Herbicides are the primary method used to control exotic, invasive plants. This study evaluated restoration efforts applied to grasslands dominated by an invasive plant, sulfur cinquefoil, 6 yr after treatments. Of the five herbicides we evaluated, picloram continued to provide the best control of sulfur cinquefoil over 6 yr. We found the timing of picloram applications to be important to the native forb community. Plots with picloram applied in the fall had greater native forb cover. However, without the addition of native perennial grass seeds, the sites became dominated by exotic grasses. Seeding resulted in a 20% decrease in exotic grass cover. Successful establishment of native perennial grasses was not apparent until 6 yr after seeding. Our study found integrating herbicide application and the addition of native grass seed to be an effective grassland restoration strategy, at least in the case where livestock are excluded.

Bushkiller (Cayratia japonica) is a herbaceous, perennial vine that reproduces from seed and vegetative root structures within its native range. However, this species is considered invasive in the United States due to prolific shoot production, which can overtop surrounding vegetation. Cultural control practices, such as mulching, have been observed to further the spread of this species through regeneration of root fragments. Research was conducted to determine the regenerative capacity of bushkiller root fragments (1 to 7 cm; 2.5 to 18 inches) buried at various depths (0 to 40 cm). Root length and planting depth affected leaf number, shoot number, plant height, and shoot biomass. Bushkiller leaf density, shoot density, plant height, and dry weight increased as root fragment length increased from 1 to 7 cm; conversely, these variables decreased as planting depth increased from 0 to 40 cm. Results indicate bushkiller regeneration capacity from root fragments is extremely high and control practices that fragment roots should be avoided to reduce further spread.

Although glyphosate is typically used as a nonselective herbicide, low rates have the potential to provide selective control of seedling annuals in the understory of established perennial plants. In a repeated experiment on two adjacent sites at a single location near Alturas, CA (2009 and 2010), we evaluated the efficacy of glyphosate at several different rates on medusahead and nontarget species in northern California sagebrush scrub. We applied glyphosate at 10 rates ranging from 0 to 709 g ae ha−1 (0 to 18 oz product acre−1) at three separate timings in each trial: mid-March (medusahead in early seedling stage), late April to early May (tillering), and late May to early June (boot to early head). Plots measured 3 m by 9 m (10 ft by 30 ft) and were arranged in randomized complete blocks with four replications for each rate and timing. We visually estimated vegetative cover for all dominant species in July before medusahead seed drop using three 1-m2 quadrats per plot. Medusahead cover declined with increasing rates of glyphosate, and the middle application timing (at tillering) was the most effective. In rate series regression models, we achieved 95% control of medusahead with 160 g ae ha−1 glyphosate in midseason 2009, compared with 463 g ae ha−1 in early season and 203 g ae ha−1 in late season. In 2010, we achieved 95% control with 348 g ae ha−1 in midseason, compared with > 709 g ae ha−1 in early season. Medusahead seed production reflected changes in cover, though individual plants tended to produce more seed at low densities. We attribute reduced control early in the season and poorer overall control in 2010 to greater tolerance of medusahead to glyphosate at lower temperatures. Treatment effects on big sagebrush, as indicated by shoot tip vigor, were minor, although the midseason timing caused a slight reduction in vigor. These results show that low rates of glyphosate (158 to 315 g ae ha−1) at a treatment timing corresponding to medusahead tillering can give economical and effective control of medusahead without long-term damage to big sagebrush.

Fire is often used in northern grasslands to control invasive grass species but has unknown effects on Tamarix spp., more recent invaders. Temperature (using an oven as a fire surrogate) and duration combinations that would be most lethal to Tamarix seeds and seedlings were determined. Tamarix seeds were sown in soil-lined dishes, water added to saturation, and seedlings grown for 1 to 5 d. Seeds were also placed in water-saturated or dry soil just before temperature exposure (79 to 204 C [175 to 400 F]) by duration (1 to 5 min) treatments. After treatment, soil water loss was measured by weight difference, and surviving seedlings were counted for 6 d. Tamarix seedling establishment and survival decreased with increasing temperature and duration. The 5-d-old seedlings were the most affected. No 5-d-old seedlings survived 1- and 2-min exposures to 204 C, whereas 1-d-old seedlings had greater than 25% survival. If soils were saturated, two to four times more seedlings established following seed exposure to 177 and 204 C. Longer durations at lower temperatures were required to reduce Tamarix survival. Increasing duration from 2 to 5 min at 121 C decreased 5-d-old seedling survival from more than 80% to less than 10% and eliminated those seedlings at 149 C. Five minutes at 149 C decreased dry-soil seed viability to about 15%, whereas germination on saturated soils remained high (∼75%). No seeds survived the exposure to 177 and 204 C. Soil moisture loss values associated with 90% mortality of 5- and 1-d-old seedlings were 1.7 and 2.2%, respectively. On saturated soils, 90% of seeds died with 2.5% water loss. Under suitable conditions, fire can decrease Tamarix seedling survival. Fire may be useful for controlling Tamarix seedlings in northern grasslands and should be considered for management of new invasions.

Temperate and boreal forests in Canada and the northeastern United States have been invaded by several exotic species, including European earthworms (family Lumbricidae) and garlic mustard. Earthworms and garlic mustard co-occur and are both known to adversely impact some native plant species. However, relatively little is known about potential interactions between these two invaders. In a series of growth chamber experiments, we determined the palatability of garlic mustard and six native herbaceous forest species (shooting star, columbine, wild geranium, sweet cicely, butterfly milkweed, and yellow jewelweed) to the common nightcrawler. We also assessed the ability of the common nightcrawler to bury and digest garlic mustard and wild geranium. When offered seeds from garlic mustard and a native plant species, the earthworms ingested more garlic mustard seeds than seeds from four of the six native species. In a mesocosm experiment, the common nightcrawlers apparently digested 72 and 27% of garlic mustard and wild geranium seeds, respectively, that were placed on the soil surface. No seeds were observed on the soil surface at the end of the experiment but the majority of recovered seeds for both species were found within the top 10 cm (3.94 in). More seeds were recovered in 0- to 10-cm and 31- to 40-cm sections for wild geranium than for garlic mustard. No difference in seed recovery was detected at the other depths. Garlic mustard seed is readily consumed by common nightcrawlers and appears to be preferred over some native plant species suggesting that common nightcrawlers may reduce the size of the garlic mustard seed bank.

Greenhouse studies were conducted on two southern Illinois star-of-Bethlehem populations to determine the influence of chilling and bulb chipping on plant growth and reproduction. Chilling was not required for leaf emergence of dormant bulbs, but an increase to 10 wk of chilling proportionally delayed leaf emergence by 41 and 42 d for the Murphysboro and the Marion populations, respectively. Bulb chipping did reduce plant height when compared to plants from nonchipped bulbs. Also, chipped bulbs produced a greater number of small daughter bulbs compared to nonchipped bulbs; however, total bulblet production was variable and dependent on population, mother bulb size, and chipping treatment. Overall, bulb chipping did not have any negative influence on star-of-Bethlehem and might promote increased daughter bulblet production. Therefore, field operations, such as tillage, that cut and chip bulbs might actually accentuate both the spread and density of star-of-Bethlehem infestations.

A species' successful invasion into a new site depends on its ability to persist in the local environment. An experiment was conducted to examine the response of giant reed to intermittent periods of shading for 2 yr. Results indicate that giant reed persisted when exposed to significant shading (i.e., 90% reduction of full sun) and that shading also caused changes in a number of plant characteristics, such as stem height, internode length, leaf nitrogen, leaf chlorophyll content, specific leaf area, total leaf area per plant, and leaf life span. Estimates of leaf photosynthetic rates did not differ across shade levels. Giant reed's ability to persist and grow under intermittent low-light conditions implies that plants would be poised to take advantage of sun flecks and disturbances that create gaps within the resident plant community.

Japanese stiltgrass, an annual grass species native to eastern Asia, has become a serious invasive-plant problem in the eastern United States. We compared the efficacy of herbicides and nonchemical options found effective for controlling stiltgrass in earlier studies, with organic herbicides and herbicides used at reduced rates in a wooded floodplain along the lower Connecticut River. We compared the effect of 2 yr of conventional and alternative treatments on cover of other nonnative and native species. Four blocks of 18 plots (3 by 4 m [9.8 by 13.1 ft]) were established in May 2008. Treatments included directed heating with a propane torch (June, July), hand-pulling (July), mowing with a string trimmer (July, August), foliar applications of household vinegar [5% acetic acid] (June, July) and the herbicides imazapic (June), pelargonic acid (June, July), and pelargonic acid plus pendimethalin (June). The following herbicides were applied at labeled doses and at one-fourth labeled doses: fenoxaprop-p-ethyl (July), glufosinate (August), and glyphosate (August). Stiltgrass cover and height were evaluated periodically, and plant samples were collected in autumn of 2008 and 2009 to determine the number of viable seeds produced. Final evaluations were conducted in June 2010 after 2 yr of treatment. Stiltgrass cover averaged 88% on untreated plots in fall. All treatments reduced stiltgrass cover and seed production. The least-effective treatments were hand-pulling, pelargonic acid, and vinegar in July. Direct heating, mowing, and vinegar in June reduced seed production by more than 90%. All treatments containing imazapic, pelargonic acid plus pendimethalin, fenoxaprop-p-ethyl, glufosinate, and glyphosate completely prevented stiltgrass seed production in the second year of treatment. Effective control of stiltgrass can be achieved during a 2-yr period with a variety of herbicides, including herbicides at one-fourth of the labeled dose, and through nonchemical treatments.

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.

Sulfur cinquefoil is an invasive, perennial forb on rangelands of western Canada and the United States. Sulfur cinquefoil reproduces solely by seed and it is a prolific seed producer. Our 2-yr study (2006, 2007) investigated the optimal timing and intensity of defoliation to decrease aboveground productivity and seed production of sulfur cinquefoil plants on foothill rangeland in southwestern Montana. Each year, 150 sulfur cinquefoil plants within a 430-m2 enclosure were tagged for identification and randomly assigned to one of 15 clipping treatments with 10 plants per treatment. Clipping treatments were conducted at three timings: (preflower [early June], flowering [late June], and seedset [mid-July]) and all possible combinations of timings for a total of seven timing treatments clipped to two stubble heights (7.5 cm or 15 cm), comprising 14 unique treatments. The final (15th) treatment consisted of an unclipped control. Response variables collected at senescence (late July) included aboveground biomass; number of buds, flowers and fruits on each plant; and number and viability of seeds produced. Results indicated that defoliation of sulfur cinquefoil can effectively reduce its yield and seed production. All clipping treatments reduced aboveground biomass of sulfur cinquefoil compared with control plants (P ≤ 0.05), except clipping to 15 cm during preflowering in the wetter year of 2006. Clipping to either 7.5 cm or 15 cm at all times or combinations of timings reduced the number of buds, flowers, fruits, and seeds produced by sulfur cinquefoil (P ≤ 0.05). Viable seed production was reduced 99 to 100% when plants were clipped once to either 7.5 or 15 cm during flowering or seedset. Results suggest that targeted livestock grazing or mowing applied one time per season during flowering or seedset could effectively suppress the biomass production and viable seed production of sulfur cinquefoil.

Paragrass is a nonnative category I invasive species in central and south Florida. This perennial grass species outcompetes native vegetation and is capable of rapid spread by vegetative reproduction. Although glyphosate and imazapyr are effective herbicides for paragrass control, the use of herbicides in certain areas may be restricted because of application timing or environmental concerns. Therefore, our objectives were to examine the effect of water depth (saturated vs. flooded) after burning or cutting, and the effect of water depth and duration after simulated roller-chopping, on paragrass regrowth under controlled conditions. In the first study, paragrass plants were cut or burned with a propane burner to 1 cm (0.39 in) above the soil surface. Plants were either watered daily (control), or were subjected to one of two water treatments: water level at the soil surface (saturated) or flooded to a depth of 44 cm. Burned-saturated or burned-flooded plants had 92% less biomass 5 wk after treatment (WAT) than cut-saturated plants. Flooding resulted in plant death regardless of the plant treatment. In the second study, simulated roller-chopping was performed by cutting paragrass stolons into one-, two-, or three-node segments; planting them into flats; and subjecting them to water treatments for 3, 7, 14, 28, and 42 d. Burning, cutting, and roller-chopping could be useful to control paragrass if subsequent flooding is applied. Future research should focus on evaluating the response of these control techniques in natural areas where water depth can be managed.

Garlic mustard is an invasive, exotic herb that is now widespread in North America. Recent research has shown that garlic mustard exudes biochemical compounds that inhibit the growth of entomopathogenic fungi. We investigated how the removal of garlic mustard would affect the abundance of entomopathogenic fungi in forest soils in eastern New York. Using a standard bioassay, we compared the abundance of entomopathogenic fungi in soil with and without garlic mustard both before and 45 d after garlic mustard had been experimentally removed. In soil from which garlic mustard had been experimentally removed 45 d earlier, the abundance of entomopathogenic fungi was restored to levels found in soil with no history of garlic mustard. These results suggest it is possible to increase the abundance of entomopathogenic fungi in the soil in a short time by eradicating garlic mustard plants from an invaded area. Recolonization by entomopathogenic fungi could be beneficial to humans if it increases the mortality of arthropods that are vectors of infectious disease, such as blacklegged ticks, but harmful if it increases the mortality of arthropods that provide valuable ecosystem services, such as bees and ants.

Competitive interactions between native plants and nonnative, invasive plant species have been extensively studied; however, within degraded landscapes, the effect of interspecific interactions among invasive plants is less explored. We investigated a competitive interaction between two sympatric, invasive mustard species that have similar life history strategies and growth forms: garlic mustard and damesrocket. Greenhouse experiments using a full range of reciprocal density ratios were conducted to investigate interspecific competition. Garlic mustard had a negative effect on the final biomass, number of leaves, and relative growth rate in height of damesrocket. Survival of damesrocket was not negatively affected by interspecific competition with garlic mustard; however, garlic mustard showed higher mortality because of intraspecific competition. These results indicated that although garlic mustard has been observed to be the dominant species in this landscape, it may not completely outcompete damesrocket in all situations. Studies of invasive species in competition are important in degraded landscapes because this is the common situation in many natural areas.

We studied the response of naturalized kudzu plants to simulated herbivory at three locations: Delaware (DE), Pennsylvania (PA), and North Carolina (NC). At the DE and PA sites, plant mortality after the first yr was 14 and 50%, respectively, and was highest for plants that had a small starting root crown size. At both sites, 50 and 75% leaf and shoot clipping, and drilling one or two large holes from the root crown into roots, had no effect on aboveground biomass. In NC, all plants survived for 3 yr. Plants subject to 50% vine removal at this site showed significant decrease in aboveground biomass compared to the control, but 50% leaf cutting and root drilling had no effect. In the greenhouse, kudzu seedlings grown in 60 and 100% light compensated for 50% leaf removal, but 75% damage reduced aboveground biomass. Plants survived for 1 to 2 mo in 0% direct light, but only one of 53 plants survived to the end of the experiment. Results suggest that established kudzu plants are able to compensate for biomass removal, seedlings can survive for several weeks without light, and that effective biocontrol might require more than 2 to 3 yr of continuous damage.

Invasive weed control within cleared, forested sites in the inland Northwest is complicated by the susceptibility of ponderosa pine to synthetic auxin herbicide injury, used to control broadleaf weeds. Herbicide injury may lead to decreased canopy volume and variable growth patterns of ponderosa pine, which is a commercially important tree species. Herbicide injury to ponderosa pine can be decreased with dormant-season applications, a timing suited to control many weeds that may occur within ponderosa pine sites. However, spring-timed herbicide applications are needed to control other weeds, such as meadow hawkweed, and that application timing coincides with active ponderosa pine growth. In this study, we determined the level of injury to ponderosa pine resulting from spring-timed aminopyralid, clopyralid, and picloram applications beneath ponderosa pine canopies. Herbicide injury to leader and lateral candles and needle elongation was evaluated 1 and 12 mo after treatment (MAT). Low rates of aminopyralid alone (0.05 kg ae ha−1 [3 fl oz ac−1]) and aminopyralid + clopyralid (0.05 + 0.10 kg ae ha−1) resulted in herbicide injury ratings that did not differ from untreated trees. The high rate of aminopyralid (0.12 kg ae ha−1) resulted in leader candle injury on 75% of treated trees, 5% of which were necrotic at 12 MAT. Herbicide injury was observed on 30% of lateral candles. In comparison, picloram (0.28 kg ae ha−1) treatments resulted in necrosis or mortality of leader and lateral candles on 65% and 40% of trees, respectively, at 12 MAT. Results suggest that use of low rates of aminopyralid alone or in combination with low rates of clopyralid minimizes the risk of nontarget injury to ponderosa pine (> 5 yr old) while controlling hawkweed with a spring application.

Widely-held, untested assumptions in many prairies are that high-intensity fires conducted during droughts will decrease native herbaceous species richness and lead to rapid invasions by alien species. We compared native and exotic herbaceous species richness and aboveground herbaceous biomass one year following the application of high-intensity growing-season fires in Texas coastal prairie. Fires were conducted in June 2008, when precipitation was 96% below the long-term monthly average, at the end of a severe 5-mo drought, resulting in high fire intensities within treatment units. Native forb species richness was greater in burned than unburned areas. In contrast, species richness of native grasses, exotic forbs, and the frequency of King Ranch (KR) bluestem [Bothriochloa ischaemum (L.) Keng.] did not significantly differ between burned and unburned treatments. The potential to use prescribed extreme fire to maintain native herbaceous species richness while not increasing KR bluestem provides preliminary evidence that growing season fires conducted during droughts can be a viable management strategy in coastal prairies.

The eradication of an invasive plant species can provide substantial ecological and economic benefits by eliminating completely the negative effects of the weed and reducing the high cost of continuing control. A 5-yr program toward the eradication of hill raspberry (Rubus niveus Thunb.) in Santiago Island is evaluated using delimitation and extirpation criteria, as well as assessment of the ecological community response to management techniques. Currently, hill raspberry is located in the humid zone of Santiago island. It is distributed over three main infestations, small patches, and many scattered individuals within an area of approximately 1,000 ha. New infestations are constantly being found; every year, new detections add an area of approximately 175 ha. Adult and juvenile individuals are still found, both beyond and within known infestations. Both plant and seed bank density of hill raspberry decreased over time where infestations were controlled. Species composition in the seed bank and existing vegetation were significantly different between areas under intensive control and adjacent uninvaded forest. After 5 yr of intensive management, delimitation of hill raspberry has not been achieved; new populations are found every year, increasing the infested area that requires management. Off-target effects on native species resulting from control efforts seem to be substantial. Although a vast increase in economic investment would allow intensive searching that might enable all individuals to be found and controlled, the resultant disturbance and off-targets effects could outweigh the conservation benefits of eradication.

Prickly nightshades are troublesome weeds of natural habitats, pastures, feedlots, right-of-ways, and croplands. Native and nonnative invasive weedy species of prickly nightshades were compared to determine growth, development, and morphological differences. Six (Solanum bahamense, Solanum capsicoides, Solanum carolinense, Solanum dimidiatum, Solanum donianum, and Solanum pumilum) of the 18 species of prickly nightshades studied are native to the US. Two species, Solanum citrullifolium and Solanum rostratum, are annuals; the others are perennials or are short lived perennials or annuals in northern extremes of their range in North America. Tables were developed from new and existing data to differentiate vegetative and reproductive characteristics among 18 species of prickly nightshade found in the southeastern US. In greenhouse experiments, average plant height ranged from 24 and 26 cm (9.45 and 10.24 inch) for S. carolinense and Solanum jamaicense, respectively, to 100 and 105 cm for Solanum tampicense and Solanum sisymbriifolium, respectively at 10 wk after emergence (WAE). By 10 WAE, the average number of leaves per plant ranged from < 10 for S. carolinense and Solanum torvum to > 40 leaves/plant for S. rostratum and S. dimidiatum. Average number of nodes/plant main stem ranged from 11, 12, and 14 nodes in S. jamaicense, S. torvum, and S. carolinense, respectively, to 54 nodes in S. rostratum. Average plant dry weights were collected at 10 WAE and were greatest for Solanum mammosum and (> 17 g/plant) (0.6001 oz/plant) and least for S. carolinense (1 g/plant). Based on these data, nightshade growth rate and dry weight were variable among some species and variability may be a result of phenology and life cycles, annual or perennial. Plants of S. rostratum, an annual, were relatively tall and produced high number of nodes and leaves and had the shortest period from emergence to flower among the prickly nightshades evaluated.

The invasive annual grass downy brome is the most ubiquitous weed in sagebrush systems of western North America. The center of invasion has largely been the Great Basin region, but there is an increasing abundance and distribution in the Rocky Mountain States. We evaluated postfire vegetation change using very large–scale aerial (VLSA) and near-earth imagery in an area where six different fires occurred over a 4-yr period at elevations ranging from 1,900 to over 2,700 m. The frequency of downy brome increased from 8% in 2003 to 44% in 2008 and downy brome canopy cover increased from < 1% in 2003 to 6% in 2008 across the entire study area. Principal component analyses of vegetation cover indicate a shift from plant communities characterized by high bare soil and forbs immediately postfire to communities with increasing downy brome cover with time after fire. The highest-elevation sampling area exhibited the least downy brome cover, but cover at some midelevation locations approached 100%. We postulate that the loss of ground-level shade beneath shrubs and conifers, accompanied by diminished perennial vegetative cover, created conditions suitable for downy brome establishment and dominance. Without a cost-effective means of landscape-scale downy brome control, and with infestation levels and climate warming increasing, we predict there will be continued encroachment of downy brome at higher elevations and latitudes where disturbance creates suitable conditions.

The use of benthic barriers alone or in combination with other control methods could initiate the eradication of pioneer populations of Eurasian watermilfoil and facilitate maintenance of acceptable population levels in water bodies where the weed is widely established. We evaluated the effects of duration of geotextile fabric panel placement on small Eurasian watermilfoil population control and nontarget plant abundance. In 2006, benthic barriers were placed over Eurasian watermilfoil infestations and removed at intervals of 4, 8, 10, and 12 wk. The 4-wk duration reduced Eurasian watermilfoil biomass 75%, and all other duration treatments reduced Eurasian watermilfoil biomass 100%. The 4-wk treatment had no effect on native plant biomass, whereas other treatments reduced native plant biomass by 79 to 93%. At the conclusion of the 12-wk study, Eurasian watermilfoil biomass had increased in the 4-wk treatment but did not reestablish within treatment plots of longer duration. Native plant biomass had increased to 21% of the untreated control in the 8-wk barrier treatment. Results suggest the 8-wk duration is sufficient for removal of Eurasian watermilfoil while allowing regrowth of native aquatic plants. A walk-in growth chamber experiment was established to evaluate the effect of sediment accumulation on the benthic barrier. Eurasian watermilfoil fragments grown on sediment depths of 0 to 3 cm (0 to 1.2 in) did not differ for shoot or root biomass. At sediment depths of 4 and 5 cm, Eurasian watermilfoil root and shoot biomass increased when compared with the control, suggesting benthic barrier maintenance should include sediment removal when sediment reaches a depth of 4 cm.