Field experiments were conducted at five locations in Kansas, Nebraska, and Wyoming to determine the effects of imazamox rate and application timing on winter annual grass control and crop response in imidazolinone-tolerant winter wheat. Imazamox at 35, 44, or 53 g ai/ha applied early-fall postemergence (EFP), late-fall postemergence, early-spring postemergence (ESP), or late-spring postemergence (LSP) controlled jointed goatgrass at least 95% in all experiments. Feral rye control with imazamox was 95 to 99%, regardless of rate or application timing at Hays, KS, in 2001. Feral rye control at Sidney, NE, and Torrington, WY, was highest (78 to 85%) with imazamox at 44 or 53 g/ha. At Sidney and Torrington, feral rye control was greatest when imazamox was applied EFP. Imazamox stunted wheat <10% in two experiments at Torrington, but EFP or LSP herbicide treatments in the Sidney experiment and ESP or LSP treatments in two Hays experiments caused moderate (12 to 34%) wheat injury. Wheat injury increased as imazamox rate increased. Wheat receiving imazamox LSP yielded less grain than wheat treated at other application timings in each Hays experiment and at Sidney in 2001. No yield differences occurred in one Torrington experiment. However, yields generally decreased as imazamox application timing was delayed in the other Torrington experiment. Generally, imazamox applied in the fall provided the greatest weed control, caused the least wheat injury, and maximized wheat yield.
Field studies using glyphosate‐resistant corn (Zea mays L.), sugarbeet (Beta vulgaris L.), and spring wheat (Triticum aestivum L.) were conducted at Scottsbluff, NE, Torrington, WY, and Fort Collins, CO, over 6 yr to evaluate weed population dynamics under glyphosate‐ and conventional herbicide–based weed control strategies. We report the response of common lambsquarters (Chenopodium album L.), wild buckwheat (Polygonum convolvulus L.), and all grasses combined to four management strategies imbedded in two crop rotations. There were no consistent or highly significant benefits from a diverse crop rotation versus continuous corn when weed control was considered. Rotating herbicide mode of action for general weed control provided no benefit above that provided by glyphosate at 0.8 kg acid equivalent (ae) ha−1 applied twice each year. There was no evidence that any weed species developed resistance to glyphosate. The most striking finding of these studies was the buildup of common lambsquarters and wild buckwheat that occurs when glyphosate is applied at 0.4 kg ae ha−1 twice each year. Such a low‐use‐rate approach is to be completely discouraged since it appears to enrich the gene pool for individuals that survive low rates of glyphosate. The continuing decline in the real cost of glyphosate should eliminate any legitimate reason for growers to consider using less than the full labeled rate of glyphosate. All treatments that included glyphosate at all three locations over 6 yr provided significantly better grass control than the nonglyphosate conventional treatments.
Irrigated field experiments were conducted near Torrington, WY, during the 2001 to 2002 (year 1) and 2002 to 2003 (year 2) winter wheat growing seasons to evaluate cultivar response to different imazamox rates, adjuvants, and application timings. Five cultivars were treated postemergence in the early fall (EF), late fall (LF), or early spring (ES) with imazamox at 54 or 108 g ai/ha, including either nonionic surfactant (NIS) at 0.25% or methylated seed oil (MSO) at 1% (v/v) as adjuvants. A 28% urea ammonium nitrate solution at 1% (v/v) was included with all treatments. Spring injury was more severe in year 1 than year 2. Severe spring injury on ‘AP502 CL’, ‘Above’, ‘IMI-Fidel’, ‘IMI-Jagger’, and ‘IMI-Madsen’ was linked to fall application of 108 g/ha imazamox with MSO. Imazamox applied at 108 g/ha plus MSO applied in the fall consistently injured all cultivars more than the same rate with NIS and 54 g/ha imazamox regardless of adjuvant and timing, although severity of injury in the experiments differed between EF and LF timings in years 1 and 2, respectively. Correlation analysis supports injury reduced reproductive tillers per meter of row and wheat yields and increased the number of seeds per spike in year 1. The reduction of reproductive tillers per meter of row in year 1 was likely the result of severe injury caused by 108 g/ha imazamox applied in the EF coupled with little snow cover to protect against cold winter temperatures. Wheat yield in year 1 was reduced by 108 g/ha imazamox applied in the early fall; however, imazamox applied at 54 g/ha with either adjuvant in EF, LF, or ES were safe. Yield parameters and wheat yields in year 2 were not affected by imazamox rate, adjuvant, timing, or interactions of these factors.
Annual medics are comparable to alfalfa in dry matter yield and forage quality (Zhu et al., 1996). When grown Many farmers in the central High Plains graze corn (Zea mays L.) in monoculture in Minnesota, annual medic yields aftermath and are looking at ways to improve the quality and amount of this fall pasture resource. However, no information is available on ranged from 0.5 to 5.7 Mg ha Ϫ1 , depending on harvest intercropping annual legumes with irrigated corn in the region. Our time and species, and had crude protein (CP) levels objective was to determine the most appropriate pasture legume speequal to or higher than those of alfalfa. In the same cies that could be used for an irrigated corn-legume system. To accomstudy, snail medic [Medicago scutellata (L.) Mill.] had plish this, field experiments were conducted under irrigation at four the highest acid detergent fiber (ADF) and neutral desites in Wyoming. Eight legume species planted with corn were comtergent fiber (NDF) while black medic and 'Harbinger' pared with monoculture corn under weed-free and weedy conditions. strand medic (Medicago littoralis Rohde ex Loisel.) had Under weed-free conditions, corn grain yields were reduced by the the highest CP concentrations. There was also evidence presence of legume in some treatments while others were comparable to the check yields. Black medic (Medicago lupulina L.) did not re-that forage quality can be quite variable across locations. duce corn yields, but barrel medic (M. truncatula Gaertn.) and sphere However, there is little data available for annual legume medic (M. sphaerocarpus L.) reduced corn yields by 17%. Corn yields production or forage quality in an intercropped irrigated were reduced 62% by the presence of weeds regardless of legume corn system. species. Legumes did not suppress weed growth. Barrel medic pro-The objectives of this study were to (i) evaluate the duced the most forage in July; however, there was little difference effects of eight intercropped legume species on irrigated among species by November. In November, when corn stalks would corn grain yield, weed populations, and weed growth; be grazed, black medic and yellow sweetclover (Melitotus officinalis (ii) determine the effect of weeds and corn on legume Lam.) produced the highest quality forage. These results indicate that production; and (iii) compare midseason forage quality a mostly weed-free field is required to maximize corn and legume production. Of the legume species evaluated, black medic appears to of the eight legume species to that after corn grain offer the greatest potential for intercropping with irrigated corn in harvest. the central High Plains. MATERIALS AND METHODS Field experiments were conducted at four locations in Gos-M any of the farmers within the irrigated regions hen County, WY, during 1996. Two experiments were at the of the central High Plains graze corn aftermath. University of Wyoming Research and Extension Center at Intercropping with a forage legume could improve the Torrington (TREC), elevation 1249...
In 1992, the USEPA proposed a ban on the use of 43 pesticides in a large portion of Albany County, Wyoming. The ban was intended to protect the habitat of an endangered species, the Wyoming toad (Bufo hemiophyrs baxterf), as required by the Endangered Species Act of 1973. For many years, portions of Albany County that included Wyoming toad habitat had been routinely sprayed with insecticides to control mosquitoes. Residents were concerned that without adequate mosquito control, recreation, tourism, agriculture, public health, and property values could be impacted. A task force comprised of local residents of diverse backgrounds and viewpoints was appointed in 1992 by the governor of Wyoming and Albany County commissioners to consider how best to (i) protect the Wyoming toad and aid its recovery, and (ii) maintain effective mosquito control. The goal of the group was to submit an alternative proposal to the U.S. Fish and Wildlife Service and to the USEPA that would meet both objectives and be more acceptable to the residents of Albany County than the USEPA's proposed ban. This case provides a focus for considering the value of endangered species, possible impacts of the Endangered Species Act on agricultural producers, local businesses, visiting tourists, and local residents. It also permits students to consider the involvement of local communities in decision-making.
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