A three-year experiment was conducted near Scottsbluff, NE, to evaluate the selectivity of POST-applied imazethapyr for weed control in alfalfa, birdsfoot trefoil, cicer milkvetch, red clover, sainfoin, and yellow sweetclover. Imazethapyr injured all legumes 15 DAT. Imazethapyr also reduced the height of birdsfoot trefoil, cicer milkvetch, red clover, and yellow sweeclover 28 DAT. Legume first cutting yields were not reduced by imazethapyr and with alfalfa, birdsfoot trefoil, cicer milkvetch, and sainfoin, first cutting yields were increased by imazethapyr. Imazethapyr reduced weed biomass in all legume seedings. Weed biomass in new seedings of alfalfa was reduced more than that of the other legumes.

Field experiments were conducted in 1988, 1989, and 1990 in Greece to investigate the combination of cultural and chemical methods for weed control in soybean. The selectivity of herbicides or the combination of herbicides used was dependent on application rate. Imazaquin applied PRE was selective on soybean even at 0.18 kg/ha, whereas imazethapyr was safer on soybean than imazaquin at 0.22 kg/ha. Metribuzin at 0.37 kg/ha tank-mixed with alachlor, metolachlor, imazaquin, and SAN 582H were not phytotoxic at their recommended rates. All herbicides satisfactorily controlled the weeds in the experiments. The early-season period threshold level for a mixed population of Amaranthus spp. occurred 3.0 to 3.5 wk after weed emergence. Density of Amaranthus spp. of about 270 to 470 plants/m2 caused soybean yield reduction equal to 11 to 35%, respectively. The treatments did not influence the oil content of the soybean seed but in one experiment the protein content was influenced slightly by some of the treatments. The results emphasize the importance of using chemical, cultural, and competition threshold levels of cultural practices for an integrated approach for weed control in soybean.

Normal field applications of both terbufos and nicosulfuron can cause decreased corn tolerance to nicosulfuron because terbufos inhibits nicosulfuron metabolism. In greenhouse studies, applications of 2,4-D at 0.07, 0.14, and 0.28 kg/ha with nicosulfuron reduced terbufos induced foliar injury by more than 50%. Plants treated with nicosulfuron, terbufos, and 2,4-D had significantly higher shoot dry weights than those treated with nicosulfuron and terbufos. When 2,4-D was applied sooner than 24 h before nicosulfuron application or later than 24 h after nicosulfuron application, it did not prevent the interaction. Uptake of 14C-nicosulfuron was increased by the presence of terbufos but was unaffected by 2,4-D. Translocation of 14C-nicosulfuron was low with the highest amounts occurring in the nicosulfuron plus terbufos treatment. Terbufos reduced metabolism of nicosulfuron at 4 and 24 h after treatment compared to plants without terbufos. Metabolism of nicosulfuron in plants treated with terbufos was increased by 2,4-D to a rate equivalent to that in plants not treated with terbufos.

Fringed sagebrush is a native, drought-resistant, increaser species in Saskatchewan pastures and rangelands. Conventional control by cultivating and reseeding is neither highly effective nor sustainable. Two field experiments were conducted in 1988 and 1989 through 1991 to develop a management plan for fringed sagebrush. Comparison of fringed sagebrush control using various applications of clopyralid, dicamba, dichlorprop, fluroxypyr, picloram, triclopyr and 2,4-D, showed control was sufficient using the low-cost herbicide 2,4-D isooctyl ester at 1.5 kg ai/ha. Total yield of crested wheatgrass plus smooth brome was compared and the plots subjected to two applications of 2,4-D yielded the greatest accumulation of grass over the length of the experiments. The economic threshold of fringed sagebrush is the density at which yield is reduced by approximately 290 kg/ha; above this density it is economically viable to use 2,4-D at 1.5 kg/ha to control fringed sagebrush. Grazing practices can aid greatly in management of fringed sagebrush by allowing the forage to out-compete fringed sagebrush.

Field experiments were established at Columbus and near South Charleston, OH to determine the effects of giant ragweed population density on soybean yield and to characterize the development of giant ragweed grown in 76-cm soybean rows. An economic threshold was calculated for Ohio using a common treatment for giant ragweed control in soybean. A cost of $41/ha was estimated for a farmer to apply 0.56 kg/ha bentazon plus 0.28 kg/ha fomesafen plus COC (1.25% v/v). Assuming a soybean value of $0.22/kg, the cost of control was equivalent to 5.4 and 7.1% of the soybean yield in 1991 and 1992, respectively, which corresponded to the yield loss caused by 0.08 and 0.03 giant ragweed plants/m2. The competitiveness of giant ragweed can be at least partly attributed to its ability to initiate and maintain axillary leaves and branches within the shaded confines of the soybean canopy.

Response of clones of Canada thistle from North America and leafy spurge from North America and Eurasia to treatment with chlorsulfuron, clopyralid, and glyphosate was determined. Roots of Canada thistle plants from different locations responded differentially to injury from chlorsulfuron and clopyralid but not to glyphosate. Clones of Canada thistle varied significantly in response to all herbicide treatments. Roots of leafy spurge plants from different locations were differentially susceptible to injury from glyphosate. Clones of leafy spurge varied significantly for all responses to each herbicide. The differential effects of chlorsulfuron, glyphosate, and clopyralid on clones of Canada thistle and leafy spurge suggest that genetically-based differences may account for the failure of the herbicides to kill all plants within collection locations or between collection locations. Cross tolerance to the herbicides was not found in leafy spurge or Canada thistle.

Research was conducted at two sites during 1991 and 1993 at Brandon, MB to determine if sodium bicarbonate antagonizes clethodim or quizalofop efficacy and if ultraviolet light is a factor in any antagonism. Sodium bicarbonate in the spray solution reduced the efficacy of clethodim. However, removal of ultraviolet light partially reversed sodium bicarbonate antagonism of clethodim activity with all adjuvants except crop oil concentrate with or without ammonium sulfate. Amigo, crop oil concentrate plus ammonium sulfate, and Merge were the most effective adjuvants for clethodim with distilled water. However, only the adjuvant crop oil concentrate plus ammonium sulfate overcame sodium bicarbonate antagonism of clethodim. Enhance increased the activity of clethodim when sodium bicarbonate was present in the spray solution but overall was not as effective an adjuvant as crop oil concentrate plus ammonium sulfate. Sodium bicarbonate in the spray solution did not reduce quizalofop efficacy.

Six experiments were conducted in three rice fields near Harrisburg, AR in Poinsett County in 1991 and 1992 to confirm barnyardgrass resistance to propanil and to compare herbicide treatments for control of propanil-resistant barnyardgrass. In all experiments, standard treatments of thiobencarb applied delayed PRE or tank mixtures of propanil + thiobencarb applied POST controlled propanil-resistant barnyardgrass. In five of six experiments, propanil failed to control barnyardgrass at 6 to 8 kg ai/ha (three times use rates) and in three experiments it provided inconsistent control at 11 kg/ha. Emulsifiable propanil at 11 kg/ha frequently controlled resistant barnyardgrass better than the dry flowable formulation. Treatments that consistently controlled propanil-resistant barnyardgrass included propanil tank-mixed with pendimethalin or quinclorac applied POST to two-leaf grass; quinclorac applied alone delayed PRE or POST or applied POST tank-mixed with thiobencarb, pendimethalin, or a formulated mixture of molinate and propanil; a formulated mixture of propanil and molinate applied POST in tank mixtures with thiobencarb or pendimethalin; and fenoxaprop or fenoxaprop-P alone applied POST to four-leaf grass prior to flood establishment. Herbicide treatments that failed to control resistant barnyardgrass included POST applications of a formulated mixture of propanil and molinate alone and propanil in tank mixtures with bromoxynil or triclopyr. These studies confirm that barnyardgrass from several farms in Arkansas have resistance to propanil and identified treatments that control propanil-resistant barnyardgrass.

The absorption of 14C-bentazon and 14C-acifluorfen by individual leaves of velvetleaf was measured from the cotyledons to the most recently developed leaf in plants that had developed seven leaves beyond the cotyledons. Herbicide absorption 1 min after application was greatly enhanced by the organosilicone adjuvant Sylgard 309 explaining previously observed enhanced efficacy and rainfastness by this adjuvant. 14C-herbicide absorption was greatest by the cotyledons and decreased upward to the most recently developed leaf. Absorption of the 14C-Sylgard 309 was similar to that of the 14C-labelled herbicides and was not related to the number of stomata or leaf area covered by the spray droplets. These results are consistent with the hypothesis that the mode of action of Sylgard 309 is to enhance cuticular absorption and not stomatal infiltration.

In a two-year study involving two sites in western Canada, the dissipation of bromoxynil octanoate alone at 0.35 or 0.42 kg phenol equivalent (pe)/ha and the tank mixture of MCPA iso-octyl ester at 0.28 kg ae/ha plus bromoxynil octanoate at 0.28 kg pe/ha was monitored in postemergence-treated triticale. Initial foliar residues on the day after application (three- to four-leaf stage of the crop) were of the order of 14 and 5 mg/kg for MCPA and bromoxynil, respectively. Residues of both herbicides decreased to less than the limit of quantification (0.025 mg/kg) of the analytical method 21 d after application. At crop maturity, herbicide residues were non-detectable in the straw and seed. There was little or no effect on the dissipation of bromoxynil residues due to tank mixing with MCPA.

Experiments were conducted to determine the influence of spray carrier salts, UV light, and temperature on sethoxydim phytotoxicity to oat or yellow foxtail. Spray solution pH and ions present were both important to sethoxydim phytotoxicity to oat. Sodium and calcium salts were antagonistic to sethoxydim phytotoxicity only when the spray carrier pH exceeded 7. Ammonium salts and ammonium hydroxide were synergistic with sethoxydim, and the synergism was independent of spray solution pH. Ammonium sulfate, but not ammonium hydroxide, overcame sodium bicarbonate antagonism of sethoxydim. The antagonism of sethoxydim phytotoxicity by sodium bicarbonate was greatest in the presence of UV light and most pronounced when treated plants were exposed to mid-day sunlight. Sodium bicarbonate or low temperature may reduce the speed of sethoxydim absorption allowing for greater UV degradation of unabsorbed sethoxydim on the leaf surface.

Field experiments were conducted in 1991 and 1992 to evaluate corn tolerance to nicosulfuron following in-furrow or surface-band applications of seven soil-applied insecticides. The organophosphate insecticides evaluated included terbufos (15G and 20CR formulations), phorate, chlorpyrifos, fonofos, and DPX-43898, as well as the synthetic pyrethroid tefluthrin. Potential for a nicosulfuron/ insecticide interaction to injure corn was ranked as follows: terbufos 15G = phorate > terbufos 20CR > fonofos. Chlorpyrifos, DPX-43898, or tefluthrin followed by nicosulfuron caused no significant corn injury. Corn injury and yield reduction were greater in corn treated in-furrow compared with surface-band. Soil moisture at nicosulfuron application was more influential in causing corn injury and loss of yield than growth stage of corn at nicosulfuron application.

The influence of incorporation vs no incorporation on the efficacy of granular triallate applied in mid-October at 1400 and 1700 g ai/ha to control wild oat was evaluated in spring wheat in west central Saskatchewan over a 7-yr period. All fall-applied triallate reduced wild oat panicles and fresh weight, and increased yield compared to untreated checks. With applications in standing wheat stubble there was no difference in wild oat control from incorporation versus no incorporation. All triallate treatments reduced wild oat panicles and fresh weight by over 95%, and resulted in wheat yield increases ranging from 29 to 67%. In tilled fallow, incorporated granules provided better wild oat control than when there was no incorporation. Wheat yield increases ranged from 50 to 85% for triallate treatments with yield for incorporated triallate approximately 15% greater than non-incorporated. The rate of triallate did not affect the level of wild oat control achieved with either incorporation method. In separate tolerance studies triallate incorporation method did not affect spring wheat emergence or subsequent development.

Fall application of a PRE herbicide offers professional lawncare applicators additional flexibility in scheduling necessary weed control operations. A 3-yr field study was established on common Kentucky bluegrass in Urbana, IL to examine the effectiveness of fall- or spring-applied prodiamine and DCPA for spring large and smooth crabgrass control. Prodiamine was effective for crabgrass control in turf (≥ 91% control) when applied in spring at ≥ 0.4 kg/ha or when it was applied in the fall at ≥ 0.6 kg/ha (≥ 82% control). In most cases, fall-applied prodiamine at the 0.8 kg/ha rate (≥ 91% control) controlled crabgrass as well as spring-applied DCPA at the 11.8 kg/ha rate (≥ 94% control). Little reduction in turf quality (≥ 8.3) occurred when prodiamine was applied in the fall at 0.8 kg/ha or less. Only when prodiamine was applied at 2.2 kg/ha was there significant quality loss (7.3) with spring applications. In a second experiment to evaluate split fall and spring prodiamine applications for crabgrass control, all split applications had 100% crabgrass control which was not significantly different from single applications of ≥ 1.4 kg/ha.

Turf managers use prodiamine to control annual grasses in mature turfs. Earlier, evaluations of prodiamine have indicated it has an elevated soil persistence and high activity on susceptible species. This persistence raises concern for prodiamine's effect on juvenile turf. An experiment was established to evaluate the effect of prodiamine on juvenile Kentucky bluegrass turf. Significant loss of quality occurred on turf less than one year old receiving a single application of prodiamine at ≥ 1.4 kg/ha. Split applications of prodiamine did not significantly decrease turf quality. Prodiamine at 0.8 and 2.2 kg ai/ha and DCPA at 23.5 kg ai/ha, applied in the fall the previous three years, significantly reduced the number of overseeded Kentucky bluegrass seedlings two years after planting. In a subsequent study, prodiamine at ≥ 0.8 kg/ha and DCPA at 23.5 kg/ha applied once the previous fall significantly reduced the number of overseeded Kentucky bluegrass dlings 56 d after planting. An analysis of prodiamine rate versus seedling density was found to be significantly correlated (r2 = 0.79).

Experiments were conducted to evaluate the effect of a 2.5-cm simulated rainfall 0.05, 0.25, 0.5,1, 3, 6, and 24 h after POST applications of AC 263,222 to sicklepod. Fresh weight reductions were directly related to increasing AC 263,222 rates and rain-free intervals. Fresh weight reductions with 9, 18, 36, 54, and 72 g ai/ha AC 263,222 were 32, 47, 55, 59, and 67%, respectively, with the rain-free treatment. A simulated rainfall 0.05 h after POST application lowered fresh weight reductions with 9, 18, 36, 54, and 72 g/ha AC 263,222 to 5, 7, 19, 23, and 28%, respectively, of the untreated control. As AC 263,222 rates increased, a simulated rainfall shortly after POST application was less detrimental. At 18 g/ha of AC 263,222, a 3-h rain-free interval was necessary for fresh weight reductions equivalent to the rain-free control. As the rate of AC 263,222 increased to 54 g/ha, the rain-free interval for fresh weight reductions equivalent to the rain-free control was reduced to 1 h. Radiolabeled studies indicated that at 3 h after application an equivalent amount of 14C was accumulated in the plant as compared with the rain-free control. The correlation coefficients for fresh weight reductions and 14C in the plant were r = 0.53, 0.75, 0.68, 0.74, and 0.70 at rates of 9, 18, 36, 54, and 72 g/ha AC 263,222, respectively.

The relative sensitivity of various crops and weeds to celery root residue incorporated into soil was determined in greenhouse experiments. A range of concentrations was used to determine the percentage of celery residue needed to cause a 50% reduction in plant growth (I50). The most sensitive weed was spiny amaranth and the least sensitive was common purslane. The most sensitive crop was radish and the least sensitive was celery. Selectivity was calculated as crop I50/weed I50 and varied from a maximum of 13 for celery and spiny amaranth to a low of 0.4 for radish and common purslane. Selective weed suppression might be obtained when celery residue is present.

In 1991 and 1993, tolerance of ‘Zenith’ and ‘Merit’ sweet corn to 35 g ai/ha nicosulfuron post-directed (PDIR) 0, 5, 10, and 15 cm up the corn stalk or applied POST was determined. In 1991, nicosulfuron applied POST to Zenith caused approximately 30% visible injury, 30% height reduction, and 50% reduction of U.S. No. 1 marketable ear weight. In 1991 no visible injury was observed in the PDIR treatments. Zenith was not injured by any treatment in 1993. Both years, Merit was killed by nicosulfuron applied POST. In 1991 and 1993, nicosulfuron PDIR 0 and 5 cm up the corn stalk of Merit caused approximately 5% and 65% visible injury, respectively, and resulted in yield loss. PDIR application increased nicosulfuron tolerance of moderately tolerant Zenith but did not improve that of least tolerant Merit.

Mixtures of herbicides have been proposed as strategies to prevent or delay the evolution of resistance to the resistance-prone sulfonylurea and imidazolinone herbicides that inhibit acetolactate synthase. These herbicides have become or are becoming widely used in soybean, wheat, rice, and other major crops. For a mixture to be efficacious in preventing resistance, the less resistance-prone component(s) should have the following traits compared to the vulnerable herbicide: a) control the same spectra of weeds; b) have the same persistence; c) have a different target site; d) be degraded in a different manner; and e) preferably exert negative cross-resistance. We compared the proposed mixing partners for use with several widely used acetolactate synthase inhibiting herbicides to these criteria and found that: a) all have somewhat different weed spectra; e.g. none control common cocklebur as well as imazaquin or imazethapyr in soybean, or kochia as well as chlorsulfuron in winter wheat; b) all are far less persistent than these vulnerable herbicides. Less persistent sulfonylureas are now on the market but are in limited use. Late in the season, the mixing partner is not present while the vulnerable herbicide remains active; c) most have different target sites; d) in soybean most mixing partners are degraded differently than vulnerable herbicides. In wheat virtually all herbicides used without safeners are degraded by monooxygenases, thus it is impossible to meet this criterion in this crop; e) none of the mixing partners exert negative cross-resistance. The present mixtures may have superior or more cost-effective weed control properties than the acetolactate synthase inhibitors used alone, but they do not meet all the criteria for resistance management. Not meeting the key criteria of identical control spectra and equal persistence aggravates future resistance problems, as has happened with insecticides.

Weed scientists regularly attend conferences, symposiums, and workshops to communicate with colleagues about their current weed research programs. Communication of research can be hindered by poor visual aids. Computer programs, film recorders, and color printers have greatly increased the ease of visual aid production but have also increased the opportunity to prepare incomprehensible presentations. The size of the text, the amount of information presented, and the contrast between the text color and background color are the most important factors that affect the legibility of visual aids. Text, tables, and graphs should be short, simple, and legible. Computers and film recorders are not essential to produce good visual aids. The greatest assets in the production of visual aids are common sense, familiarity with the production equipment, sufficient preparation time, and critical assessment of the visual aids well in advance of the presentation date.