The productivity and native species diversity of Great Plains grasslands have been substantially reduced by past management that facilitated the establishment of invasive exotic weeds and displacement of native species. Management strategies are needed to rapidly restore the productive capacity and biological diversity of these degraded grasslands. Critically important phases of the grassland restoration process are the reintroduction and establishment of native species. Weed interference is the primary constraint to successful establishment of native plants. The goal of our research is to develop strategies that use multiple technologies, including herbicides, to expedite grassland revegetation with native grasses and forbs. Imidazolinone herbicides (AC 263,333, imazapyr, and imazethapyr) were used successfully to improve establishment of native perennial grasses (big bluestem, switchgrass, little bluestem) and selected forbs (blackeyed-susan, purple prairieclover, Illinois bundleflower, trailing crownvetch, and upright prairie coneflower) on cropland and as components of a strategy to revegetate leafy spurge-infested rangeland with native tallgrasses. Imazethapyr at 70 or 110 g ai/ha applied at planting resulted in stands of big bluestem and little bluestem that were similar or superior to stands established where atrazine was applied. Seedling grasses were susceptible to imazapyr at two of three study sites. Imazapyr at 560 g ai/ha plus sulfometuron at 100 g ai/ha applied in fall was the optimum treatment for suppression of leafy spurge and exotic cool-season grasses and establishment of big bluestem and switchgrass on degraded rangeland sites. Establishment of selected forbs was improved by PRE treatment with AC 263,222 or imazethapyr at 70 g ai/ha. This research provides evidence that the imidazolinone herbicides can be important components of integrated weed management strategies designed to reverse deterioration of grasslands by reestablishing native species, improving grassland productivity, and decreasing the prevalence of exotic weeds.

Miscanthus 9 giganteus is a C 4 perennial grass that shows great potential as a high-yielding biomass crop. Scant research has been published that reports M. 9 giganteus growth and biomass yields in different environments in the United States. This study investigated the establishment success, plant growth, and dry biomass yield of M. 9 giganteus during its first three seasons at four locations (Urbana, IL; Lexington, KY; Mead, NE; Adelphia, NJ) in the United States. Three nitrogen rates (0, 60, and 120 kg ha À1 ) were applied at each location each year.Good survival of M. 9 giganteus during its first winter was observed at KY, NE, and NJ (79-100%), and poor survival at IL (25%), due to late planting and cold winter temperatures. Site soil conditions, and growing-season precipitation and temperature had the greatest impact on dry biomass yield between season 2 (2009)

A waterhemp population from a native-grass seed production field in Nebraska was no longer effectively controlled by 2,4-D. Seed was collected from the site, and dose-response studies were conducted to determine if this population was herbicide resistant. In the greenhouse, plants from the putative resistant and a susceptible waterhemp population were treated with 0, 18, 35, 70, 140, 280, 560, 1,120, or 2,240 g ae ha−12,4-D. Visual injury estimates (I) were made 28 d after treatment (DAT), and plants were harvested and dry weights (GR) measured. The putative resistant population was approximately 10-fold more resistant to 2,4-D (R:S ratio) than the susceptible population based on both I50(50% visual injury) and GR50(50% reduction in dry weight) values. The R:S ratio increased to 19 and 111 as the data were extrapolated to I90and GR90estimates, respectively. GR50doses of 995 g ha−1for the resistant and 109 g ha−1for the susceptible populations were estimated. A field dose-response study was conducted at the suspected resistant site with 2,4-D doses of 0, 140, 280, 560, 1,120, 2,240, 4,480, 8,960, 17,920, and 35,840 g ha−1. At 28 DAT, visual injury estimates were 44% in plots treated with 35,840 g ha−1. Some plants treated with the highest rate recovered and produced seed. Plants from the resistant and susceptible populations were also treated with 0, 9, 18, 35, 70, 140, 280, 560, or 1,120 g ae ha−1dicamba in greenhouse bioassays. The 2,4-D resistant population was threefold less sensitive to dicamba based on I50estimates but less than twofold less sensitive based on GR50estimates. The synthetic auxins are the sixth mechanism-of-action herbicide group to which waterhemp has evolved resistance.

Annual bluegrass (Poa annua var. reptans (Hausskn.) Timm.) is a weedy species that is a component of most close‐cut, irrigated fairways. Research was conducted to determine the effect of five management factors and their interactions on the species composition of a mixed stand of annual bluegrass and creeping bentgrass (Agrostis palustris Huds.) maintained at 13 mm. Soil was an Owosso‐Marlette sandy loam (fine‐loamy, mixed, mesic, Typic and Glossoboric Hapludalfs). Management factors investigated for 3 yr were irrigation (daily at 75% open pan evaporation (OPE), triweekly at 110% OPE, and at wilt); clipping treatments (returned or removed); N fertility (98 or 293 kg N ha−1 yr−1); plant growth regulator (PGR) treatments (mefluidide, N‐[2,4‐dimethyl‐5‐[[(trifluoromethyl)‐sulfonyl] amino] phenyl] acetamide, at 0.14 kg ha−1; EL‐500, α‐(1‐methylethyl)‐α‐[4‐(trifluoromethoxy)phenyl] 5‐pyrimidine methanol, at 1.12 kg ha−1 and a control) and ‘Penncross’ creeping bentgrass overseeded (49 kg ha−1 yr−1) or not overseeded). Changes in annual bluegrass (AB) populations for each growing season were determined utilizing the point quadrat method. The effect of clipping removal on AB seed in the soil was determined. Returning clippings increased annual bluegrass 12% over plots in which clippings were removed. Overseeding with creeping bentgrass (CB) increased CB populations 8% compared to plots irrigated daily at 75% OPE and not overseeded. Mefluidide in combination with high N fertility resulted in AB populations 8% higher than control or EL‐500 plots at the same fertility level. Mefluidide also increased AB populations relative to control or EL‐500 treatments when clippings were removed. The greatest significant decrease in AB (28%) occurred with the treatment combination of clippings removed, overseeded, and no PGR. Removing clippings reduced the number of viable AB seeds in the soil by 60%.

Current knowledge of yield potential and best agronomic management practices for perennial bioenergy grasses is primarily derived from small-scale and short-term studies, yet these studies inform policy at the national scale. In an effort to learn more about how bioenergy grasses perform across multiple locations and years, the U.S. Department of Energy (US DOE)/Sun Grant Initiative Regional Feedstock Partnership was initiated in 2008. The objectives of the Feedstock Partnership were to (1) provide a wide range of information for feedstock selection (species choice) and management practice options for a variety of regions and (2) develop national maps of potential feedstock yield for each of the herbaceous species evaluated. The Feedstock Partnership expands our previous understanding of the bioenergy potential of switchgrass, Miscanthus, sorghum, energycane, and prairie mixtures on Conservation Reserve Program land by conducting long-term, replicated trials of each species at diverse environments in the U.S. Trials were initiated between 2008 and 2010 and completed between 2012 and 2015 depending on species. Field-scale plots were utilized for switchgrass and Conservation Reserve Program trials to use traditional agricultural machinery. This is important as we know that the smaller scale studies often overestimated yield potential of some of these species. Insufficient vegetative propagules of energycane and Miscanthus prohibited farm-scale trials of these species. The Feedstock Partnership studies also confirmed that environmental differences across years and across sites had a large impact on biomass production. Nitrogen application had variable effects across feedstocks, but some nitrogen fertilizer generally had a positive effect. National yield potential maps were developed using PRISM-ELM for each species in the Feedstock Partnership. This manuscript, with the accompanying supplemental data, will be useful in making decisions about feedstock selection as well as agronomic practices across a wide region of the country.