Andrew R. Kniss

Nonlinear Regression Analysis of Herbicide Absorption Studies

Abstract Although foliar herbicide absorption has been studied intensively, there is currently no standardized method for data analysis when evaluating herbicide absorption over time. Most peer-reviewed journals require the treatment structure of data be incorporated in the analysis; however, many herbicide absorption studies published in the past 5 yr do not account for the time structure of the experiment. Herbicide absorption studies have been presented in a variety of ways, making it difficult to compare results among studies. The objective of this article is to propose possible nonlinear models to analyze herbicide absorption data and to provide a stepwise framework so that researchers may standardize the analysis method in this important research area. Asymptotic regression and rectangular hyperbolic models with similar parameterizations are proposed, so that the maximum herbicide absorption and absorption rate may be adequately modeled and statistically compared among treatments. Adoption of these models for herbicide absorption analysis over time will provide a standardized method making comparison of results within and among studies more practical.

Glyphosate-Induced Weed Shifts in Glyphosate-Resistant Corn or a Rotation of Glyphosate-Resistant Corn, Sugarbeet, and Spring Wheat

A field trial was conducted for 6 yr (1998 through 2003) at Scottsbluff, NE, to measure weed shifts following multiple applications of two rates of glyphosate or alternating glyphosate with nonglyphosate treatments in continuous corn or in a crop rotation of corn, sugarbeet, and spring wheat with all three crops resistant to glyphosate. After 6 yr, plant densities of common lambsquarters, redroot pigweed, hairy nightshade, and common purslane increased in the crop-rotation treatment compared with continuous corn. There were four weed control subplot treatments consisting of two in-crop applications of glyphosate at 0.4 or 0.8 kg ae/ha each spring, alternating two applications of glyphosate at 0.8 kg/ha one year with a nonglyphosate treatment the next year, or a nonglyphosate treatment each year. The composition of the weed population averaged across all four treatments shifted from kochia and wild proso millet to predominately common lambsquarters. After 3 yr of using glyphosate at 0.4 kg/ha twice each year, common lambsquarters density increased compared with that in the 0.8 kg/ha rate of glyphosate or alternating glyphosate treatments. By the sixth year, the density of common lambsquarters in the glyphosate at 0.4 kg/ha treatment had increased to the extent that corn grain yield was reduced 43% compared with corn grain yield in the 0.8 kg/ha glyphosate treatment. Using glyphosate at either rate for 6 yr decreased the densities of kochia, wild proso millet, and longspine sandbur, did not alter densities of redroot pigweed and green foxtail, and increased the density of hairy nightshade. In the low-rate treatment of glyphosate, the number of common lambsquarters seeds in the seed bank were 134 seeds/kg soil in 1998, declined to 15 seeds/kg by 2002, but began to increase in 2003 as the densities of plants not controlled by glyphosate increased. Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L. CHEAL; common purslane, Portulaca oleracea L. POROL; green foxtail, Setaria viridis (L.) P. Beauv. SETVI; hairy nightshade, Solanum physalifolium Rusby SOLSA; kochia, Kochia scoparia (L.) Schrad. KCHSC; longspine sandbur, Cenchrus longispinus (Hack.) Fern. CCHPA; redroot pigweed, Amaranthus retroflexus L. AMARE; wild proso millet, Panicum miliaceum L. PANMI; corn, Zea mays L; spring wheat, Triticum aestivum L; sugarbeet, Beta vulgaris L.

Economic Evaluation of Glyphosate-Resistant and Conventional Sugar Beet

Field experiments were conducted near Scottsbluff, NE, in 2001 and 2002 to compare economic aspects of glyphosate applied to different glyphosate-resistant sugar beet cultivars with that of conventional herbicide programs applied to near-equivalent, non–glyphosate-resistant conventional cultivars. Glyphosate applied two or three times at 2-wk intervals, beginning when weeds were 10 cm tall, provided excellent weed control, yield, and net economic return regardless of the glyphosate-resistant sugar beet cultivar. All conventional herbicide treatments resulted in similar net economic returns. Although the conventional sugar beet cultivars ‘HM 1640’ and ‘Beta 4546’ responded similarly to herbicide treatments with respect to sucrose content, ‘Beta 4546RR’ produced roots with 1% more sucrose than ‘HM 1640RR’. When averaged over herbicide treatments, a producer planting Beta 4546RR could afford to pay US

Winter Wheat Response to Preplant Applications of Aminocyclopyrachlor

185/ha more for glyphosate-resistant technology as could a producer planting HM 1640RR. When averaged over cultivars and herbicide treatments, it is estimated that a producer could afford to pay an additional US

Long-term trends in the intensity and relative toxicity of herbicide use

385/ha for glyphosate-resistant technology without decreasing net return. Nomenclature: Glyphosate; sugar beet, Beta vulgaris (L.) ‘Beta 4546’, ‘Beta 4546RR’, ‘HM 1640’, ‘HM 1640RR’. Additional index words: Herbicide-tolerant crops, technology fee, weed management, clopyralid, desmedipham, ethofumesate, phenmedipham, triflusulfuron. Abbreviations: DES, desmedipham; fb, followed by; PHEN, phenmedipham; RG, gross return; TRIF, triflusulfuron; Y, root yield.

Carfentrazone Improves Broadleaf Weed Control in Proso and Foxtail Millets

Abstract Field studies were conducted in Wyoming and Nebraska in 2007 through 2009 to evaluate winter wheat response to aminocyclopyrachlor. Aminocyclopyrachlor was applied at rates between 15 and 120 g ai ha−1 6, 4, and 2 mo before winter wheat planting (MBP). Redroot pigweed control was 90% with aminocyclopyrachlor rates of 111 and 50 g ha−1 when applied 4 or 2 MBP. Aminocyclopyrachlor at 37 g ha−1 controlled Russian thistle 90% when applied 6 MBP. At Sidney, NE, winter wheat yield loss was > 10% at all aminocyclopyrachlor rates when applied 2 or 4 MBP, and at all rates > 15 g ha−1 when applied 6 MBP. At Lingle, WY, > 40% winter wheat yield loss was observed at all rates when averaged over application timings. Although the maturing wheat plants looked normal, few seed were produced in the aminocyclopyrachlor treatments, and therefore preharvest wheat injury ratings of only 5% corresponded to yield losses ranging from 23 to 90%, depending on location. The high potential for winter wheat crop injury will almost certainly preclude the use of aminocyclopyrachlor in the fallow period immediately preceding winter wheat. Nomenclature: Aminocyclopyrachlor; redroot pigweed, Amaranthus retroflexus L., AMARE; Russian thistle, Salsola tragus L. SASKR; winter wheat, Triticum aestivum L

Glyphosate Susceptibility in Common Lambsquarters (Chenopodium Album) Is Influenced by Parental Exposure

Herbicide use is among the most criticized aspects of modern farming, especially as it relates to genetically engineered (GE) crops. Many previous analyses have used flawed metrics to evaluate herbicide intensity and toxicity trends. Here, I show that herbicide use intensity increased over the last 25 years in maize, cotton, rice and wheat. Although GE crops have been previously implicated in increasing herbicide use, herbicide increases were more rapid in non-GE crops. Even as herbicide use increased, chronic toxicity associated with herbicide use decreased in two out of six crops, while acute toxicity decreased in four out of six crops. In the final year for which data were available (2014 or 2015), glyphosate accounted for 26% of maize, 43% of soybean and 45% of cotton herbicide applications. However, due to relatively low chronic toxicity, glyphosate contributed only 0.1, 0.3 and 3.5% of the chronic toxicity hazard in those crops, respectively.

Research Methods in Weed Science: Statistics

Proso and foxtail millets are regionally important dryland crops for the semiarid portions of the Central Great Plains. However, few herbicides are registered for use in either crop. The efficacy of carfentrazone was studied in proso millet from 2003 through 2005 at the University of Nebraska High Plains Agricultural Laboratory located near Sidney, NE, and in foxtail millet in 2004 and 2005 at the University of Wyoming Sustainable Agriculture Research and Extension Center near Lingle, WY. Carfentrazone was applied POST at 9.0, 13.5, and 18.0 g ai/ha with combinations of 2,4-D amine, prosulfuron, and dicamba. Although leaves of treated plants exhibited localized necrosis, leaves emerging after treatment were healthy. Grain and forage yields were not affected by the application of carfentrazone. Dicamba and 2,4-D amine provided visual control of 30% or less for buffalobur. Adding carfentrazone to one or both of these herbicides improved buffalobur control to 85% or greater. Carfentrazone applied at 18.0 g/ha improved Russian thistle, kochia, and volunteer sunflower control in 2003, when plants were drought-stressed, but did not help with these and other weeds during wetter years. Carfentrazone provides proso millet producers with a way to selectively control buffalobur, a noxious weed in several western states. In foxtail millet, carfentrazone provides POST broadleaf weed control with little risk for serious crop injury. Crop injury has been a concern with 2,4-D, which is currently the only other herbicide registered for use in foxtail millet. Nomenclature: Carfentrazone, 2,4-D, dicamba, prosulfuron, buffalobur, Solanum rostratum Dun. SOLCU, kochia, Kochia scoparia (L.) Schrad. KCHSC, Russian thistle, Salsola iberica Sennen & Pau SASKR, foxtail millet, Setaria italica (L.) P. Beauv, proso millet, Panicum miliaceum L, sunflower, Helianthus annuus L

Proso Millet Tolerance to Saflufenacil

Abstract Field studies were carried out at two sites in 2005 using common lambsquarters seed collected from long-term research plots near Scottsbluff, NE; Fort Collins, CO; and Torrington, WY, to determine the effect of herbicide selection pressure on glyphosate susceptibility. Parental herbicide exposure influenced the level of glyphosate susceptibility exhibited by a subsequent generation. Common lambsquarters selected from historical plots receiving continuous and exclusive use of glyphosate exhibited lower mortality in response to 420 g ae ha−1 glyphosate compared with selections from nonglyphosate treatment histories. Selections from rotating glyphosate treatment histories demonstrated an intermediate tolerance response. Differences in response were also influenced by environmental conditions. Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L., CHEAL

Quantitative Evaluation of the Environmental Impact Quotient (EIQ) for Comparing Herbicides

Nomenclature: Bromoxynil; ioxynil; oxitril.