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When invasive weeds are removed with herbicides, revegetation of native species is often desirable. The extended soil activity of aminocyclopyrachlor is important for long-term weed control but could reduce recovery of native species as well. The effect of aminocyclopyrachlor applied alone or with chlorsulfuron on cool- and warm-season grass species commonly used for revegetation was evaluated. The cool-season grasses included green needlegrass, intermediate wheatgrass, and western wheatgrass, whereas the warm-season grasses were big bluestem, sideoats grama, and switchgrass. A separate experiment was conducted for each species. Aminocyclopyrachlor was applied at 91 to 329 g ha−1 alone or with chlorsulfuron from 42 to 133 g ha−1 approximately 30 d after emergence. Warm-season grasses generally were more tolerant of aminocyclopyrachlor than the cool-season grasses evaluated in this study. Switchgrass and big bluestem were the most tolerant of the warm-season species when aminocyclopyrachlor was applied at 168 g ha−1 and averaged 199 and 150% forage production, respectively, compared with the control. Green needlegrass was the most tolerant cool-season grass. Western wheatgrass was the least tolerant species evaluated because forage production only averaged 32% of the control the year after treatment and thus would not be suitable for seeding if aminocyclopyrachlor was applied. The effect of chlorsulfuron applied with aminocyclopyrachlor varied by grass species. For example, green needlegrass injury 8 wk after treatment (WAT) averaged 30 and 48% when aminocylopyrachlor was applied alone, respectively, but injury was reduced to less than 16% when aminocyclopyrachlor was applied with chlorsulfuron. However, injury on the less-tolerant intermediate wheatgrass ranged from 48 to 92% by 4 WAT when aminocyclopyrachlor was applied alone and from 60 to 86% when chlorsulfuron was included in the treatment.
Nomenclature: Aminocyclopyrachlor; chlorsulfuron; big bluestem, Andropogon gerardii Vitman; green needlegrass, Nassella viridula (Trin.) Barkworth; intermediate wheatgrass, Thinopyrum intermedium (Host) Barkworth & D. R. Dewey; sideoats grama, Bouteloua curtipendula (Michx.) Torr.; switchgrass, Panicum virgatum L.; western wheatgrass, Pascopyrum smithii (Rydb.) A. Löve.
Management Implications: Land managers often utilize an integrated program to control invasive weed species. Methods can include the use of fire, herbicides, and/or grazing followed by revegetation with native species. However, reseeding previously weed-infested plant communities more often results in failure and return of the invasive weed rather than successful reestablishment of desirable species. Recently restored prairies are especially vulnerable to invasive species because the plant community has not yet become established. Three cool- and three warm-season grass species were evaluated for tolerance to the rangeland and wildland herbicide aminocyclopyrachlor. The herbicide was applied alone and with chlorsulfuron approximately 30 d after seeded grasses emerged. The warm-season grasses (big bluestem, sideoats grama, and switchgrass) generally were more tolerant to aminocyclopyrachlor than the cool-season grasses (green needlegrass, intermediate wheatgrass, and western wheatgrass), with green needlegrass the most tolerant of the cool-season species evaluated. Warm-season grass yield the year after treatment was similar to or exceeded the control as long as aminocyclopyrachlor was applied at 168 g ha−1 or less. Western wheatgrass was the least tolerant grass evaluated; forage production averag
Nonnative M. vimineum has been expanding rapidly in the eastern United States, where it can negatively affect plant communities. Locally, the species is assumed to spread from roadsides into nearby forests, where it can form dense populations after disturbances, especially in light gaps. Using microsatellite markers, we quantified patterns of genetic variation and structure among populations at nine sites in West Virginia. We then examined patterns of local dispersal within each population, focusing on subpopulations along the roadside, those coalescing nearby along the forest edge, and subpopulations in the interior forest. We found that levels of genetic variation of M. vimineum were relatively low overall across populations but with genetic structure present among populations (Fst = 0.60). Within populations, subpopulations along the roadside were genetically variable, containing 4 to 22 unique, multilocus genotypes. Many of these genotypes were also identified in the adjacent forest, consistent with local, diffusive spread from the roadway. However, several genotypes in the interior forest were unique to the population, indicating that dispersal from other sites may also occur. Overall, it appears that genetic diversity and structure in M. vimineum reflects a variety of processes, including localized dispersal and long-distance migration.
Nomenclature: Japanese stiltgrass, Microstegium vimineum (Trin.) A. Camus.
Management Implications: Our research highlights the importance of evaluating local and regional patterns of genetic diversity when defining management strategies of an invasive plant. Microstegium vimineum has low genetic diversity, which could potentially make it susceptible to disease or unable to adequately respond to other stochastic events. Despite this paucity of diversity, M. vimineum has evolved within its invasive range, and the presence of at least one effective pathogen (Bipolaris spp.) has not forestalled its rapid spread.
Our results show that roadsides, despite having a relative abundance of chasmogamous seeds, are not a significant source of genetic variation. Instead, any new genotypes in an area are likely the product of long-distance dispersal. Second, our results indicate that forest interior subpopulations are more often not the product of spread from the immediately adjacent roadside but, instead, may come from a long-distant source. Finally, our study shows there is genetic differentiation among regional populations, which could serve as a source of new or highly fit (i.e., able to withstand a range of environments) genetic information.
The key to stopping this influx of new genotypes into a site appears to be stopping or slowing the long-distance dispersal of the seed. Effective preventative measures could include strategically located cleaning stations (e.g., highway intersections, rest areas, gas stations) for vehicles and equipment and the use of certified clean gravel and other road construction/maintenance materials. Based on our results, priority locations would be intersections between the regionally different populations.
Although our research highlights the complexity of the success of M. vimineum as an invader, it also supports a focus on preventative management to reduce long-distance spread.
Gene flow between Dalmatian toadflax (DT) and yellow toadflax (YT), both aggressive invaders throughout the Intermountain West, is creating hybrid populations potentially more invasive than either parent species. To determine the direction of gene flow in these hybrid populations, species-diagnostic cytoplasmic markers were developed. Markers were based on polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) polymorphisms in the trnT-D chloroplast DNA (cpDNA) region digested with Alu1, and single-nucleotide polymorphisms (SNPs) in the matK and trnL-F chloroplast-barcoding regions. Four hybrid toadflax populations sampled from Colorado, Montana, and Washington contained both DT and YT cytoplasm, with YT predominating; 25 individuals from a fifth hybrid population from Idaho all had identical YT cpDNA haplotypes. Thirteen plants from two Colorado populations, assumed to be DT based on morphology and geographic isolation from any known YT population, were found to have YT cpDNA haplotypes. These results indicate that gene flow between invasive YT and DT populations is more widespread that previously realized and confirms that cryptic introgression of YT alleles has occurred in multiple western U.S. DT populations. The presence of YT genetic material in presumed DT populations may negatively affect host recognition and establishment by biocontrol agents used for toadflax management.
Nomenclature: Dalmatian toadflax, Linaria dalmatica (L.) P. Mill.; yellow toadflax, Linaria vulgaris P. Mill.
Management Implications: Yellow toadflax (YT) and Dalmatian toadflax (DT) are not reported to hybridize in their native European ranges, but cross-pollination between these two invasive species has been confirmed in several Rocky Mountain states. This produces novel hybrid-toadflax populations that are more vigorous and robust than either parent species, presenting even greater management challenges. Experimental hand-pollinations under controlled greenhouse conditions to produce hybrid toadflax plants previously showed that hybrids were more likely to result from pollination of YT by DT than vice versa, and results of DNA analysis in this study indicate this is also true when cross-pollination occurs in the field. Hybrid toadflax presents particular problems for biocontrol. Two stem-boring weevils, Mecinus janthinus and Mecinus janthiniformis, are released as approved biocontrol agents on YT and DT, respectively; however, each of these weevils exhibits a strong preference for its natural host toadflax species. Whether weevils will establish on, and control, hybrid toadflax infestations is unknown. An unexpected finding of this study was that some Colorado toadflax populations, presumed to be pure DT based on their morphology and habitat, in fact, contained YT DNA. This is most likely the result of previous hybridization between YT and DT, followed by repeated crossing back to DT, and suggests that hybridization between these two invasive toadflaxes is more widespread and has been occurring for longer than previously realized. The presence of DNA from the nonpreferred toadflax species in a host-plant population may explain why weevil releases fail to establish at apparently favorable sites, and undetected transfer of DNA between YT and DT could undermine the efficacy of biocontrol in managing toadflax invasion.
Phragmites australis (common reed) is one of the most widely distributed flowering plants in North America. The introduced lineage occurs in wetland and riparian areas covering a range of climatic types. In Nebraska, an abundance of livestock could help to reduce P. australis with proper timing and grazing intensities. In 2011, a 3-yr study was initiated to evaluate targeted cattle grazing and herbicide effects and the nutritive value of this species. Treatments included a single application of imazapyr (Habitat®, BASF Corporation, Research Triangle Park, NC) herbicide applied in the first year, grazing, and a control. Grazing was applied for up to five consecutive days in June and August 2011 and 2012 and in June 2013. Stem density, height, and biomass of P. australis were determined before each grazing period and in 2014. Diet samples were collected from rumenally fistulated steers each grazing period. Imazapyr provided 100% control of P. australis; however, re-establishment began 2 yr posttreatment. Grazing significantly reduced pregrazing P. australis biomass in the second and third growing season (P < 0.05). Stem density and height in the grazed treatment was similar to the control through 2012; however, in 2013 and 2014, control stem density was 1.5 times greater and height was 1.4 times that of the grazed treatment. Crude protein content of diet samples was greater in 2011 (16.8%) compared with 2012 (14.3%, P < 0.05). In vitro dry matter digestibility (IVDMD) of diet samples (45.4%) was not affected by year or month (P > 0.05). The relatively low IVDMD suggests that some form of energy supplementation would be needed to create a better nutritional balance. The cumulative effect of grazing does have the potential to reduce P. australis populations, but other methods would have to be used for greater control and site restoration.
Nomenclature: Common reed, Phragmites australis (Cav.) Trin. ex Steud. PHRCO.
Management Implications: Integrated management is important to control invasive plant species effectively. Reliance on a single technique can lead to poor containment, a failed eradication effort, and re-establishment of the target species over the long term. Natural areas can be challenging to implement integrated approaches effectively because of inaccessibility issues for machinery and lack of available biocontrol agents. By investigating previously untested techniques, the potential for implementing integrated management in an existing system could be high.
Targeted cattle grazing and herbicides can reduce the density and growth of common reed [Phragmites australis (Cav.) Trin. ex Steud.], which is a widely established invasive plant species in wetlands and riparian areas. To date, no biocontrol agent has been identified or released for P. australis. The presence of cattle in pastures and meadows adjacent to riparian areas infested with P. australis could be combined with herbicides for an integrated management approach.
We found that cattle effectively reduced stem density and height of P. australis over a 3-yr period. A single herbicide application was more effective than grazing. Although crude protein content of P. australis was adequate for most livestock classes, in vitro dry matter digestibility was relatively low, suggesting that some form of energy supplementation would be
Ventenata dubia is an exotic annual grass that has become increasingly invasive in various perennial grass systems throughout the Intermountain Pacific Northwest. Currently, little information is available to landowners about herbicide control options. In our first field study, we evaluated V. dubia control efficacy and perennial grass tolerance of herbicides applied pre-emergence (PRE) at two locations and as an early postemergence (EPOST) application at four different conservation reserve grasslands, with each grassland dominated by different perennial grass species. Treatments included flufenacet plus metribuzin (303 76 g ai ha−1 [0.27 0.07 lb ai ac−1]), propoxycarbazone-sodium (49 g ai ha−1 [0.04 lb ai ac−1]), rimsulfuron (53 g ai ha−1 [0.05 lb ai ac−1]), sulfosulfuron (53 g ai ha−1 [0.05 lb ai ac−1]), and imazapic (105 g ai ha−1 [0.09 lb ai ac−1]). Rimsulfuron and flufenacet plus metribuzin applied PRE provided > 90% control 10 mo after treatment (MAT). Rimsulfuron and sulfosulfuron applied EPOST provided > 90% control 9 MAT. Herbicide injury to bluebunch and intermediate wheatgrass was negligible across treatments. Imazapic and sulfosulfuron applied EPOST resulted in significant injury to smooth brome and timothy. In our second study, we addressed the following question: Will fall herbicide plus fertilizer treatments improve V. dubia control compared with herbicide treatments alone? We imposed fall herbicide treatments in main plots and fertilizer treatments (fall N, fall P, fall K, fall PK, spring N, NPK) in split plots at three study locations. Herbicide treatments resulted in high levels of V. dubia control. Differences in V. dubia abundance among fertilizer treatments were negligible 9 MAT. Within herbicide control plots, spring N and NPK treatments resulted in significant increases in perennial grass cover and decreases in V. dubia cover (9 MAT). This result indicates that spring N applications timed to the onset of perennial grass growth could be utilized as a component of an integrated management strategy for V. dubia in invaded perennial grass systems.
Management Implications:Ventenata dubia is an increasingly problematic invasive annual grass in the Intermountain Pacific Northwest. In the Palouse Bioregion, V. dubia has reduced forage production in hay and pasture, can negatively affect wildlife habitat and soil erosion management goals within Conservation Reserve Program (CRP) lands, and has invaded canyon grasslands and Palouse Prairie remnants. Currently, little information is available to land managers about how to control V. dubia across the range of perennial grass systems in which it invades. We used two field experiments to identify effective herbicide control options that also limit potential herbicide injury to perennial grass s
Establishment of nonindigenous (NI) aquatic plants in the nearshore regions of freshwater ecosystems has resulted in environmental degradation, recreation concerns, economic impacts, and substantial management challenges. To reduce these undesirable effects, NI aquatic plants are often targeted for removal or control by management agencies, but the efficacy of implementation is often not documented or sustained. In this study, we developed a management plan to completely remove all NI plants from Emerald Bay, Lake Tahoe, CA, using only physical control techniques. Management plan priorities were based on previous research and lessons learned, including the need for (1) integrated weed management using multiple physical control techniques, (2) a large initial treatment investment, (3) ongoing early detection and rapid response, (4) detailed ecological monitoring, and (5) a long-term commitment to annual maintenance removal. Application of this management plan resulted in complete removal of all NI aquatic plants from Emerald Bay and substantial cost savings each year after the initial large investment. Annual maintenance removal and monitoring will need to continue as long as NI aquatic plants continue to enter Emerald Bay on boats and currents from other areas of Lake Tahoe.
Multiple weed control strategies employed in combination can often aid the successful management of perennial weed species. This review article provides examples of integrated control programs that could aid in the management of several invasive perennial weed species that are problematic in the Pacific Northwest and elsewhere in North America. The development of an integrated management control program for wild chervil, a relatively recent invader to the Pacific Northwest of the United States and adjacent Canada, provides an example for this process. Through use of mechanical (mowing and tillage), cultural (establishment of competitive vegetation), and chemical (specific herbicides) strategies, control of this short-lived perennial species was greatly improved as compared to foliar herbicide applications alone. Such integrated strategies have been shown to enhance control of many perennial weed species, while potentially reducing the amount of herbicide applied, lessening the possibility of injury to adjacent desirable vegetation and increasing the stability of the ecological community at the site.