Field studies were conducted to evaluate the effects of chlorimuron + linuron combinations on soybean growth and yield. PRE applications of chlorimuron + linuron were applied at rates of 0.03 + 0.31, 0.04 + 0.50, 0.05 + 0.62, and 0.10 + 1.24 kg ai/ha. Soybean emergence was not reduced by any herbicide rate. Plant heights were significantly reduced by all rates 5 WAT but the plants recovered from this injury by 19 WAT. Pod production and yield were not reduced by chlorimuron + linuron combinations.

The dinitroaniline herbicides, trifluralin and pendimethalin, are applied to approximately 90% of land seeded to cotton on the Texas Southern High Plains. Trifluralin and pendimethalin at 0.6 and 1.1 kg ai/ha were applied annually to plots from 1983 through 1994. Cotton stand counts, lint yield, and fiber quality varied from year-to-year due to environmental conditions. Differences in lint yield or fiber quality over the 11-yr period were not related to herbicide applications.

Field experiments evaluated barnyardgrass, broadleaf signalgrass, and rhizomatous johnsongrass control with clethodim applied with Agri-Dex® crop oil concentrate at 1.0% v/v, the adjuvant Dash® at 1.0% v/v, the methylated seed oil Sun-It II® at 1.0% v/v, a blend of silicone surfactant plus methylated seed oil (Dyne-Amic® at 0.5% v/v) or nonionic surfactant (Kinetic® HV at 0.125% v/v), two silicone surfactants (Sylgard® 309 and Silwet L-77® surfactant) at 0.125% v/v, two other conventional nonionic surfactants (Latron AG-98™ and Induce®) at 0.25% v/v, and the acidified soya phospholipid LI-700®. When compared with the conventional nonionic or silicone-based surfactants and LI-700, clethodim at 70 g ai/ha controlled barnyardgrass more effectively when applied with Dash or Sun-It II. Broadleaf signalgrass and rhizomatous johnsongrass were controlled more effectively when clethodim was applied with Agri-Dex, Dash, Sun-It II, or Dyne-Amic. Clethodim at 70 g/ha applied with Dash or Sun-It II controlled grasses equally or greater than clethodim at 140 g/ha.

Success of postemergence weed management often depends upon application timing and weed seedling size. To develop a predictive tool for estimating green foxtail development and optimizing timing of management operations, seedling growth was monitored in fields for two years, as well as in a single greenhouse experiment, and compared with elapsed thermal time (growing degree days, GDD, base 10 C). The relationship between seedling height (mm) and GDD was similar both years and could be described by the following equation: Height = (-0.27 + 0.033 * GDD)2. A comparable equation described seedling growth in a greenhouse. Leaf number was linearly related to GDD. Green foxtail in corn was controlled with nicosulfuron applied at seven intervals between 100 and 450 GDD after corn planting in 1993 and 1994. In 1993 corn yield losses due to green foxtail interference were least when nicosulfuron was applied 200 to 300 GDD after planting, at which time green foxtail height was 50 to 100 mm. In 1994 corn yield losses were minimized if nicosulfuron was applied any time before 300 GDD.

Seedling emergence was characterized for five weeds that infest summer annual crops in the central Great Plains as affected by crop canopy or tillage. The study was established in winter wheat stubble between 1987 and 1990, with seedling emergence recorded weekly between April 1 and November 1. Kochia emerged primarily from early April to late June, whereas green foxtail, wild-proso millet, and redroot pigweed began emerging in late May and continued until August. Volunteer wheat emerged throughout the growing season. Tillage did not affect the emergence pattern of any species, but the numbers of kochia, volunteer wheat, and green foxtail seedlings were increased in no-till. Conversely, wild-proso millet emergence was greater with tillage. Only volunteer wheat's emergence was affected by crop canopy, as fall emergence of volunteer wheat was more than three times greater in corn than in proso millet.

A field experiment was conducted over five years to determine the effect of season-long kochia interference on oat yield and quality. Kochia interference did not affect oat height, test weight, 500-kernel weight, or groat percentage. Similarly, ash, starch, and total β-glucan percentages in oat groat were not affected by kochia interference. Oat grain yield was reduced in 1991 and 1994 by 30 kochia plants/m2, the highest density. Lipid and protein content were not affected by kochia except in 1992 where protein content was reduced and lipid content was increased by kochia.

The efficacy of the safeners naphthalic anhydride (NA), CGA-92194, and CGA-133205 as protectants of grain sorghum and of NA, R-29148, CGA-154281, and dichlormid as protectants of corn against injury from the chloroacetamide herbicide, SAN 582H, was evaluated under greenhouse conditions. SAN 582H applied alone reduced the shoot growth of ‘Funk G522DR’ and ‘Funk G623’ sorghum, but had no effect on the growth of the ‘GP-10’ genotype of sorghum. Corn (‘Northrup-King 9283’ hybrid) was considerably more tolerant than grain sorghum to SAN 582H. The rate of SAN 582H causing 50% reduction of corn shoot height (GR50) was 5.1 kg/ha as compared to 1.1 kg/ha for grain sorghum. NA applied as seed dressing at 5 or 10 g/kg seed, provided moderate protection to ‘G522DR’ and ‘G623’ sorghum and no protection to corn against SAN 582H injury. Dressing of sorghum seeds with CGA-133205 provided moderate protection to G522DR sorghum, whereas seed-applied CGA-92194 provided moderate protection to G623 sorghum against SAN 582H. The dichloroacetamide safeners R-29148, dichlormid, and CGA-154281 were all effective as protectants of corn against SAN 582H injury. These results demonstrate that, as with other chloroacetamide herbicides, the tolerance of corn and grain sorghum to SAN 582H can be enhanced with the use of safeners of the dichloroacetamide type and oxime ether type, respectively.

Preplant control of mannagrass was greater than 90% with clethodim, glyphosate, sethoxydim, and sulfosate. Glyphosate at 0.5 to 1.0 kg ai/ha controlled mannagrass greater than 97%, and was not increased with any adjuvant. Fenoxaprop applied POST controlled mannagrass 97% but injured rice 33%. Except for fenoxaprop-ethyl, all POST treatments increased rice yields at least 1560 kg/ha more than the non-treated check. Southern watergrass was controlled 79 and 89% with 1.0 kg ai/ha glyphosate and 4.5 kg ai/ha sulfosate, respectively, while control was less than 55% with other herbicides.

Research was conducted at the Brandon Research Centre to determine the effect of spray solution pH or adjuvants on the efficacy of two cyclohexanedione (CHD) herbicides, clethodim and tralkoxydim, and two aryloxyphenoxypropionate (APP) herbicides, fenoxaprop-P and quizalofop, and if ultraviolet light is a factor influencing their activity. CHD herbicide efficacy decreased as spray solution pH increased above 7. APP herbicide efficacy was not affected by spray solution pH, probably due to their formulation as proherbicide esters. The choice of adjuvant affected CHD herbicide efficacy but not APP herbicide efficacy. Amigo®, Canplus-411® plus ammonium sulfate, and Merge® were usually the most effective adjuvants with the two CHD herbicides. Physical removal of ultraviolet light did not improve APP herbicide efficacy but did improve CHD herbicide efficacy.

This study characterized seedling emergence of downy brome from August to early December over a 6-yr period. Seedlings were counted weekly in quadrats established in winter wheat stubble at Akron, CO. Seedling emergence varied among years, which was caused by erratic seasonal precipitation. Producers delay planting of winter wheat to reduce downy brome density in the crop, but in only 1 yr out of 6 would producers have benefited from this control strategy. Furthermore, delayed planting has negative crop consequences: less grain yield and more susceptibility to plant diseases and wind erosion because of less fall plant growth. Because fall precipitation is erratic in the semiarid Great Plains, other control strategies, such as nitrogen placement and increased seeding rates of winter wheat, would be more effective for downy brome management, yet not detrimental to winter wheat production.

Field studies were conducted for two years at two locations near Pendleton and Moro, OR to evaluate the influence of single sub-surface nitrogen (N) fertilizer application timings and multiple N applications on downy brome and winter wheat growth and yield. N applications in fallow, at planting, during the crop season, and several split N application timings were compared to evaluate downy brome interference in winter wheat. N application rates varied between locations as a function of average annual precipitation and accepted agricultural practice. Pendleton and Moro were considered high and low precipitation sites, respectively. At Pendleton in a year of above average precipitation, N applied at planting, in-crop, or split applications of N with part of N applied at planting and part in-crop, increased downy brome dry matter production compared to N applied in fallow. Downy brome infestation eliminated otherwise positive wheat yield benefits of split N application compared to the conventional commercial practice of N application in fallow. In a year of moderate precipitation, N applications at planting, in-crop, or split N applications did not benefit wheat yield compared to N application in fallow, but downy brome dry matter was increased. In a dry season, N rates and timings did not increase downy brome dry weight or wheat grain yield. In the absence of downy brome, alternative N application techniques increased wheat yield only under high growing season precipitation.

The efficacy of sulfonylurea herbicides impregnated on granular fertilizers applied PPI or POST was compared to broadcast spray applications for annual broadleaf weed control in winter wheat. Henbit and bushy wallflower were controlled by chlorsulfuron or triasulfuron impregnated onto diammonium phosphate granular fertilizer applied PPI. Efficacy of these herbicides for annual broadleaf weed control was reduced by applying them POST with granular urea fertilizer carrier instead of with water carrier.

Field studies were conducted in 1993 and 1994 to evaluate sicklepod control with combinations of imazaquin + metribuzin at lower than normal use rates. Soybean was seeded in late-May to early-June each year and imazaquin and metribuzin were applied PPI alone at 0.75 and 1x and 0.5, 0.75, and 1x their registered rates, respectively, and in factorial combinations of their 0.5 and 0.75x rates. The registered (1x) rates for imazaquin and metribuzin on this soil type are 0.14 and 0.43 kg/ha, respectively. Several standard sequential treatments and flumetsulam + trifluralin PPI at 0.06 + 0.70 and 0.07 + 0.95 kg/ha were included for comparison. Sicklepod control and soybean seed yield responses differed between 1993 and 1994. In 1993, the combinations of imazaquin + metribuzin averaged 90% control 6 wk after planting (WAP) and soybean seed yield increased 75% compared to the untreated check. Imazaquin + metribuzin at their respective 0.5x rate was as effective as any treatment evaluated. In 1994, sicklepod control was generally lower with all treatments. Soybean seed yield was reduced due to sicklepod interference with soil-applied treatments alone. However, imazaquin + metribuzin at their respective 0.75x rate provided sicklepod control levels and reductions in weed biomass similar to those observed with flumetsulam + trifluralin at 0.07 + 0.95 kg/ha and the sequential treatments, and increased soybean seed yield 19% compared to the untreated check.

Field experiments were conducted to determine whether residual sulfonylurea herbicides applied at cheat suppression rates affect hard red winter wheat forage production and grain yield. Triasulfuron at 30 g/ha or chlorsulfuron plus metsulfuron at 26 g/ha applied PRE and metribuzin applied early POST alone at 280 g/ha or tank-mixed with triasulfuron at 158 + 30 g/ha or chlorsulfuron plus metsulfuron at 210 + 21 g/ha, all decreased total forage production of weed-free wheat. Conversely, all herbicide treatments except triasulfuron applied PRE increased wheat grain yield.

Time of hilling (4, 5, or 6 weeks after planting; WAP) and 0.5x, 1x, and split (0.5x + 0.5x) rates of metolachlor + metribuzin were evaluated in conventional tillage (CT) and rye-stubble, reduced tillage (RT) potato plots. Weed populations 4 to 10 WAP were generally higher in CT than in RT. Weed control was excellent in both tillage systems when 1x rates of metolachlor + metribuzin were applied delayed preemergence, or in a split application where 0.5x was applied delayed PRE and hilled 6 WAP, and followed with a second application of 0.5x metolachlor + metribuzin 7 days after hilling (DAH). Weed control with 0.5x rates of metolachlor + metribuzin applied 7 DAH, when hilled 4 and 5 WAP, was equivalent to the lx and split-rate treatments. Weed control was reduced only when hilling was delayed to 6 WAP and 0.5x of metolachlor + metribuzin applied 7 DAH. Total yields were not influenced by tillage, hilling, or herbicide treatment, however, larger numbers of green and small-sized tubers reduced marketable yields in RT.

A 3-yr study investigated highbush blackberry control in bahiagrass turf using selective herbicides. Triclopyr applied alone at ≤ 0.56 kg/ha and in combination with other herbicides provided best (75 to 95%) control for up to 52 wk after treatment with minimal damage to bahiagrass turf. Triclopyr formulations (3A vs 4EC) provided similar highbush blackberry control and bahiagrass tolerance. The addition of either 2,4-D, dicamba, hexazinone, or sulfometuron to triclopyr provided slightly better blackberry control, but increased bahiagrass turf damage. Fluroxypyr applied at 0.14 to 0.28 kg/ha provided 60 to 80% control of highbush blackberry 12 WAT. Glyphosate and glufosinate treatments provided unacceptable highbush blackberry control and/or unacceptable bahiagrass turf injury. The addition of oxadiazon for residual control of subsequent highbush blackberry emergence was ineffective.

An in-row competition study was conducted in 1991 and 1992 near Silver Lake, KS to determine the relationship of noncultivated common sunflower density to soybean yield, PAR at the soybean canopy, and common sunflower dry matter production. Because of environmental differences, year main effect interactions occurred, so results are presented by year. For example, 0.3 common sunflower plant/m2produced 4030 kg/ha of aboveground dry matter in 1991 and 1300 kg/ha in 1992. Soybean yield reduction ranged from 19 and 17% with 0.3 common sunflower plant/m2to 97 and 95% with 4.6 plant/m2, in 1991 and 1992, respectively. Assuming a treatment cost of $35/ha and a soybean market price of $0.21/kg, economic threshold levels were 0.1 common sunflower plant/m2in 1991, and 0.07 in 1992. Common sunflower at 0.3 plant/m2reduced PAR at the soybean canopy by 390 and 300 μE/m2/s, or 24 and 18% in 1991 and 1992, respectively. We conclude that the ability of common sunflower to intercept PAR above the soybean canopy is an important component in its interference with soybean.

A seed bioassay was developed and tested for the rapid identification of aryloxyphenoxypropionate (APP) and cyclohexanedione (CHD) resistance in wild oat. Two susceptible (S) genotypes, UM5 and Dumont, were treated with fenoxaprop-P and sethoxydim over a range of dosages on filter paper and agar. The former is a wild oat line and the latter a tame oat cultivar. Within 5 d, shoot and root development of both genotypes were completely inhibited by 10 μM fenoxaprop-P and 5 μM sethoxydim. These dosages were then tested to determine if they were suitable for distinguishing between resistant (R) and susceptible (S) plants. Agar medium was preferred over filter paper because of the ease of preparation and maintenance. Four known R wild oat populations were included in the tests. Those with high levels of resistance produced significantly longer coleoptiles and roots than S genotypes, but those with moderate or low levels of resistance could not be separated statistically from S biotypes based on quantitative measurements. However, after exposing the germinating, treated seeds to light for 24 to 48 h, all the R populations produced green coleoptiles and initiated a first leaf, unlike the S genotypes which did not turn green or produce any new growth. This procedure proved useful in discriminating between R and S genotypes and in ranking populations in terms of relative levels of resistance.

Experiments were conducted at three locations in Louisiana from 1992 to 1994 to evaluate broadleaf weed control with sulfentrazone. Sulfentrazone at 0.42 kg ai/ha applied PPI or PRE provided at least 93% control of entireleaf morningglory in all years at all locations, which was greater than control with metribuzin PRE. Prickly sida control with sulfentrazone ranged from 83 to 94%, which was equal to or greater than control with metribuzin. Hemp sesbania and sicklepod control with sulfentrazone was unacceptable (≤75%) regardless of application method and generally was lower than control with metribuzin. Greater than 90% control of smellmelon and hophornbeam copperleaf was observed with all treatments. Minor but transient soybean injury was noted at one location in one year. Soybean yields following sulfentrazone PRE at St. Joseph were greater than yields with metribuzin as a result of the general increase in broadleaf weed control.

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.