Buffelgrass [Pennisetum ciliare (L.) Link] is an invasive C4 perennial bunchgrass that is a threat to biodiversity in aridlands in the Americas and Australia. Topography influences P. ciliare occurrence at large spatial scales, but further investigation into the relationship between local-scale topography and P. ciliare growth and reproduction would be beneficial. Further, density-dependent effects on P. ciliare growth and reproduction have been demonstrated in greenhouse experiments, but the extent to which density dependence influences P. ciliare in natural populations warrants further investigation. Here we present a study on the relationships between local-scale topography (aspect and slope gradient) and vegetation characteristics (shrub cover, P. ciliare cover, and P. ciliare density) and their interactions on individual P. ciliare plant size and reproduction. We measured slope gradient, aspect, shrub cover, P. ciliare cover, P. ciliare density, and the total number of live culms and reproductive culms of 10 P. ciliare plants in 33 4 by 4 m plots located in 11 transects at the Desert Laboratory at Tumamoc Hill, Tucson, AZ, USA. We modeled the relationships at the local scale of (1) P. ciliare cover and density with aspect and slope gradient and (2) P. ciliare size and reproduction with abiotic (slope gradient and aspect) and biotic (P. ciliare cover and density and native shrub and cacti cover) characteristics. Aspect and slope gradient were poor predictors of P. ciliare cover and density in already invaded sites at the scale of our plots. However, aspect had a significant relationship with P. ciliare plant size and reproduction. Pennisetum ciliare plants on south-facing aspects were larger and produced more reproductive culms than plants on other aspects. Further, we found no relationship between P. ciliare density and P. ciliare plant size and reproduction. Shrub cover was positively correlated with P. ciliare reproduction. South-facing aspects are likely most vulnerable to fast spread and infilling by new P. ciliare introductions.

An in-depth understanding of the germination response of troublesome weed species, such as feather fingergrass (Chloris virgata Sw.), to environmental factors (temperature, soil moisture, etc.) could play an essential role in the development of sustainable site-specific weed control programs. A laboratory experiment was conducted to understand the germination response of 10 different biotypes of C. virgata to five temperature regimes (ranging from 15/5 to 35/25 C) under a 12/12-h (light/dark) photoperiod. No consistent germination behavior was observed between biotypes, as some biotypes demonstrated high final cumulative germination (FCG) at low alternating temperature regimes (15/5 and 20/10 C) and some biotypes exhibited high FCG at a high alternating temperature regime (30/20 C). All biotypes revealed late germination initiation (T10, time taken to reach 10% germination) at the lowest temperature range (15/5 C), ranging from 171 to 173 h. However, less time was required to reach 90% germination (T90), ranging from 202 to 756 h. At higher alternating temperature regimes (30/20 and 35/25 C), all biotypes initiated germination (T10) within 40 h, and a wide range of hours was required to reach 90% germination (T90), ranging from 284 to 1,445 h. Differences in FCG of all the biotypes at all the temperature ranges showcased the differential germination nature among biotypes of C. virgata. The cool temperatures delayed germination initiation compared with warmer temperatures, even though FCGs were similar across a wide range of thermal conditions, indicating that this species will be problematic throughout the calendar year in different agronomic environments. The data from this study have direct implications on scheduling herbicide protocols, tillage timing, and planting time. Therefore, data generated from this study can aid in the development of area- and species-specific weed control protocols to achieve satisfactory control of this weed species.

The invasion of Lehmann lovegrass (Eragrostis lehmanniana Nees) in rangelands of Chihuahua, Mexico, has resulted in a need for revegetation to recover lost forage productivity. Thus, new knowledge on generating alternatives to improve these invaded grasslands is of great importance. This study evaluated seedbeds prepared with unconventional tillage implements and seeded with a grass mixture to reduce the plant density of E. lehmanniana while increasing the productivity of an invaded semiarid grassland of Chihuahua. The unconventional tillage implements were: a Rangeland Harrow, which was used to prepare the Striped Harrowing and Full Harrowing seedbeds; Rangeland Rehabilitator, which was used to prepare the Deep-Stingray Subsoiler seedbed; and a Tandem-type Aerator Roller, which was used to prepare the Double-Digging Aeration seedbed. An area without tillage was left as a control. The seed mixture was composed of blue grama [Bouteloua gracilis (Willd. ex Kunth) Lag. ex Griffiths var. Hachita] (25%); sideoats grama [Bouteloua curtipendula (Michx.) Torr. ‘6107 Kansas’] (25%); green sprangletop [Leptochloa dubia (Kunth) Nees var. Van Horn] (5%); weeping lovegrass [Eragrostis curvula (Schrad.) Nees var. Ermelo] (40%), and Columbus grass [Sorghum almum Parodi] (5%). The experiment was conducted across 4 yr, and the evaluation started at the second year. Plant density and dry matter (DM) production were evaluated per species. In the control plot, the plant density of E. lehmanniana increased approximately 180% from the 2nd to the 4th year (18 to 50 plants m−2). The use of unconventional tillage implements for seedbed preparation and the inclusion of E. curvula in the seed mixture decreased E. lehmanniana density in more than 50% of plots and increased DM production in around 100% of plots. Considering the whole experimental period, in all the prepared seedbed treatments, E. curvula had the highest establishment and DM production of all the seeded species. The native species B. gracilis, B. curtipendula, and L. dubia had poor establishment in all the prepared seedbeds.

Burmareed [Neyraudia reynaudiana (Kunth) Keng ex Hitchc.] is an aggressive invader of pine rockland communities in south Florida. Currently, it is managed by clipping the stems and later returning, when plants have regrown to approximately 50 cm in height, to administer applications of glyphosate to new foliar growth (a “cut–return–treat,” or CRT, strategy). This multi-visit strategy is time-consuming and may result in off-target effects due to the broad-spectrum nature of glyphosate. With this study we evaluated a cut-stem (CS) approach, in which stems are cut and immediately treated with herbicide. Further, we tested the efficacy of the selective graminicides sethoxydim and fluazifop-P-butyl. In a pot study, CS treatments included: glyphosate (239.7 g ae L−1) in water, sethoxydim (9.0 g ai L−1) or fluazifop-P-butyl (12.1 g ai L−1) in either basal oil or water, and triclopyr (47.9 g ae L−1) in basal oil. All CS treatments provided mortality and growth reduction comparable to the best CRT treatments (glyphosate, sethoxydim, and fluazifop-P-butyl) and were therefore evaluated under field conditions using the same application rates. Mortality was low in the field (≤30%) regardless of herbicide treatment. Overall, fluazifop-P-butyl provided greater control than sethoxydim, resulting in 71% and 94% relative growth reduction in total shoot length with oil and water carriers, respectively, compared with 50% and 43% reduction for sethoxydim. Fluazifop also provided control similar to triclopyr and glyphosate (≥65% reduction in total shoot length). Results suggest that CS treatments may be a viable strategy for managing N. reynaudiana and reducing management costs. However, more research is needed to optimize rates. Further, fluazifop-P-butyl allows for a more selective option than glyphosate that may decrease off-target effects on native understory vegetation in pine rocklands.

Buffelgrass [Pennisetum ciliare (L.) Link] is a drought-tolerant invasive grass that is a threat to native biodiversity in the drylands of the Americas and Australia. Despite efforts from land managers to control P. ciliare, management approaches tend to have mixed success, treatment results can be poorly communicated among entities, and there are few long-term controlled studies. In this literature review, we synthesize data from both peer-reviewed and “gray” literature on the efficacy of management techniques to control P. ciliare and the secondary impacts to native plant communities. Our search resulted in 42 unique sources containing a total of 229 studies that we categorized into 10 treatment types, which included herbicide, seeding, manual removal, fire, grazing, biocontrol, fire + additional treatments, manual removal + additional treatments, herbicide + additional treatments, and herbicide + manual removal. We found that treatments that used multiple techniques in tandem along with follow-up treatments were the most effective at controlling P. ciliare. Fewer than one-third of the studies reported impacts of management on native species, and the most commonly studied treatment (herbicide, N = 130) showed detrimental impacts on native plant communities. However, the average time between treatment and outcome measurement was only 15 mo; we suggest the need for more long-term studies of treatment efficacy and secondary impacts of treatment on the ecosystem. Finally, we conducted a second literature review on P. ciliare biology and traits for mechanisms that allows P. ciliare to alter the invaded environment to facilitate a competitive advantage over native species. We found evidence of self-reinforcing feedbacks of invasion being generated by P. ciliare through its interactions with water availability, nutrient cycling, and disturbance regimes. We developed a conceptual model of P. ciliare based on these feedback loops and offer management considerations based on its invasion dynamics and biology.

Natural grasslands are one of the most threatened ecosystems in North America. Conservation efforts are often hampered by exotic plant invasions in existing remnant natural grasslands. Tall fescue [Schedonorus phoenix (Scop.) Holub.] is an introduced cool-season (C3) forage/turf grass which readily invades natural grasslands in Kentucky and neighboring states. Our study objectives were to (1) compare the efficacy and application timing effect of clethodim to that of imazapic to selectively remove tall fescue from natural grasslands and (2) evaluate the response of the nontarget grassland plant community (i.e., native grass and forb canopy cover) following herbicide treatments. Clethodim and imazapic treatments consisted of early (April 4, 2001) and late (April 20, 2001) applications, and these were applied at 0.23 and 0.21 kg ai ha−1, respectively. Both herbicides reduced tall fescue cover (P ≤ 0.05); herbicide application timing had no effect on herbicide efficacy to control tall fescue. Native grass cover was higher (P ≤ 0.05) in all herbicide-treated plots compared to the untreated controls, except for the late clethodim-treated plots. All herbicide treatments increased forb abundance compared to controls. Spring applications of clethodim were equally effective to those of imazapic at controlling tall fescue in natural grasslands. Imazapic released native grasses better than clethodim, whereas clethodim was better at increasing forb abundance. Furthermore, early clethodim treatments had fewer nontarget effects on native C4 grasses compared to late clethodim treatments. Overall, clethodim shows promise as a beneficial management tool for tall fescue control in C4-dominated natural grasslands.

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.

Brachypodium sylvaticum, a shade-tolerant, forest dwelling, and aggressive invasive grass native to Eurasia, is a noxious weed in California, Oregon, and Washington. This species could cause ecosystem collapse by altering forest fire regimes. To examine interactions with fire, we divided two Willamette National Forest sites into eight units and randomly selected half for treatment with prescribed fire in spring 2011. We assessed the effect of B. sylvaticum on fire (severity and intensity) as well as the effect of fire on B. sylvaticum (cover, seedling emergence, and dispersal). We found that B. sylvaticum cover decreased fire severity but had no effect on intensity. Furthermore, fire severity influenced B. sylvaticum cover; in areas receiving low-severity fire, the grass increased from 21 ± 15.05 to 34 ± 15.81%, but in areas of high-severity fire, cover remained consistently around 0% (0 ± 0% cover in yr 1 to 0.2 5± 0.25% in yr 3). In the field, prescribed fire decreased seedling emergence by 32% compared to controls, but not in an associated greenhouse experiment. However, in the greenhouse, severely burned plots had zero emergence, compared to 0.29 ± 0.14 seedlings low-severity m−2 plot. Fire severity also influenced dispersal in the field; we monitored plots with < 0.5% cover B. sylvaticum initially; when these plots experienced low severity fire, they had greater B. sylvaticum cover (increasing 1,200%), suggesting increased dispersal with less severe fires. High-severity dispersal plots did not experience increased cover. High severity fires have the potential to control the grass, but low-severity fires will likely increase its cover.

Microstegium vimineum is a widespread invasive grass that poses significant threats to forests and disturbed areas throughout the United States. Often, the large-scale, rapid spread of Microstegium prohibits management by traditional methods. Control of Microstegium may be possible through the use of a pathogen (referred to here as Bipolaris Mv) that causes leaf blight on Microstegium. Members of the fungal genus Bipolaris are known pathogens of many plants, including important agronomic crops. However, little is known about the biology and host range of Bipolaris Mv. We used a series of growth chamber and light bank experiments to determine the variation in Bipolaris Mv from different geographic origins and its ability to cause foliar lesions and chlorosis on Microstegium. We used petri plate and soil infestation assays to determine the effects of Bipolaris Mv on Microstegium emergence from seed, biomass, and root necrosis. Finally, we tested the host range of these fungi on economically and ecologically important plant species. All isolates increased disease on Microstegium foliage relative to controls, although the effects varied among isolates. Isolates increased root necrosis by 97% in petri plate assays and by 4% in soil infestation trials compared to controls. Infestation of soils with Bipolaris Mv reduced emergence of Microstegium from seed by 31% compared to controls, but did not affect root or stand biomass. Bipolaris Mv produced lesions on a range of grasses, including corn, sorghum, rye, and wheat, although lesion size varied with isolate. These results indicate that Bipolaris Mv may be an effective pathogen on Microstegium, but its use as a bioherbicide may be impractical because of its effects on a wide range of grasses.