Greenhouse and laboratory experiments were conducted to evaluate the influence of clopyralid formulation, spray droplet size, and spray volume on deposit of clopyralid on greenhouse-grown honey mesquite. The addition of surfactant WK at 0.5% (v/v) of the spray solution caused a twofold increase in deposition of spray of the monoethanolamine salt (MEA) of clopyralid but not the oleylamine salt (OLA). There were no differences in spray deposit between spray droplet size spectrums of 160 or 330 μm Dv.5 or spray solution applications of 47 or 187 L ha-1. Dye and gas chromatography measurements of spray deposit of clopyralid compared favorably except where surfactant WK was used with the OLA formulation.

Glyphosate plus 2,4-D at 0.3 + 0.5 or 0.4 + 0.7 kg ae ha-1 applied 31 to 1 d before seeding did not affect wheat yields or grain test weights, in field experiments in conventionally tilled and no-till winter wheat. In the conventionally-tilled system in each of two years and in the no-till system in a year with 48 mm rain within 7 d before wheat was seeded, picloram applied at 0.14 kg ai ha-1 from 31 to 1 d before seeding reduced crop yields by 7 to 8%. In the conventionally-tilled system in a year with only 2 mm rain within 7 d before wheat was seeded, 2,4-D at 3.4 kg ae ha-1 and dicamba at 0.14 kg ae ha-1 applied 30 to 1 d before seeding, reduced wheat yields by 7 and 4%, respectively. Grain test weights in both tillage systems were increased slightly by picloram at 0.14 kg ha-1, but were decreased slightly by dicamba at 0.14 kg ha-1, in the year with little rain before sowing. Test weights did not differ among herbicides or tillage systems in the year with significant rain a few days before seeding.

Field experiments were conducted to determine if aldicarb, disulfoton, or phorate applied in-furrow at 0.84 or 1.12 kg ai ha–1 affected cotton response to clomazone applied PPI or PRE at rates ranging from 0 to 1.12 kg ai ha–1. Disulfoton and phorate greatly reduced clomazone-induced chlorosis, stunting, and death of cotton seedlings. Compared with no insecticide or with dimethoate applied POST, aldicarb did not affect cotton response to clomazone. A clomazone rate by insecticide interaction was not observed for cotton yield. Clomazone reduced cotton yield at one of five locations. Insecticides affected yield at three locations, where highest yields were from cotton treated with aldicarb. In a separate experiment with 0.56, 1.12, and 2.24 kg ha–1 of phorate applied in-furrow and 1.12 kg ha–1 of clomazone applied PPI, phorate at all rates protected cotton from clomazone phytotoxicity.

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.

Greenhouse and field herbicide evaluation, flooding, and soil saturation studies were conducted to investigate the control of oldfield cinquefoil in cranberry. Chlorimuron ethyl and dichlobenil were found to be promising herbicides for control of this weed in both greenhouse and field studies. The number of leaves, leaf area, shoot, root, and total dry weight of oldfield cinquefoil were reduced by dichlobenil at 1.1 to 4.5 kg ha-1 and chlorimuron ethyl at 17.5 to 35 g ha-1, at 12 wk after treatment. The higher rate of dichlobenil, however, caused reduction in cranberry height and total dry weight. Field treatment at time of cinquefoil emergence did not provide adequate weed control. Postemergence application to cinquefoil of 4.5 kg ha-1 dichlobenil, 35 g ha-1 chlorimuron ethyl, and 2.2 to 4.5 kg-1 ha terbacil reduced the number of leaves and shoot dry weight. Only terbacil at 4.5 kg ha-1 reduced cranberry shoot and fruit fresh and dry weight. Flooding for up to 72 h did not affect oldfield cinquefoil growth. At 22/18 C, 4 wk of soil saturation reduced runner development and fresh and dry weight of oldfield cinquefoil. At 13/9 C, no runners developed in either saturated or control soils, and there was no effect of soil saturation on fresh and dry weights. This suggests that oldfield cinquefoil grows better in an unsaturated soil condition, but needs a relatively warm climate to develop.

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.

Response of seedling alfalfa to four herbicides applied at the 2nd, 4th, and 8th trifoliate leaf stages was evaluated in 1988 and 1989. There was no interaction between the herbicides and alfalfa growth stages at the time of herbicide application in either year. Bentazon did not reduce alfalfa height or yield of the first cutting in either year. The dimethylamine salt of 2,4-DB and bromoxynil reduced first-cutting alfalfa yield in 1988 and 1989, respectively, and the butoxyethanol ester of 2,4-DB reduced first-cutting alfalfa yield both years. Each herbicide affected one or more measurements of alfalfa quality in at least one year.

Experimental plots treated with 2,4-D amine at 2.2 kg ae ha-1 in 1968 and 1969 to control California false-hellebore were evaluated in July 1989 to determine long-term control of California false-hellebore, changes in foliar cover, and increases in production of desirable species. Control of California false-hellebore was 100% on all treated plots. The foliar cover on treated plots averaged 78% grasses and sedge, 20% broadleaf plants, and no California false-hellebore. Control plots averaged 85% California false-hellebore, 10% grasses and sedge, and 4.5% broadleaf plants. Vegetative production of grasses and sedge was 3.8 times greater on treated plots compared with controls.

A 2-yr field study was conducted to evaluate the efficacy of ICIA-0051 for the control of annual grass and broadleaf weed species in conventional tillage corn. Treatments consisted of postemergence applications of ICIA-0051 alone and in combination with cyanazine or atrazine. ICIA-0051 at 0.6 kg ha-1 alone and in combination with cyanazine or atrazine at 1.1 kg ha-1 controlled large crabgrass, yellow foxtail, fall panicum, common lambsquarters, and redroot pigweed effectively (over 90%). The addition of cyanazine or atrazine at 1.1 kg ha-1 to the lowest rate (0.3 kg ha-1) of ICIA-0051 also improved large crabgrass, yellow foxtail, and fall panicum control by 9, 7, and 26%, respectively. None of the treatments of ICIA-0051 except the highest rate (1.1 kg ha-1) reduced either silage or grain yields of corn.

Greenhouse and field experiments were conducted to evaluate the control of eastern black nightshade and velvetleaf in tomato with bentazon, metribuzin, pyridate, and acifluorfen. Metribuzin controlled velvetleaf but not eastern black nightshade, whereas pyridate controlled eastern black nightshade but not velvetleaf. A combination of metribuzin + pyridate controlled both weeds, but caused tomato injury 4 wk after application. Bentazon neither controlled the weeds nor injured the crop. Acifluorfen controlled both eastern black nightshade and velvetleaf. Diammonium phosphate and oxysorbic (5 POE) improved bentazon and acifluorfen activity against velvetleaf. Although initial crop injury from some treatments applied prior to fruit initiation was severe, the crop recovered and there were no reductions in fruit weight compared with the control. However applying acifluorfen with oxysorbic (5 POE) during fruit development reduced yield 50%.

Preemergence herbicides were applied on February 28 at the recommended and three times the normal rate to determine the tolerance of tall fescue that was seeded in September, October and November of the preceding year. Fall seeding date of tall fescue significantly affected its tolerance to spring-applied preemergence herbicides. Generally, preemergence herbicides at normal rates were safe to apply to September- or October-seeded tall fescue. No herbicide was completely safe to apply to November-seeded tall fescue. The density of November-seeded tall fescue was generally reduced less with benefin, bensulide, dithiopyr, oxadiazon G and WP than with benefin plus oryzalin, oryzalin, or pendimethalin.

Experiments were conducted at 12 locations in North Carolina and Virginia to determine soybean response to postemergence application of 2,4-DB in combination with 420 g ae ha-1 of sodium salt of acifluorfen, 13 g ae ha-1 of ethyl ester of chlorimuron, and 70 g ae ha-1 of ammonium salt of imazethapyr. Adding dimethylamine salt of 2,4-DB at 35 or 70 g ae ha-1 to acifluorfen, chlorimuron, or imazethapyr increased soybean injury 2 to 14% 7 d after application. Soybean quickly recovered and no injury was observed 21 d after application. Acifluorfen, chlorimuron, or imazethapyr alone or in combination with 2,4-DB at 35 g ha-1 did not reduce soybean yield. Adding 2,4-DB at 70 g ha-1 reduced yield at four of the 12 locations.

Thirty-six postemergence-directed (PDIR) herbicide treatments, applied with a precision PDIR sprayer, were evaluated for wild-proso millet (PANMI) control in sweet corn field trials in Wisconsin from 1987 to 1990. The performance of butylate and cyanazine (B + C), applied to suppress PANMI early in the season and to provide a height differential between corn and PANMI, greatly influenced PANMI control with PDIR treatments. PDIR treatments controlled PANMI greater than 90% when PANMI was effectively suppressed by B + C, but poor PANMI suppression reduced PDIR herbicide efficacy. Generally, PDIR treatments of paraquat or sethoxydim most effectively controlled PANMI. Paraquat alone at 545 g ha–1 or combined with simazine or sethoxydim at 57 and 114 g ha–1, and sethoxydim at 170 and 227 g ha–1 plus an adjuvant controlled PANMI greater than 95%. PDIR applications of ametryn, linuron, sethoxydim at 57 to 227 g ha–1 alone, sethoxydim at less than 114 g ha–1 plus an adjuvant, and sethoxydim at 114 g ha–1 tank mixed with either of four other herbicides controlled less than 86% of PANMI. Tank mixing a photosynthetic inhibitor or sethoxydim with paraquat did not improve PANMI control compared with paraquat alone. PANMI control with sethoxydim plus an adjuvant at 114 g ha–1 was similar to 227 g ha–1. There was no difference in PANMI control with sethoxydim applied with crop oil concentrate or BCH-815. With the exception of glyphosate at 318 g ha–1 and sethoxydim at 227 g ha–1 plus an adjuvant, PDIR treatments did not injure sweet corn in 1987, 1988, or 1990. However, sethoxydim in 1989 at all rates severely injured corn.

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.

Runoff and sediment yield were monitored from 1983 through 1986 on a range site dominated by creosotebush. The site was rootplowed and seeded, treated with tebuthiuron at 36 kg ai ha-1, or left untreated. Runoff from rootplowed and herbicide-treated plots was no different from untreated plots for 1 yr, but sediment yield from treated plots was lower than that from the untreated plots. Rootplowing and seeding increased sediment yield in the second year (1984), whereas treating with herbicide decreased sediment yield. Runoff and sediment yield during 1985 and 1986 were greatest from the untreated areas and least from the rootplowed and herbicide-treated areas. Total cover was nearly the same for each treatment. The untreated plots had 13% shrub cover; the others had none. Between shrubs in untreated plots, bare ground occupied large interconnected areas that contributed to the higher runoff and erosion rates.

Horsenettle was described quantitatively in two grazed bermudagrass pastures for two years. Six times from April through October, plants were counted, phenologically documented, and tops were harvested for estimation of above-ground phytomass. Roots were sampled for carbohydrate, N fraction, and macronutrient analyses. Top growth, flowering, fruiting, and chemical composition were similar between sites within years, but differed between years. Starch and total non-structural carbohydrates in roots increased following reproductive periods both years. Root concentrations of protein and non-protein N increased and concentrations of P decreased in August and September in one year only. Analysis of the relationship between seasonal trends in carbohydrate fluctuation and pasture management practices suggests that systemic herbicide application in mid-summer may lead to more effective control than application in spring.

Optimal rates and time of application of glyphosate for control of the native perennial bluejoint reedgrass [Calamagrostis canadensis (Michx.) Nutt.] were determined from 1986 to 1989 near Delta Junction, AK. Applications were made 2 wk apart from late May or early June to September. Glyphosate did not provide control before June 15 or after September 1. Bluejoint reedgrass was controlled best when glyphosate was applied from late July to mid-August. Ammonium sulfate (2.2 kg ha-1) or nonionic surfactant (0.5% v/v) increased control except on the earliest and latest application dates. Control was consistently better with 1.1 than 0.6 kg ha-1 (ai) of the isopropylamine salt of glyphosate.

Stands of four-year-old loblolly pines grown with and without herbaceous competition were compared to determine whether early increases in soil moisture and plant water status had been maintained throughout the first four years. Non-weeded stands tended to have greater soil moisture than weeded stands, although these differences were never statistically significant (P > 0.05). Plant water potential was remarkably similar between treatments, as were photosynthesis and stomatal conductance. The increase due to weed control in foliage production early in stand development apparently caused a depletion in available soil moisture to levels similar to non-weeded stands. Therefore, the direct benefit of increased soil resources with weed control is short lived.

Postemergence spring applications of picloram and picloram plus 2,4-D frequently reduced mature height and peduncle length of hard red winter wheat in field experiments. Yield reductions were more severe from picloram applied alone to the first joint growth stage than late tillering stage wheat. In two of six experiments picloram plus 2,4-D reduced yield more than picloram alone. Yields of four wheat cultivars were reduced by picloram and picloram plus 2,4-D at one of two locations. At the second location only the yield of ‘Chisholm’ and ‘Rohm and Haas Seed 7837’ were reduced by those herbicides.

Field experiments in 1984 and 1985 near Headland, AL involved the influence of 18 integrated weed management systems incorporated from nine herbicide-tillage systems (H-T) and two row patterns on control of large crabgrass and Texas panicum, crop yield, and net returns in grain sorghum. The conventional-tillage system plus herbicide combinations; alachlor preplant incorporated (PPI), atrazine postemergence (POST), and paraquat POST directed, provided 90% or greater control of large crabgrass throughout the season and high sorghum yields in one of two years; and 90% or greater control of Texas panicum from mid-June through mid-August and high sorghum yields in both years. Results in 1984 and 1985 similar to those above were obtained with strip tillage plus herbicide combinations; alachlor PPI, atrazine POST, and paraquat POST directed; alachlor PPI and tridiphane plus atrazine POST; and tridiphane plus atrazine POST and paraquat POST directed. Row patterns did not consistently influence control of large crabgrass, Texas panicum, or sorghum yield. Economic net returns ranged from – $20 to $210 per hectare for the large crabgrass control systems in 1984; however, low sorghum yields in 1985 resulted largely in negative returns. Similar net returns were obtained in the Texas panicum experiment.