Total vegetation control (TVC) is an essential management practice to eliminate all vegetation for the purpose of protecting infrastructure, people, or natural resources on sites where vegetation poses major fire, visibility, and infrastructure risks. TVC is implemented on sites such as railroads, power substations, airports, roadsides, and oil and gas facilities. Current research has identified that tank-mixing two effective mechanisms of action is a superior resistance management strategy compared to rotating mechanisms of action; however, effective tank mixes for TVC have not been thoroughly evaluated. A field experiment was conducted from 2013 to 2014 at five sites in Colorado to compare 32 treatment combinations to two industry standards for TVC. Research objectives were (1) to identify herbicide tank-mix combinations for TVC with multiple effective mechanisms of action for resistance management, (2) to evaluate lower use rate alternatives to minimize nontarget impacts, and (3) to determine the efficacy of fall versus spring application timings. Seven treatments were identified as top-ranking treatments, averaging 96% bare-ground (BG) across five sites and two application timings. Four out of the seven top-ranked treatments included aminocyclopyrachlor, chlorsulfuron, and indaziflam. The industry standard diuron plus imazapyr was in the top ranking, whereas the other industry standard bromacil plus diuron performed inconsistently across sites. Probability modeling was used to predict the probability of achieving 97% or 100% BG with various treatment combinations. The combination of aminocyclopyrachlor, chlorsulfuron, indaziflam, and imazapyr had the highest predicted BG probability, with 88% predicted probability of achieving 100% BG, compared to 67% and 52% predicted probabilities for the industry standards diuron plus imazapyr and bromacil plus diuron, respectively. In three of the five sites, fall applications outperformed the same treatments applied in the spring. Several top-ranking treatments represent newer, lower use rate herbicide combinations that provide multiple mechanisms of action to manage herbicide-resistant weeds and minimize nontarget impacts.

Cut-leaved teasel is an invasive weed along highway corridors and is classified noxious in four states, including Missouri. Few herbicides have been examined for cut-leaved teasel control. Herbicides were evaluated for efficacy on established plants and residual activity for suppressing seedling emergence. Various growth regulator herbicides, amino acid inhibitors, and paraquat were applied on established teasel at two locations in central Missouri in fall 2003 and spring 2004, and two additional locations in fall 2004 and spring 2005. At 2 wk after treatment (WAT), paraquat resulted in the highest injury of teasel (85%), but injury declined over time. At 4 WAT, teasel control was most consistent with dicamba + diflufenzopyr applied in spring, ranging from 75 to 94% control. At 8 wk, glyphosate, dicamba + diflufenzopyr, metsulfuron-methyl, imazapyr, and combinations of growth regulator herbicides with 2,4-D were most effective, with teasel control from 86 to 100%. Control with 2,4-D alone was inconsistent; sulfosulfuron, sulfometuron-methyl, and paraquat were ineffective. Residual herbicides did not reduce teasel seedling emergence the following year. A number of herbicides were effective in managing emerged plants but reinfestations of treated sites is likely, even with the residual herbicides used in this research.

Cutleaf teasel (Dipsacus laciniatus) is an exotic, invasive plant that infests roadsides and other minimally disturbed areas. Plants in established stands appear to be a mixture of rapidly growing rosettes and rosettes with developing reproductive structures. Research that is focused on seed characteristics and their contribution to the spread of plants may be a key to precluding spread of cutleaf teasel in the field. Field studies were conducted to determine the viability and germinability of seeds after flowering, seedling emergence patterns, and seed persistence. Flowering (60% of anthesis) was observed under natural conditions on July 24, 2004, and July 16, 2005. Seeds harvested 12 d after flowering exhibited 43% viability and 2.5% germination. Seed weight and viability were greatest 30 d after flowering, but germination was < 32%. Seedling emergence was monitored over a 12-mo period with the greatest emergence in April and October with 33% of seeds germinating. Seed persistence was evaluated over a 3-yr period under field conditions. Up to 84% of the germinated seeds had germinated during the first year, with 6% of seeds remaining viable after 3 yr. Although seed persistence was relatively short, the rapid development of seeds following flowering as well as seedling emergence in both fall and spring suggests management practices are needed throughout the year to restrict reestablishment spread of cutleaf teasel.

Cutleaf teasel is an invasive, biennial plant that poses a significant threat to native species along roadsides in Missouri. Flowering plants, together with understory rosettes, often grow in dense patches. Detection of cutleaf teasel patches and accurate assessment of the infested area can enable targeted management along highways. Few studies have been conducted to identify specific species among a complex of vegetation composition along roadsides. In this study, hyperspectral images (63 bands in visible to near-infrared spectral region) with high spatial resolution (1 m) were analyzed to detect cutleaf teasel in two areas along a 6.44-km (4-mi) section of Interstate I-70 in mid Missouri. The identified classes included cutleaf teasel, bare soil, tree/shrub, grass/other broadleaf plants, and water. Classification of cutleaf teasel reached a user's accuracy of 82 to 84% and a producer's accuracy of 89% in the two sites. The conditional κ value was around 0.9 in both sites. The image-classified cutleaf teasel map provides a practical mechanism for identifying locations and extents of cutleaf teasel infestation so that specific cutleaf teasel management techniques can be implemented.

Cutleaf teasel is an exotic weed that infests roadside environments in Missouri. As a growing biennial, the plant develops as a rosette during the first year and bolts during the second. Dense patches contain flowering plants with understory rosettes. The objective of this work was to develop approaches for detecting cutleaf teasel patches with accurate assessment in a complex of species along a roadside. Thus, management of cutleaf teasel could be located at specific sites. Two hyperspectral images (63 bands with 1-m spatial resolution) were analyzed to detect cutleaf teasel along the Interstate Highway I-70 in mid Missouri. Classification of cutleaf teasel reached a user's accuracy of 82 to 84% and a producer's accuracy of 89% at the two sites. The image-classified teasel map provides a practical mechanism for identifying the locations and extents of cutleaf teasel infestation so that specific management techniques can be implemented.

Miscanthus sinensis is a perennial grass native to Asia, but since its introduction to the United States in the late 19th century, it has become both a major ornamental crop and invasive species. Previous studies of the ecology of M. sinensis in both its introduced and native ranges have suggested that it may be occupying a novel ecological niche in the introduced range. Miscanthus sinensis and its daughter species, Miscanthus × giganteus, are under evaluation as bioenergy crops; therefore, characterization of the ecology and environmental niche of M. sinensis is essential to mitigate the risk of fostering future invasion in the United States. In July 2011, we surveyed 18 naturalized M. sinensis populations spanning the U.S. distribution, covering a 6° latitudinal gradient from North Carolina to Massachusetts. Miscanthus sinensis populations ranged in size from 3 to 181,763 m2 with densities between 0.0012 and 2.2 individuals m−2, and strongly favored highly disturbed and unmanaged habitats such as roadsides and forest edges. Population size and individual plant morphology (i.e., tiller height, basal diameter, and tiller number) were not affected by soil characteristics and nutrient availability, though increased tree canopy cover was associated with reduced population size (P < 0.0001). Plant size and vigor were not significantly affected by low light availability, which supports previous suggestions of shade tolerance of M. sinensis. In summary, M. sinensis can tolerate a broad range of climatic conditions, light availability, and nutrient availability in the eastern United States, suggesting risk of further invasion beyond its current distribution in the United States.

Field research was conducted to evaluate plant growth-regulator efficacy for tall fescue growth and seedhead suppression applied using application placement equipment. Specially designed equipment outfitted with fluid application systems applies low-volume plant growth regulator directly on plant foliage, reducing opportunity for drift and visible application. Wet-blade mowers are equipped to apply plant growth regulators and mow in a single pass, whereas rotary-wick applicators simply wipe chemicals directly on uncut vegetation. Therefore, a wet-blade, rotary-wick, and broadcast sprayer system were chosen to apply imazapic at three rates (9, 35, and 53 g ai/ha), and a mefluidide + chlorsulfuron tank mix at 7 + 140 g ai/ha to tall fescue roadsides for vegetative growth and seedhead suppression. Experiments were conducted during the spring and summer of 2004 in central and western North Carolina. Tall fescue was slightly injured and discolored by all treatments but fully recovered by 2 mo after treatment. Imazapic suppressed new vegetative growth 3 mo after treatment compared with the nonmowed–nontreated control (16.1 cm of growth) and the mowed–nontreated control (21.1 cm) when applied with the rotary-wick applicator (8.5 cm) and broadcast sprayer (6.2 cm). However, differences in vegetative height primarily occurred when application placement equipment treatments were compared with nontreated vegetation as opposed to mowed–nontreated plants. Although mowed–nontreated and wet-blade–treated plots had more new vegetative growth, nonmowed–nontreated plots still consistently had the greatest vegetative height. Seedhead suppression ranged from 87 to 100% when compared with the nonmowed–nontreated control, with wet-blade treatments consistently providing the least-effective seedhead suppression. Overall, application placement equipment did not improve plant growth-regulator efficacy when compared with the foliar broadcast spray.

The occurrence of 36 arable weed species across 13 counties in the eastern Arkansas–Mississippi Delta area on 489 randomly selected road sites was surveyed in 2012. Palmer amaranth, johnsongrass, large crabgrass, barnyardgrass, prickly sida, and broadleaf signalgrass were the top six weed species, with occurrence noted at 313, 294, 261, 238, 176, and 136 sites, respectively. Factors found to affect weed occurrence along Mississippi Delta roadsides included topographical characteristics, weed species, ditch slope, road type, and nearby land use. Among roadside topographical characteristics, road shoulder was found to strongly affect weed occurrence. In addition, paved and gravel road types with moderate roadside slope explained most of the variability of weed occurrence at each sampling site. Additionally, nearby arable land use affected weed occurrence more so than natural, residential, and pastoral land. Barnyardgrass, johnsongrass, and Palmer amaranth were 3.6 to 4.3 times more likely to occur than all other species identified. An effective weed management plan along eastern Arkansas–Mississippi Delta roadsides should focus on road shoulder, adjacent arable land use, road type, and specific weed species (e.g., Palmer amaranth, johnsongrass, and barnyardgrass). The inclusion of these parameters in future weed control programs can prove invaluable for preventing the spread of the herbicide-resistant Palmer amaranth, barnyardgrass, and johnsongrass.

Broomsedge populations have increased substantially over the last decade on roadsides in Georgia. The invasiveness of this species might have resulted from imazapic use for bermudagrass growth regulation and the limited use of MSMA on roadsides. The objectives of this research were to evaluate (1) differential growth inhibition of bermudagrass and broomsedge to imazapic, (2) susceptibility of isolated acetolactate synthase (ALS) enzymes of bermudagrass and broomsedge to imazapic, (3) broomsedge control with tank mixtures of imazapic with MSMA, and (4) the influence of imazapic on absorption and translocation of 14C-MSMA. In greenhouse experiments, imazapic reduced bermudagrass shoot biomass ~ 2 times more from the nontreated than broomsedge. Isolated ALS enzymes of bermudagrass were ~ 100 times more susceptible to inhibition by imazapic than broomsedge. In field experiments, imazapic provided no control of broomsedge, but MSMA alone controlled broomsedge 81% at 12 mo after initial treatments (MAIT). Broomsedge control was reduced to 45% when MSMA was tank mixed with imazapic at 12 MAIT. In laboratory experiments, imazapic tank mixtures did not reduce broomsedge absorption or translocation of 14C-MSMA. Overall, bermudagrass is more susceptible to imazapic due to greater target-site inhibition than broomsedge. Results emphasize the importance of MSMA use for broomsedge control, but agronomists should avoid tank mixtures with imazapic to reduce potential antagonism.

Roads function as prime habitats and corridors for invasive plant species, and can contribute significantly to the spread and establishment of weeds inside protected areas. Smooth bedstraw (Galium mollugo) populations have recently expanded in the abandoned agricultural fields of Bic National Park (Quebec, Canada), and may represent a threat to the preservation of plant diversity and to the quality of visitor experience. The main objective of this study was to map the distribution of the species in the park and to delineate factors influencing the abundance of the plant in fallow fields. We hypothesized that road proximity was the main factor explaining the presence and abundance (frequency of recording) of smooth bedstraw in fields. Vegetation surveys were conducted in abandoned agricultural fields, and two logistic regression models were built to examine the relationship between the presence and abundance of smooth bedstraw and environmental and historical variables. Smooth bedstraw populations were also mapped along transportation corridors. The abundance of smooth bedstraw significantly increases within 125 m (410 ft) of a paved road. The recent proliferation of smooth bedstraw in Bic National Park is likely associated with the construction of road embankments during the paving of gravel roads. The paved road network has probably acted as a dispersal corridor for smooth bedstraw, while the abandoned agricultural fields located close to the paved roads provided suitable habitats facilitating population establishment over large areas. We recommended to the park's authorities to cease paving all remaining gravel roads in the park, not only to stop smooth bedstraw invasion, but also the spread of other invasive species of concern.

Kochia poses a challenge to vegetation management in both agricultural and noncrop areas. This species has developed widespread resistance to several herbicides with differing modes of action, including acetolactate synthase inhibitors and photosynthesis inhibitors. Resistance is also beginning to appear against the synthetic auxins and glycines. Therefore, alternative PRE and POST herbicides are needed for effective kochia management, especially in roadside bare-ground zones. Both PRE and POST herbicides were screened on rights-of-way in Pennsylvania. Mixtures containing diuron, flumioxazin, sulfentrazone, pendimethalin, prodiamine, and bromacil were evaluated for PRE activity in combination with glyphosate. POST kochia control was assessed for 15 noncrop herbicides. Results from all trials varied with kochia size and vigor at time of treatment. Although diuron is the current industry standard for PRE control in tank mixes, sulfentrazone appeared to have the most POST activity against vigorously growing kochia. All PRE herbicides evaluated performed better than the standard, sulfometuron plus chlorsulfuron alone. Dicamba, dicamba plus diflufenzopyr, fluroxypyr, and glyphosate performed best against kochia when applied POST. The recently available chemistries saflufenacil and aminocyclopyrachlor require further evaluation of application timing and use rates, respectively, for POST activity on kochia.