Broadleaf weed control and tulip, daffodil, and iris response to alachlor, dithiopyr, diuron, isoxaben, napropamide, oryzalin, oxadiazon, oxyfluorfen, pendimethalin, pronamide, and thiazopyr applied preemergence were evaluated. All herbicides controlled broadleaf weeds for five months after application, but control with oxyfluorfen, pendimethalin, alachlor, pronamide, and napropamide decreased six months after application. The greatest weed control was with oxadiazon, isoxaben, thiazopyr, dithiopyr, and diuron, whereas the least weed control was with napropamide and alachlor. In general, tulip was more sensitive to herbicides than daffodil and iris. All herbicides injured tulips at early growth stages but bulb yield of tulip was reduced only by oxadiazon, oxyfluorfen at 0.28 kg ai/ha, pronamide, and dithiopyr. Tulip flower quality was reduced only by oxadiazon, oxyfluorfen at 0.28 lb/ha, and pronamide. Daffodil and iris were tolerant to thiazopyr, isoxaben, pronamide, alachlor, oryzalin, napropamide, and diuron.

Greenhouse experiments were conducted to evaluate seedling rice tolerance to haloxyfop and to determine soil moisture effects on root, shoot, and root plus shoot uptake. Visible injury to rice at 4 wk after treatment increased with each increase of haloxyfop rate from 40 to 160 g ai/ha, regardless of growth stage. Less injury was observed at equivalent rates in four-leaf than in younger rice. Similarly, equivalent haloxyfop rates reduced shoot fresh weight of one- to three-leaf rice more than shoot fresh weight of four-leaf rice. There was no interation between soil moisture levels (19 and 24%) and haloxyfop activity. Fresh weights were less when haloxyfop at 40 or 80 g/ha was absorbed by both roots and shoots than when absorption was by either roots or shoots alone. However, at 80 g/ha fresh weight was similar whether haloxyfop was absorbed by roots or shoots alone. Root uptake, in the presence of 160 g/ha haloxyfop, did not contribute to reduced fresh weight with root plus shoot treatments because of the initial foliar activity incurred.

Field studies were conducted to determine response of ‘Atlantic’ and ‘Fontenot’ potato varieties and eight weed species to rimsulfuron and metribuzin. Rimsulfuron was applied at 9, 18, 27, 35 and 70 g ai/ha and metribuzin at 69, 140, 210, 280 and 560 g ai/ha. Each herbicide was applied PRE or POST alone or in 1:8 combinations of rimsulfuron to metribuzin. Yield of either variety was not reduced by any treatment. Rimsulfuron applied PRE or POST at the suggested field use rate of 35 g/ha controlled smooth pigweed, redroot pigweed, ivyleaf morningglory, and common cocklebur 100%, common lambsquarters 90%, and jimsonweed 60%. Large crabgrass and fall panicum were controlled 92% by rimsulfuron at 35 g/ha. Reduced rates of 9 g/ha rimsulfuron plus 69 g/ha metribuzin, applied PRE or POST, controlled all weeds 100% except jimsonweed, fall panicum, and large crabgrass. For complete control of these weeds, rimsulfuron at 35 g/ha plus metribuzin at 280 g/ha was required.

Sweet corn tolerance to nicosulfuron as affected by interactions between nicosulfuron applied postemergence (POST), sweet corn hybrid, and rootworm insecticide applied at planting was determined in 1992 and 1993 field experiments. Sweet corn vigor was reduced as nicosulfuron rate increased from 35 to 140 g ai/ha. Sweet corn vigor was reduced 4% more by nicosulfuron with oil emulsifier mixture than nicosulfuron with non-ionic surfactant one week after treatment (WAT). Adjuvant selection did not influence nicosulfuron injury to sweet corn 2 WAT. Nicosulfuron applied postemergence directed (PDIR) caused less sweet corn injury than nicosulfuron applied broadcast POST. ‘Jubilee’ sweet corn was more sensitive to nicosulfuron and insecticide treatments than ‘Excellency’ or ‘Green Giant 40.’ Nicosulfuron reduced sweet corn vigor twice as much when terbufos was applied at planting compared to no insecticide at planting. Neither chlorpyrifos or chlorethoxyfos at planting increased sweet corn injury due to nicosulfuron compared to no insecticide. Excellency and Green Giant 40 yields were not reduced by any treatment. Yields were reduced only when nicosulfuron was applied to Jubilee treated with terbufos. Jubilee yield reduction from nicosulfuron and terbufos was prevented by applying nicosulfuron PDIR.

A two-year experiment was conducted to determine if tank-mixes of postemergence (POST) herbicides would consistently control large crabgrass and goosegrass in common bermudagrass turf compared to herbicide alone treatments. Tank-mixes of MSMA plus quinclorac at 2.2 + 0.6 kg/ha effectively controlled large crabgrass (≥ 81%) for 10 to 11 weeks during 1993 and 1994. The control from MSMA plus dithiopyr at 2.2 + 0.3 kg/ha was higher during this period than when each herbicide was applied alone at the same rate. There was no increase in large crabgrass control from tank-mixes of MSMA and diclofop applied in a single application, when compared with two applications of MSMA applied at 2.2 kg/ha. Goosegrass control at 9 wk after tank-mixed treatments of MSMA (2.2 kg/ha) and diclofop (≥ 0.3 kg/ha) in 1994 was lower (12 to 28%) than when diclofop at 1.1 kg/ha was applied alone (85%). Tank-mixes of MSMA with quinclorac or dithiopyr did not control goosegrass. In general, common bermudagrass injury was no higher from herbicide combinations than when each was applied alone. An exception occurred at 1 wk after treatment in 1993 when common bermudagrass injury was higher from tank-mixes of MSMA plus diclofop at 2.2 + 1.1 kg/ha, than when either herbicide was applied alone.

Studies determined the effect of common lambsquarters, goosegrass, and a mixture of these on ‘Beauregard’ and ‘Jewel’ sweetpotato transplant production with or without polyethylene bed covers. Effects of herbicides on Beauregard in propagation beds were also studied. Black and infrared transmissible (IRT) plastic covers gave near 100% control of goosegrass and common lambsquarters, resulting in the greatest number and weight of Jewel transplants per plot. Common lambsquarters reduced transplant number and weight per plot with Jewel under clear plastic covers when compared with black and IRT plastic covers. Beauregard transplant number was not affected by row cover treatment. However, with data combined over all covers, Beauregard transplant weight per plot was lowest for treatments with weeds compared to weed-free plots. With the exception of DCPA, no significant (10% or greater) injury to Beauregard was observed with diphenamid, napropamide, chloramben, or chloramben plus fluazifop.

Field studies were conducted from 1986 through 1989 to determine the feasibility of using clomazone in a winter wheat-corn-fallow rotation. Clomazone at 1.1 kg ai/ha did not control emerged downy brome in autumn nor did it control redroot pigweed and tumble pigweed that emerged after a spring application of paraquat at 0.6 kg ai/ha. However, clomazone plus atrazine at 0.6 plus 2.2 kg ai/ha provided weed control in winter wheat stubble from October to corn harvest 12 mo later. Corn yields from this treatment were equal to or greater than the conventional practice of applying atrazine plus glyphosate at 2.2 plus 0.4 kg ae/ha in the fall followed by a spring application of metolachlor plus dicamba at 2.8 ai plus 0.3 kg ae/ha. When kochia densities were high, clomazone plus atrazine controlled triazine-resistant kochia better than metolachlor plus dicamba. Atrazine at 2.2 kg/ha applied in autumn followed by clomazone at 0.8 kg/ha in April generally caused more corn injury than when the same rate of clomazone was applied in autumn with the atrazine. The percent of bleached corn plants varied with planter, year, time of application, and rate of clomazone applied. The optimum time to apply clomazone at 0.6 kg/ha was in autumn with atrazine. This treatment caused some corn bleaching but produced the highest corn yield over 3 yr. In a dry autumn and spring, less clomazone injury occurred with a planter equipped with row cleaners than those without. The injury pattern associated with planters was inconsistent when precipitation was average and no injury occurred in a wet autumn and spring.

A soil sampler, elutriator, and associated sample flushing device were designed and constructed for an intensive study of weed seedbanks. This equipment was used in 1993 to collect and process 4980 soil samples. The sampler was durable, core size was consistent, and sampling was efficient. Cores were approximately 200 cm3 and two people could take 120 cores/h. The elutriator separated weed seeds from 36 of these cores at a time. Washing required 60 to 75 min depending on soil texture. Seeds as small as 0.3 mm in diam were recovered and almost 100% of the seeds were recovered from samples spiked with barnyardgrass, redroot pigweed, velvetleaf, and witchgrass. The flushing device was used to transfer sample contents from strainers of the elutriator to propyltex bags for drying and storing. Equipment like this, plus improved technology for identifying and counting seeds, is needed to make weed seedbank studies more feasible.

Field studies were initiated in 1985 and 1986 to evaluate the effects of dalapon, glyphosate, imazapyr, and sulfometuron applications to established cogongrass alone or in combination with either mowing or discing. Mowing and discing treatments were performed 4 mo before and 8 months after the herbicide treatments in the 1985 experiments and 2 months before and 7 months after the herbicide treatment in the 1986 experiments. When applied alone, glyphosate at 3.4 kg ai/ha and imazapyr at 0.8 kg ai/ha caused the greatest reduction in shoot and rhizome biomass about 2 yr after application. However, the rhizome infestation was reduced only 43% by glyphosate and 51% by imazapyr, as compared to the nontreated control. With no herbicide, two mowing or discing were generally more effective than a single mowing or discing treatment. The reduction in shoot and rhizome biomass for two mowing without herbicide was 65 and 38% and for two discing, 73 and 66%, respectively. Acceptable (> 80%) levels of cogongrass control, based on reductions in rhizome biomass occurred only when applications of dalapon, glyphosate, or imazapyr were made in combination with two discing despite the fact that mowing before and after treatment reduced shoot biomass by at least 89%.

Experiments were conducted to determine the productivity and the competitive ability of a large crabgrass accession (PW2) resistant to acetyl-coenzyme A carboxylase (ACCase) inhibitors relative to a susceptible accession (A310). Under noncompetitive conditions in the field, shoot dry biomass and plant height over time were similar for the two accessions. Leaf area was slightly greater for A310 than for PW2. The instantaneous relative growth rate was similar for the accessions. The instantaneous net assimilation rate was slightly greater for A310 than for PW2; however, the instantaneous leaf area ratio was slightly greater for PW2 than for A310. At maturity, the seed yield was similar for the accessions. The inter-accession competitive ability of PW2 and A310 plants in the field was similar, based on shoot dry biomass or seed yield. In the greenhouse, interspecific competitive ability of the accessions with corn was similar, based on shoot dry biomass or seed yield. These results suggest that resistance to ACCase inhibitors is not associated with reduced fitness of the PW2 accession.

Cultivations in conjunction with POST applications of AC 263,222 were evaluated for their effects on sicklepod and pitted morningglory control and soybean yield. Cultivation alone controlled sicklepod and pitted morningglory season-long no more than 30%. In most instances, one cultivation with herbicides improved sicklepod and pitted morningglory control compared with no cultivation, but two cultivations did not further improve control. Two applications of AC 263,222 at 9 or 13 g ai/ha per application with a single cultivation caused the most soybean injury and were no more efficacious than imazaquin applied PRE followed by 9 g/ha AC 263,222. Imazaquin applied PRE followed by AC 263,222 at 18 g/ha plus one or two cultivations were the only treatments that controlled sicklepod and pitted morningglory more than 90% season-long. Cultivation in combination with herbicides increased yields over that of herbicides used alone. Soybean yield was the highest following imazaquin applied PRE followed by AC 263,222 at 9 g/ha plus two cultivations.

Field studies conducted from 1989 through 1991 evaluated methods of metolachlor application including POST followed by irrigation for yellow nutsedge control and peanut response. Metolachlor PPI stunted peanut in two of three years while metolachlor applied at emergence, 10, 20, or 30 days after peanut emergence (DAE) caused no peanut injury. Metolachlor 20 DAE provided > 95% yellow nutsedge control. Metolachlor soil-applied and again POST controlled yellow nutsedge at least 70%; however, some peanut stunting was noted. Bentazon plus metolachlor at 2.24 kg ai/ha controlled yellow nutsedge at least 92% when applied 30 DAE. Peanut yields were consistently the highest with metolachlor PRE at 1.40 kg ai/ha followed by a POST application of 1.40 kg ai/ha at 45 DAE.

Transplanted cabbage was grown in conventional-tillage (100% cultivated) and strip-tillage (25% cultivated and 75% residue) production systems with various herbicide treatments to evaluate weed control and cabbage yield. DCPA at 9 kg ai/ha, napropamide at 1.1 kg ai/ha, oxyfluorfen at 0.3 kg ai/ha, and oxyfluorfen at 0.2 kg ai/ha plus napropamide at 1.1 kg ai/ha provided commercially acceptable (> 80%) control of carpetweed, swinecress, large crabgrass, redroot pigweed, and common lambsquarters under both tillage systems. However, only oxyfluorfen plus napropamide provided control of eclipta. At a second location, all herbicides controlled common purslane and barnyardgrass and all but DCPA controlled hairy galinsoga. Overall, cabbage yields were the same between conventional and strip-tillage systems, and among herbicide treatments when average cabbage head weights across tillage method were pooled.

Surfactant concentrations from 0.0008 to 12.5% (w/w) in spray volumes from 19 to 475 L/ha were tested with and without rimsulfuron on giant foxtail. Both factors varied at 5-fold increments so treatments with equal surfactant concentrations and rates could be compared. As surfactant concentration increased from 0.0008 to 0.1%, rimsulfuron activity increased from less than 20% to more than 90% growth inhibition. This increase was dependent on surfactant concentration. As surfactant concentration increased from 0.5 to 12.5%, rimsulfuron activity decreased to less than 20% at all spray volumes. This decreased activity and the associated surfactant phytotoxicity was dependent on surfactant rate, not concentration. Thus rimsulfuron can be much less active when applied with too little or too much surfactant.

Controlled environmental chamber experiments were conducted for a 14-d incubation period to measure the effect of temperature, light, light intensity, water potential, and pH on eclipta seed germination. In full light, seed germinated over a range of 10 to 35 C; however, germination was highest at 83% at 35 C. Seeds were strongly photoblastic with none germinating in the dark. Seeds germinated in light intensities between 6 and 100% of full light. Seeds germinated 78 to 88% in water potentials of 0.0, −0.1, and −0.2 MPa. In distilled water (pH ∼ 5.5) and a buffered solution pH 6 and 7, seeds germinated 85 to 89%; however, some seeds germinated in a buffered solution pH range of 5 to 8. After the first 14-d incubation period, ungerminated seeds were transferred to distilled water and incubated at 35 C in full light for 4 to 6 d as a second incubation period. Seeds germinated 89 to 96% after this second incubation period when first incubation was at temperatures 10 to 35 C in full light or darkness, light intensities 0 to 100% of full light, water potentials 0.0 to −0.8 MPa, and buffered solution pH levels of 5.5 to 7.

Phytotoxins produced by the naturally-occurring rhizobacterium, Pseudomonas fluorescens strain D7 (strain D7), in shake cultures from several media sources adversely affected downy brome at several growth stages and affected seeds, whole plants, and isolated cells. These uncharacterized phytotoxins inhibited root and shoot growth of downy brome by 80% in a seed germination agar assay at 2 and 400 ng total solids/ml, respectively. In a hydroponics assay, downy brome and winter wheat dry weights were reduced 50% by cell-free broth concentrations of 15 and 26% of the initial broth concentration, respectively, indicating an almost 2x selectivity between winter wheat and downy brome. Plant water use was reduced similarly. Plasma membranes of isolated protoplasts of downy brome were damaged within 2 h by diluted cell-free broth. Cold-precipitated phytotoxins of strain D7 produced in semi-synthetic and synthetic media reduced dry weight of downy brome seedlings by 100 and 89%, respectively, and killed plants rapidly.

Field experiments were conducted to determine the effect of CGA184927 rate, weed growth stage, and tank mixes with various broadleaf herbicides on the control of green foxtail and wild oat in spring wheat. CGA 184927 controlled green foxtail and wild oat equally well when applied at the 2- to 3- or 4- to 5-leaf stages. Green foxtail and wild oat were controlled at similar rates of CGA 184927 but the application rate giving > 90% control ranged from 22 to 90 g/ha over locations and years, indicating that CGA 184927 efficacy is sensitive to environmental conditions. CGA 184927 in tank mixtures was compatible with bromoxynil, clopyralid, and 2,4-D ester. However, tank mixing with metsulfuron or dicamba reduced activity on green foxtail and wild oat. Broadleaf herbicide activity on kochia and redroot pigweed was not reduced when such herbicides were tank-mixed with CGA 184927. Spring wheat tolerated 120 g/ha of CGA 184927. CGA 184927 provides growers with another herbicide option to control green foxtail and wild oat in wheat.

DPX-79406 was evaluated for POST annual grass weed control in both controlled environment and field experiments. In controlled environment experiments, green foxtail was most susceptible to DPX-79406; whereas yellow foxtail was least susceptible of the species evaluated. DPX-79406 at 12 g/ha completely controlled six leaf black-seeded proso millet, yellow foxtail, green foxtail, and barnyardgrass. In the field, DPX-79406 at 3.0 to 25.0 g/ha effectively controlled annual grass weeds without injury to three- to six-leaf corn. There was more variation in the effectiveness of DPX-79406 applied in the field. Early POST applications provided less weed control than the late application, especially for barnyardgrass, because of weeds emerging after application. As a result, higher doses were sometimes needed for effective control. In weed-free field trials at two sites in 1990 and 1991, corn tolerated doses up to 75 g/ha of DPX-79406 applied at the three- to six-leaf growth stage. However, doses as low as 18.8 g/ha applied at the six- to nine-leaf growth stage reduced grain yield. In 1991, corn tillering increases and height and yield reductions were related linearly to the dose of DPX-79406 applied during later growth stages. DPX-79406 should be applied early POST in order to avoid crop injury while providing effective weed control.

Dry edible bean tolerance to PPI-applied EPTC, alachlor and POST-applied imazethapyr was evaluated over two years at Scottsbluff, NE. Eight market classes of dry edible beans comprising 12 cultivars were studied. Crop tolerance was assessed by measuring crop injury, stand, leaf area index, leaf chlorosis, plant canopy volume, projected canopy cover, crop maturity, and seed yield. Leaf area index measured late in the growing season provided the best correlation with seed yield in both years. In 1993 and 1994, imazethapyr treatment caused crop injury, which resulted in a decrease of leaf area and in 1994 decreased seed yield. Differences in herbicide tolerance existed between market classes and cultivars, although the level of herbicide tolerance varied between years.

We compared applications of trifluralin or ethalfluralin granules incorporated with a sweep plow or pendimethalin (ec) applied without incorporation to incorporating trifluralin (ec) by tandem-disk harrowing for sunflower production. The study was established in winter wheat stubble at three sites in the northern and central Great Plains. Crop residues on the soil surface following sunflower planting was greater than 30% (level required to protect soil from erosion) with all conservation-tillage strategies, but not with disk incorporation. Weed control and sunflower seed yield with conservation-tillage strategies were similar to the disk incorporation practice, demonstrating that producers can use these strategies for sunflower production and to protect soil from erosion.