Proso millet (Panicum miliaceum L. # PANMI) was controlled in corn (Zea mays L. ‘Pioneer 3747’) with postemergence-directed herbicides applied following a standard preplant-incorporated application of butylate [S-ethylbis(2-methylpropyl)carbamothioate] plus dichlormid (2,2-dichloro-N,N-di-2-propenylacetamide) plus cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile}. Postemergence-directed applications of ametryn [N-ethyl-N′-(1-methylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine], cloproxydim {(E,E)-2-[1-[[(3-chloro-2-propenyl)oxy]imino]butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid}, butyl ester of fluazifop-p {(R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid}, glyphosate [N-(phosphonomethyl)glycine], methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid}, and sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} in 40-cm-tall corn gave greater than 90% control of 5- to 15-cm-tall proso millet while causing little or no corn injury at selected rates. Season-long proso millet control was obtained with sethoxydim at rates as low as 56 g ai/ha with no visible corn injury. Unacceptable injury to 40-cm-tall corn occurred with all but the lowest rate of sethoxydim (56 g ai/ha) when a crop oil concentrate was used. Sethoxydim applied as a directed spray at rates up to 110 g ai/ha plus 1.25% (v/v) crop oil concentrate did not injure 60-cm-tall corn.

Adsorption of 14C-imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} and imazethapyr [2-(4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl)-5-ethyl-3-pyridinecarboxylic acid] to soil increased as soil pH decreased from 8.0 to 3.0 in laboratory studies. Significantly more imazethapyr3 (AC-263,499) than imazaquin was adsorbed at soil pH levels 3.0 and 5.5, while the greatest difference in adsorption behavior between the two herbicides was observed at a soil pH of 5.5. In greenhouse studies, phytotoxicity to corn (Zea mays L.) was greater for imazaquin than AC-263,499 applied at 26 and 53 g ai/ha. There were significant pH by herbicide and pH by rate interactions, but in trend analysis only a small proportion of the corn response (r2 = 0.01 to 0.35) was attributed to increasing soil pH values. In field studies where imazaquin was applied to soil pH levels of 4.2 to 4.8, 5.4 to 5.5, and 5.8 to 6.2, injury to corn across all pH levels decreased as the time delay between herbicide application and corn planting increased. There was no significant effect of soil pH on imazaquin injury to corn planted in July or August. Decreased injury from imazaquin was observed in 1985 on corn planted in June on the soil pH of 5.8 to 6.2. Imazaquin injury was less for June-planted corn in 1984 than in 1985, across all soil pH levels.

Field bindweed and Russian knapweed were grown from seed or rhizome segments under 520, 325, or 236 μmol·m–2 · s–1 photosynthetic photon flux density (PPFD) to determine vegetative and reproductive response. Flower production in both species declined with decreasing light level. Leaf area of field bindweed decreased as light level decreased, but Russian knapweed leaf area increased as light intensity decreased from 520 to 325 μmol·m–2 ·s–1 PPFD or from 520 to 236 μmol·m–2 ·s–1. Dry matter of shoots, roots, and rhizomes of field bindweed grown from seed declined as light level decreased, but the only response of plants grown from rhizome segments was complete inhibition of rhizome production. Dry matter of Russian knapweed shoots and roots in plants grown from seed or rhizome segments decreased as light decreased. In both species the total PPFD was more important than whether low or high light level occurred first.

Monoculture velvetleaf had greater dry weight, growth rate, leaf area index, and height than velvetleaf grown in association with conventional or no-tillage corn. Velvetleaf planted 5 weeks after corn had significantly lower dry weight, leaf area index, and height compared to velvedeaf planted at the same time as corn. The combination of interference from corn and delayed planting caused a significant reduction in velvetleaf population at the end of the season, delayed the date of 50% velvetleaf flowering, increased the number of days required for 50% flowering, and reduced the number of capsules per plant. Velvetleaf dry weight/hectare and leaf area index increased as plant population increased. Velvetleaf dry weight, leaf area, capsules, and seed/plant decreased as plant density increased. There were no differences in vegetative or reproductive growth between velvetleaf grown in conventional or no-tillage areas.

Sorption and desorption of metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] were measured in Dundee silty clay loam surface and subsurface soils. Soil samples were taken from a profile that had been divided into six sections from the surface to a depth of 175 cm. Metribuzin sorbed weakly to all soils from this profile with Freundlich distribution constants ranging from 0.78 to 1.34 μmole/kg. Soils from lower depths of the profile having higher pH (>7.0) and clay contents (>35%) sorbed significantly more metribuzin than the lower clay content, higher organic matter surface soils. Stepwise regression of the distribution constants against the variables pH, organic matter, clay content, and sand content showed that clay was the single best predictor, with sorption increasing as clay content increased (r2 =0.750). The combination of two variables most related to sorption was clay and pH (r2 =0.860, P= 0.15). Organic matter was not one of the primary variables related to sorption. Metribuzin was easily desorbed in all soils with less than 5% of the originally applied metribuzin remaining after three desorption treatments. This would indicate little tendency for irreversible sorption. This study demonstrates that soil properties within a profile determine sorption and, subsequently, movement of metribuzin.

Consecutive annual applications of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] were made to continuous no-till corn (Zea mays L. ‘Pioneer 3184’ in 1982 and 1983, ‘Pioneer 3744’ in 1984, and ‘Pioneer 3378’ in 1985 to 1987). In a 5-yr study, control of the dominant annual grass species, large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA], by alachlor declined to less than 50% by the fifth year. Control of large crabgrass by metolachlor remained greater than 80% throughout the study but metolachlor allowed the establishment of a greater fall panicum (Panicum dichotomiflorum Michx. # PANDI) population in this and an additional 3-yr study than in chloroacetamide-free checks. In the 3-yr study in which giant foxtail (Setaria faberi Herrm. # SETFA) was dominant, annual applications of metolachlor and a microencapsulated formulation of alachlor provided better control in the second year than the emulsifiable concentrate formulation of alachlor, but formulation differences diminished in the third year.

Research was conducted from 1983 through 1986 to compare the competitiveness of three cotton cultivars of different height with johnsongrass. Cultivars evaluated were: ‘1209-619-7’, ‘TAMCOT SP37-H’, and 'Stoneville 213’, which had an average height at maturity of 66, 122, and 168 cm, respectively. Each cultivar was grown with johnsongrass densities of 0, 4, and 6 plants/6 m of row with a 1-m row spacing. Johnsongrass biomass data confirmed that all three cultivars did compete with johnsongrass, but regression analyses using cultivar as a covariate revealed no difference in the competitiveness of the three cultivars.

The efficacies of microencapsulated (ME) and emulsifiable concentrate (EC) formulations of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] were compared in petri dish and soil bioassays. At equimolar concentrations, EC-alachlor inhibited shoot growth of barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG], large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA], and fall panicum (Panicum dichotomiflorum Michx. # PANDI) more than ME-alachlor. ME- and EC-metolachlor caused similar effects on the three grass weeds tested. ME- and EC-alachlor in combination caused effects on barnyardgrass shoot growth intermediate to results with either formulation alone. Air-drying and remoistening of alachlor-treated filter paper or soil before sowing barnyardgrass or fall panicum caused greater shoot length and fresh weight reduction than ME-alachlor that was not dried.

The growth and development of leafy spurge (Euphorbia esula L. #3 EPHES) collected during postsenescent dormancy and grown in the greenhouse was increasingly stimulated by chilling treatments longer than 14 days duration at 0 to 6 C. Production of stems with flower buds, primary flowers, and secondary flowers was greater in plants chilled for 42 days or more. The effects of chilling on total number of stems, number of strictly vegetative stems, or number of stems with vegetative branching were not significant. The height of the tallest stem per pot was influenced by chilling longer than 42 days. Growth rate also increased as a function of chilling duration. Based on our findings, we believe that there is little possibility that any significant growth can occur in the postsenescent period because of the prevailing climatic conditions found in areas of leafy spurge distribution in North America.

Acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} and bentazon [3-(1-methylethyl-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] plus acifluorfen were applied through hydraulic flat-fan nozzles or controlled-droplet applicators (CDA) in water plus surfactant, soybean [Glycine max (L.) Merr.] oil and water emulsions, and soybean oil alone. Except for inadequate weed control with CDA applications at 7 L/ha, method of application did not affect weed control of common cocklebur (Xanthium strumarium L. #3 XANST) or smooth pigweed (Amaranthus hybridus L. # AMACH) at high rates of bentazon plus acifluorfen (560 plus 280 g ai/ha or above). With low rates (280 plus 140 g/ha or less), hydraulic flat-fan nozzles were more effective than CDA applications. Early CDA applications of acifluorfen in an oil carrier at a volume of 9 L/ha were as effective as hydraulic nozzle applications at a carrier volume of 47 L/ha. Later applications resulted in inadequate weed control. Increasing soybean oil concentration from 2.5 to 40% (v/v) in acifluorfen spray mixtures did not significantly increase the phytotoxicity of acifluorfen.

Preplant-incorporated (PPI) applications of 280 g ai/ha of imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} had significantly greater persistence than preemergence surface (PES) applications throughout the growing season in 1985. In 1984 there was no statistical difference in imazaquin remaining between PPI and PES treatments. Very little imazaquin was detected below 10 cm in the soil profile for all sampling dates each year. Imazaquin dissipated rapidly both years during the first 30 days following PPI and PES applications. A subsequent decrease in the dissipation rate occurred in the next 120 days of the growing season. Spring tillage had no significant effect on injury to corn (Zea mays L.) planted into the field the year following imazaquin application. Corn planted in 1986 into imazaquin-treated plots of 1985 had no growth reduction when compared to corn grown in plots where zero imazaquin had been applied. However, corn planted in 1985 into imazaquin applications of 1984 had significant injury. Greatest injury occurred where imazaquin had been incorporated, and injury increased as imazaquin rate was increased.

Field experiments were conducted to evaluate johnsongrass control in no-till grain sorghum with glyphosate treatments applied in mid-June, late July, and mid-September before planting grain sorghum the following spring. Mid-June applications provided the best johnsongrass control. Ammonium sulfate enhanced the activity of glyphosate for only the late-July applications. In separate experiments, herbicide systems comprised of fall applications of glyphosate and/or spring applications of foliar and residual herbicides were evaluated. Fall applications of glyphosate provided superior johnsongrass control and grain sorghum yields.

Experiments conducted for two consecutive years indicated measurable interference of barnyardgrass, large crabgrass, and giant foxtail with container-grown Bailey's redosier dogwood as early as 21 days after transplanting of grass seedlings into the containers. Few differences in interference were seen among the three grass weeds. Grass weed densities ranging from one to six weeds per container reduced the dogwood growth. By the termination of the studies, dogwood shoot dry weight, averaged over all grass weeds, was decreased as much as 72% by five weeds per container. Eight weeks after recommended rates of fenoxaprop, haloxyfop, and ethyl ester of quizalofop were applied to dogwood, no phytotoxicity was apparent. These compounds exhibited selectivity for postemergence use in Bailey's redosier dogwood.

The growth regulator NAA was investigated to determine whether it would control creeping woodsorrel (Oxalis corniculata L. # CYPES) with no phytotoxicity to container ornamental species. Dosage, carrier volume, number of applications, and plant age and growth stage were examined as factors in the phytotoxicity of NAA. Creeping woodsorrel response to the ethyl ester formulation of NAA was linear for dosages up to 5.6 kg/ha; this rate resulted in about 80% injury in all experiments. NAA applied at 8.4 and 11.2 kg/ha achieved 99 and 100% control, respectively. Neither carrier volume nor split applications had any effect on phytotoxicity of NAA. In all experiments, phytotoxicity appeared to increase until around 2 to 3 weeks from application. Phytotoxicity to creeping woodsorrel was related to plant age; as plant age at the time of treatment increased, the level of injury decreased. When plants treated with NAA at rates up to 2.8 kg/ha were cut back to soil level, some regrowth occurred in all cases. Rates of NAA that controlled creeping woodsorrel (5.6 and 11.2 kg/ha) were not phytotoxic to several ornamental species.

Field experiments were conducted during 1985 and 1986 to determine the response of soybean [Glycine max (L.) Merr. ‘Coker 156’], pitted morningglory (Ipomoea lacunosa L. # IPOLA), and ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. # IPOHE] to acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, fomesafen {5-[2-chloro-4-(trifluoromethyl) phenoxy]-N-(methylsulfonyl)-2-nitrobenzamide}, and lactofen {(±)-2-ethoxy-1-methyl-2-oxoethyl-5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-dinitrobenzoate}. Acifluorfen and lactofen were more phytotoxic to soybean 15 days after treatment (DAT) than fomesafen. All herbicides at low rates controlled 80% or more pitted morningglory. However, only the high rates (0.6 kg ai/ha) of acifluorfen and fomesafen controlled 80% or more ivyleaf morningglory 90 DAT. Full-season competition from untreated pitted morningglory reduced soybean seed yields 44 and 22% in 1985 and 1986, respectively, compared to 58 and 49% with untreated ivyleaf morningglory. Soybean seed yields were higher in plots receiving acifluorfen or fomesafen applications than lactofen applications.

Field and laboratory experiments were conducted with unicorn-plant to determine conditions required for germination and to measure seed production. Field-grown plants produced an average of 122 pods/plant with an average of 71 seed/pod. The highest percent germination from seed harvested in 1980 occurred following a 2-week prechill treatment of 4 C. Germination increase was greater by removing the seed coat and the membrane enclosing the embryo than by removing the seed coat alone. Germination of seed from all pod compartments was similar. Aqueous extracts of unicorn-plant testa, leaf, stem, root, and exocarp were inhibitory in petri dish bioassays to cotton radicle growth. Extracts of stem, root, and exocarp were inhibitory to wheat radicle growth, and extracts of endocarp, leaf, and exocarp were inhibitory to unicorn-plant radicle growth. Seed buried in the field 10 cm deep for 1 to 8 months showed increased germination over time. Germination was lower when seed were stored at 4 C for 1 to 8 months in a soil having 25% (v/v) water.

In field studies, wild oat control with AC 222,293 and difenzoquat was not reduced when each herbicide was applied in combination with thiameturon or DPX-L5300. Mixtures of barban with thiameturon gave wild oats control similar to barban applied alone, but mixtures of barban with DPX-L5300 sometimes gave less wild oats control than barban applied alone. Control was reduced when diclofop was applied in combination with thiameturon in 1985 but not in 1986. When antagonism occurred, addition of crop oil concentrate (COC) at 1.2 L/ha to the diclofop-thiameturon spray mixture overcame the antagonism. When diclofop was applied in combination with DPX-L5300, control was reduced and antagonism could not be overcome by increasing the diclofop rate or by adding COC to the spray mixture. In greenhouse studies the inert ingredients in the thiameturon and DPX-L5300 formulations did not antagonize diclofop activity on wild oats. TLC analysis of 14C-diclofop solutions with and without thiameturon or DPX-L5300 revealed neither degradation products of diclofop nor evidence of complexing between diclofop and thiameturon or diclofop and DPX-L5300. Diclofop antagonism by thiameturon or DPX-L5300 was not due to a chemical or physical interaction between the herbicides in the spray mixture.

Corn cultivars differed in their response to imazaquin applied from 35 to 280 g ai/ha, as measured by shoot length. No cultivar was tolerant to all imazaquin application rates. There was less corn injury from imazaquin in studies conducted during the second and third years of research than in the first year. Preplant-incorporated applications caused significantly more injury than preemergence applications in two out of three studies. Lack of rainfall in 1985 and 1987 may have limited movement of imazaquin in the soil profile, which resulted in preemergence applications of imazaquin, causing very little corn injury. In all years of research, 35 g/ha of imazaquin incorporated in the top 6 cm of the soil profile resulted in 17 to 33% reduction in corn height 28 days after planting, when averaged across all the corn cultivars. Significant yield reductions (LSD = 0.10) of 45, 19, and 18% occurred in 1987 from preplantincorporated applications of 140, 70, and 35 g/ha, respectively, which had reduced corn height 46, 23, and 19%, respectively, when measured 28 days after planting.

Several herbicides were evaluated for control of white locoweed (Oxytropis sericea Nutt. T & G # OXRMA) and changes in botanical composition on two sites on high-elevation rangeland. White locoweed was more abundant and its population more stable on the rocky subalpine wind-swept ridge site than on the subalpine loam site. Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) at 0.6 and 1.1 kg ae/ha, and 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 2.2 and 4.5 kg ae/ha eliminated white locoweed on the subalpine loam site, although the population on this site declined naturally. Clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) was the most effective herbicide on the subalpine wind-swept site. Clopyralid at 0.3 and 0.6 kg ae/ha, dicamba (3,6-dichloro-2-methoxybenzoic acid) at 2.2 kg ae/ha, and 2,4-D at 1.1 kg ae/ha plus clopyralid or picloram at 0.3 kg/ha killed all white locoweed plants. Lower rates of clopyralid (0.1 kg/ha), dicamba (0.6 and 1.1 kg/ha), 2,4-D (2.2 and 4.5 kg/ha), and triclopyr {[(3,5,6-trichloro-2~pyridinyl)oxy] acetic aicid)} (0.6, 1.1, and 2.2 kg ae/ha) killed 45 to 84% of white locoweed plants. Grass cover increased on most treated areas where white locoweed, forbs, and sagebrush declined. Cattle consumption of white locoweed declined following application of 2,4-D.

Reduced effectiveness of carbamothioate (thiocarbamate) herbicides in certain soils has been attributed to rapid herbicide degradation by soil microorganisms. Studies were conducted to determine if greater populations of EPTC (S-ethyl dipropyl carbamothioate)-degrading microorganisms were responsible for increased rates of degradation observed following repeated applications of EPTC to a Grenada silt loam soil. EPTC-degrading microorganism populations, measured with a 14C-MPN (most-probable-number) technique, were not larger in soils with accelerated rates of EPTC degradation, and degrader populations did not increase after application of 6 mg EPTC/kg of soil. Degrader populations increased after application of 60 mg EPTC/kg of soil only in soil previously treated for 6 yr with EPTC. Increased rates of metabolism of EPTC were apparently responsible for the increased rates of degradation, rather than increased populations of degraders.