Greenhouse and field experiments were conducted at the Lacombe Research Station to evaluate mixtures of sethoxydim and fluazifop on green foxtail, wild oat, wheat, and barley in canola. In both environments the two herbicides interacted on the grass species in a synergistic manner. Many of the observed responses to mixtures of sethoxydim and fluazifop were 100% greater than those expected assuming an additive interaction between the herbicides. Mixtures with at least 80 g ha-1 of sethoxydim and 80 g ha-1 of fluazifop controlled more than 90% of green foxtail, wild oat, wheat, and barley under field conditions. These experiments indicate that the sethoxydim/fluazifop mixture is both complementary and synergistic. The mixture may allow reduced herbicide application rates and therefore reduced herbicide costs and less potential for negative environmental impact.

Greenhouse and field studies were conducted to examine the interaction of sethoxydim or fluazifop-P tank mixed with chlorsulfuron or thiameturon for selective weed control in safflower. Under greenhouse conditions, the addition of chlorsulfuron to sethoxydim or fluazifop-P slightly improved the control of green foxtail above that achieved with either herbicide alone. Control of wild oat and wild mustard was similar with the tank mixes and each herbicide alone. In the field, control of wild oat with sethoxydim or fluazifop-P was not altered by adding chlorsulfuron or thiameturon in tank mixes. Similarly, control of common lambsquarters and wild mustard with chlorsulfuron or thiameturon was not affected by adding either sethoxydim or fluazifop-P in tank mixes. Plant height, date of flowering, seed yield, and quality data indicated that safflower tolerated these herbicides applied alone or in combination. Sethoxydim or fluazifop-P tank mixed with chlorsulfuron or thiameturon provide a postemergent alternative for selective control of grass and broadleaf weeds in safflower.

Field studies were undertaken in 1992 and 1993 to investigate the control of wild oat and green foxtail in flax with reduced rates of fluazifop-P and clethodim applied as tank-mixtures. Fluazifop-P plus clethodim at 50 + 18 g ai/ha controlled wild oat and green foxtail and was as effective as full rates of either herbicide applied alone. These rates represent a 20% reduction in total amount of active ingredient required to control wild oat and green foxtail. Application of fluazifop-P, and/or clethodim prior to the 3- to 4-leaf stage failed to control late emerging grass weeds. Application of graminicide mixtures at or after the 3- to 4-leaf stage controlled late emerging grass weeds and did not affect flax yield. When applied late, fluazifop-P at 175 g/ha tended to reduce flax yield, although weed control was acceptable and no foliar injury was observed following treatment. The efficacy of graminicide mixtures was reduced by addition of bromoxynil plus MCPA to the spray mix.

Addition series field experiments were conducted near Moscow, ID, in 1987 and 1988 to determine the relative aggressiveness of spring barley and wild oat and to determine the effect of barley and wild oat density and proportion on barley grain yield and wild oat seed rain. Regression analysis was used to describe the relationship of the aboveground biomass and grain yield to species density. Barley was more aggressive than wild oat. Barley biomass was affected most by intraspecific competition, while wild oat biomass was affected most by interspecific competition. Barley aggressiveness changed little throughout the growing season. Wild oat aggressiveness varied but was always less than barley aggressiveness. Increasing wild oat density had a negative, asymptotic-type effect on barley grain yield at all barley densities. However, the effect of wild oat was greatest at the lower density of barley. Increasing barley density decreased wild oat seed rain.

Field experiments were conducted to determine the efficacy of fluazifop-P-butyl for the control of green foxtail, wild oat, barley, and wheat in flax as influenced by spray nozzle orientation, time of day, and growth stage. Under drought conditions in 1988, control of wild oat, wheat, and barley with fluazifop-P-butyl was enhanced 75%, 53% and 78%, respectively, when nozzles were oriented to spray forward 45°. Under adequate soil moisture conditions enhancement of control was minimal. Green foxtail control improved when fluazifop-P-butyl was applied from 1700 to 2100 h, but time of day had no effect on control of wild oat, barley, or wheat. Fluazifop-P-butyl effectiveness was reduced when applied 4 d after flax emergence due to late emerging grass seedlings. Green foxtail was the most tolerant to fluazifop-P-butyl, whereas wild oat, wheat, and barley were the most susceptible.

This review considers the development of herbicide-resistant weed biotypes in Australia. Biotypes of the important annual weed species, capeweed, wall barley, and hare barley are resistant to the bipyridylium herbicides paraquat and diquat. These resistant biotypes developed on a small number of alfalfa fields that have a long history of paraquat and diquat use within a distinct geographical area in central western Victoria. The resistant biotypes are controlled by alternative herbicides and pose little practical concern. Some populations of wild oat are resistant to the methyl ester of diclofop. Of greatest concern is the development of cross resistance in biotypes of rigid ryegrass to aryloxyphenoxypropionate, cyclohexanedione, sulfonylurea, and dinitroaniline herbicides. The cross-resistant rigid ryegrass infests crops and pastures at widely divergent locales throughout the cropping zones of southern Australia. The options for control of cross-resistant rigid ryegrass by herbicides are limited. A biotype of rigid ryegrass on railway tracks treated for 10 yr with amitrole plus atrazine has resistance to amitrole and atrazine and other triazine, triazinone, and phenylurea herbicides. Management tactics for cross resistance are discussed.

The effect of barley seeding rate and row spacing, and triallate, diclofop, and difenzoquat herbicide rate on barley grain yield and quality, and wild oat control were evaluated in field experiments near Bonners Ferry, Idaho, in 1989 and 1990. The purpose of the study was to develop integrated control strategies for wild oat in spring barley. Barley row spacing (9 and 18 cm) did not affect barley grain yield. Barley grain yield was greatest when barley was seeded at 134 or 201 kg ha–1 compared to 67 kg ha–1. Wild oat control increased as wild oat herbicide rate increased and barley grain yield was greatest when wild oat herbicides were applied. However, barley grain yield was similar when wild oat biomass was reduced by either 65 or 85% by applications of half and full herbicide rates, respectively. Net return was greatest when the half rate of herbicide was applied to 100 wild oat plants per m2 and was greatest when half or full herbicide rates were applied to 290 wild oat plants per m2. Net return increased when the seeding rate was increased to 134 or 201 kg ha–1 when no herbicide was applied and when 290 wild oat plants per m2 were present.

The potential of imazethapyr as a selective herbicide in four pulse crops was investigated at Melfort, Saskatchewan in 1988 and 1989. Lentil, field pea, faba bean and annual vetch were tolerant to imazethapyr applied preemergence to a silty clay loam soil at 0.05, 0.10, 0.15, and 0.20 kg ai ha-1. Postemergence treatments above 0.05 kg ha-1, however, stunted lentil and vetch in both years. Environmental factors, the dominant weed in the experimental site, as well as timing of application strongly influenced the performance of imazethapyr. Seed yield increases observed with imazethapyr treatments, compared to metribuzin or untreated check, were greater in 1989 when wild oat was the dominant weed and moisture was not a limiting factor in the early stages of crop development, than in 1988 when field pennycress was the dominant weed. Mean seed yield for all imazethapyr treatments, compared to the check, increased 0 and 930%, 24 and 89%, 21 and 600%, and 47 and 44% in 1988 and 1989, for lentil, field pea, faba bean and vetch, respectively. Significant increases in lentil seed density, seed size, and germination were also obtained though protein content decreased 2%.

Dose-response experiments showed that three samples of green foxtail collected from fields in southern Manitoba where trifluralin had not controlled the weed in 1987 were resistant to the herbicide. GR50 values indicated that the resistant populations were about 5 times more resistant to trifluralin than susceptible populations, about twice as resistant as wild oat, and about equally resistant as wheat. An additional 33 samples collected in 1988 from southwestern Manitoba where trifluralin has been used for nearly 20 yr in both cereal and oilseed crops were resistant to trifluralin.

Wild oat, a competitive weed in corn, can be controlled by atrazine applied postemergence but at rates causing carryover problems on high pH soils rotated to susceptible crops. Experiments at Fargo, ND and Barnesville, MN were established in corn using atrazine rates ranging from 0.14 to 0.84 kg ai ha–1 supplemented with cyanazine to provide 1.68 kg ai ha–1 total triazine herbicide. Atrazine at 0.84 kg ha–1 plus cyanazine at 0.84 kg ha–1 controlled 2- to 3-leaf wild oat 40 to 55%, but control increased to 90 to 95% by adding tridiphane at 0.56 or 0.84 kg ai ha–1. In greenhouse experiments, tridiphane synergistically increased wild oat control by atrazine and cyanazine. Tridiphane applied 1 or 2 d before atrazine or before an atrazine-cyanazine mixture generally controlled wild oat similar to the tridiphane-triazine tank mix.