Imazapyr, imazaquin, and imazethapyr were evaluated for control of leafy spurge. Herbicides were applied at 70, 140, and 280 g ae/ha in Fall 1989, 1990, or 1991 on a sub-irrigated meadow near Ainsworth, NE and a tallgrass prairie near Columbus, NE. Imazapyr, imazaquin, imazethapyr at 280 g/ha controlled leafy spurge 58, 82 and 73%, respectively, 9 mo after treatment (MAT) at Ainsworth. Leafy spurge control averaged 49% 9 MAT at Columbus where 280 g/ha of the imidazolinone herbicides were applied. Leafy spurge yields were reduced at Ainsworth by 29 and 78% where the imidazolinones were applied at 140 and 280 g/ha. By 11 MAT, leafy spurge control on areas treated with 280 g/ha declined to less than 60% at Ainsworth and 10% at Columbus. Perennial forage grass yields at both sites were generally unaffected by imazaquin or imazethapyr, but imazapyr at 280 g/ha reduced yields by 69 and 44% at Ainsworth and Columbus, respectively. Imidazolinone herbicides applied in the fall partially controlled leafy spurge, but did not increase perennial forage grass yields.

Field experiments were conducted during 1981 to 1984 to evaluate paraquat for weed control in alfalfa established for less than one year. Treatments were applied in March to alfalfa up to 4 cm tall and/or after cuttings to alfalfa up to 10 cm tall. Weeds were up to 20 cm tall. Paraquat applied in March controlled common chickweed and shepherd's-purse in some experiments. It did not control birdsrape mustard when applied after cuttings. Paraquat suppressed growth of perennial broadleaf weeds and grasses and reduced pressure from annual grasses in some experiments. March treatments generally did not increase, but sometimes decreased alfalfa yields. Paraquat applied after cuttings did not affect alfalfa yields in the majority of the experiments.

Leafy spurge is an exotic perennial weed that infests more than 1 million ha in North America and reduces rangeland carrying capacity. Experiments were initiated on range sites in Nebraska and North Dakota in 1994 and 1995 to determine the response of leafy spurge and other vegetation to AC 263,222. Herbicide treatments evaluated included AC 263,222 at 0 to 280 g ai/ha, picloram at 560 g ai/ha plus 2,4-D at 1,120 g ae/ha, and quinclorac at 1,120 g ai/ha. In Nebraska, a single application of AC 263,222 in the fall at 140 g/ha provided ≥ 90% leafy spurge control 11 to 12 mo after treatment. At Jamestown, ND, leafy spurge control increased to almost 90% and stem density declined to two shoots/m2 12 mo after the second consecutive fall application of AC 263,222 at 140 g/ha. At Hankinson, ND, leafy spurge control was ≤ 50% when AC 263,222 was applied in the fall only, but increased to > 80% when AC 263,222 was applied in the fall and again at 70 or 140 g/ha in the spring. There were no differences in herbage biomass of established cool- and warm-season grasses where AC 263,222 at 140 g/ha, picloram plus 2,4-D, quinclorac, or no herbicide was applied in the fall. In contrast, application of AC 263,222 in the fall and again in the spring usually reduced cool-season grass biomass.

Field experiments were conducted at two locations in Virginia to evaluate the following herbicides: alachlor, diphenamid, diuron, metolachlor, napropamide, norflurazon, oryzalin, oxyfluorfen, paraquat, pendimethalin, and simazine. One experiment involved newly-transplanted apple trees; the others, three in apple and one in peach trees, involved one-year-old trees. Treatments were applied in the spring (mid-April to early-May). Control of annual weed species was excellent with several treatments. A broader spectrum of weeds was controlled in several instances when the preemergence herbicides were used in combinations. Perennial species, particularly broadleaf species and johnsongrass, were released when annual species were suppressed by the herbicides. A rye cover crop in nontreated plots suppressed the growth of weeds. New shoot growth of newly-transplanted apple trees was increased with 3 of 20 herbicide treatments and scion circumference was increased with 11 of 20 herbicide treatments compared to the nontreated control. Growth of one-year-old apple trees was not affected. Scion circumference of one-year-old peach trees was increased with 25 of 33 herbicide treatments.

Annual bromes (downy brome and Japanese brome) have been shown to decrease perennial grass forage production and alter ecosystem functions in northern Great Plains rangelands. Large-scale chemical control might be a method for increasing rangeland forage production. Although fall application has been shown to be the most effective and least likely to impact co-occurring native species, spring germination of downy brome may reduce the efficacy of fall-only herbicide application. We assessed the impact of a low glyphosate dose rate (210 g ha−1) applied to rangelands in fall or in fall and spring on nontarget species and on annual brome abundance at two sites in eastern Montana over 2 yr. We tested the following hypotheses: (1) nontarget effects are greater with spring herbicide application, (2) fall and spring herbicide application are necessary for effective downy brome control, and (3) fall herbicide application is sufficient to control Japanese brome. Few nontarget effects occurred; two dicotyledonous species exhibited small increases in response to herbicide. We found that that a single fall application reduced downy brome cover and seed bank density, but after the second fall application in the following year, downy brome did not continue to show a response to herbicide. After 2 yr of fall herbicide application, Japanese brome had denser seed banks in plots where herbicide had been applied. Blanket glyphosate application on rangelands is an unreliable method for controlling annual brome invasions in the northern Great Plains.

Desert grasslands of the southwestern United States have experienced an increase in the abundance and distribution of woody plant species over the past century. Shrub encroachment has caused a substantial loss of grasslands in the northern Chihuahuan Desert. The Chihuahuan Desert has also been invaded by Lehmann lovegrass, a fire-adapted species from southern Africa. In 1999, the U.S. Department of Agriculture–Agricultural Research Service burned a remnant desert grassland to determine the effects of prescribed fire on shrub–perennial grass dynamics. The grassland also contained the nonnative perennial grass Lehmann lovegrass. I am reporting on a study that was initiated to determine whether prescribed burning would alter the vegetative community within and proximal to a Lehmann lovegrass–dominated patch. Cover of Lehmann lovegrass showed no significant response to the burn treatment. Of the dominant native species, only black grama and broom snakeweed had a significant year by treatment interaction. No species or growth form had a significant vegetation type by year by treatment interaction. After 6 yr, differences between burned and unburned transects were not significant for any species or growth form.

Himalaya blackberry is a nonnative shrub that has invaded sites throughout the Pacific Northwest. Its persistent canopy and large underground crowns create a competitive environment that prevents desirable species from germinating, establishing, or both. Cutleaf blackberry grows in association with Himalaya blackberry, and control efforts frequently target these two species. Control of Himalaya blackberry is complicated by vigorous vegetative regrowth after mechanical control, including mowing, and variable response to chemical methods. Recent interest in the use of goat browsing for invasive plant control has led land managers to use a variety of browsing regimes to control unwanted species through disturbance by herbivory. This study examined changes in functional group percent cover in a perennial grass pasture invaded by Himalaya blackberry and cutleaf blackberry in the southern Willamette Valley of Oregon. The appearance of species and their functional group membership after three treatment protocols are evaluated. Changes in the percentage of cover by Himalaya and cutleaf blackberries, annual grasses, perennial grasses, annual forbs, and perennial forbs were examined after two annual treatments with (1) high-intensity–short-duration goat browsing, (2) mowing, and (3) high-intensity–short-duration goat browsing followed by mowing. These data were then compiled by functional group to assess trends in the plants' revegetating the pasture after treatment. All treatments caused a significant decline in the percent cover of the invasive blackberries (P < 0.0001), but differences among treatments were not significant. The increase in the percent cover of perennial forbs for plots treated with goat browsing followed by mowing was significantly greater (P = 0.008) than it was in plots browsed only and those mowed only. Changes in percent cover of other functional groups were not significantly different with browsing or mowing treatments. Individual species within the perennial grass and perennial forb groups are discussed.

Cotton and peanut grown under irrigation make up over 769,000 ha in the Southeast USA. The consumptive use of water for irrigation has significantly impacted groundwater resources, spring flows and streamflows in many parts of this region, particularly during severe droughts. This situation is further complicated with extreme weather events and climate variability. In this study, we compare yields and water use in a non-irrigated sod-based rotation system (SBR; bahiagrass–bahiagrass–peanut–cotton) to an irrigated conventional rotation system (ICR; peanut–cotton–cotton). Root mass of oat cover crop following peanut or cotton in a SBR and ICR system was also measured. A soil water assessment model (SWAT) was used to simulate irrigation water demands over a 34 yr period (1980–2013) under different soil types to quantify water saving potential of SBR. The average peanut yield in ICR from 2002 to 2013 was 4509 kg ha−1, while that in SBR was 4874 kg ha−1. Likewise the average cotton yield in ICR during the same period was 1237 kg ha−1, while that in SBR was 1339 kg ha−1. Oats had greater root mass in SBR than ICR. Simulation results indicate that crops in SBR consistently had substantially lower irrigation requirements (between 11 and 22 cm yr−1) than those in ICR in dry years. The water-saving potential of SBR varies positively with increasing sand content in soil.