No abstract

In response to farmer complaints of poor triallate performance, wild oat seed was collected from 34 fields in Alberta in the fall of 1990. Screening trials in the greenhouse indicated that 15 of the populations were highly resistant to triallate applied at the equivalent of the recommended field rate (1.7 kg ha-1), whereas the other 19 populations were adequately controlled. All triallate-resistant populations were also highly resistant to difenzoquat applied at 1.7 kg ha-1(equivalent to twice the recommended field rate). The effect of increasing rates of both herbicides on dry weight of five of the resistant and two of the susceptible populations was determined in greenhouse experiments. Triallate applied up to 3.4 kg ha-1had little or no effect on the resistant populations, whereas the susceptible populations were controlled at 1.7 kg ha-1. At rates of 6.8 kg ha-1or higher, there were differences among the resistant populations and among individuals within the populations in the response to triallate. Response of the resistant populations to increasing difenzoquat rates was variable between experiments, but in all cases the effect of difenzoquat on wild oat dry weight was considerably less in triallate-resistant than triallate-susceptible populations. Effects of increasing rates of triallate and difenzoquat on resistant and susceptible wild oat populations growing with barley in field experiments were generally similar to the responses in the greenhouse.

. 1994. Investigation of a chlorsulfuron'resistant chickweed lstellaria medtu (L.) Vill.l population. . A chickweed population (R) from a farm near Stony Plain, Alberta, was more resiitant to chlorsulfuron than a population (S)

. 1995. Companion crop, herbicide and weed effects on estab' tfutt-"nt and yields of alfalfa-bromegrass mixtures. . Nfalfa (Medicago sativa L.) and bromegrass (Bromus spp.; 'oere seeded with and without a companion crop and with and without herbicides at Westlock and Lethbridge' Alberta, to issess the effect of weed control, companion crop and the herbicide-by-companion crop interaction on forage establishment and subsequent yields. A companion cropreduced both alfalfa and bromegrass yields for at least 2 yr after establishment on a rain fed site atWestlock and for f yr after establishment on an irrigated site at lrthbridge. At both sites, weed yields were higher after establishment with a companion crop than after establishment without a companion crop-Unchecked weeds in the eriablishment year had less effect than a companion crop on subsequent forage yields. At both locations, weed biomass in the establishment y""r *ur less than that of the companion crop. The combined stress of a companion crop and 2,4-DB application had a derimental effect on alfalfa yield for 3 yr after establishment at Lethbridge.

. 2005. Field evaluation of regression equations to estimate crop yield losses due to weeds. Can. J. Plant Sci. 85: 955-962. Various regression equations based on weed density alone, or relative time of weed and crop emergence or crop density in addition to weed density have been developed in western Canada to estimate the effects of wild oat (Avena fatua L.) and volunteer cereals on yield loss of field crops, and to advise farmers on the economics of weed control with herbicides. In , 1998, several of these equations were evaluated in 9 barley (Hordeum vulgare L.), 9 wheat (Triticum aestivum L.) and 11 canola (Brassica napus L.) fields in Alberta. Wild oat was the dominant weed in the barley and wheat fields, and wild oat or volunteer cereals in the canola fields. In barley and wheat, more complex equations based on both weed density and either crop density or relative time of weed and crop emergence were more reliable in estimating yield losses due to wild oat than those based on weed density alone. In canola, an equation based on volunteer barley and canola density provided the most reliable estimates. Under the assumed crop prices and herbicide costs, these equations also resulted in the best estimates of whether or not a herbicide application resulted in a net profit or loss. Herbicide application was rarely economical in barley, but usually economical in wheat and canola reflecting the different market value of the crops. The implementation of the weed economic threshold concept is likely to be more feasible in low-value crops such as feed barley than in higher-value crops such as canola. Dans l'ouest du Canada, on se sert d'équations de régression pour estimer l'incidence de la folle avoine (Avena fatua L.) et de la repousse spontanée des céréales sur le rendement des cultures d'après la densité de peuplement des adventices, la levée des mauvaises herbes et des cultures ou la densité de peuplement des adventices et de la culture, l'objectif étant de conseiller les agriculteurs sur le désherbage chimique. Les auteurs ont évalué plusieurs de ces équations dans 9 champs d'orge (Hordeum vulgare L.), 9 de blé (Triticum aestivum L.) et 11 de canola (Brassica napus L.) de l'Alberta en 1997, 1998 et 1999. La folle avoine était la principale adventice dans les champs d'orge et de blé alors que ceux de canola étaient surtout envahis par la folle avoine et les repousses spontanées de céréales. Dans les champs de blé et d'orge, les équations plus complexes, reposant à la fois sur la densité de peuplement des mauvaises herbes et sur celle de la culture ou sur la levée relative de l'adventice et de l'espèce cultivée sont plus fiables que les équations se fondant uniquement sur la densité de peuplement de la mauvaise herbe pour estimer les pertes de rendement attribuables à la folle avoine. Dans les champs de canola, c'est l'équation reposant sur la densité des repousses spontanées d'orge et sur la densité du canola qui donne les estimations les plus sûres. Compte tenu du prix hypothétique de la culture et des herbicide...