Dinitroaniline herbicides are major herbicides used to control annual grass weeds in cool-season turfgrasses. At least three herbicides, benefin, pendimethalin, and trifluralin are labeled preemergence to control weeds in established turfgrass. Prodiamine could be a competitive product. Benefin at 2.2 to 3.4 kg ai/ha, pendimethalin at 1.7 to 3.4 kg ai/ha, prodiamine at 0.6 to 1.7 kg ai/ ha, and benefin plus trifluralin at 1.1 plus 0.6 to 2.3 plus 1.1 kg ai/ha effectively control many annual grass weeds, including large and smooth crabgrass, yellow and green foxtail, barnyardgrass, goosegrass, fall panicum, and annual bluegrass. Most dinitroaniline herbicides provide residual preemergence weed control for the entire growing season. In general, Kentucky bluegrass, perennial ryegrass, tall fescue, red fescue, and other cool-season turfgrasses tolerate most of these herbicides, although higher-than-normal rates of any dinitroaniline herbicide could restrict root growth and cause stand thinning in turfgrass species.

In west central Minnesota the extent and duration of weed seed shed was measured for two years in corn that received cultivation but no herbicides. Percentage of seed production represented by viable (filled) seeds was about 79% for green foxtail, 68% for wild mustard, 49% for Pennsylvania smartweed, 48% for common lambsquarters, and 35% for redroot pigweed. Percentage viable seeds varied from 11% in 1993 to 59% in 1994 for redroot pigweed, but was more stable for other species. Seed shed commenced in late August in a cool year (1993) and early August in a warm year (1994). Average growing degree days (base 10 C) from corn planting until 25% seed shed was 983 for common lambsquarters, 984 for wild mustard, 1004 for Pennsylvania smartweed, and 1034 for both green foxtail and redroot pigweed. Brief weather events, such as wind storms, dispersed large percentages of total seed production within a single day. More than one-fifth of all viable seeds of green foxtail, redroot pigweed, and common lambsquarters were retained by the seedheads and dispersed by combines at harvest. In contrast, seeds of early-maturing species, such as wild mustard, were completely dispersed before corn harvest in the warmer year, but one-third of seeds were retained by seedheads at harvest in the cooler year. Measurement of seed shed was compared using five seed trap designs. The preferred design consisted of a 10-cm-diam plastic cup, whose bottom was replaced by a brass screen, and the entire unit attached to a small wooden stake for support. This design provided, on average, the highest estimates of seed production, least among-replication variability, highest correlation with weed population density and aboveground dry-weight, lowest assembly cost, and greatest ease for sample access and seed processing.

The goal of this research was to determine whether crop management practices could substitute for a herbicide for managing mixed populations of green and yellow foxtail in hard red spring wheat. Crop yield and foxtail growth were measured in two years of field research in North Dakota. Spring wheat yields were as great or greater when early seeding date or 2× seeding rate were substituted for POST diclofop3 at 0.75 kg ai ha−1 for managing foxtail in spring wheat. Yield of spring wheat competing with foxtails was greater for the high seeding rate (2× = 270 kg ha−1) than both the normal (1× = 130 kg ha−1) and low (0.5× = 70 kg ha−1) seeding rates for early or middle seeding dates, but not for the late seeding date. For both early and middle seeding dates, wheat yield at the 2×seeding rate without diclofop was equal to or greater than that of the 1× seeding rate with diclofop. Late-seeded wheat did not yield well in competition with dense foxtail stands for any treatment combination. Early and middle seeding dates favored the relative increase of green foxtail over yellow foxtail in wheat, whereas late seeding favored yellow foxtail over green foxtail. Economic analysis demonstrated that early seeding date was the most critical factor in determining the stochastic dominance of treatments without diclofop over treatments with diclofop. Seeding rate was much less important than seeding date in determining the ranking of treatments in stochastic dominance analysis.

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.

Two field experiments were conducted between 1990 and 1992 under sprinkler irrigation at the Research and Extension Center, Torrington, WY to determine the influence of mixed densities and durations of kochia and green foxtail interference in sugarbeet. Sugarbeet root yield and top weight generally decreased as densities of green foxtail and kochia increased whether alone or in combination. Reductions in sugarbeet root yield and above ground biomass from mixed densities of kochia and green foxtail were additive at the low and intermediate density but less than additive at the high density of either species. Sugarbeet root yield decreased as the duration of interference after sugarbeet emergence from a mixed density of kochia and green foxtail increased. Since sugarbeet plants were irrigated to avoid water stress and adequate nutrients were applied, it appears that kochia and green foxtail interfered with sugarbeet primarily for light, based on light and height measurements. Season-long as well as duration of interference did not show any significant effect on sucrose content. Based on regression analysis the lowest densities of kochia and green foxtail required to reduce root yield were approximately 0.3 and 0.06 plants/m of row, respectively. The minimum duration of time that 0.5 kochia and 3.0 green foxtail plants/m of row can interfere with sugarbeets before root yield is economically reduced was approximately 3.5 wk after sugarbeet emergence.

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.

Temperature, soil moisture, green foxtail density, relative emergence dates, and soil fertility effects on green foxtail and spring wheat competition were evaluated in controlled environments. Green foxtail competition was highest at 30 C and without moisture stress. Early green foxtail emergence increased competition with wheat more than changes in temperature, soil moisture, or green foxtail density. At 30 C, wheat fresh weight was reduced 50% by green foxtail seeded 4 d before wheat, but only 13% by foxtail seeded 4 d after wheat. Doubling the nitrogen and total nutrient concentration did not increase wheat growth, but increased foxtail weight 41 and 75%, respectively.

Field studies were conducted to determine the influence of annual herbicide treatments plus cultivation on weed populations and corn yields in ridge-till corn during a 3-yr period at Mitchell, NE, and a 7-yr period at North Platte, NE. When the experiment was initiated at North Platte, no weeds were present before corn planting. It took 4 yr before triazine-resistant kochia became a problem before corn planting in plots treated with atrazine, but these were controlled by other operations prior to corn harvest. In the cultivated check, green foxtail densities before harvest increased from 0 in 1985 to 32 plants 100 m−2 in 1991. Annual applications of dicamba plus 2,4-D 10 d early preplant followed by cultivation controlled triazine-resistant kochia and velvetleaf, but common lambsquarters, nightshade species, and green foxtail increased. Volunteer corn was controlled with cultivation. After 3 yr at Mitchell, the annual weed population increased 10-fold in the cultivated check. Thus, corn yields were reduced 64% with two cultivations compared with an annual early preplant application of dicamba plus 2,4-D followed by alachlor plus cyanazine PRE and two cultivations. With two cultivations under low annual weed populations at North Platte, grain yield from the cultivated check treatment was not different from annual treatments of herbicides after 7 yr. Metolachlor plus atrazine occasionally caused a reduction in corn grain yields.

Six commercial petroleum oil (PO) adjuvants differed in their enhancement of imazethapyr phytotoxicity to green foxtail and kochia but not to redroot pigweed, when imazethapyr was applied postemergence at 17 g ha–1. Imazethapyr at 5 g ha–1 plus 27 combinations of three oils and nine emulsifiers reduced kochia growth by 61 to 88%. Optimum emulsifier concentration in a PO adjuvant ranged from 15 to 20% (v/v). All PO adjuvants tested produced fair to excellent oil-inwater emulsions with imazethapyr; however, emulsion stability did not correlate with weed control.

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.

Yield reductions due to green foxtail competition with hard red spring wheat varied with environment in field experiments conducted in 1984, 1985, and 1986 at Oakes, Langdon, Prosper, and Fargo, North Dakota. Wheat yield reductions ranged from 0 to 47% from 720 green foxtail plants per m2. Inclusion of early season temperature and precipitation, soil texture, and foxtail density into multiple regression analysis of wheat yield reductions significantly increased the coefficient of determination to 0.62 compared with 0.12 for regression based on green foxtail density alone. Wheat yield reduction decreased as green foxtail seeding was delayed after wheat seeding in 1986. Wheat yield generally decreased as time of diclofop application was delayed from 2 to 6 wk after wheat emergence in 1986.

Experiments were conducted in the greenhouse and the field to determine the influence of various oil adjuvants on small grain and grass weed susceptibility to foliarly applied BAS-514 OO H (BAS-514). Barnyardgrass, green foxtail, and yellow foxtail were more susceptible to BAS-514 at 0.56 kg ai ha-1 applied with than without an oil adjuvant. Shoot fresh weight reductions of barnyardgrass, green foxtail, and yellow foxtail were greater when BAS-514 at 0.56 kg ha-1 was applied with a methylated seed oil than with a petroleum oil adjuvant in the greenhouse. Differences in the effectiveness among oil adjuvants in enhancing BAS-514 phytotoxicity were more evident in greenhouse than in field experiments. Oil adjuvant enhancement of BAS-514 varied with plant species. Oats, hard red spring wheat, and winter wheat tolerated BAS-514 at 1.1 kg ha-1 foliarly applied with or without an oil adjuvant in the greenhouse. BAS-514 at 0.56 kg ha-1 applied with oil adjuvants caused less than 5% injury to wheat in the field.

Chlorsulfuron or metsulfuron applied POST at 10 g ai ha–1 at the four-leaf stage prevented yellow foxtail from forming seed, whereas seed production per pot was 53 to 77% of untreated checks following POST tribenuron or CGA-131036 treatments in greenhouse experiments. Chlorsulfuron applied POST at the two- and four-leaf stage severely reduced total seed production of yellow foxtail primarily by increasing plant mortality, rather than only reducing seed production per plant. Chlorsulfuron at 10 g ha–1 applied at the six- and eight-leaf stages decreased total seed production less than at the two earlier stages, by reducing both plant mortality and seed production per surviving plant. Yellow foxtail was much more susceptible than green foxtail to either chlorsulfuron or metsulfuron.

The objectives of this research were to compare the weed control efficacy of liquid, granular, and microencapsulated formulations of preemergence herbicides in moldboard plow, chisel plow, ridge tillage, and no-tillage corn and soybean production systems, and to determine whether herbicide formulation can influence herbicide interception and retention on surface corn residue. Common lambsquarters populations were threefold higher in corn than in soybeans. A mixed population of giant foxtail and green foxtail was highest in the chisel plow and lowest in the ridge tillage system as were total weed numbers. Percent weed control was not influenced by tillage when considered across all herbicide treatments. Weed control was not influenced by herbicide formulation in the moldboard plow, chisel plow, or ridge tillage systems, but granular herbicide applications provided better weed control than liquid applications in the no-tillage system and across various rates of corn residue in an experiment with no tillage variables. Two- to threefold less granular-applied herbicide was intercepted by surface corn residue at the time of application compared to liquid-applied herbicide. Increasing amounts of postapplication rainfall decreased the difference among formulations with regard to both total soil reception of the herbicide and resultant weed control. There was no consistent advantage for the microencapsulated formulation over the other herbicide formulations. Surface corn residue controlled many weeds without the aid of a herbicide and actually contributed to overall weed control even where herbicides were applied. This suggests that the binding of preemergence herbicides on surface crop residue may not be the cause of weed control failures in reduced-tillage systems as is often assumed to be the case.

Field trials were conducted in 1986 and 1987 to determine the effects of moisture on herbicidal activity of cinmethylin applied preemergence at 0.0, 0.3, 0.6, and 0.9 kg ai ha to both dry and moist sandy loam soil. Herbicide application was followed by varying amounts of irrigation. Weed species included velvetleaf, prickly sida, green foxtail, and barnyardgrass. When cinmethylin was applied to a moist soil or when 2.5 cm of irrigation was applied 5 days after cinmethylin application to a dry soil, overall weed control was reduced. Optimum weed control resulted from cinmethylin application to dry soil followed either by a 2.5-cm irrigation within 8 h or a 7.6-cm irrigation within 36 h.

Seedling timothy tolerated fenoxaprop at 0.09 kg ai ha-1 whereas seedling orchardgrass tolerated applications as high as 0.13 kg ai ha-1. Several fenoxaprop treatments increased perennial grass yields the year following establishment. Fenoxaprop appears to solve annual foxtail problems in new plantings of orchardgrass or timothy seeded alone. Over a 2-yr period, alfalfa yields in on alfalfa-grass mixture were maintained or increased from fenoxaprop applied the seedling year. In the mixtures, timothy yield declined in relation to fenoxaprop applied, but orchardgrass did not. Use of fenoxaprop on seedling alfalfa-timothy or alfalfa-orchardgrass mixtures is questionable.