Noxious Weed Lists Research Articles

Agronomic non‐native species are overrepresented across habitat types in central Canada

Abstract In response to non‐native plant invasions, many governments have established noxious weed lists to control and eradicate introduced invasive plants. However, invasive agronomic species are often unregulated, and the extent of their invasion across habitat types has never been determined. Using vegetation surveys across 222 plots, we investigated the contribution of agronomic versus noxious non‐native species to the levels of invasion across seven habitat types in central Canada. Although agronomic non‐native species, such as Poa pratensis and Bromus inermis, only made up 21.3% of the non‐native species pool, they accounted for 43.6% of non‐native plant species frequency and 74.4% of relative non‐native plant cover. They were also disproportionately overrepresented compared with noxious non‐native species across all habitat types, except saline marshes. The overabundance of agronomic non‐native plants in central Canada is likely the legacy of cultivar breeding, intentional seeding of introduced forage species and a lack of incentive for the use of native species. Synthesis and applications: Decelerating the invasion by agronomic non‐native plants will require approaches beyond noxious weed lists and initiatives in research, policy and education. These tools can include incentives to use native seed material, for example, in reclamation and forage and turf production, to reduce propagule pressure from invasive agronomic non‐native plants.

Scanning the horizon for invasive plant threats using a data-driven approach

Early detection and eradication of invasive plants are more cost-effective than managing well-established invasive plant populations and their impacts. However, there is high uncertainty around which taxa are likely to become invasive in a given area. Horizon scanning that combines a data-driven approach with rapid risk assessment and consensus building among experts can help identify invasion threats. We performed a horizon scan of potential invasive plant threats to Florida, USA—a state with a high influx of introduced species, conditions that are generally favorable for plant establishment, and a history of negative impacts from invasive plants. We began with an initial list of 2128 non-native plant taxa that are known invaders or crop pests. We built on previous invasive species horizon scans by developing data-based criteria to prioritize 100 taxa for rapid risk assessment. The semi-automated prioritization process included selecting taxa “on the horizon” (i.e., not yet in the target location and not on a noxious weed list) with climate matching, naturalization history, “weediness” record, and global commonness. We derived overall invasion risk scores with rapid risk assessment by evaluating the likelihood of each of the taxa arriving, establishing, and having an impact in Florida. Then, following a consensus-building discussion, we identified six plant taxa as high risk, with overall risk scores ranging from 75 to 100 out of a possible 125. The six taxa are globally distributed, easily transported to new areas, found in regions with climates similar to Florida’s, and can impact native plant communities, human health, or agriculture. Finally, we evaluated our initial and final lists for potential biases. Assessors tended to assign higher risk scores to taxa that had more available information. In addition, we identified biases towards four plant families and certain geographical regions of origin. Our horizon scan approach identified taxa conforming to metrics of high invasion risk and used a methodology refined for plants that can be applied to other locations.

Mottled Water Hyacinth Weevil Neochetina eichhorniae Warner (Insecta: Coleoptera: Curculionidae)

Sometimes referred to as the ‘mottled water hyacinth weevil’, Neochetina eichhorniae Warner is a weevil that attacks the invasive, aquatic plant, water hyacinth, Eichhornia crassipes (Mart.) Solms. Water hyacinth is considered one of the most destructive plants in aquatic ecosystems in the United States and, as a result, is listed in both the federal noxious weed list and Florida’s list of prohibited aquatic plants. Neochetina eichhorniae is host specific and causes substantial damage to water hyacinth, making it a valuable biological control agent for this invasive weed in many parts of the world. The insect was first introduced into the United States from Argentina in 1972, when scientists released the insect in Broward County, Florida, to manage water hyacinth (Perkins 1973). Since then, the insect has been introduced in more than three dozen countries worldwide (Winston et al. 2014). Post-introduction studies indicate the insect substantially suppresses the growth of water hyacinth, significantly reducing biomass, flowers production, and water surface coverage (Grodowitz et al. 1991, Center et al. 1999, Tipping et al. 2014, Nesslage et al. 2016) and the need for herbicide applications (Haag 1986).

Biology and Management of Praxelis (Praxelis clematidea) in Ornamental Crop Production

Praxelis is a newly emerging weed species in Florida, one that Plant Protection and Quarantine (PPQ) is considering adding to the federal noxious weed list. The plant can be easily misidentified and confused with Ageratum houstonianum (bluemink) and Conoclinium coelestinum (blue mistflower) as well as several other species that have similar flower characteristics. This new 5-page article is written for green industry professionals and others to aid in the identification and management of praxelis in and around ornamental plants. Written by Yuvraj Khamare, Chris Marble, Shawn Steed, and Nathan Boyd, and published by the UF/IFAS Environmental Horticulture Department.https://edis.ifas.ufl.edu/ep585

Kikuyugrass germplasm collections in the United States and Australia show low levels of genetic diversity as revealed by DArTseq genotyping

AbstractKikuyugrass [Cenchrus clandestinus (Hochst. ex Chiov.) Morrone (= Pennisetum clandestinum Hochst. ex Chiov.)] is a warm‐season grass native to Africa. It was introduced into the United States as forage in Hawaii and for erosion control in California. Kikuyugrass is considered invasive and currently is on the USDA's noxious weed list. Since complete eradication is difficult, it has become the primary species on several golf courses, athletic fields, and lawns. Kikuyugrass possesses exceptional quality with considerable cultural inputs, and little or no winter dormancy compared with other warm‐season turfgrasses. With breeding efforts directed specifically at reducing aggressiveness and improving texture, thus reducing inputs, it could become a valuable turf‐type species in coastal and inland California. The genetic diversity of kikuyugrass was investigated using single nucleotide polymorphism (SNP) and silicoDArT (presence or absence) markers revealed by the Diversity Arrays Technology sequencing (DArTseq) platform. Accessions were sampled throughout California, Hawaii, and Australia, both from natural stands and various collections. Among the 254 accessions tested, two distinct groups were discovered, and there was no geographic pattern to this differentiation. The overall level of SNP polymorphism was low (polymorphic information content [PIC] average = .33, PIC median = .38). Most (76%) of the observed genetic variation was within populations, whereas 24% was among populations. Average genetic distances within populations ranged from 0.09 to 0.16, whereas distances among populations ranged from 0.13 to 0.36. Accessions from Hawaii and Australia were the most diverse; however, a detectable level of genetic diversity of kikuyugrass also exists in California, mostly because of the past introductions from Australia.

Testing the Australian Post-Border Weed Risk Management (WRM) system for invasive plants in Iran

Given the global threat from invasive plant species, management systems are needed to determine the risk posed. Whilst pre-border weed risk assessment systems have been tested and applied broadly, risk assessment systems for species post-border (or weed risk management) are yet to be subjected to such levels of scrutiny. Here we adapted the Australian Weed Risk Management (AWRM) approach to the geographic, climatic and weed management context of Iran. Then we evaluated and tested the performance of the adapted WRM system using 38 candidate species, comprising both native and non-native invasive plant species present in Iran. Additionally we modified the post-border WRM approach by specifically focusing on the feasibility of containment, rather than control per se, given that eradication of native species is not appropriate; even when considered to be invasive. We also subsequently modified the management emphasis associated with each cell of the WRM matrix of weed risk and feasibility of containment levels, to account for the changes outlined above. We examined the effectiveness of the system using receiver operating characteristic (ROC) curves for the 38 candidate species, which showed that our results were similar to those observed during testing and evaluations of the WRM systems developed in Australia. Examination of the outcomes revealed that the current management and research for five of the highest priority species did not match or align with the level of risk derived from the WRM assessment. Additionally at least seven invasive plants species currently not on the lists examined should be included on the Noxious Weed lists of Iran based on our assessment of the risk posed. The two highest priority species (Ambrosia psilostachya and Imperata cylindrica) are both alien species and should be priorities for containment. Despite successfully modifying the AWRM for Iran, additional studies are required to further examine and test the best cut-off values for each risk level in the WRM matrix using larger numbers of plant species. Our results show that the AWRM can be modified for use in other countries, which could see broader adoption of post-border WRM systems for managing established alien plant species.

Gymnocoronis spilanthoides

Gymnocoronis spilanthoides

Quantifying "apparent" impact and distinguishing impact from invasiveness in multispecies plant invasions.

The quantification of invader impacts remains a major hurdle to understanding and managing invasions. Here, we demonstrate a method for quantifying the community-level impact of multiple plant invaders by applying Parker et al.'s (1999) equation (impact = range x local abundance x per capita effect or per unit effect) using data from 620 survey plots from 31 grasslands across west-central Montana, USA. In testing for interactive effects of multiple invaders on native plant abundance (percent cover), we found no evidence for invasional meltdown or synergistic interactions for the 25 exotics tested. While much concern exists regarding impact thresholds, we also found little evidence for nonlinear relationships between invader abundance and impacts. These results suggest that management actions that reduce invader abundance should reduce invader impacts monotonically in this system. Eleven of 25 invaders had significant per unit impacts (negative local-scale relationships between invader and native cover). In decomposing the components of impact, we found that local invader abundance had a significant influence on the likelihood of impact, but range (number of plots occupied) did not. This analysis helped to differentiate measures of invasiveness (local abundance and range) from impact to distinguish high-impact invaders from invaders that exhibit negligible impacts, even when widespread. Distinguishing between high- and low-impact invaders should help refine trait-based prediction of problem species. Despite the unique information derived from evaluation of per unit effects of invaders, invasiveness 'scores based on range and local abundance produced similar rankings to impact scores that incorporated estimates of per unit effects. Hence, information on range and local abundance alone was sufficient to identify problematic plant invaders at the regional scale. In comparing empirical data on invader impacts to the state noxious weed list, we found that the noxious weed list captured 45% of the high impact invaders but missed 55% and assigned the lowest risk category to the highest-impact invader. While such subjective weed lists help to guide invasive species management, empirical data are needed to develop more comprehensive rankings of ecological impacts. Using weed lists to classify invaders for testing invasion theory is not well supported.

Adaptive Development of Yellow Toadflax (Linaria vulgaris) Chemical Control Recommendations

AbstractYellow toadflax (Linaria vulgaris P. Mill.) infestations in North Dakota increased 300-fold from 1997 to 2011, when the plant was added to the state noxious weed list. Long-term control of other invasive species had included biological control agents, but no effective agents for yellow toadflax had been identified, so a control program using herbicides was needed. The objective was to shift from short-term control with picloram applied in the fall at maximum allowed rates to long-term management with minimal nontarget species impact with an adaptive management approach. Yellow toadflax control was increased from an average of 64% with picloram at 1,120 g ha−1 alone 12 mo after treatment (MAT) to over 90% when applied with diflufenzopyr while the picloram rate was reduced 50%. Yellow toadflax control with aminocyclopyrachlor applied at 140 g ha−1 ranged from 91 to 49% 12 MAT when applied in June or September, respectively. In contrast, yellow toadflax control with picloram plus dicamba plus diflufenzopyr averaged > 90% regardless of application date during the growing season. Land managers now have at least two options for long-term yellow toadflax control with a wide window of application timing. The goal of replacing a single high-use–rate herbicide treatment was met but both picloram and aminocyclopyrachlor can injure many desirable forbs. However, application timing can now be adjusted to have the least impact on nontarget species. The adaptive development program led to a 58% reduction in yellow toadflax infestations in North Dakota by 2014.

Science and Management of the Introduced Seagrass Zostera japonica in North America

Healthy seagrass is considered a prime indicator of estuarine ecosystem function. On the Pacific coast of North America, at least two congeners of Zostera occur: native Zostera marina, and introduced, Zostera japonica. Z. japonica is considered "invasive" and therefore, ecologically and economically harmful by some, while others consider it benign or perhaps beneficial. Z. japonica does not appear on the Federal or the Oregon invasive species or noxious weed lists. However, the State of California lists it as both an invasive and noxious weed; Washington State recently listed it as a noxious weed. We describe the management dynamics in North America with respect to these congener species and highlight the science and policies behind these decisions. In recent years, management strategies at the state level have ranged from historical protection of Z. japonica as a priority habitat in Washington to eradication in California. Oregon and British Columbia, Canada appear to have no specific policies with regard to Z. japonica. This fractured management approach contradicts efforts to conserve and protect seagrass in other regions of the US and around the world. Science must play a critical role in the assessment of Z. japonica ecology and the immediate and long-term effects of management actions. The information and recommendations provided here can serve as a basis for providing scientific data in order to develop better informed management decisions and aid in defining a uniform management strategy for Z. japonica.

Natural Area Weeds: Skunkvine (Paederia foetida)

Native to eastern and southern Asia, skunkvine is an invasive plant species introduced to the USDA Field Station near Brooksville before 1897. It has been included on the Florida Exotic Pest Plant Council List of Invasive Species as a Category I, defined as “species that are invading and disrupting native plant communities in Florida.” It was added to the Florida Noxious Weed List in 1999, making it illegal to possess, move, or release in Florida. This 3-page fact sheet was written by K. A. Langeland, R. K. Stocker, and D. M. Brazis, and published by the UF Department of Agronomy, February 2013. 
 http://edis.ifas.ufl.edu/wg208

Navigating the “Noxious” and “Invasive” Regulatory Landscape: Suggestions for Improved Regulation

In the United States, only species listed on state or federal noxious weed lists are regulated. According to our analysis, these regulatory lists poorly represent invasive plants in unmanaged (i.e., nonagricultural) systems. To improve the representation of invasive plants on state regulatory lists, we recommend allocating listing authority to invasive species councils and provide guidance for the science-based reform of noxious weed lists. We also recommend commercial best practices to test for invasiveness prior to intentional introduction of new plant products. Finally, we introduce a negligence liability scheme to discourage the introduction of potential invaders. If adopted, our recommendations could benefit nonagricultural ecosystems and could have positive consequences for bioenergy producers and others in plant industry, who are under scrutiny for promoting potentially invasive species as energy crops. As the bioenergy industry gains momentum, a revised regulatory regime may alleviate the concerns regarding one potential negative consequence of novel plant introduction.

First phase of Hilgardia Project under way

Letters species. In fact, our lab was involved in those studies. By 2010, switchgrass had been removed from the state noxious weed list. In support of this, our research re- sults showed that it has a very low potential to become invasive in the state. Joseph DiTomaso Cooperative Extension Weed Specialist Department of Plant Sciences, UC Davis Seaweed as a source of omega-3 fatty acids Regarding “Food as Medicine” (July-September 2011): The authors must be aware of the sources of omega-3 fatty acids. Seaweed salad from Korea solves the prob- lem without using fish. I consume some with my no- palitos for breakfast every morning. The public should be aware of this source of omega-3 fats. Andrew A. Benson Scripps Institution of Oceanography UC San Diego First phase of Hilgardia Project under way T he Hilgardia Project, launched in April 2011 to bring the classic UC publication to the Web, has received $26,550 in donations and pledges and is nearing its fundraising goal of $30,000. The project’s first phase — preparing the Wine and Grape Collection for posting online — is under way. For 70 years, until publication ceased in 1995, Hilgardia was the pri- mary technical publication of UC Agriculture and Natural Resources. The archive includes classic research in agricultural, environmental and nutritional sciences, content that is still widely cited and valuable to industry and scholars. At present, Hilgardia has virtually no online presence, and half of pub- lished issues are out of print. The rest are paperbound, subject to wear and tear. When digitized, these works will be posted on a sister site to California Agriculture journal and become freely available to scholarly and lay readers. To make a donation or for more information, write to calag@ucdavis.edu, e-mail Deborah Golino at dagolino@ucdavis.edu or go to http:/ /californiaagriculture.ucanr.edu/hilgardia.cfm. The Hilgardia Project gratefully acknowledges the following donors, whose generosity has made it possible to begin scanning and posting this vital work (31,304 pages and 966 articles): CALIFORNIA AGRICULTURE • VOLUME 66 , NUMBER 3 Angela Zivkovic, author of “Dietary omega-3 fatty acids aid in the modulation of inflammation and metabolic health” (July-September 2011), responds: While seaweed (wakame) is a source of omega-3 fatty acids, it contains modest amounts. According to the U.S. Department of Agriculture nutrient database, there are 186 milligrams of eicosapentaenoic acid (EPA) per 100 grams of raw seaweed. This is one-third of the amount in an equivalent portion of raw pink (wild) salmon. There is even less in dried seaweed: 87 milligrams EPA per 100 grams. An entire package of dried seaweed usually contains 100 grams of seaweed, which is typically not consumed by one July–September 2011 person in 1 day. California Agriculture Anonymous gift in memory of Harry Lawton, UC Riverside, honoring his contributions to UC Lodi Winegrape Commission, in support of the Wine and Grape Collection Northern California Entomological Society, in sup- port of the Entomology Collection Frank G. Zalom, UC Cooperative Extension Specialist, Integrated Pest Management Anonymous gift in tribute to Donald Burdick, recognizing his contributions to CSU Fresno James Doyle, retired UC Davis plant breeder Paramount Farming Company Ernest P. Peninov Plant Sciences, Inc. Vintage Nurseries LLC John Neal Friends of Hilgardia (under $500) G. Stuart Pettygrove, UC Cooperative Extension Soils Specialist — Janet White

First Report of Phytophthora infestans Causing Late Blight on Solanum viarum in Colombia.

Solanum viarum Dunal (tropical soda apple) belongs to the section Acanthophora in the genus Solanum, which includes nearly 20 neotropical species of herbs and small shrubs (2). The species in this section are sometimes called the 'spiny Solanums' (2) and are adapted mainly to highly disturbed habitats and open secondary forests. The center of diversity is eastern Brazil (3). Since the early 1990s, S. viarum has been a problematic weed in Florida where it was listed as a noxious weed in 1993, followed in 1994 by its addition to the Federal Noxious Weed List of the USDA. On 17 April 2010, 12 plants of S. viarum located close to a S. betaceum crop (tree tomato) in the province of Caldas (Department of Antioquia, central northwestern Colombia) were found with symptoms similar to late blight caused by Phytophthora infestans on S. tuberosum (potato). Fifteen leaves from 12 plants with blackish, water-soaked lesions showing a white sporulation on the abaxial side were collected and processed within 3 days. The leaves were placed in a humid chamber and incubated in darkness at room temperature (18°C mean temperature) until sporulation was observed. Microscopic characteristics were consistent with Phytophthora spp. Only one axenic culture was obtained by successive subcultures in rye B agar plates. After an incubation period of 8 days, plates were washed with distilled water and ovoid, semipapillate caduceus sporangia ranging from 38 to 41 μm long (average 39; N = 86) and 23 to 29 μm wide (average 26; N = 86) were observed. To fulfill Koch's postulates and test the isolate for the ability to infect potato as well as Solanum spp. associated with potato crops in Colombia, triplicate pathogenicity tests were carried out on three detached leaves of S. viarum, S. tuberosum, and S. americanum (American nightshade). A 1 × 104 sporangia/ml suspension of the Phytophthora isolate, estimated using a haemocytometer, was obtained from 8-day-old cultures grown on rye B agar. The suspension was incubated at 4°C for 2 h to induce zoospore release. The leaves were then inoculated by spraying them until runoff. After an incubation period of 5 days at 18°C in a humidity chamber, mycelia, sporangia, and brownish lesions, similar to those described above, were observed in the leaves of all three hosts, indicating pathogenicity. DNA extraction was performed from the P. infestans isolate (4). Four nuclear loci, ITS, β-tubulin, Ras, and Avr3a, as well as one mitochondrial gene, cytochrome c oxidase 1 (Cox1), were amplified and sequenced. Sequences were compared with GenBank databases using Blastn. In all cases, the best hits corresponded to P. infestans (GenBank Accession No. HQ639930 for Avr3A, HQ639931 for β-tubulin, HQ639932 for Cox1, HQ639933 for iRas, HQ639934 for Ras, and JF419363 for ITS). Reports of P. infestans causing typical late blight symptoms on wild solanaceous plants are becoming more frequent and have been made from other countries such as Peru (1). To our knowledge, this is the first time that P. infestans has been observed and isolated from S. viarum in Colombia, introducing the possibility of this wild solanaceous weed as another late blight host.

Herbivorous Insect Fauna of Mile-a-minute Weed, Persicaria perfoliata (Polygonaceae), in Japan

The mile-a-minute weed, Persicaria perfoliata (L.) H. Gross (Polygonaceae), was first established in the United States in Pennsylvania and Mary land in the 1930s (Wu et al. 2002), and has been placed on noxious weed lists in several states of the United States because of the damage it causes in infested orchards, nurseries, and horticultural crops (Oliver & Coile 1994; Wu et al. 2002). Be cause of its rapid growth, the weed readily invades forests or forest edges (Wu et al. 2002). In addition, the weed's thorny vines impede movement of wild life and interfere with human activities (Okay 1997). By 2003, the plant was found in 8 states (Delaware, Maryland, New York, Ohio, Pennsylva nia, Virginia, West Virginia, and Connecticut) and the District of Columbia (Lamont & Fitzgerald 2000; Price 2001). Fifteen additional states are cur rently at risk of becoming infested with this weed (Okay 1997). In the southern United States, mile a-minute weed could behave as a perennial plant (Stevens 1994; Ding et al. 2000). Recently, mile-a minute weed was targeted for biological control. Several natural enemies of mile-a-minute weed have been recognized in China (Ding et al. 2004), but little information is available on other potential biological control agents from other re gions of the plant's large native range (Ohwi 1965; Satake et al. 2000). We examined the weed in Japan because parts of Japan are in the native range of mile-a-minute weed (Ohwi 1965) and those areas are a good climatic match to the northeastern United States, where release of nat ural enemies is intended (Reardon, unpublished data). Here we report the results of a survey made in 2004 and 2005 of the herbivorous insect fauna

Noteworthy Collections: KENTUCKY

Triadica sebifera (L.) Small [Sapium sebiferum (L.) Roxb.] (EUPHORBIACEAE)—Fayette County: Collected from residence on Athens-Walnut Hill Road, southeast of Lexington; 37u57.4889N, 084u24.8749W; 1 Sept. 2007, Eric B. Comley 61 (EKY). Significance. This is the first collection of Triadica sebifera (L.) Small, the Chinese tallowtree, from Kentucky. According to the United States Department of Agriculture, Natural Resources Conservation Service (USDA, NRCS 2007), this invasive species is known from the southern states of Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, and Texas. Chinese Tallow-tree, or Popcorn Tree, is a native of China, Taiwan, and Japan (USDA, NRCS 2007). The species was introduced by Benjamin Franklin and promoted by the U.S. Forest Service for soap potential and later as an ornamental due to the tree’s beautiful fall color. According to the Invasive and Exotic Species website (Douce et al. 2007) Chinese Tallow-Tree was brought to South Carolina in the 1700’s as an ornamental, and was widely planted by the U.S. Forest Service for seed oil production from 1920 to 1940. This Kentucky record is from a single tree 2.5 m tall and nearly 9 cm in diameter just above ground level. It was located near the end of the carport about 1 m from the driveway and 2 m from a bird feeder. The resident owner’s son brought a sample of the plant to the Fayette County Cooperative Extension Office for identification. After an initial identification, the specimen was confirmed by Dr. Ross Clark, Eastern Kentucky University. The resident’s son, once the tree displayed foliage, noted the tree showed some similarities in leaf shape to native species (Cercis canadensis L. and Populus deltoides Bartram ex Marshall), so the tree was left to grow. The tree was not planted by the property owner. After explanation of the toxicity of the plant to livestock and its listing on State and Federal Noxious Weed lists (USDA, NRCS 2007), the owner agreed to destroy the plant. No other Chinese tallowtrees were found on the 0.6 ha property, but continued observations are planned for the area

The biology of Canadian weeds. 3. Lepidium draba L., L. chalepense L., L. appelianum Al-Shehbaz (updated)

This paper updates an earlier paper by Mulligan and Findlay (1974) on the cruciferous weeds Lepidium draba, L. chalepense and L. appelianum (treated in the previous paper as Cardaria draba, C. chalepensis and C. pubescens, respectively). Known collectively as hoary cresses, these species reached North America in the 19th and early 20th centuries as contaminants in seed or in ballast. The three species spread extensively in the western parts of the continent by the mid 20th century, partly through seed dissemination, but also by establishment of clonal patches and rhizomatous spread. In the prairie provinces the three species are weeds in grainfields, hayfields and forage crops, and have been largely under control in those crops since the 1970s. By the 1970s all three species had spread into agricultural regions of south central British Columbia and remain a serious problem there. They have also spread into forest, range, and riparian areas of Alberta and British Columbia and are among weedy threats to native ecosystems. Populations in Saskatchewan and Manitoba appear to have stabilized, but remain on noxious weed lists. In the western United States, the species have also spread from cultivated areas into rangelands, and L. draba in particular competes successfully with native vegetation, resulting in reduced local biodiversity. Lepidium draba can also reduce forage production, quality and palatability. Biocontrol measures for L. draba are under investigation. Mechanical controls have proved to be generally ineffective in large populations. Herbicides are effective in the short term in some agricultural crops, but do not provide long-term control, and are of restricted use on rangelands and at riparian sites. Potential beneficial uses of Lepidium draba in phytoremediation and as a source of disease-fighting chemical derivatives are reported. Key words: Lepidium draba, Lepidium chalepense, Lepidium appelianum, Cardaria draba, Cardaria chalepensis, Cardaria pubescens, hoary cress, white-top

Germination of Invasive Plant Seeds after Digestion by Horses in California

Using a unique sterile design intended to eliminate outside seed contamination of horse feces, we investigated whether weed seeds germinate after digestion by horses. Feces were collected from selected National Parks and other locations in central and northern California. All potted fecal samples were irrigated and grown in an enclosed sterile nursery environment. Thirty-two plant species emerged from these fecal samples, 24 of which were not native to California. None of these were identified on the California Department of Agriculture's Noxious Weed List, which is used as a basis to certify equine feed as weed free. However, seven of the non-native species are identified as moderately invasive on the California Invasive Plant Council's (Cal-IPC) list. These species are: Hirschfeldia incana, Hordeum marinum, Lolium multiflorum, Mentha pulegium, Rumex acetosella, Trifolium hirtum, and Vulpia myuros. In addition, the following four non-native plants are listed at the limited invasiveness level on the Cal-IPC list: Hypochaeris glabra, Lythrum hyssopifolium, Medicago polymorpha, and Poa pratensis. Because we did not survey invasive plant cover in locations from which we sampled, we cannot guarantee that species identified in our samples would have also germinated in the field. Our results add to a growing body of literature documenting germination of seeds after passing through the digestive system of horses and suggest that conscientious horse owners should select feed sources that are free of weeds. We also find that the current list of noxious weeds used to certify weed-free feed for equines should be comprehensive.

California’s Reaction to Caulerpa taxifolia: A Model for Invasive Species Rapid Response*

The invasive marine alga Caulerpa taxifolia was discovered June 12, 2000, in California at Agua Hedionda Lagoon. Due to a 15-year history of spread in the Mediterranean Sea, C. taxifolia had already been placed on the US Federal Noxious Weed list in 1999. Awareness of this threat greatly facilitated consensus building and setting clear eradication goals among a large number of state, federal and local agencies as well as private groups and non-governmental organizations (NGOs) that became the ‘Southern California Caulerpa Action Team’ (SCCAT). Field containment and treatments began 17 days after the discovery due to: (1) timely identification and notification of the infestation; (2) the proactive staff of the San Diego Regional Water Quality Control Board who deemed this invasion tantamount to an ‘oil spill’, thus freeing up emergency funding; (3) the mobilization of diver crews already working at the site. Three well-integrated components of this rapid response have resulted in an effective eradication program: (a) expertise and knowledge on the biology of C. taxifolia; (b) knowledge on the uses, ‘ownership’ and characteristics of the infested site; (c) knowledge and experience in the implementation of aquatic plant eradication. Together, with the requisite resources (approximately $US1.2 million per year), this approach has resulted in containment, treatment and excellent progress toward eradication of C. taxifolia. Successful rapid response to other aquatic invasive species will require similar readiness to act, and immediate access to adequate funding.

Key West Nightshade, a New Experimental Host for Plant Viruses.

Key West nightshade (Solanum bahamense) is a perennial solanaceous weed found in the extreme southern portion of Florida. It can be propagated by seed and cuttings and is absent from the noxious weed lists of all U.S. states. Its susceptibility to five viruses common to Florida was evaluated by mechanical inoculation of leaves with Tomato spotted wilt virus (TSWV), Tobacco mosaic virus (TMV), Pepper mild mottle virus (PMMoV), Cucumber mosaic virus (CMV), and a putative tobamovirus recently isolated from hibiscus in Florida (HV). TSWV induced chlorotic rings on inoculated leaves and mosaic and malformation of uninoculated leaves. CMV induced necrotic local lesions on inoculated leaves. No symptoms were observed following inoculation with TMV, PMMoV, or HV. TSWV, TMV, and PMMoV systemically infected S. bahamense as determined by the use of enzyme-linked immunosorbent assay, reverse transcription-polymerase chain reaction, viral-associated double-stranded RNA analysis, and/or indicator hosts. Active growth of infected plants continued for 7 months following inoculation, making S. bahamense suitable for long-term maintenance of viruses in planta. We suggest that S. bahamense may be a useful host for virus culture collections and for studies involving large numbers of virus isolates where fresh, infected tissue is continuously required.