Field studies were conducted in 1991 and 1992 to determine potential soybean injury due to 2,4-D ester at 560, 1120, and 1680 g ai/ha applied 0, 7, and 14 d before planting (DBP). Delayed emergence and increased injury of soybean were observed as 2,4-D rate increased and interval between application and planting decreased. Delay in emergence ranged from 0 to 67% and 0 to 50% in 1991 and 1992, respectively. Injury at 15 days after planting (DAP) combined over years ranged from 0 to 61%. Minimal (0 to 8%) delay in emergence and minimal (0 to 5%) injury at 15, 30, 45, and 60 DAP occurred when 2,4-D at 560 or 1120 g/ha was applied 7 or 14 DBP. No significant yield reduction occurred due to 2,4-D rate, application timing, or their interaction.

Torpedograss has invaded fine turfgrasses in the Southern U.S. due to its tolerance to most commonly used turfgrass herbicides. Research was conducted to determine torpedograss and ‘Tifway’ bermudagrass tolerance to quinclorac and tank-mix combinations with other turf herbicides. Quinclorac rates in excess of 2.2 kg ai/ha were required for control (≥ 80%) of torpedograss. Sequential applications were more effective than single applications. Generally, sequential applications made 3 wk after the initial were more effective than delaying sequential applications until 4 wk after the initial application. Tifway bermudagrass injury from quinclorac applied at 4.5 kg/ha, or at 2.2 kg/ha followed by a sequential application of 1.1 or 2.2 kg/ha, was observed at 4 to 10 wk; however, turf recovered thereafter. Sequential applications of quinclorac plus imazaquin (1.1 + 0.6 kg/ha) increased torpedograss control (approximate 35%) as compared to quinclorac plus MSMA (1.1 + 1.1 kg/ha) but also decreased turf quality versus quinclorac applied alone or in combination with MSMA. Quinclorac applied at 2.2 kg/ha followed by 1.1 kg/ha applied 3 or 6 wk after the initial controlled torpedograss best with least reduction in bermudagrass quality. Quinclorac is the first herbicide reported to selectively control torpedograss in bermudagrass turf.

Experiments were conducted in the greenhouse and the field to determine if a seaweed extract and its component alginates could enhance the activity of sethoxydim on barley (five- to six-leaf stage). In greenhouse trials, sethoxydim with 0.5% oil concentrate was applied at 0.05, 0.1, and 0.15 kg ai/ha; in field trials, sethoxydim with 0.5% oil concentrate was applied at 0.1, 0.2, and 0.3 kg/ha. In both sets of trials the seaweed extract was applied at a rate of 1 and 2 L/ha, and the alginates were applied at 250 and 500 g/ha. When either the seaweed extract, or the calcium ammonium salt of alginic acid was used as an adjuvant a significant increase in sethoxydim activity was usually observed. At the highest rates of these adjuvants, sethoxydim (0.2 kg/ha) activity increased from 59% control (1321 g/m2 fresh weight) with only oil concentrate, to 87% control (224 g/m2 fresh weight) with seaweed extract, or 89% control (184 g/m2 fresh weight) with the calcium ammonium salt of alginic acid. Sodium salts of alginic acid, both low and medium viscosity, were much less effective.

In field studies conducted over two years, soybean cultivars ‘Deltapine 415’, ‘Forrest’, ‘Asgrow 6785’, ‘Centennial’, 'Sharkey’, ‘Terra Vig 616’, ‘Hartz 6686’, and ‘Pioneer 9791’ responded similarly to POST application of AC 263,222. With supplemental overhead irrigation of 5.1 cm weekly for 4 wk initiated 21 d after herbicide applications, mature soybean height for the cultivars averaged 18% less than that of the untreated check for 27 g/ha AC 263,222, but only 8% less when not irrigated. Although nonirrigated soybean seed yield following AC 263,222 application the first year was not reduced compared with the untreated check, with irrigation seed yield reductions of 12 and 32% were noted for 13 and 27 g/ha AC 263,222, respectively. Seed yield the second year was not negatively affected with herbicide application whether soybean was irrigated or not irrigated. For individual years, seed yield for the untreated irrigated and nonirrigated checks was similar. In the first year soybean yield following AC 263,222 at 13 and 27 g/ha with irrigation was 16 and 30% lower, respectively, than when soybean was not irrigated. Decreases in soybean 100-seed weight accompanied the yield reductions.

Woolly cupgrass control with acetochlor, alachlor, and metolachlor in corn was evaluated at Stratford, IA from 1985 through 1990. Averaged over application techniques, acetochlor at 3.4 kg/ha controlled more than 85% of woolly cupgrass five out of six years, whereas alachlor at 4.5 kg/ha and metolachlor at 3.4 kg/ha controlled more than 85% of this weed one and two years out of six, respectively. Herbicide incorporation did not consistently improve woolly cupgrass control. PRE applications were more effective than incorporated treatments in years with greater than 7 mm rainfall occurring within 3 d after application.

DPX PE350, an experimental herbicide, has shown excellent potential for controlling a wide range of problem broadleaf weeds in cotton. PPI, PRE, and POST applications of DPX PE350 at 0.1 and 0.2 kg ai/ha were evaluated under weedfree conditions in 1991 and 1992 for effects on ‘Paymaster HS26’ cotton growth, yield, and fiber quality. In 1991, DPX PE350 applied PPI, PRE, or POST did not affect cotton population, height, yield, or fiber quality. In 1992, DPX PE350 applied PPI at 0.1 or 0.2 kg/ha or PRE at 0.2 kg/ha injured the cotton and reduced yield and micronaire value.

Field experiments were conducted in Michigan, Minnesota, and Wisconsin in 1990 to explore interactions between nicosulfuron applied POST and terbufos insecticide at 0.06 or 0.11 g ai/m of row applied in-furrow on ‘Pioneer 3751’ field corn and ‘Jubilee’ sweet corn. Nicosulfuron at 0, 70, and 140 g ai/ha plus nonionic surfactant and 28% nitrogen fertilizer was applied to both corn types. Field corn response to nicosulfuron and terbufos was similar at all locations, whereas sweet corn injury varied with location. Nicosulfuron injured field corn more when applied at the four-leaf than the three-leaf stage. Injury to both corn types increased as nicosulfuron rate increased or when applied following terbufos. Nicosulfuron at 140 g/ha without terbufos did not reduce yield of either corn type; however, corn previously treated in-furrow with terbufos reduced yield.

Weed management experiments with kidney beans were conducted at one irrigated site in 1991 and at two irrigated sites near Staples, MN during 1992. Green foxtail was the most difficult weed to control at the three research sites which agrees with survey results from dry bean growers regarding their worst weed problems. Hairy nightshade increased rapidly when weed management methods were reduced. Dry bean seed yields were highest in cultivated check plots on the farmer's field and in conventional practices plots at the Irrigation Research Center. Net economic returns, averaged over 1991 and 1992, for producing kidney beans at the Irrigation Research Center were $899/ha using conventional practices, $791/ha with cover crop practices, $734/ha with cultivated checks, $690/ha with herbicides only, and $208/ha on weedy checks. Kidney beans are an economical crop for North Central growers, but adequate weed management technologies are necessary for profitable production.

In greenhouse studies, tralkoxydim applied POST at 100 to 300 g ai/ha during the three-to four-leaf stage of development were differentially toxic to three Hordeum species. Tralkoxydim severely injured wall barley by cessation of growth and death of the whole plant. Hordeum spontaneum, barley, and wheat were less affected by the herbicide in declining order, respectively. However, 4 wk after treatment, full recovery was observed in barley and wheat, but not in H. spontaneum, as reflected in the shoot fresh weight. Tralkoxydim could be considered as a selective herbicide in wheat and barley fields for the control of wall barley.

The response of oat, foxtail millet, proso millet, and sunflower to atrazine and clomazone applied the previous fall was investigated two years in field studies near Akron, CO and Sidney, NE. Foxtail millet biomass, and proso millet and sunflower grain yields were not reduced when these crops were seeded into soil that had been treated the previous fall with atrazine and/or clomazone at rates of 0.6 or 1.1 kg ai/ha. Forage yield of oat was reduced 11 to 18% by some treatments, but this effect was not consistent over years or sites. Treatments containing 1.1 kg/ha of atrazine provided 1 to 5 wk of residual weed control in foxtail millet, proso millet, and sunflower. The study indicated that producers have flexibility in crop selection when using atrazine and clomazone in reduced- and no-till production systems.

A range of herbicide treatments was evaluated for long-term control of rush skeletonweed, a perennial weed of crops and pastures in North and South America, the Mediterranean region, central Europe, and Australia. Clopyralid (75 to 300 g ai/ha) and clopyralid mixtures with 2,4-D, MCPA, or dicamba were effective, resulting in survival rates of 0 to 4% for the most successful treatments applied for three consecutive seasons. Metsulfuron (9 g ai/ha) and 2,4-D (850 g ai/ha) significantly reduced survival when applied at high rates for three years. Barley yield in the season following control was increased by up to 195 to 199% of yield from untreated plots. Evidence was found for differences in herbicide susceptibility between narrowleaf and broadleaf forms of rush skeletonweed.

Field studies were conducted to evaluate weed control with paraquat and glyphosate applied at various rates alone and in combination with residual herbicides. Morningglory, prickly sida, and hemp sesbania control 28 d after treatment was similar regardless of herbicide treatment. In contrast, barnyardgrass control when paraquat was tank mixed with pendimethalin plus imazaquin was equal to that of paraquat alone but less than that for tank mixtures with metolachlor plus metribuzin plus chlorimuron or metolachlor plus metribuzin. Barnyardgrass control and soybean yield when paraquat was applied at 1050 g ai/ha in combination with metolachlor plus metribuzin plus chlorimuron or metolachlor plus metribuzin was greater than when the same residual herbicide treatments were applied with paraquat at 350 g/ha. Yield following glyphosate at 840 and 1120 g ai/ha in combination with residual herbicides was no greater than when glyphosate was applied alone, which was reflective of barnyardgrass control. Tank mixtures of glyphosate at 1680 g/ha with metolachlor plus metribuzin plus chlorimuron or metolachlor plus metribuzin resulted in soybean yield higher than for glyphosate alone. Regardless of the glyphosate and residual herbicide combination, soybean yield was no greater than when paraquat was applied at 350 g/ha in combination with metolachlor plus metribuzin plus chlorimuron.

Experiments were conducted under controlled environment and field conditions to evaluate the influence of growth stage and fluroxypyr dosage on control of field bindweed. In controlled environment studies fluroxypyr effectively controlled 8- to 12-leaf field bindweed. Shoot number, length, and dry weight, and root dry weight decreased as herbicide dose increased. The estimated ED50 (effective dose for 50% reduction) values for shoot and root dry weight were 50 and 33 g ai/ha, respectively. The ED50 for shoot length was 98 g ai/ha. Fluroxypyr was applied at rates from 0.2 to 0.4 kg/ha under field conditions to field bindweed at selected stages of growth. Regardless of herbicide dosage, fluroxypyr applied at the late flowering stage of growth controlled field bindweed better than when applied at the bud or early flower stage. Corn grain yield increased as a function of fluroxypyr dose in 1988 but not in 1987. Dry weight of roots and shoots of field bindweed harvested one year after treatment decreased with increasing rates of fluroxypyr. These studies demonstrate the potential of fluroxypyr for the control of field bindweed.

Field studies were conducted for three years in each of two successive experiments and analyzed to determine net return from stale seedbed plantings of soybean. Treatments in the first experiment were early May and late May/early June plantings in seedbeds that had combinations of tillage at various times between harvest and planting, incorporation of trifluralin, or no preplant tillage. Treatments in the second experiment were irrigated and nonirrigated stale or no-till seedbed plantings with weed control treatments that included POST cultivation plus combinations of preplant foliar-applied (PFA) glyphosate, PRE metribuzin, and POST herbicides. Results indicate that 1) early planting of soybean resulting from use of a stale seedbed will result in higher net returns when irrigation is used, 2) use of a wheat cover crop does not justify the expense, 3) soybean planted in a no-till seedbed will result in net return similar to that from plantings in fall-tilled, spring-tilled, or prepared seedbeds, 4) use of only a PFA herbicide plus POST cultivation in a stale seedbed planting where competitive weeds such as common cocklebur appear later will result in a significant reduction in net returns, and 5) use of PRE herbicides in conjunction with PFA herbicide and POST cultivation in a stale seedbed planting will result in the highest net return with the least input.

Blackbrush acacia and huisache, two troublesome woody legumes on Texas rangelands, could be distinguished on conventional color aerial video imagery. The integration of a global positioning system with the video imagery permitted latitude/longitude coordinates of blackbrush acacia and huisache infestations to be recorded on each image. Global positioning system coordinates were entered into a geographic information system to map blackbrush acacia and huisache populations over an extensive rangeland area.

One year after application under irrigated conditions, atrazine at 1.2 kg/ha injured oat but there was no effect after two years. On dryland, wheat and barley were injured for up to two years after atrazine was applied at 1.5 kg/ha. Atrazine concentrations in the soil were related to accumulated rainfall in an exponential equation. The equation predicted that, under the most severe drought conditions ever recorded for southern Alberta, injury to cereal crops could occur for at least three years after atrazine application at 1.2 to 1.5 kg/ha. Cyanazine did not injure subsequent crops under either irrigated or dryland conditions.

The efficacy of reduced rates of POST herbicides for weed control in sweet corn was evaluated over a three-year period in field studies conducted at the Horticultural Experiment Station, Simcoe, Ontario. POST applications of metolachlor/cyanazine, cyanazine/atrazine and metolachlor/atrazine at 1/2X and 1/4X of labelled rates controlled broadleaf weeds comparable to that of standard labelled rates. Control exceeded 94% each year. Annual grass control was reduced with below-label rates, especially for cyanazine/atrazine and metolachlor/atrazine. A 1/2X application of nicosulfuron/rimsulfuron, following the 1/4X rate of cyanazine/atrazine, significantly improved grass control, compared to cyanazine/atrazine applied alone. Below-label rates did not result in decreased sweet corn yields.

Combinations of rotary hoeing, cultivation, and band- or broadcast-applied herbicides were compared for weed management in corn at 64 locations in Iowa from 1987 to 1991. Cultivation alone resulted in denser weed populations than herbicide treatments at 41% of the locations; however, corn yields were reduced at only 22% of the locations when weeds were controlled mechanically rather than with herbicides. Compared with broadcast applications, herbicides applied in a band resulted in increased weed populations at 8% of the locations; however, corn yields were reduced at only 1% of the locations.

Cogongrass [Imperata cylindrica (L.) Beauv. # IMPCY] is an aggressive, pernicious, rhizomatous perennial in the Poaceae (Graminae). It is native to tropical and subtropical areas of the eastern hemisphere. Introductions of cogongrass into the southeastern United States have been tracked to several separate sources, both accidental and intentional, in southern Alabama, southern Mississippi, and Florida. It was found to be unacceptable for use as a forage and in erosion control. Cogongrass is a highly variable species and has adapted to a variety of environmental conditions in its native and introduced range. Today cogongrass infests 200 million ha in Asia, several thousand ha in the Southeastern United States, and over 500 million ha worldwide. It has been reported to be a weed problem in many annual and perennial crops. In addition to competing for light, water and nutrients, cogongrass interference is caused by alleopathy and physical injury when rhizome apices penetrate crop roots, bulbs, and tubers. Holm et al. designated cogongrass as the world's seventh worst weed.