Lack of consistent weed control has been a major limiting factor in the adoption of no-till soybean production. Field studies were conducted at Waseca, MN from 1987 through 1990 to evaluate the efficacy of imazethapyr applied either alone or in combination with other herbicides for weed control in no-till soybean. Fall applications of imazethapyr did not provide acceptable weed control. Imazethapyr applied 2 to 4 wk before planting provided a weed-free seedbed whereas burndown treatments applied 1 to 3 d before planting failed to do so. Early preplant imazethapyr applied during the second week of April did not control weeds as well as imazethapyr applied during the last week of April. Imazethapyr applied alone PRE failed to control weeds adequately. A split application of early preplant plus PRE imazethapyr resulted in excellent weed control, especially when metribuzin was added with each application. Imazethapyr is a promising herbicide for weed control in no-till soybean production.

Hoary cress germination decreased with lower osmotic potential. Knapweed germination was greatest at 0.0 and −0.5 MPa of osmotic potential. Salinity increases up to an electrical conductivity (EC) of 12 dS m-1 had no effect on germination of either species. Hoary cress and knapweed root growth were reduced by decreases in osmotic potential. Hoary cress root growth was not affected by increasing salinity up to an EC of 12 dS m-1. Knapweed root growth was reduced by the initial increase in salinity (4 dS m-1), but not by higher salt concentrations.

Experiments were conducted from 1987 through 1989 to determine the most effective and consistent control of velvetleaf in cotton with soil-applied herbicides. Norflurazon was applied at 1.1 or 1.7 kg ha-1 either preplant (PPI) or preemergence (PRE) or by splitting these rates and applying half PPI and the other half PRE. All methods of norflurazon application were compared with and without a PRE application of diuron at 1.1 kg ha-1. The most consistent control was achieved with PPI norflurazon at either 1.1 or 1.7 kg ha-1 followed by diuron. In 1988, crop injury at 2 wk varied and was 29% or greater for preemergence norflurazon tank-mixed with diuron.

Understory vegetation was studied following treatment by herbicides and fire on grazed pastures within the Cross Timbers vegetation type. Tebuthiuron and triclopyr at 2.2 kg ha-1 were applied in March and June of 1983, respectively. The pastures were burned in late spring of 1985, 1986 and 1987. Frequency of horseweed, rosette panicgrass, and little bluestem increased with both herbicides, but the increase was usually larger with tebuthiuron than triclopyr. Burning as a follow-up to either herbicide had little effect on frequency of rosette panicgrass and little bluestem. Horseweed increased following burning in 1985 and 1987. Standing crop of grasses and forbs increased dramatically following herbicide treatments. Grass production was greater with tebuthiuron, whereas production of forbs and browse was generally greater with triclopyr.

Temporal changes in factors that contribute to the competitiveness of Florida beggarweed in peanuts were studied in 1986 and 1987. Florida beggarweed leaves were unifoliolate to the ninth node and trifoliolate thereafter. Peanuts grew taller than Florida beggarweed until the R-3 stage of peanuts, after which Florida beggarweed height increased logarithmically. Florida beggarweed branching was suppressed by the peanut canopy until the weed overtopped the peanuts. Florida beggarweed dry weight was reduced 80% by peanuts compared with Florida beggarweed grown alone. Peanuts reduced Florida beggarweed leaf area and canopy area. Percent light attenuation as a function of Florida beggarweed canopy area was described by the equation Y = lnX/25.5. Peanut yields in 60 cm of row on either side of a single Florida beggarweed plant were reduced 19%.

Field experiments were conducted in 1986 to 1990 to determine the effect of different rates and application times of BAS 514 and dithiopyr alone and in combination on control of large crabgrass and dandelion in Kentucky bluegrass, tall fescue, and perennial ryegrass. Herbicides evaluated were applied PRE, early POST, and late POST. Results indicated that both herbicides provided excellent PRE control in all years. BAS 514 rates ranged from 0.84 to 0.56 kg ai ha-1. Rates of dithiopyr ranged from 0.43 to 0.56 kg ai ha-1. In addition to crabgrass control, both herbicides controlled dandelion, BAS 514 exhibiting slightly better activity than dithiopyr. BAS 514 at 0.84 to 1.12 kg ai ha-1 and dithiopyr at 0.26 to 0.56 kg ai ha-1 resulted in excellent early POST crabgrass control when applied at the one- to three-leaf stage of crabgrass. BAS 514 and dithiopyr applied late POST (2 to 3 tillers of crabgrass) resulted in 63 to 85% control of crabgrass and 29 to 85% control of dandelion at 10 wk after application. No weed control enhancement was evident from tank mixing the two herbicides. Excellent turf safety was demonstrated by both herbicides on all three turf species.

The critical weed-control period in field seeded cabbage using natural weed stands was 2 wk in 1988 and 4 wk in 1989. Regression analysis showed that the length of weed-free period, weed density, and ambient light reduction by competing weeds were factors affecting cabbage yield. Weeds that emerged after the initial weed-free period shaded the soil and subsequently lowered soil surface temperatures in 1989. Velvetleaf densities of 1.2 and 3.6 plants per m2 that competed all season with cabbage reduced cabbage yields 52% and 71% of the weed-free treatment in 1988 and 76% and 92% in 1989, respectively. Cabbage yields were reduced at all velvetleaf densities seeded 0, 1, and 2 wk after cabbage, but cabbage yield was not reduced when velvetleaf was seeded 4 or 6 wk after cabbage. Cabbage yield was not different between parallel and staggered velvetleaf configurations at 0.6 plants per m2, but was reduced with longer periods of competition. Velvetleaf seed production was prevented with 6 wk weed-free period after cabbage emergence and subsequent destruction of emerging velvetleaf after cabbage harvest.

Field experiments were conducted in Oklahoma to evaluate the effect of three imidazolinone herbicides and metsulfuron on established field bindweed and hard red winter wheat followcrops. Imazapyr at 280 g ai ha-1 and imazethapyr at 560 g ai ha-1 controlled field bindweed from 78 to 100% for 48 wk, but imazaquin at 560 g ai ha-1, metsulfuron at 17.5 g ai ha-1, and 2,4-D plus picloram at 1120 plus 280 g ae ha-1 did not. Imidazolinone herbicides reduced forage and grain yield of wheat seeded 8 to 14 wk after herbicide application. Only imazapyr reduced grain yield of wheat seeded 15 mo after treatment.

Herbicides can persist in the soil and injure sensitive crops planted in the years following herbicide application. The response of sugarbeet to clomazone, imazaquin, imazethapyr, and chlorimuron residues in soil was examined. Clomazone at 1.1 or 2.2 kg ai ha-1 did not reduce yield of sugarbeet planted 1 or 2 yr after application. Imazaquin at 0.07 to 0.28 kg ai ha-1, and imazethapyr at 0.09 to 0.14 kg ai ha-1, can reduce yield of sugarbeet planted 1 yr after application. Imazaquin at 0.07 to 0.14 kg ha-1 caused 28 to 47% sugarbeet injury and imazethapyr at 0.09 kg ha-1 caused 54% injury 2 yr after application in soybean. A 25% yield loss occurred from the imazethapyr treatment. Sugarbeet injury 2 yr after application was greatest when sugarbeet also was planted the year following soybean. Chlorimuron at 0.02 to 0.08 kg ai ha-1 plus linuron at 0.4 to 0.9 kg ai ha-1 reduced yield of sugarbeet planted 1 yr after application when compared with linuron alone, regardless of soil pH. Visible sugarbeet injury of 38 to 66% was still evident from chlorimuron plus linuron treatments 2 yr after application. Sugarbeet should not be planted less than 25 mo following imazaquin, imazethapyr, or chlorimuron application.

Field experiments were conducted in 1988 and 1989 to evaluate timing of POST herbicide application in peanut for annual broadleaf weed control, peanut yield, and net returns. Bentazon tank-mixtures with either acifluorfen or paraquat controlled common lambsquarters, prickly sida, and morningglory species equally when applied either at ground-cracking (GC) or 2 wk after ground-cracking (2WGC). Paraquat controlled common lambsquarters least (32 to 33%). Bentazon plus acifluorfen plus BCH 81508S controlled 82% common lambsquarters at 2WGC compared with 66% control from bentazon plus acifluorfen plus a crop oil concentrate. Lactofen controlled 86% common lambsquarters when applied at GC compared to 34% at 2WGC. All applications applied at 4 wk after GC (4WGC) controlled essentially no annual broadleaf weeds. Higher yields and net returns were generally obtained with earlier herbicide applications. Bentazon tank-mixtures with acifluorfen provided equivalent peanut yields and net returns for GC and 2WGC applications.

The efficacy of herbicides applied broadcast by hand with a soil carrier or sprayed with water carrier were compared for Italian ryegrass control in winter wheat in central Oklahoma. Italian ryegrass was controlled 77 to 100% with BAY SMY 1500, chlorsulfuron, and CGA-131036 applied with both carriers. Metribuzin applied POST with 187 L ha–1 water was less phytotoxic to Italian ryegrass and wheat than with 200 kg ha–1 soil. All herbicides applied with 200 kg ha–1 silt loam soil as carrier at two locations controlled Italian ryegrass 96 to 100%. Increasing herbicide rate, soil carrier quantity, or broadcasting soil-carried herbicide in two directions rather than one did not significantly improve herbicide efficacy over that of conventional spraying.

Preplant-incorporated (PPI) herbicides were applied to suppress annual weeds in new seedings of alfalfa, then additional annual weed control and crop tolerance from selected bentazon treatments were evaluated. Bentazon applied at 0.8 kg ai ha-1 without an adjuvant caused an average of 8% visual injury to newly seeded alfalfa but did not reduce first-harvest alfalfa yields. Bentazon improved common lambsquarters control in newly seeded alfalfa and reduced weed biomass in first-harvest forage. No significant difference in crop injury, weed control, alfalfa yield, or weed yield was observed when bentazon was applied at 0.6, 0.8, or 1.1 kg ha-1. Greater alfalfa injury occurred when bentazon was applied with 1.25% v/v oil-emulsifier mixture, than when applied alone or with 5% v/v 28% liquid nitrogen fertilizer (28% N). Ten alfalfa cultivars did not differ in sensitivity to bentazon applied early postemergence (POST) or POST.

The effects of topsoil thickness on winter annual weed growth and nutrient concentration were assessed for three consecutive years in soybean plots. The topsoil treatments had high fertility levels, uniform textures, and no herbicides were used in the study. Common chickweed composed 75% of the winter annual weed species. Weed biomass production decreased as topsoil thickness decreased from 22.5 cm to 0. Topsoil thickness of 22.5 cm produced 800 kg ha–1 more weed growth than 0 cm topsoil. The weed biomass grown in thicker topsoil had higher total amounts of N, K, Mg, and Ca.

Field research was conducted at Fargo, Langdon, and Prosper, ND to determine carryover of clopyralid applied at 70 to 560 g ae ha-1 in soil as indicated by response of crops planted 1 yr after application. Flax, potato, and safflower growth at Fargo were not affected by clopyralid residues. At Fargo, soybean height, stand, and yield were reduced by residues from clopyralid at 560 g ha-1, and sunflower heads ha-1 and yield were reduced by residues from clopyralid at 280 and 560 g ha-1 and 560 g ha-1, respectively. Potato and sunflower at Langdon and Prosper and lentil at Langdon were not affected by clopyralid residues. Soybean yield at Prosper was not affected by clopyralid residues, but plant height was reduced by residues from clopyralid at 280 and 560 g ha-1. These results indicate that residues from clopyralid applied at labeled cropland rates, of 280 g ha-1 or less, in silty clay, clay loam, and silty clay loam soils in North Dakota probably will not adversely affect the dicot crops tested in these experiments planted 11 mo or more after application.

In 1988, mowing C. thoermeri once at the bud stage, twice at the bud stage, or once at early bloom of the primary inflorescences, eliminated emergence of Rhinocyllus conicus, a weevil introduced as a biological control agent. Mowing at full bloom reduced weevil survival by 78.8%, whereas mowing at senescence had no effect. In 1989, mowing at full bloom or senescence did not affect weevil survival. Dicamba applied at the full bloom or senescence stage did not affect R. conicus survival, whereas hexazinone reduced R. conicus survival when applied at all growth stages.

The effect of glyphosate applied alone and with 2,4-D as a commercial mixture on 30 native or introduced grass species was evaluated. Grass yield averaged 98 and 87% of the untreated controls when glyphosate was applied in the fall at 0.2 or 0.4 kg ae ha-1, respectively, alone or with 2,4-D at 0.35 or 0.7 kg ae ha-1. Western wheatgrass production decreased more than any other species present in a native rangeland site following either a spring or fall glyphosate application. In seeded plots, intermediate wheatgrass was the most and ‘Fairway’ crested wheatgrass the least susceptible to glyphosate plus 2,4-D with average yields of 57 and 97% compared with untreated controls of each species, respectively. Glyphosate reduced the yield of ‘Nordan’ standard crested wheatgrass more than that of Fairway crested wheatgrass or other diploid cultivars. The greater the spring precipitation following a fall application of glyphosate, the less effect of glyphosate on forage yield. Glyphosate plus 2,4-D can be used for weed control in pasture and rangeland provided some yield reduction is acceptable.

In field studies trifluralin and pendimethalin at 1.7 kg ai ha-1 applied PPI controlled itchgrass 87 and 78%, respectively, in late season when averaged over a 2-yr period. Clomazone at 1.1 kg ai ha-1 applied PRE to the soil surface in one year controlled 80% of itchgrass compared with 51% when applied PPI. POST application of 0.15 kg ai ha-1 fluazifop-P, 0.21 kg ai ha-1 haloxyfop, 0.10 kg ai ha-1 quizalofop, and 1.1 kg ai ha-1 diclofop controlled at least 90%. Itchgrass control was less effective with 0.43 kg ai ha-1 sethoxydim and 0.07 kg ai ha-1 clethodim POST and poor with 0.15 kg ai ha-1 imazaquin and 0.07 kg ai ha-1 imazethapyr.

Research was conducted to determine the tolerance of flue-cured tobacco to fomesafen and the potential for weed control in tobacco with fomesafen. Treatments consisted of fomesafen at 0.4 or 0.6 kg ai ha–1 applied pretransplant incorporated (PTI), pretransplant (PRE-T), post-transplant (POS-T), postemergence-over-top (POT), or post-directed (PD). Tobacco injury within 30 d of application was as high as 30%, but tobacco recovered and few significant differences in tobacco yield, grade index, or price were observed except where fomesafen was applied PTI at 0.6 kg ha–1. Tobacco tolerance relative to time of application was generally PRE-T = POT > POS-T = PTI. Florida pusley and large crabgrass control was > 80% for all fomesafen treatments. Yellow and purple nutsedge control was approximately 30% before cultivation.

Field experiments were established to investigate the influence of terbufos on the response of five corn hybrids to postemergence applications of CGA-136872. In 1987, Asgrow RX404, Dekalb DK656, Funk's G4673A, and Pioneer P3165 were tolerant to CGA-136872 when no soil insecticides were applied. In 1988, terbufos was applied at 1.1 kg ai ha-1 in-furrow at planting. Injury was observed on all hybrids following CGA-136872 application in 1988. With the exception of Funk's G4307, all hybrids were tolerant to CGA-136872 in 1989 when no soil insecticide was used. When terbufos was applied in-furrow, injury increased with increasing herbicide rate for these hybrids.

EPTC applied at the time of ‘Saranac AR’ alfalfa establishment resulted in higher levels of crop injury from the octanoic acid ester of bromoxynil applied postemergence compared to alfalfa in areas not treated with EPTC. EPTC applied at 1.7 or 3.4 kg ai ha-1 did not injure alfalfa. At Rock Springs, PA, 0.54 kg ai ha-1 bromoxynil caused 28, 43, and 55% foliar injury in areas treated with 0, 1.7, and 3.4 kg ai ha-1 EPTC, respectively. A similar interaction was observed at Landisville, PA, although the level of injury due to bromoxynil was less severe. EPTC also predisposed ‘WL 316’ alfalfa to bromoxynil injury in greenhouse experiments.