R. N. Stougaard

Effects of Variable Tralkoxydim Rates on Wild Oat (Avena fatua) Seed Production, Wheat (Triticum aestivum) Yield, and Economic Return1

Field experiments were conducted at Lacombe, Lethbridge, and Vegreville, Alberta, Canada and Kalispell, MO, over several years to determine the influence of recommended (minimum label) and lower-than-recommended tralkoxydim rates on wild oat seed production, spring wheat yield, and economic return. Wild oat seed production as a function of tralkoxydim rate varied considerably among locations and years. For example, at the recommended rate, wild oat seed production varied from none at both Lethbridge and Vegreville in 1994 to over 800 seeds/m2 at Vegreville in 1995. At 50% of recommended rate, seed production varied from none at Lethbridge in 1994 to over 3,000 seeds/m2 at Vegreville in 1995. In most cases, wheat yield response to tralkoxydim rate was curvilinear. Yields generally increased exponentially as rates increased up to about 40 or 50% of the recommended rate, but then plateaued as rates were increased further. In some cases economic returns tended to plateau or decrease at rates higher than this, but reductions in economic returns at the recommended herbicide rates were, in most cases, relatively slight. In contrast, at Lethbridge in 1993 and 1995 and at Kalispell in 1994 and 1996, yield and economic returns generally increased as herbicide rate increased, and there was an economic disadvantage to reducing the tralkoxydim rate below that recommended. In view of the variable effects on wild oat seed production, and the questionable economic benefit, our study suggests that reducing the rate of tralkoxydim below that recommended may not be without risk. Further studies are necessary to determine the long-term implications of returning relatively large amounts of wild oat seed to the soil seedbank at reduced herbicide rates. Nomenclature: Tralkoxydim; wild oat, Avena fatua L. #3 AVEFA; wheat, Triticum aestivum L. ‘Hi-line’, ‘Katepwa’, ‘Newana’, ‘Roblin’. Additional index words: Reduced herbicide rates.

Camelina (Camelina sativa) Tolerance to Selected Preemergence Herbicides

Abstract Camelina is an emerging oilseed crop suitable for biofuel production in dryland cropping systems of the northwestern United States. Currently, camelina growers have limited herbicide options available for weed control. Tolerance of camelina to PRE applications of quinclorac, S-metolachlor, dimethenamid-P, pendimethalin, and pyroxasulfone was evaluated at two locations (Kalispell in 2009 and 2010, and Huntley in 2010 and 2011) in Montana. Susceptibility to each herbicide was determined at three different rates. Quinclorac applied PRE at 280 to 840 g ai ha−1 did not significantly injure camelina, and had no negative effect on plant density, biomass, flowering, and yield at either location. S-Metolachlor at 1,060 to 2,140 g ai ha−1 caused less than 20% injury to camelina, with no reductions in plant density, biomass, and yield compared with the nontreated check. Dimethenamid-P applied at 630 g ai ha−1 did not affect camelina density, biomass, flowering, and yield; however, at the 1,260 g ha−1 rate, injury was as high as 60% (in the coarse-textured Kalispell soil), and plant density and yield were reduced as much as 50 and 31%, respectively, in addition to delayed flowering. Despite causing some visual injury to camelina, crop yield was not reduced by pendimethalin at the 1,060 or 2,130 g ai ha−1 rate. Pyroxasulfone caused significant crop injury, stand loss, and yield reductions, and thus does not appear to be a viable option for weed control in camelina. Camelina plants that exhibited early-season injury showed robust growth and compensatory abilities, with lack of significant effect of herbicides on late-season plant height and biomass at least in one of the two locations. On the baseis of this research, quinclorac was the safest of all herbicides tested in camelina. Dimethenamid-P, S-metolachlor, and pendimethalin also may have an acceptable level of crop safety at lower use rates for possible registration in camelina. Nomenclature: Quinclorac; S-metolachlor; dimethenamid-P; pendimethalin; pyroxasulfone; camelina, Camelina sativa (L.) Crtz. Resumen Camelina es un cultivo oleaginoso nuevo que es adecuado para la producción de biocombustibles en sistemas de producción en zonas secas del noroeste de los Estados Unidos. Actualmente, los productores de camelina tiene opciones limitadas de herbicidas para el control de malezas. Se evaluó la tolerancia de camelina a aplicaciones PRE de quinclorac, S-metolachlor, dimethenamid-P, pendimethalin, y pyroxasulfone en dos localidades (Kalispell en 2009 y 2010, y Huntley en 2010 y 2011) en Montana. La susceptibilidad a cada herbicidas se determinó con tres dosis diferentes. Quinclorac aplicado PRE de 280 a 840 g ai ha−1 no dañó la camelina significativamente, y no tuvo un efecto negativo en la densidad de plantas, la biomasa, la floración, y el rendimiento en ninguna de las localidades. S-metolachlor aplicado con dosis de 1,060 a 2,140 g ai ha−1 causó menos de 20% de daño a camelina, y no redujo la densidad de plantas, la biomasa, o el rendimiento, al compararse con el testigo no tratado. Dimethenamid-P aplicado a 630 g ai ha−1 no afectó la densidad de la camelina, la biomasa, la floración o el rendimiento. Sin embargo, a 1,260 g ha−1, el daño alcanzó 60% (en suelos Kalispell de textura gruesa), y la densidad de plantas y el rendimiento fueron reducidos hasta 50 y 31%, respectivamente, además de que se observó un retraso en la floración. A pesar de que causó daño visual a la camelina, el rendimiento del cultivo no se redujo con aplicaciones de pendimethalin a dosis de 1,060 ó 2,130 g ai ha−1. Pyroxasulfone causó daño significativo al cultivo, pérdida de plantas, y reducciones en el rendimiento, por lo que parece que no es una opción viable para el control de malezas en camelina. Las plantas de camelina que exhibieron daños temprano durante la temporada de crecimiento, mostraron un crecimiento robusto y la habilidad de compensar dicho daño, lo que se vio en la ausencia de efectos significativos de los herbicidas sobre altura de planta y biomasa tarde en la temporada, en al menos una de las dos localidades. Con base en esta investigación, quinclorac fue el herbicida evaluado más seguro para camelina.

Selection of a Barley Yield Model Using Information–Theoretic Criteria

Abstract Empirical models of crop–weed competition are integral components of bioeconomic models, which depend on predictions of the impact of weeds on crop yields to make cost-effective weed management recommendations. Selection of the best empirical model for a specific crop–weed system is not straightforward, however. We used information–theoretic criteria to identify the model that best describes barley yield based on data from barley–wild oat competition experiments conducted at three locations in Montana over 2 yr. Each experiment consisted of a complete addition series arranged as a randomized complete block design with three replications. Barley was planted at 0, 0.5, 1, and 2 times the locally recommended seeding rate. Wild oat was planted at target infestation densities of 0, 10, 40, 160, and 400 plants m−2. Twenty-five candidate yield models were used to describe the data from each location and year using maximum likelihood estimation. Based on Akaikes Information Criterion (AIC), a second-order small-sample version of AIC (AICc), and the Bayesian Information Criterion (BIC), most data sets supported yield models with crop density (Dc), weed density (Dw), and the relative time of emergence of the two species (T) as variables, indicating that all variables affected barley yield in most locations. AIC, AICc, and BIC selected identical best models for all but one data set. In contrast, the Information Complexity criterion, ICOMP, generally selected simpler best models with fewer parameters. For data pooled over years and locations, AIC, AICc, and BIC strongly supported a single best model with variables Dc, Dw, T, and a functional form specifying both intraspecific and interspecific competition. ICOMP selected a simpler model with Dc and Dw only, and a functional form specifying interspecific, but no intraspecific, competition. The information–theoretic approach offers a rigorous, objective method for choosing crop yield and yield loss equations for bioeconomic models. Nomenclature: Wild oat, Avena fatua L. AVEFA; barley, Hordeum vulgare L.

Effects of Spring Wheat Seed Size and Reduced Rates of Tralkoxydim on Wild Oat Control, Wheat Yield, and Economic Returns

Spring wheat competitive ability has recently been demonstrated to co-vary with seed size. The objective of this study was to determine if spring wheat seed size would influence the effects of variable tralkoxydim rates on wild oat control, wheat yield, and economic returns. The factorial treatment arrangement consisted of three spring wheat seed size classes and five tralkoxydim rates. Wild oat density, panicles, and biomass decreased as spring wheat seed size and tralkoxydim rate increased, with the combined effect being additive. Wild oat variables decreased in a log-logistic manner as tralkoxydim rate increased during both years. However, tralkoxydim was less effective in 2000 than 2002, as indicated by the higher dosage required to reduce the wild oat variables by 50% (greater I50 values). In contrast, the effect of large seeded wheat in suppressing wild oat was more consistently expressed, with wild oat variables decreasing linearly as seed size increased. Wheat yield and economic returns increased exponentially as tralkoxydim rate increased. At the same time, wheat yield and economic returns were greater for wheat plants derived from large seed compared to those derived from small seed. Averaged over all other factors, adjusted gross returns of 578, 657, and 703

Imidazolinone Herbicides Improve Restoration of Great Plains Grasslands

/ha were realized for the small, medium, and large seed size classes, respectively. The combined use of large seeded wheat plus tralkoxydim applications provided greater wild oat control than did either single tactic. The use of large seeded wheat had a stabilizing effect that increased the consistency and durability of the weed management system while simultaneously improving economic returns. Nomenclature: Tralkoxydim; wild oat, Avena fatua L. #3 AVEFA; wheat, Triticum aestivum L. ‘McNeal’. Additional index words: Seed size, dose response, integrated weed management. Abbreviations: AGR, adjusted gross return; TKW, thousand kernel weights.