Native aquatic macrophytes such as Vallisneria americana Michx. are often desirable in aquatic ecosystems due to the ecological benefits they provide but are threatened by competition from invasive taxa including nonnative Vallisneria taxa and hydrilla (Hydrilla verticillata L.f. Royle). Identifying potential selective herbicide management options can provide options to minimize impacts to native taxa in restoration and aquatic invasive plant management programs. Greenhouse mesocosm experiments were conducted in 2023 to investigate herbicide efficacy on two native eelgrass species (V. americana and V. neotropicalis Vict.), two nonnative taxa (V. australis S.W.L. Jacobs & Les and V. spiralis × V. denseserrulata Makino) and H. verticillata. Herbicide applications included endothall, diquat, florpyrauxifen-benzyl, fluridone, and flumioxazin and select combinations of these herbicides used in H. verticillata management. Endothall alone provided 90 to 100% aboveground biomass reduction at 3000 µg L-1 with at least 24 hours of continuous or intermittent exposure to all native and invasive species at six weeks after exposure, whereas florpyrauxifen-benzyl applied alone resulted in minimal aboveground biomass reduction. A 45 day of exposure of fluridone (10 µg L-1) resulted in 95% biomass reduction on V. americana and 7 to 48% other tested taxa. The combination of flumioxazin and florpyrauxifen-benzyl resulted in 90 to 100% aboveground biomass reduction and endothall combined with florpyrauxifen-benzyl resulted in 93 to 100% aboveground biomass reduction across taxa. Reductions in belowground biomass mirrored trends observed in aboveground biomass. No treatments selectively controlled invasive Vallisneria without injury to native Vallisneria, although efficacy was observed on hydrilla. These insights provide an understanding for differences between these Vallisneria for researchers moving forward with selectively targeting H. verticillata in the presence of native Vallisneria species and two new aquatic invasive plants. Future research should expand treatment scenarios, increase the study period, and identify potential integrated plant management strategies for field scenarios.

Current dam discharge patterns in Noxon Rapids Reservoir reduce concentration and exposure times (CET) of herbicides used for aquatic plant management. Herbicide applications during periods of low dam discharge may increase herbicide CETs and improve efficacy. Applications of rhodamine WT dye were monitored under peak (736 to 765 m3 s−1) and minimum (1.4 to 2.8 m3 s−1) dam discharge patterns to quantify water-exchange processes. Whole-plot dye half-life under minimal discharge was 33 h, a 15-fold increase compared with the dye treatment during peak discharge. Triclopyr concentrations measured during minimum discharge within the treated plot ranged from 214 ± 25 to 1,243 ± 36 µg L−1 from 0 to 48 h after treatment (HAT), respectively. Endothall concentrations measured during minimum discharge in the same plot ranged from 164 ± 78 to 2,195 ± 1,043 µg L−1 from 0 to 48 HAT, respectively. Eurasian watermilfoil (Myriophyllum spicatum L.) occurrence in the treatment plot was 66%, 8%, and 14% during pretreatment, 5 wk after treatment (WAT), and 52 WAT, respectively. Myriophyllum spicatum occurrence in the nontreated plot was 68%, 71%, and 83% during pretreatment, 5 WAT, and 52 WAT, respectively. Curlyleaf pondweed (Potamogeton crispus L.) occurrence in the treatment plot was 29%, 0%, and 97% during pretreatment, 5 WAT, and 52 WAT, respectively. Potamogeton crispus increased from 24% to 83% at 0 WAT to 52 WAT, respectively, in the nontreated plot. Native species richness declined from 3.3 species per point to 2.1 in the treatment plot in the year of treatment but returned to pretreatment numbers by 52 WAT. Native species richness did not change during the study in the nontreated reference plot. Herbicide applications during periods of low flow can increase CETs and improve control, whereas applications during times of high-water flow would shorten CETs and could result in reduced treatment efficacy.

Aphthona spp. flea beetles were released in two ecological sites of the Little Missouri National Grasslands in southwestern North Dakota in 1999 to control leafy spurge. The change in leafy spurge density and soil seedbank composition was monitored to evaluate the effectiveness of the biological weed control agent and the associated change in plant communities 5, 10, and 15 yr after release in loamy overflow (valleys) and loamy sites (ridges). In 2014, 15 yr after release, leafy spurge stem density had decreased 94% from 110 to 7 stems m−2 in the loamy overflow sites and 88% from 78 to 9 stems m−2 in the loamy sites. Leafy spurge represented only 2% and 6% of the loamy overflow and loamy seedbanks in 2004, respectively, compared with nearly 67% and 70%, respectively, in 1999. There was a slow shift to reintroduction of native species into the seedbank over the last 15 yr. The number of desirable species increased to 21 by 2014 (more than three times the number of species in 1999) in the loamy overflow sites, and doubled to 14 species in the loamy sites, while less desirable forb species doubled in both sites. Desirable grass species doubled in the loamy overflow sites by 2014 but remained unchanged in loamy sites. Aphthona spp. successfully controlled leafy spurge for more than 15 yr without any additional control methods or costs to land managers and resulted in the slow return of a subset of native species.

The distribution, growth, and seed germination ability of the exotic lead tree in Penghu Islands, Taiwan, were studied. Survey results have shown that all lead tree plants existing throughout these islands belonged to the Hawaii type. Subsequently a comparison of germination requirements between this and the rare Salvador type, which distributes only in the island of Taiwan, was carried out. The objective of this research was to compare the germination requirements of the Salvador- and Hawaii-type lead tree plants. Lead trees in Penghu Islands have formed a pure forest with a height ranging from 2 to 4 m. All growth stages of the lead tree, i.e., vegetative, flowering, podding, and depodding stages, were found simultaneously in fall, but only vegetative and podding stages were observed in summer. Germination of both the Hawaii- and Salvador-type lead tree was evaluated under different environmental conditions, including temperature, pH, osmotic potential, burial depth, and lighting condition. The Salvador-type exhibited more than 60% seed germination after 14 d at temperatures between 20 and 35 C, whereas the seed germination of the Hawaii type increased from 20 to 60% with temperature increases from 20 to 35 C. The optimal temperature for seed germination of these two types of lead tree was 35 C. Increasing burial depth beneath the soil surface and darkness, as well as an osmotic potential below −0.4 MPa, also reduced seed germination. However, the germination of both types was not affected by pH ranging from 4.0 to 9.0. On the basis of the climatic and soil environment conditions in Penghu Islands, it is reasonable to predict that the summer season, in which lead tree seeds readily germinate on the ground or in shallow soils, is the optimal time for controlling this plant.

Yellow starthistle is a problematic invasive plant in the western United States. Attempts to control it often include the use of herbicides although herbicides can have detrimental effects on desired native species. We studied the effect of clopyralid on a native bunchgrass and vernal pool community in the Central Valley of California. Areas invaded by yellow starthistle were treated with clopyralid, and the presence and cover of all species was monitored for 2 yr. There were significant differences in species cover between treated and untreated plots 2 yr after treatment (P = 0.0001). These included a decline in cover of yellow starthistle and other native and exotic members of the Asteraceae and Apiaceae families in both years and a decline of exotic members of the Fabaceae family in the second year. There also were decreases in the frequency of the Asteraceae (P < 0.0001), Apiaceae (P < 0.05), Fabaceae (P < 0.05), and Polygonaceae (P < 0.05) families 1 yr after treatment, and the Asteraceae (P < 0.05) and Fabaceae (P < 0.05) families 2 yr after treatment. We also observed a significant negative effect of clopyralid on fecundity measures of a native Viola species during the first year of application (P = 0.0074). This effect did not persist into the second year, when violets were more common and produced more flowers in treated plots (0.02 < P < 0.05).

Black henbane is a poisonous, invasive plant in the family Solanaceae, and is typically associated with highly disturbed environments, such as pipelines, roadsides, and mammalian burrows. Often, such disturbances require reseeding for successful restoration; thus, the potential exists for competition between henbane and perennial grasses commonly used in restoration projects. These competitive interactions have not, to our knowledge, been evaluated. We conducted a greenhouse study to compare the response of henbane when grown alone and in combination with three common, cool season, perennial, northern mixed prairie grass species. We examined both seedling and mature grass response to the presence or absence of henbane and the response of henbane to the grasses. Using the relative neighbor-effect index, black henbane was found to be a very poor competitor with mature grasses and two out of three seedling grasses tested. All measures of henbane growth were significantly lower among plants grown with a mature grass pot companion. Total biomass of henbane was up to 99% lower when grown with mature grasses. Mature grasses were not negatively affected when grown in combination with henbane. Western wheatgrass (Pascopyrum smithii) was the only seedling grass that was competitive with henbane but was also the only seedling grass negatively affected by henbane in both biomass and tiller production. These experiments suggest that henbane is not well suited for invasion of mature grass stands but may negatively influence some perennial grass seedlings in restoration situations.

Invasive annual grasses, such as medusahead, can reduce forage production capacity and interfere with revegetation projects in California rangelands. Because of the taxonomic similarity to other more desirable grasses, achieving selective control of invasive annual grasses can be difficult. In selectivity trials conducted in Yolo and Siskiyou counties, CA, the herbicide imazapic gave control of many nonnative annual grasses yet provided some level of selectivity to specific perennial grasses used in revegetation projects throughout the western United States. The selectivity difference between newly seeded perennial and annual grasses was greater with PRE applications than with POST treatments. Both perennial and annual grasses within the tribe Hordeae were more tolerant to imazapic than other grass species. In addition, field experiments were conducted at three sites in northern California (Yuba, Yolo, and Lassen counties) and one in southern Oregon (Lake County) to test the response of imazapic to varying management conditions. Imazapic was applied PRE in fall (and also spring in Lake County) at rates from 35 to 210 g/ha on undisturbed rangeland, in comparison with rangeland cleared of standing plant material and thatch by either tillage, mowing and raking, or burning. Imazapic generally showed enhanced weed control when applied following disturbance. Rates as low as 70 g/ha, if combined with thatch removal, provided significant suppression of medusahead. In addition, disturbance alone generally reduced medusahead cover in the following year. Although imazapic showed potential for control of medusahead and other annual grasses, its selectivity window was relatively narrow.

Recent floristic study of the island of Limnos (NE Aegean, Greece) has resulted in the addition of 69 new plant taxa. As a result the flora of the island now comprises 750 taxa. New alien species such as Erigeron sumatrensis, Erigeron canadensis, Symphyotrichum squamatum, Amaranthus retroflexus and Amaranthus blitoides nowadays colonise thousands of hectares of fertile ground and present the highest rates of invasion. Ecological factors such as soil texture, high winds and human intervention, in combination with their seed dispersal mode and genetic background, may explain their successful establishment and impressive abundance especially in the eastern part of the island. Among the new records of indigenous plants are some interesting taxa from a phytogeographical point of view, such as Bupleurum euboeum and the Greek endemic Polygonum icaricum.

The multifunctional agronomic, ecological, economic and social uses of grass-based agricultural systems in peri-urban Marion County, Iowa, were the subject of investigation from 2003 to 2005. Following a sociocultural analysis that identified diverse motivations of cow–calf operators, an on-farm, agroecological experiment was established with a member of the study group. The objective of the experiment was to investigate the feasibility of establishing a multifunctional prairie pasture in response to the operator's interest in certified organic, warm-season plant species paddocks. At the field level, the implementation of native grasses and legumes into fallow pasture without the use of herbicides under flash grazing, mowing and unmanaged control treatments showed differences in species establishment and pasture composition. After three growing seasons, native species were evident in all treatments, with no significant differences between grazing and mowing in total native species establishment. There was a trend toward greater native legume establishment in the control over the managed treatments. Thus, total species abundance was greatest in control plots, suggesting this treatment for maximum prairie pasture establishment without herbicides. Concurrence was observed between motivations expressed by cow–calf operators in the sociocultural study (i.e. biodiversity preservation and sustainable management of natural resources) and outcomes from the prairie pasture experimental system. Support for grass-based systems from local institutions at the community level is necessary for the expansion of prairie pastures in Iowa and throughout the tallgrass prairie region.

The cryptic invasion of the Asian macroalga Codium fragile (Suringar) Hariot ssp. fragile on north-eastern Atlantic shores has been long considered a classical example of a successful invader that has competitively displaced native congeners. Yet, the lack of quantitative information about morphologically similar native congeners, namely Codium tomentosum Stackhouse and C. vermilara (Olivi) Delle Chiaje, has hindered interspecific comparisons and ecological predictions. From September 2002 to 2005, we made extensive intertidal surveys on 12 northern and 26 southern rocky shores of the English Channel, specifically documenting the abundance, distribution and identity of Codium assemblages. On the north side of the English Channel, the native C. tomentosum and alien C. fragile were both sparsely distributed in intertidal pools in Devon. In contrast, the natives were absent from and the alien was locally abundant in shallow lagoons and rocky reefs around Bembridge and Whitecliff on the Isle of Wight. Finally, in the Channel Islands off the Atlantic coast of France, Codium spp. were abundant in pools and on low-shore emergent substrata with native species predominating. Patterns of distribution varied substantially among Guernsey, Jersey and Alderney, despite their close proximity. The regional variation in the algal distributions merits further investigation to determine whether the pattern is produced by: (1) anthropogenic activities and effects; (2) ecological interactions; (3) oceanographic factors; or (4) some combination of these.

The relative ozone resistance of 20 European and two American populations of Plantago major was examined, and relationships with climatic factors at the source of the plant material were explored using data provided by participants in the ICP-Crops initiative (International Co-operative Programme to Investigate the Effects of Air Pollutants and Other Stresses on Agricultural and Semi-Natural Vegetation). Plants grown from seed were exposed to either charcoal/Purafil® filtered air (CF<5 nmol mol−1 O3) or CF+ozone (70 nmol mol−1 O37 h d−1) over a 2-wk period in controlled environment chambers, and effects on mean plant relative growth rate (R) and allometric root/shoot growth (K) determined. Ozone resistance (R%) was calculated from (R03/RCF)×100.

Populations exhibited contrasting sensitivities to ozone, without the development of typical visible symptoms of injury. A positive relationship was found between relative ozone resistance and descriptors of the ozone-climate at the site of seed collection for the year of, and the 2 yr before, seed collection. The best predictors of inherent ozone resistance were shown to be cumulative ozone exposure indices calculated according to current United Nations Economic Commission for Europe (UN-ECE) critical level guidelines for the pollutant (i.e. the accumulated hourly average ozone exposure over a threshold level of 40 nmol mol−1 (AOT40) or 30 nmol mol−1 (AOT30) calculated during daylight hours for the consecutive 3-month period of the year experiencing the highest ozone concentrations). No relationships were found between ozone resistance and climatic factors (temperature, precipitation, sunshine hours, humidity) or the concentrations of other air pollutants (SO2, NO2, NO).

These findings support the view that current ambient levels of ozone in many regions of Europe are high enough to promote evolution of resistance to the pollutant in native plant populations. The significance of these findings to the debate over the establishment of separate critical levels for the protection of natural and semi-natural vegetation is discussed.