Field research was conducted in Nebraska to evaluate the efficacy of herbicides for the control of summer annual weeds in sorghum [Sorghum bicolor (L.) Moench.]. During 1976 to 1979, no-till plots treated with a mixture of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], and terbutryn [N-(1,1-dimethylethyl)-N′-ethyl-6-(methylthio)-1,3,5-triazine-2,4-diamine] yielded 33% more sorghum grain than plots receiving the same herbicides when a seedbed was prepared by disking. During 1981 to 1983, season-long weed control was obtained with acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl) acetamide], alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile}, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], or terbutryn added to paraquat plus atrazine and metolachlor plus cyanazine plus paraquat applied 10 days prior to planting. The use of seed safeners did not increase sorghum yield.

Spring-applied herbicides were evaluated in the field in 1982 through 1984 in western Nebraska for selective weed control in irrigated seedling alfalfa (Medicago sativa L. ‘Appollo’). Weed densities were least in plots treated preplant with benefin [N-butyl-N-ethyl-2,6-dinitro-4-(trifluoromethyl)benzenamine] in combination with postemergence applications of 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid]. Combinations of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} with bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and fluazifop-butyl {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} with bromoxynil provided less grass control than sethoxydim or fluazifop-butyl applied alone. Annual weeds did not reduce alfalfa stand density.

Laboratory photolysis rates of 2,4-D [(2,4-dichlorophenoxy)acetic acid], bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], and haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} in dilute aqueous solution were enhanced by the presence of adjuvants. Addition of 1.0% (v/v) petroleum oil concentrate (POC), 1.0% (v/v) soybean oil concentrate (SBOC), and 0.15% (v/v) emulsifier package (EP) enhanced herbicide photolysis rates more than addition of 0.15% (v/v) oxysorbic (20 POE) (polyoxyethylene sorbitan monolaurate). Bioassays showed that phytotoxicity of photolyzed herbicide solutions was negatively correlated with time of exposure to ultraviolet light. Addition of 0.85% (v/v) acetophenone to aqueous herbicide solutions containing 0.15% (v/v) oxysorbic strongly sensitized photodegradation of 2,4-D, and to a lesser extent, haloxyfop. Acetophenone had no effect on bentazon photolysis in the presence of oxysorbic. In another study, herbicides were dissolved in white mineral oil or once-refined soybean oil and exposed to ultraviolet light. After a 6-h exposure, there was 92% loss of haloxyfop in mineral oil and 36% loss in soybean oil. There was no difference between oils in affecting the photolysis rate of 2,4-D or bentazon.

White horehound (Marrubium vulgare L. # MAQVU) is one of the few perennial, herbaceous alien weeds to successfully colonize semiarid to arid rangelands in the Great Basin. Seeds of white horehound, collected from diverse habitats within the Lahontan Basin of northwestern Nevada, were incubated at constant or alternating temperatures ranging from 0 to 40 C. Germination was low and largely limited to alternating temperatures (10 to 25 C alternating with 35 to 40 C). At least a 15-C range in diurnal fluctuation was required for optimum germination (defined as not lower than the maximum observed minus one-half of the confidence interval with 1% probability). Cool-moist stratification at 2 C for 4 to 8 weeks enhanced germination at optimum temperature regimes by as much as 70% and increased overall average germination by 35 to 40%. Cool-moist stratification caused a shift in temperature optima for germination from widely fluctuating temperatures to constant 15 or 20 C. The magnitude of this shift varied among sources of seeds.

Integration of preplant-incorporated molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate) at 4.5 kg ai/ha and a brief postseeding drainage period in water-seeded rice (Oryza sativa L.) gave the best red rice (Oryza sativa L. # ORYSA) control without a significant reduction in cultivar stand density. This combination of practices provided higher cultivar grain yield and lower red rice grain yield than any water management practice alone. Continuous-flood water management provided a substantial reduction in red rice stand density, but it also caused a significant reduction in the cultivar stand density. Under the reduced stand density conditions, the red rice was very competitive and yielded more than the cultivar. Although brief drainage alone gave a significantly lower level of red rice control, it had no significant effect on the cultivar stand density, and the red rice and cultivar yields were not significantly different from the continuous-flood yields. Prolonged drainage had the highest red rice and cultivar stand densities and the highest red rice grain yield, but the cultivar yield was not significantly different from the other plots that were not treated with herbicide. Although this treatment gave the highest total grain yield, its composition had the highest percentage of red rice. Puddling the seedbed did not alter the stands or yields of red rice or cultivar compared to the nonpuddled plots with the same water management and herbicide rate. The application of molinate as a preplant-incorporated treatment or as a preplant postflood treatment before or after puddling gave results that were not significantly different from each other. The superior performance of preplant application of molinate in water-seeded rice in conjunction with a brief postseeding drainage period provides an excellent tool for red rice suppresion.

Red rice (Oryza sativa L. # ORYSA) control in soybeans [Glycine max (L.) Merr.] was 93% or more with shallow-incorporated alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] at 3.9 kg ai/ha, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 2.8 kg ai/ha, and trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] at 1.7 kg ai/ha. Junglerice [Echinochloa colonum (L.) Link. # ECHCO] control was 80% with alachlor but 90% or more with metolachlor and trifluralin when applied at the same rates. Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 560, fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy]phenoxy]propanoic acid} at 280, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} at 140, and mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} plus bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4 (3H)-one 2,2-dioxide] at 140 plus 840 g ai/ha applied postemergence on two- to four-leaf red rice provided at least 87% control. Junglerice control with these treatments was 85% or more with the exception of fluazifop and mefluidide plus bentazon.

Ten herbicides were evaluated for broomrape (Orobanche ramosa L. # ORARA) control and their effect on growth, yield, and chemical composition of four tobacco (Nicotiana tabaccum L.) cultivars. Of the preplant-incorporated (PPI) herbicides, only pebulate (S-propyl butylethylcarbamothioate) at 7.2 kg ai/ha and metham (methylcarbamodithioic acid) at 66 kg ai/ha provided, although inconsistently, 30 to 50% broomrape control in oriental but not in burley tobacco. Single postemergence (POE) applications of glyphosate [N-(phosphonomethyl)glycine] at 0.2 kg ai/ha or MH (1,2-dihydro-3,6-pyridazinedione) at 0.7 kg ai/ha at 40 days after transplanting resulted in 60 to 80% broomrape control. Glyphosate or MH applications at 40 days after transplanting and again at 60 days resulted in 100% and 80 to 90% control, respectively. Very good (80 to 90%) control also occurred with pebulate (PPI) at 7.2 kg ai/ha followed by glyphosate (POE) at 0.2 kg ai/ha at 40 days after transplanting. Tobacco yield increased significantly, compared to that of untreated plots, where glyphosate or MH was used, but nicotine, total nitrogen, and reducing sugar contents were not significantly affected.

Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} at 2 or 4 ppmw placed 0 to 3, 8 to 11, or 15 to 18 cm deep in soil columns reduced root and shoot weights of buffelgrass [Pennisetum ciliare (L.) Link # PESCI] 30 days after emergence. Plains bristlegrass (Setaria macrostachya H.B.K.) seedling shoot weights were not reduced when 2 ppmw tebuthiuron was placed 8 to 11 cm deep or deeper. Effects of tebuthiuron at 0.13 to 0.50 ppmw on buffelgrass shoot and net tiller production were not moderated by the presence of honey mesquite (Prosopis glandulosa # PRCJG) in the pots. However, regardless of tebuthiuron dosage, average height and shoot weight of buffelgrass seedlings were greater when seedlings were grown in soil collected from beneath honey mesquite canopies compared to growth in soil from interspaces. Therefore, spatial variations in buffelgrass response to applications of tebuthiuron for control of invading shrubs may largely be attributed to soil changes induced by woody plants rather than to presence of shrubs.

Field experiments were conducted over a 3-yr period to evaluate the efficacy of herbicides for the control of volunteer Jerusalem artichoke [Helianthus tuberosus (L.) # HELTU] in barley (Hordeum vulgare L.) and on summer fallow. In barley, Jerusalem artichoke was controlled with a single postemergence application of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) at 1 kg ae/ha, or at 0.5 kg/ha when combined with 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 0.5 kg ae/ha. Dicamba (3,6-dichloro-2-methoxybenzoic acid) at 0.2 kg ae/ha plus 2,4-D at 0.4 kg/ha was also an effective combination. Split applications of 2,4-D at 0.4 kg/ha each were more effective than a single treatment at 0.8 kg/ha. On summer fallow, glyphosate [N-(phosphonomethyl)glycine] applied at 0.5 to 2 kg ai/ha, as a single or repeated treatment, provided only marginal control of Jerusalem artichoke during the season of treatment and, in one of three experiments, reduced regrowth in the year following treatment.

The growth and development of field horsetail (Equisetum arvense L. # EQUAR) was measured outdoors using potted plants grown from one-node rhizome fragments. Shoot growth rate increased slowly after planting in March, accelerating to a maximum during July with maximas for shoot height during August and shoot number in September. Rhizome system growth rates initially followed a similar pattern to that of the shoots achieving a maximum during July. Dry matter accumulated in the rhizomes until October and declined thereafter throughout the winter. Tubers initiated during August grew in size and number until November, well beyond the period of active shoot growth and onset of senescence. The characteristics of the growth and development of field horsetail are discussed in relation to achieving weed control via cultural and herbicide treatments.

Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, RO-13-8895 {acetone-O-[d-2-[p-[α,α,α-trifluoro-p-tolyl-oxy]phenoxy] propionyl] oxime}, and KK-80 {4-[4-[4-(trifluoromethyl)phenoxy] phenoxyl]-2-pentenoic} were evaluated for potential use for controlling quackgrass [Agropyron repens (L.) Beauv., # AGRRE] in perennial ryegrass (Lolium perenne L. ‘NK200’), smooth bromegrass (Bromus inermis Leyss. ‘Sac’), orchardgrass (Dactylis glomerata L. ‘Nordstern’), timothy (Phleum pratense L. ‘Climax’), Kentucky bluegrass (Poa pratensis L. ‘Park’), Reed canarygrass (Phalaris arundinaceae L. ‘Rise’), meadow fescue (Festuca elatior L.), and red fescue (Festuca rubra L.). The three herbicides, when applied postemergence at 1.1 kg ai/ha, caused severe injury to all species except red fescue. ‘Pennlawn’, ‘Ruby’, ‘Dawson’, MN67123, MN673, and MN6354 red fescue entries were tolerant to the three herbicides in both greenhouse and field experiments. Sethoxydim and RO-13-8895 effectively controlled quackgrass in Pennlawn red fescue, but KK-80 was not effective.

In field experiments at Prosser, WA, black nightshade (Solanum nigrum L. # SOLNI), eastern black nightshade (S. ptycanthum Dun. # SOLPT), American black nightshade (S. americanum Mill. # SOLAM), hairy nightshade (S. sarrachoides Sendtner # SOLSA), and sometimes accessions within a species responded differentially to herbicides applied preplant incorporated, preemergence, or postemergence. Also, the response of the nightshades to some of the herbicides varied significantly between years. Generally, black nightshade was more tolerant of herbicides than were the other three species. An accession of black nightshade from England and an accession of eastern black nightshade from Minnesota were the most tolerant of herbicides of eight accessions evaluated. Of the 25 herbicides evaluated, preplant-incorporated applications of ethalfluralin [N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl) benzenamine] and preemergence applications of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], chloramben (3-amino-2,5-dichlorobenzoic acid), lactofen [1′-(carboethoxy)ethyl 5-[2-chloro-4-(trifluoromethyl) phenoxy]-2-nitrobenzoate], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl] acetamide] controlled all species best. These herbicides reduced the oven-dry weights of both accessions of all four species of nightshades by 93% or more. Nightshades varied widely in their response to the thiocarbamates.

The potential for yellow nutsedge (Cyperus esculentus L. var. leptostachyus Boeck. # CYPES) regrowth was reduced by increasing plant age and by glyphosate [N-(phosphonomethyl)glycine] and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene]. Of the amount of glyphosate transported to underground parts, most was found in the tubers, with immature rhizomes, roots, and tubers having 2 to 3 times higher concentrations than comparable mature tissues. Addition of unlabeled oxyfluorfen as a tank mixture with glyphosate increased absorption and translocation, mainly into leaves and new tubers, of radioactivity from 14C-glyphosate in 30-day-old plants. In contrast to the younger plants, the addition of oxyfluorfen decreased 14C-glyphosate detected in 60-day-old plants. The greater effectiveness of glyphosate when applied with oxyfluorfen on yellow nutsedge at the early growth stage has important implications in the field because the tuberization process must be stopped early in the development of the plant for successful control.

CGA 82725 {2-propynyl [2-[4-[(3,5-dichloro-2-pyridinyl)oxy)] phenoxy] propanoate}, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy]phenoxy] propanoic acid}, sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, and fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} were applied postemergence to Texas panicum (Panicum texanum Buckl. # PANTE), large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA], and broadleaf signalgrass [Brachiaria platyphylla (Griseb.)Nash. # BRAPP] in peanut (Arachis hypogaea L. ‘Florunner’). Fluazifop applied at 280 and 410 g ai/ha, sethoxydim at 340 g ai/ha, haloxyfop at 140 g ai/ha, and CGA 82725 at 280 g ai/ha usually gave better control when applied to annual grasses in the two- to four-leaf stage than when applied at the six- to eight-leaf stage. Higher rates of application were required to provide acceptable weed control at the later stage of growth. Peanut yields were usually higher following the early applications, indicating that timing of application is important in obtaining improved yields.

Kentucky bluegrass (Poa pratensis L. ‘Parade’, ‘Adelphi’, ‘Glade’, and ‘Rugby’ # POAPR) and tall fescue (Festuca arundinacea Schreb. ‘Kentucky 31’ # FESAR) were treated in field experiments with chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide}. The objectives of the two experiments were to determine if this herbicide has the potential to be used for selective control of tall fescue in Kentucky bluegrass turf. Chlorsulfuron treatments included single rates of 0, 18, 35, 71, 141, 212, and 282 g ai/ha and split rates, applied 14 days apart, of 18 + 18, 35 + 35, 71 + 71, 141 + 141, and 212 + 212 g/ha. Clipping weights and turfgrass quality ratings were taken in both experiments. Kentucky bluegrass showed a higher tolerance to the chemical, with no decrease in turf quality at the highest single and split application rates in both experiments. However, as the chlorsulfuron rate increased, clipping weight decreased. Tall fescue showed a low tolerance to the chemical and was controlled at single rates of 141 g/ha and split rates of 141 + 141 g/ha and greater. Although the tall fescue recovered from damage at single rates of 71 g/ha and split rates of 71 + 71 g/ha, severe growth inhibition and discoloration of aboveground tissue occurred at the lower rates. Twelve months after the first chlorsulfuron was applied in each experiment, glyphosate [isopropylamine salt of N-(phosphonomethyl)glycine] was sprayed over the plots to kill all existing plant material, and Kentucky bluegrass was seeded into the plots 2 weeks later at the rate of 0.75 kg/100 m2. There was no inhibition of bluegrass seed germination at any of the rates of chlorsulfuron.

Ground applications of pelleted tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} at 0.6 kg ai/ha (20% formulation) reduced big sagebrush (Artemisia tridentata Nutt. # ARTTR) density by an average of 84 and 92% after 28 months, whereas 1.1 kg/ha killed 94 and 97% of the plants when applied in January or May, respectively. Total standing crop of grasses was unaffected 4 months after tebuthiuron applications. Significant increases in grass production occurred during the second and third growing seasons following tebuthiuron treatment. Desirable forage grasses such as galleta [Hilaria jamesii (Torr.) Benth.], blue grama [Bouteloua gracilis (Wild. ex H.B.K.) Lag. ex Griffiths], and crested wheatgrass [Agropyron cristatum (L.) Gaertn.] generally increased in tebuthiuron-treated plots, whereas sand dropseed [Sporobolus cryptandrus (Torr.) Gray # SPECR] and ring muhly [Mulenbergia torreyii (Kunth.) Hitchc. & Chase] production remained unchanged in comparison with untreated areas.

Field studies were conducted for 4 yr to investigate the effects of tillage and herbicide programs on weed control and wheat (Triticum aestivum L. ‘Potomac’ in 1981 and ‘Wheeler’ from 1982 to 1984) grain yields in a wheat-soy bean [Glycine max (L.) Merr.] double-crop rotation. Predominant weed species were common chickweed [Stellaria media (L.) Vill. # STEME], corn chamomile (Anthemis arvensis L. # ANTAR), and annual bluegrass (Poa annua L. # POAAN) at the onset of research and cheat (Bromus secalinus L. # BROSE) and soft brome (Bromus mollis L. # BROMO) at the conclusion of the study. Control of all species was excellent with conventional tillage and no-till plus nonselective herbicides but was significantly less with no-till without nonselective herbicides and with minimum tillage. After 4 yr, maximum wheat grain yields were significantly higher in conventional- than in minimum- or no-till systems.

Field experiments conducted over a 7-yr period have demonstrated that common buckwheat (Fagopyrum esculentum Moench. cv. ‘Mancan’) has acceptable tolerance to many herbicides that are known to selectively control grass-type weeds in broadleaf crops. Herbicides for broadleaf weed control that showed some selectivity in common buckwheat were desmedipham {ethyl [3-[(phenylamino) carbonyl] oxy] phenyl] carbamate} applied postemergence and fluorochloridone {3-chloro-4-(chloromethyl)-1-[3-(trifluoromethyl)phenyl]-2-pyrrolidinone} applied either preplant soil incorporated or preemergence shallow incorporated. Tank mixtures of desmedipham plus sethoxydim {2-[1-(ethoxyimino)butyl-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} also showed adequate tolerance to common buckwheat at rates recommended for weed control in other crops.

Field and greenhouse studies were conducted to evaluate annual bluegrass (Poa annua L. # POAAN) control and phytotoxicity of ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] to selected warm- and cool-season turfgrass species. Annual bluegrass control in non-overseeded dormant hybrid bermudagrass [Cynodon dactylon (L.) Pers. X C. tranvaalensis Burtt-Davy Tifgreen’ # CYNDA] was 75% or greater with at least two ethofumesate applications at monthly intervals starting in December. Tifgreen bermudagrass spring growth was delayed with more than two applications of ethofumesate at 1.1 kg ai/ha, or when the second application was made after January. Under greenhouse conditions the growth of both Tifgreen and Tifdwarf bermudagrass was less when treated with ethofumesate. Stand and shoot growth of 29 cultivars of ryegrass (Lolium spp.), bluegrass (Poa spp.), bentgrass (Agrostis spp.), and red fescue (Festuca rubra L. # FESRU) were reduced by ethofumesate at 1.1 kg/ha as a preemergence or split (0.5 kg/ha preemergence + 0.5 kg/ha postemergence) application. Postemergence applications were less phytotoxic to cool-season turfgrasses than preemergence applications. Perennial ryegrass stands were generally not reduced by postemergence application of ethofumesate at 1.1 kg/ha. However, shoot growth of perennial ryegrass was reduced.

Field studies were conducted over a 7-yr period at Lacombe, Alberta, to study the relationship between the duration of Tartary buckwheat interference [Fagopyrum tatarium (L.) Gaertn. # FAGTA] and yield of barley (Hordeum vulgare L.), oats (Avena sativa L.), wheat (Triticum aestivum L.), flax (Linum usitatissimum L.), and rapeseed (Brassica campestris L.). The data were pooled over years and analyzed by multiple regression. The equations were as follows: ŷ = 15.46 + 0.39X1 + 0.00x2 −0.11x3 (barley), ŷ = −15.44 + 0.49x1 + 0.02x2 + 0.08x3 (oats), ŷ = −2.04 + 0.39X1 + 0.05x2-0.03x3 (wheat), ŷ = −4.38 + 1.14x1 −0.04x2 + 0.01x3 (flax), and ŷ = −13.85 + 0.40x1 – 0.01x2 + 0.04x3 (rapeseed); where ŷ was the estimated percent yield loss of the crop, x1 was the duration (days) of the Tartary buckwheat in the crop, x2 was the number of Tartary buckwheat plants/m2, and x3 was the number of crop plants/m2. The time that Tartary buckwheat remains in the crop contributed most to the yield loss observed in all crops. Yield loss between 0.4 and 1.1% per day was attributed to this variable alone. For a given x1, x2, and x3 value the order of percent yield loss was flax>oats>wheat> barley>rapeseed.