysis of the 190 surveys returned (19% of 980 mailed) revealed that 76% of industry member respondents were genuinely concerned about invasive plant issues, and the same percentage felt the horticulture industry is responsible for educating customers about invasive plants. Industry members (68%) did not feel compelled to sell invasive plants merely on the basis of customer attraction to the plant, or due to competition with a neighboring business that sells the invasive plant. Self-reporting of sales indicated that Norway maple ($96K), burningbush ($68K), and Japanese barberry ($44K) constituted the largest portion of annual industry revenue (maximum values reported for 2006 to 2008) derived from the sale of seven identified invasive plants. Industry self-regulation was the most favored form of regulation, although the industry likely would not be significantly affected by legislated state-wide bans of at least purple loosestrife and oriental bittersweet. Bans on other popular invasive plants, including burningbush, Japanese barberry, and Norway maple likely would have a relatively small, short-term impact on the horticulture industry until alternative plants with similar properties were identified. The results of this survey demonstrated a need for identifying which plants are truly invasive or potentially invasive in Maine, as well as a need for open discussion of invasive plant issues among all interested parties in Maine.

Nomenclature: Burningbush, Euonymus alatus (Thunb.) Siebold; Japanese barberry, Berberis thunbergii DC.; Japanese honeysuckle, Lonicera japonica Thunb.; multiflora rose, Rosa multiflora Thunb.; Norway maple, Acer platanoides L.; oriental bittersweet, Celastrus orbiculatus Thunb.; purple loosestrife, Lythrum salicaria L.

Interpretive Summary: A survey of Maine landscape and nursery industry members was conducted to obtain information regarding industry views on invasive plant issues, opinions about invasive plant regulatory methods, and to identify the potential economic impact the industry would incur if invasive plant sales were banned. Survey results will assist policymakers, research investigators, and industry members in making educated decisions regarding invasive plant regulation in Maine. Industry self-regulation was the most popular form of regulation among landscape and nursery professionals, although the industry likely would not be significantly affected by legislated state-wide bans of at least purple loosestrife and oriental bittersweet. Bans on other popular invasive plants including burningbush, Japanese barberry, and Norway maple likely would have a relatively small, short-term impact on the horticulture industry until alternative plants with similar properties are identified. Data from this survey also highlight some of the apparent contradictions between the industry survey responses and what action currently is being taken by industry professionals to reduce invasive plant distributions, as illustrated by the following: (1) If customer satisfaction and/or business competition is not driving the selection of stock plants, what is the motivation for stocking and selling an invasive plant? (2) If industry professionals are willing to label potentially invasive plants, why is this not being done already? and (3) What is the level of efficacy or compliance the industry members perceive as the goal for self-regulation and what do they think is the best way to monitor participation? Future research is needed to identify motivations of industry members who knowingly sell invasive plants, what sources

Species distribution modeling is a tool that is gaining widespread use in the projection of future distributions of invasive species and has important potential as a tool for monitoring invasive species spread. However, the transferability of models from one area to another has been inadequately investigated. This study aimed to determine the degree to which species distribution models (SDMs) for cogongrass, developed with distribution data from Mississippi (USA), could be applied to a similar area in neighboring Alabama. Cogongrass distribution data collected in Mississippi were used to train an SDM that was then tested for accuracy and transferability with cogongrass distribution data collected by a forest management company in Alabama. Analyses indicated the SDM had a relatively high predictive ability within the region of the training data but had poor transferability to the Alabama data. Analysis of the Alabama data, via independent SDM development, indicated that predicted cogongrass distribution in Alabama was more strongly correlated with soil variables than was the case in Mississippi, where the SDM was most strongly correlated with tree canopy cover. Results suggest that model transferability is influenced strongly by (1) data collection methods, (2) landscape context of the survey data, and (3) variations in qualitative aspects of environmental data used in model development.

Nomenclature: Cogongrass, Imperata cylindrica (L.) Beauv. IMPCY.

Interpretive Summary: Early detection of, and rapid response to, new populations of invasive plants optimizes economic and environmental considerations for weed management, but efficient means of appropriately targeting monitoring sites is a critical missing component to such an approach. Species distribution modeling is a tool that could enhance detection efforts for invasive weeds during the earliest stages of spread into new geographic areas. This approach was tested within a geographic information system (GIS) framework, using data on locations of cogongrass in southeastern Mississippi and southwestern Alabama to determine the reliability of models and their transferability among study areas. Initial model development agreed with prior work on cogongrass habitat within the southeastern United States, in terms of the environmental variables found to be important, but there was weak transferability of models between the two study areas. Two potential explanations for this low transferability were that the data were collected in different portions of the landscape in the two areas (along road corridors in Mississippi but throughout commercially managed forests in Alabama) and that there seemed to be some incongruence in soil data within and between study areas. This suggests that, although relatively robust SDMs can be developed for a given area, those models should not be extrapolated to other areas without careful examination of the underlying environmental predictors. Nevertheless, results do suggest that within an individual area of interest and with proper care, modeling approaches such as that used in this study have potential to contribute to efforts at developing scientifically and statistically based weed management programs for invasive species.

Giant reed is an invasive weed throughout the southern half of the United States, with the densest stands growing along the coastal rivers of southern California and the Rio Grande in Texas. The objective of this study was to use aerial photography to map giant reed infestations and to estimate infested areas along the Texas–Mexico portion of the Rio Grande. Aerial color-infrared photographs were taken along the Rio Grande between Brownsville and El Paso, TX, in June and July 2002. Based on the aerial photographs and ground surveys, the portion of the river from San Ygnacio to Lajitas, which has a river length of 898 km (558 mi), was found to be infested with giant reed. To estimate infested areas along both sides of the river, 65 (13.5%) of the 480 aerial photographs taken between Lajitas and San Ygnacio were randomly selected. The aerial photographs were digitized, rectified to Google Earth imagery, and then classified using maximum-likelihood classification techniques. The infested areas on both sides of the river, as well as water area and river length, from each photographic image were determined. Based on the estimates from the 65 aerial photos, the ratio of giant reed area to water area and the ratio of giant reed area to river length were calculated. The total giant reed area along the Rio Grande between Lajitas and San Ygnacio was estimated to be 5,981 ha (14,779 ac) with 3,714 ha or 62% on the U.S. side and 2,267 ha or 38% on the Mexican side. This study provides the first accurate estimates of giant reed infestations along the Texas–Mexico portion of the Rio Grande and will be useful for both land owners and government agencies for the estimation of water usage and economic loss and for the management and control of giant reed.

Nomenclature: Giant reed; Arundo donax L.

Interpretive Summary: Giant reed is an invasive weed throughout the southern half of the United States, with the densest stands growing along the coastal rivers of southern California and the Rio Grande in Texas. One of the most important steps for successful management of giant reed is to map its spatial distribution and determine infested areas. Because of the great expanse and inaccessibility of these areas, remote sensing provides a useful tool for mapping the spatial extent of giant reed infestations and for distinguishing it from associated plant species. This study provides the first accurate estimates of giant reed infestations along the Texas–Mexico portion of the Rio Grande based on 2002 aerial photography. The total giant reed area along the Rio Grande between Lajitas and San Ygnacio, TX, was estimated to be 5,981 ha with 3,714 ha (62%) on the U.S. side and 2,267 (38%) on the Mexican side. Furthermore, the United States and Mexico each had about 50% of the giant reed along the portion of the river between Lajitas and Del Rio, TX, whereas the United States had two-thirds of the giant reed on the portion of the river between Del Rio and San Ygnacio, TX. The results from this study will be useful for both land owners and government agencies for the management and control of this invasive weed along the Rio Grande in both the United States and Mexico. These results and the aerial photographs are currently being used for the planning and release of biological agents for the control of giant reed along the river and for the estimation of water usage and economic loss. Moreover, this study is an important first step toward the complete documentation of giant reed infestations along the river and for the long-term control and management of giant reed in the entire Rio Grande basin.

Old World climbing fern (OWCF) is a highly invasive fern that disrupts natural communities in central and southern Florida. OCWF produces copious, wind-blown spores that have propelled its rapid invasion of Florida's natural areas over the last few decades. Current management of OWCF is limited to herbicides and natural resource managers in Florida have questioned if herbicides inhibit spore germination. This study compared spore germination rates of OWCF exposed to six herbicides and a surfactant from 1 to 24 h under laboratory conditions. Spores of OWCF were highly susceptible to metsulfuron, but exhibited tolerance to imazapyr, glyphosate, fluroxypyr, asulam, and triclopyr. Spore germination rates were 0.4% for spores exposed to 0.1 g ai L⁻¹ of metsulfuron, but 0% for rates greater than or equal to 0.2 g ai L⁻¹ at 30 d after treatment (DAT). Reduction in spore germination was observed with all other concentrations of herbicides tested, ranging from 10.4% with triclopyr (40 g ai L⁻¹) to 42.6% with asulam (4.2 g ai L⁻¹) compared to 47.9% germination for untreated checks 30 DAT. Spores were highly sensitive to metsulfuron with herbicide concentrations required for 50 and 95% inhibition of spore germination (I₅₀ and I₉₅) measuring 0.014 and 0.063 g ai L⁻¹, respectively; spores were greater than 1,000-fold more sensitive to metsulfuron compared to I₉₅ concentrations of any other herbicide tested. These results indicate that metsulfuron exhibits potential to control OWCF spore germination but spores are tolerant to the five other herbicides tested.

Nomenclature: Asulam; fluroxypyr; glyphosate; imazapyr; metsulfuron; triclopyr; Old World climbing fern, Lygodium microphyllum (Thunb.) Swartz.

Interpretive Summary: Old World climbing fern is a highly invasive plant in natural areas of Florida and spreads by wind-blown spores. Herbicide control of OWCF can be achieved but long-term management is required for new growth from germinated spores blown in by wind currents. No previous research has examined the effects of any herbicide on the spores of this species. In this study, metsulfuron inhibited OWCF spore germination to less than 0.5% at rates below 0.1 g ai L⁻¹ at 30 d after treatment compared to 47.9% germination for untreated checks. No other herbicide tested on Old World climbing fern spores inhibited spore germination by less than 11%. With the exception of metsulfuron, there was a gradual decrease in percentage of spore germination for imazapyr, glyphosate, fluroxypyr, triclopyr and asulam, but the concentrations of these herbicides required for 95% inhibition of spore germination were well above the legal label limit. Our results suggest that the standard aerial application rate of 0.084 kg ai 76 L⁻¹ metsulfuron used in Florida for control of OWCF may inhibit greater than 95% of the spores if it contacts the spores or translocates into the sporangia, whereas the standard ground aerial application rate of 0.084 kg ai 379 L⁻¹ is unlikely to inhibit 95% of the OWCF spores.

Kudzu is an invasive perennial climbing vine characterized by fast growth rates and tolerance to control measures. Repeated applications with high rates of 2,4-D plus picloram provide effective kudzu control, but picloram use is not permitted in certain states due to groundwater pollution concerns. Studies were conducted in Alabama and Florida to compare kudzu control with aminocyclopyrachlor, a new herbicide, to control provided by aminopyralid, clopyralid, metsulfuron methyl, and picloram plus 2,4-D, which are common treatments for kudzu management. Two annual applications of the same herbicide treatment were evaluated for effects on kudzu cover, kudzu volume index, and cover of other vegetation. Aminocyclopyrachlor at 140 to 280 g ae ha⁻¹ (2 to 4 oz ae ac⁻¹) was as effective as the standard 4.48 kg ae ha⁻¹ (4 lb ae ac⁻¹) 2,4-D amine plus 1.2 kg ae ha⁻¹ picloram for kudzu control. There were no differences in kudzu control among the three rates of aminocyclopyrachlor tested. Colonization by graminoids, forbs, and Rubus spp. at 2 yr was greatest for herbicides providing the best kudzu control: aminocyclopyrachlor, and 2,4-D plus picloram. Herbicide treatments were more effective in controlling kudzu at the Alabama location, but repeated annual applications for 2 yr did not completely eliminate kudzu with any treatment at either site.

Nomenclature: 2,4-D; aminocyclopyrachlor; aminopyralid; clopyralid; metsulfuron methyl; picloram; kudzu, Pueraria montana (Lour.) Merr., USDA code PUMOL, EPPO code PUELO.

Interpretive Summary: The new herbicide, aminocyclopyrachlor, applied at 140 to 280 g ae ha⁻¹ controlled kudzu as well as the standard treatment for kudzu management, 4.48 kg ae 2,4-D amine plus 1.21 kg ae picloram, and generally better than the other common kudzu herbicides metsulfuron methyl, aminopyralid, and clopyralid. Graminoids, Rubus spp., and forbs recolonized plots receiving the most effective treatments for kudzu control. Graminoid (grasses, sedges) cover increased following aminocyclopyrachlor treatments, an important consideration for restoration of infestations where kudzu was planted for erosion control in the region. Annual herbicide applications for 2 yr did not eradicate kudzu, confirming the need for multiple years of treatment or more frequent applications.

Controlled burns and grazing are being tested to manage invasive grasses in the Prairie Pothole region of the Northern Great Plains. These practices, however, may inadvertently promote saltcedar infestations from seed by opening the vegetative canopy. Saltcedar seedling establishment was investigated in greenhouse experiments using intact soil cores from one summit and three footslope sites in eastern South Dakota. Establishment tests were conducted in soil cores collected from treatment and control plots immediately after spring fire treatment (postburn) and in cores that contained peak cool- or peak warm-season vegetation, with or without clipping (simulated grazing treatment), to simulate vegetation conditions typical of saltcedar seed-shed in northern regions. Cores were seeded with 100 saltcedar seeds and subirrigated to maintain high soil water conditions, characteristic of the environment near potholes during late spring/early summer. Seedlings were counted during the first 3 wk to estimate establishment and the height of five seedlings core⁻¹ were measured weekly to estimate growth rates. Opening the canopy with fire or clipping increased saltcedar establishment. Cores taken immediately after fire treatment had two times more seedlings establish (38% vs. 19%) and greater average seedling growth rate (1.5 mm d⁻¹ vs. 0.9 mm d⁻¹) when compared with no-fire controls. Fire after seeding reduced seedling establishment to 5%, but did not affect growth rate. Saltcedar establishment in peak cool-season vegetation cores was 6% regardless of earlier fire treatment, whereas in peak warm-season vegetation, establishment ranged from 8% (no spring fire) to 17% (spring fire). If soils remain wet, invasion risk following spring fire may be greatest when warm-season grasses are flowering because this time coincides with northern saltcedar seed production. Areas adjacent to viable saltcedar seed sources should be managed to maximize canopy cover when seeds are released to limit further establishment. Fire after saltcedar seed deposition may control propagules and young seedlings.

Nomenclature: saltcedar, Tamarix ramosissima Ledeb. TARA, Tamarix chinensis Lour. TACH, and Tamarix hybrids.

Interpretive Summary: Saltcedar spread to higher elevations and latitudes was previously thought to be limited by the plant's sensitivity to cold temperatures. Recent invasions in Montana and South Dakota suggest that saltcedar has developed a tolerance to cold temperature extremes or that more moderate temperatures in these areas have occurred. The best mechanisms for minimizing saltcedar spread in northern grasslands are to prevent and minimize contamination of uninfested areas. Land managers in the northern United States are in the position to prevent saltcedar establishment by ensuring that management and production practices such as fire and grazing do not unintentionally promote invasion. To effectively manage saltcedar, practices that maximize vegetation cover when seeds are being released should be used. Fire increased saltcedar seedling establishment immediately after the burn and also when warm-season grasses were flowering after 2 yr of annual spring burning. Over time, if cool-season grasses are controlled, saltcedar establishment may be more likely to occur in early summer when water is more abundant and if vegetation cover is not replaced by other species. Areas should be monitored throughout the growing season after fire and grazing to determine if seedlings are present. If present, seedlings should be controlled soon after germination using effective treatments. Strategically timed fire (e.g., after seed-shed or soon after seedling establishment) can be used to control the spread of saltcedar from seed.

As invasive species become increasingly abundant in forests, their presence may influence a number of key nutrient cycling processes. For example, Chinese privet has become well established in southeastern forests and continues to spread. Two studies, a multisite field investigation and a controlled approach on a single site, were conducted to examine the role of Chinese privet (Ligustrum sinense) on decomposition within riparian forests of the Georgia Piedmont. The field study also investigated the effects of privet presence on soil nitrogen (N) mineralization and microbial carbon and N immobilization. Both studies utilized a litterbag approach to examine how increasing proportions of privet in foliar litter influenced mass loss rates and nutrient dynamics. The field investigation included litterbags with representative proportions of the five dominant species from 16 sites. Litterbags in the controlled study were composed of specific levels of privet litter within bags (0, 10, 20, 30, 40, and 50% Chinese privet) as treatments. The litter quality of four native species was compared to Chinese privet in the controlled study. Both studies showed significant positive relationships between percentage of Chinese privet in litterbags and decomposition rates (2.6-fold rate increase with 30% privet in litterfall). Chinese privet leaf litter had lower lignin and cellulose concentrations, higher N concentrations, lower lignin ∶ N ratios, and narrower C ∶ N ratios than the native species. The positive relationship between mass loss rates and the proportion of Chinese privet in litter indicates that Chinese privet enhances decomposition rates as it becomes more abundant. During summer, N mineralization showed approximately a fivefold increase; during winter, microbial biomass N increased by approximately 30% on sites with the highest levels of privet in the understory. Consequently, C and N dynamics in Piedmont riparian forests were significantly influenced in direct proportion to the amount of privet present in the understory.

Nomenclature: Chinese privet, Ligustrum sinense Lour.

Interpretive Summary: This study examined the influence of a common invasive species, Chinese privet, on the biogeochemical functioning of deciduous riparian forests in the southeastern United States. Although Chinese privet is widely established as a component of floodplain forests, we know very little about how its presence might affect key drivers of forest productivity such as nutrient cycling. We found that C turnover rates in the forest floor increased by 260% on sites where litterfall was composed of 30% or more of Chinese privet. Similarly, during summer, N availability in surface soils increased fivefold on severely invaded sites. The implications of these changes for C storage and forest productivity are likely to be pronounced. Faster turnover times for C may stimulate a net decrease in soil storage since lower soil storage tends to be associated with faster decomposition. Given that virtually all forest sites in the southeastern United States are N deficient, increased N availability should stimulate net primary production. Because extensive control of Chinese privet is only feasible on a small-scale basis, it is important to understand how invasion may alter key societal values of these forests. Although forest productivity may increase, there may be a redistribution of growth toward forest components that have less economic value than many overstory species. In addition, wetland forests are stereotypically known as hotspots for C storage and sequestration and, consequently, that role may change in systems in which Chinese privet is a major component. The latter possibility is important in considerations of C mitigation strategies.

Serpentine grasslands are relatively free of the invasive species that typify other California grasslands, but recently are threatened by the spread of barb goatgrass, a Eurasian annual that is unique in its tolerance of serpentine soils. We evaluated two graminicides (clethodim and fluazifop), one broad-spectrum herbicide (glyphosate), mowing, and hand pulling for their effectiveness in controlling barb goatgrass and for restoring native species cover and diversity. We also evaluated application timing for the graminicides: before goatgrass flowering (early season), at flower initiation (midseason), and at early seed development (late season). Glyphosate was applied at early seed development. The 10 treatment combinations were applied to 10 blocks of 4-m² (43-ft²) experimental plots in an inner Coast Range serpentine grassland with high cover of barb goatgrass but few other nonnative species. After 2 yr of treatment, all treatments except glyphosate reduced goatgrass frequency. Hand pulling, fluazifop, and mowing were most effective at controlling goatgrass, reducing frequency by 60, 51, and 48%, respectively (compared to a 30% increase on control plots). Midseason applications of clethodim and fluazifop were more effective than those applied early or late. Hand pulling, fluazifop, and clethodim increased native forb frequency by 31, 46, and 74%, respectively, with the benefit of the graminicides decreasing with later applications. Native grasses were at least partially resistant to the graminicides. Cover of one sided blue grass (Poa secunda), the most widespread native grass, might have been reduced slightly by early-season applications but was increased by late-season applications. Cover of soft brome (Bromus hordeaceus), the only other widespread nonnative species in the study, was reduced by early-season applications of the graminicides. Clethodim and fluazifop show great potential to selectively remove barb goatgrass and other nonnative annual grasses in grasslands that are otherwise dominated by native grasses and forbs. Mowing is a less selective, but viable alternative.

Nomenclature: Clethodim; fluazifop; glyphosate; barb goatgrass, Aegilops triuncialis L.; Sandburg bluegrass, Poa secunda J. Presl.

Interpretive Summary: Few studies have addressed the management of barb goatgrass, which is a recent and aggressive invader of serpentine grasslands in California. In nonserpentine grasslands, 2 successive yr of prescribed fire can control barb goatgrass, but the slow fuel build up in serpentine grasslands generally prevents a complete burn in the second year. As a potential alternative or follow up to fire, we evaluated two graminicides (clethodim and fluazifop), one broad-spectrum herbicide (glyphosate), mowing, and hand pulling for their effectiveness in controlling barb goatgrass and restoring diversity and cover of native species. We also evaluated application timing for the graminicides: before barb goatgrass flowering (early season), at flower initiation (midseason), and at early seed development (late season). Glyphosate was applied at early seed development and mowing occurred at flowering. Hand pulling, which is impractical at a large scale, was included purely as a reference for the most selective possible control. All treatments except glyphosate reduced the frequency of barb goatgrass, but the best control (besides hand pulling) was provided by fluazifop and mowing. Clethodim and fluazifop are most effective when applied midseason. Clethodim provides poor control early-season, but adequate control midseason. Application of graminicides early in the season provides the most benefit to native forbs (probably because of their early release from competition), but can reduce populations of native grasses, which benefit more from applications later in the season when

Land managers must set weed management priorities if limited resources are to be utilized effectively. Weed surveys and inventories assist land managers in this process by providing information regarding the identity, location, and relative abundance of weeds on their land. Although this information is vital, it can be challenging to select a method that provides the necessary data to meet management objectives while remaining accurate and cost effective. This paper critically evaluates four wildland weed mapping methods. These methods were defined as (1) paper-drawn, (2) buffered-point, (3) screen-drawn, and (4) perimeter-walked. Polygons were drawn by hand on topographic maps in the paper-drawn method. The other methods utilized handheld geographic positioning system (GPS) technology to digitally record infestations. Six experienced weed mappers independently recorded the location and size of eight sagebrush patches using each method. Time and accuracy were evaluated for each method based upon mapping time, distance walked, horizontal precision error, estimated size error, and shape error. The paper-drawn method was significantly less accurate than GPS-based methods at recording patch size and location. There was no significant difference in the accuracy of the buffered-point, screen-drawn, and perimeter-walked methods at reporting patch size and location. The need to cover land area quickly and efficiently favors the selection of the buffered-point or screen-drawn method because of time and distance factors. However, if patch shape is an important factor, the perimeter-walked or buffered-point methods may be the best choices of methods tested.

Interpretive Summary: Weed inventories provide land managers with valuable information regarding the distribution, identity, location, and relative abundance of weeds on the landscape. This information can then be used to guide the development of successful management strategies. It can be difficult to select a mapping method that will provide necessary data while remaining efficient and cost effective. This study demonstrates that mapping weed patches using paper-drawn features provides the least accurate data. Although a degree of error remains, the use of GPS technology can significantly improve the accuracy of data collected. If weed patch size and location are important factors, there is no accuracy advantage in using the screen-drawn or perimeter-walked methods over the buffered-point technique. Further, the need for most weed mapping programs to cover land quickly and efficiently favors the selection of the buffered-point or screen-drawn methods. However, if accurately depicting the shape of a patch is important, either the perimeter-walked or the buffered-point method would be the best choice. It is important to remember that the accuracy of any data collected is dependent upon the proficiency of the weed mapper in using the selected method. The screen-drawn method will require more training than the buffered-point and perimeter-walked methods. This technique requires a mapper to evaluate and illustrate patch size, shape, and location on a GPS screen, which provides more opportunities for mistakes. Overall, the buffered-point method may be the best technique for obtaining useful, accurate, and cost effective weed data.