Fluazifop-P-butyl, a selective graminicide, has been widely used to control annual grass weeds for more than three decades in Taiwan, and a resistant (R) biotype of goosegrass has consequently appeared. In this study, liquid chromatography/tandem mass spectrometry (LC/MS/MS) was applied to analyze metabolites of fluazifop-P-butyl in a R biotype of goosegrass. Six signals, including mass-to-charge ratios (m/z) 512, 432, 423, 415, 314, and 160, in positive scanning mode, and four signals, including m/z 788, 623, 593, and 162, in negative scanning mode, were found in the metabolites of the R and S biotypes, respectively. All of the signals of these metabolites in the R biotype showed higher intensity than those of the S biotype, except for m/z 162. Based on the molecular weights of the fragments (MS2 signal) from the molecules (MS1 signal) and comparison with the Metabolite Link Metabolomics database, MassBank database, and related references, one reduced form of fluazifop acid, i.e., 2-[4-(5- trifluoromethyl-2-pyridyloxy) phenoxy] propanol (MW 313); two types of intermediates of MW 163, i.e., 5-trifluoromethyl-2-pyridone and 5-trifluoromethyl-2-hydroxypyridine (or 2-hydroxy-5-trifluoromethyl pyridine); and five possible conjugated compounds containing a common core fragment (MW 255) from fluazifop acid were identified. In addition, another compound, likely degraded from one of the five conjugated compounds, was also detected. Accordingly, the metabolic pathway of fluazifop-P-butyl in goosegrass is described in this study. An enzyme kinetic study on glutathione S-transferase showed that the R biotype has higher affinities to the substrates reduced glutathione (GSH) and 1-chloro-2, 4-dinitrobenzene, with S/R Km ratios of 3.0 and 2.4, respectively. No difference in Vmax was found, revealing that the S biotype has a strong ability to bind GSH and herbicide or target molecules and showed susceptibility to fluazifop.

Under the erractic rainfall distribution of the Southern Great Plains, average pigweed (Amaranthus sp.) control in five studies with seven herbicides was enhanced by incorporation in 1 or 3 inches of soil with a power rototiller. Compared to no incorporation, 9-inch incorporation improved pigweed control with two herbicides, had no effect on weed control with two others, and decreased weed control with another three. Soil incorporation at 1 or 3 inches did not increase weed control with three compounds if 0.4 inch of rainfall occurred within 2 weeks after application. Incorporation into 1 or 3 inches of soil improved weed control with four herbicides even when rainfall occurred within 2 days after application. In four of the trials, neither herbicides nor incorporation depth affected cotton stand or vigor. Under the soil moisture conditions prevailing in the one trial where yield data were obtained, cotton (Gossypium hirsutum L.) stand and lint yield decreased lineally with depth of soil incorporation. Herbicides did not affect cotton stand or yield.

The environmental effect of weed control systems has stimulated research into new practices for weed control, such as selective herbicide application methods on weed-infested crop areas. This research used the color co-occurrence method (CCM) texture analysis to determine the effects of plant maturity on the accuracy of weed species classification of digitized images. Two different experimental combinations of weed species and maturity level were examined. The weed species evaluated were ivyleaf morningglory, giant foxtail, large crabgrass, and velvetleaf, with soil image sets added to each experiment. One study examined classification accuracies for two weed species at three maturity levels, and the second study examined four weed species at two maturity levels. For each species-maturity level combination, 40 digital images were collected from a manually seeded outdoor plant bed. Digitized images were transformed from the red–green–blue (RGB) color format into hue–saturation–intensity (HSI) format to generate CCM texture feature data. Stepwise variable reduction procedures were used to select texture variables with the greatest discriminant capacity. Then discriminant analysis was used to determine the classification accuracy for the two different experiments. When using HSI texture statistics, discriminant analysis correctly classified weed species within and across maturity levels with an accuracy above 97% for both experimental groups. These image processing algorithms demonstrate potential use for weed scouting, weed infestation mapping, and weed control applications using site-specific farming technology.

Integrated weed management (IWM) decision strategies in herbicide-resistant canola-production systems were assessed for net returns and relative risk. Data from two field experiments conducted during 1998 to 2000 at two locations in Alberta, Canada, were evaluated. A herbicide-based experiment included combinations of herbicide system (glufosinate-, glyphosate-, and imazethapyr-resistant canola varieties), herbicide rate (50 and 100% of recommended dose), and time of weed removal (two-, four-, and six-leaf stages of canola). A seed-based experiment included canola variety (hybrid and open-pollinated), seeding rate (100, 150, and 200 seeds m−2), and time of weed removal (two-, four-, and six-leaf stages of canola). For the herbicide-based experiment, strategies with glyphosate were profitable at Lacombe, but both imazethapyr and glyphosate strategies were profitable at Lethbridge. Weed control at the four-leaf stage was at least as profitable as the two-leaf stage at both sites. For the seed-based experiment, the hybrid was more profitable than the open-pollinated cultivar, seed rates of 100 and 150 seeds m−2 were more profitable than 200 seeds m−2, and weed control at the two- and four-leaf stages was more profitable than at the six-leaf stage. When risk of returns and statistical significance was considered, several strategies were included in the risk-efficient set for risk-averse and risk-neutral attitudes at each location. However, the glyphosate-resistant cultivar, the 50% herbicide rate, and weed control at four-leaf stage were more frequent in the risk-efficient IWM strategy set. The open-pollinated cultivar, 200 seeds m−2 rate, and weed control at the six-leaf stage were less frequent in the set. The risk-efficient sets of IWM strategies were consistent across a range of canola prices.

When glyphosate [N-(phosphonomethyl)glycine] at 0.075 kg/ha, DCPA (dimethyl tetrachloroterephthalate) at 10 kg/ha, and H 26905 [O-ethyl-O-(3-methyl-6-nitrophenyl)-N-sec-butyl phosphorothioamidate] at 0.25 and 0.5 kg/ha were sprayed on foliage of alfalfa (Medicago sativa L. ‘Vernal’) on which field dodder (Cuscuta campestris Yunck.) and largeseed dodder (Cuscuta indecora Choisy) were attached and growing vigorously, almost all visible dodder tissue was killed and alfalfa was not injured noticeably. Some dodder recovered from haustoria within the alfalfa stems and from remnants of twined tendrils, but devastation of the alfalfa by uncontrolled dodder was prevented. PP 009 (butyl 2-[4-(5-trifluoromethyl-2-pyridyloxy)phenoxy] propionate), BAS 9052 (2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one) and RO 13-8895 (acetone-O-[D-2-[p-[(α,α,α-trifluoro-p-tolyl)-oxy] phenoxy] propionyl] oxime) at 0.25, 0.50, or 1.0 kg/ha did not control dodder.

Greenhouse and growth chamber experiments with potted plants were conducted to determine the effects of interspecific root and canopy interference, light intensity, and soil moisture on water uptake and biomass of soybean, common cocklebur, and sicklepod. Canopy interference and canopy plus root interference of soybean with common cocklebur increased soybean water uptake per plant and per unit leaf area. Root interference with soybean decreased common cocklebur water uptake per plant. Canopy interference of soybean with sicklepod increased soybean water uptake per unit leaf area, while root interference decreased uptake per plant. Combined root and canopy interference with soybean decreased water uptake per plant for sicklepod. Soybean leaf area and shoot weight were reduced by root interference with both weeds. Common cocklebur and sicklepod leaf area and shoot weight were reduced by root and canopy interference with soybeans. Only common cocklebur root weight decreased when canopies interfered and roots did not. The relationship between light intensity and water uptake per unit leaf area was linear in both years with water uptake proportional to light intensity. In 1991 water uptake response to tight was greater for common cocklebur than for sicklepod. The relationship between soil moisture level and water uptake was logarithmic. Common cocklebur water uptake was two times that of soybean or sicklepod at −2 kPa of pressure potential. In 1991 common cocklebur water uptake decreased at a greater rate than soybean or sicklepod in response to pressure potential changes from −2 to −100 kPa.

The persistence of hormone-type herbicides in tissues of susceptible crop plants was studied under growth-chamber and field conditions. The susceptible plants selected were tomatoes (Lycopersicon esculentum Mill.), soybeans [Glycine max (L.) Merr.], and turnips (Brassica rapa L.). Foliage of each species was exposed to herbicides at levels that represented spray drift situations, and the decline of residues was investigated through subsequent chemical analysis. The disappearance of 2,4-D [(2,4-dichlorophenoxy)-acetic acid], 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid], mecoprop {2-[(4-chloro-o-tolyl)oxy]propionic acid}, 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and dicamba (3,6-dichloro-o-anisic acid) was almost linear when concentration data were plotted against the logarithm of time. The results indicate that for practical purposes a kinetic rate equation [conc. = a – b log (time)] would describe the residue decline.

Amine formulations of 2,4-D [(2,4-dichlorophenoxy) acetic acid] and MCPA {[(4-chloro-o-tolyl)oxy] acetic acid} caused a reduction in paraquat (1,1-dimethyl-4,4′-bipyridinium ion) phytotoxicity to barley (Hordeum vulgare L. 'Summit′), wheat (Triticum aestivum L. ‘Neepawa′), and wild oats (Avena fatua L.). Dicamba (3,6-dichloro-o-anisic acid) reduced paraquat activity in barley only. Paraquat phytotoxicity was antagonized more by 2,4-D amine at high than at low rates. Higher rates of paraquat relative to a fixed rate of 2,4-D amine overcame the antagonism. Paraquat phytotoxicity was not antagonized by 2,4-D or MCPA amine applied as a separate treatment. The technical components of the 2,4-D- or MCPA-amine formulations were solely responsible for the antagonism. Ester formulations did not affect paraquat phytotoxicity.

The effect of time, flow rate, and temperature on the volatilization of technical grade n-butyl ester of 2,4-D [(2,4-dichlorophenoxy)acetic acid] in a closed air-flow system was evaluated. The amount of ester volatilized was linear with time, at constant temperature and air flow. Volatility increased approximately 8-fold when the temperature was increased from 30 C to 50 C. At 30 C, volatility increased with each doubling of air flow rate from 0.86 nmole/cm2 per hr at 14 L/hr to 1.62 nmole/cm2 per hr at 57.6 L/hr. The effects of temperature, flow rate, and the relationship between vapor pressure and rate of volatilization were also analyzed. The system provided a simple and quantitative method for determining the relative volatilities of both technical and formulated herbicides.

On-farm field experiments were conducted in the Piedmont Plateau and Coastal Plain of North Carolina in 1981 and 1982 to investigate the integration of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} with other chemical and cultural weed control tactics into soybean [Glycine max (L.) Merr.] weed management systems. Sethoxydim at 0.2 kg ai/ha provided control of broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash. # BRAPP], large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA], and fall panicum [Panicum dichotomiflorum Michx. # PANDI) equal to control achieved with registered rates of the soil-applied herbicides alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl)acetanilide] and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). Control of broadleaf weed species with the postemergence herbicides bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4-(3H)-one 2,2-dioxide] and acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} equaled or exceeded the control obtained with the soil-applied herbicides linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5-(4H)-one]. Applications of 0.22 kg/ha of sethoxydim 2, 3, 4, and 5 weeks after soybean planting provided season-long control of fall panicum and crabgrass in 1981. In 1982, crabgrass control was 88 to 99% up to 4 weeks after planting. Later applications provided inadequate control of the grass species. Variations in volume and pressure of application had no effect on control of 10-cm goosegrass [Eleusine indica (L.) Gaertn. # ELEIN] or broadleaf signalgrass with 0.2 kg/ha of sethoxydim. Increasing pressure increased control of 30-cm goosegrass and broadleaf signalgrass. Increasing volume increased only control of goosegrass. Bentazon and acifluorfen provided better control of broadleaf weeds when applied early than when applied late. In two of four experiments tank mixtures of sethoxydim and bentazon resulted in an initial decrease in grass control compared to corresponding sequential applications. Soybean yields were comparable, however.

Germination of dormant wild oat (Avena fatua L. # AVEFA) seed was examined in response to various concentrations of ethephon (2-chloroethylphosphonic acid), KNO3, or both together in the dark at temperatures ranging from 7 to 32 C. Both chemicals significantly (P = 0.05) promoted germination and their effects were additive. Maximum stimulation of germination in response to all treatments occurred at 7 C, with a gradual decrease in reponse as temperature or duration of after-ripening, the seed that retained dormancy during storage remained responsive to ethephon also occurred during storage of mature seed at 3 to 32 C. The rate and extent of this dormancy loss increased with an increase in storage temperature. Regardless of the temperature or duration of after-ripening, the seed that retained dormancy during storage remained responsive to ethephon and KNO3 treatments. Suitable combinations of after-ripening, ethephon, and KNO3 induced over 90% germination of seed that was dormant at maturity. Experimental evidence has been obtained that suggests that this percentage may represent the total number of viable seed in the population. While ethephon promoted seed germination, it severely stunted root and shoot growth of the resulting seedlings. It appears that strategies could be developed to combine the use of ethephon and nitrate with the natural process of after-ripening to enhance and synchronize wild oat germination.

A laboratory study was conducted to determine the effects of two adjuvants and temperatures at time of treatment on efficacy, absorption, and translocation of thidiazuron defoliant on cotton. Five days after treatment at 30/21 C day/night temperatures, leaf drop was 17% with no adjuvant, 37% with addition of crop oil concentrate, 40% with ammonium sulfate, and 75% with two adjuvants combined. At 21/13 C day/night temperatures, there was less than 10% leaf drop with all treatments. At 10 d after treatment, leaf drop was not different among treatments at the high or low temperatures. Shoot regrowth at high and low temperature was reduced 55 to 60% with addition of both adjuvants and 44 to 50% with each adjuvant or with no adjuvant when compared to plants defoliated by hand. Absorption of 14C-thidiazuron was not affected by variations in temperature during the time of treatment but was affected by adjuvants. With no adjuvants, absorption was 7 to 10%. With 1.25% by vol crop oil concentrate, absorption was 33 to 46%. Addition of ammonium sulfate resulted in 18 to 19% absorption, and the combination of ammonium sulfate and crop oil concentrate increased absorption to 65 to 68%. There was no movement of radiolabel away from treated leaves as determined by autoradiographs of treated plants.

Flurtamone and atrazine adsorption to soil was examined using a batch equilibrium method. Flurtamone mobility in packed soil columns under saturated flow conditions was also evaluated. Adsorption was greater for flurtamone than atrazine in the three soils, and the order of adsorption to soil for both herbicides was Greenville sandy clay loam > Cecil loam > Dothan loamy sand. Greater adsorption of each herbicide corresponded to soils with greater organic matter and clay content. The 14C–flurtamone movement under saturated flow conditions in 28–cm soil–packed columns was limited to 16 cm, with no flurtamone leaching from any soil column after the addition of two pore volumes of water. Seventy–five percent of the applied 14C–flurtamone remained in the 0– to 4–cm soil depth in the Greenville sandy clay loam, with less than 5 percent moving to a depth > 4 cm. Flurtamone movement was greater in the Cecil loam and the Dothan loamy sand, with movement in each soil to a depth of 16 and 12 cm, respectively.

Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)-acetanilide] mixed with plaster-of-paris in concentrations of 0.5, 1, 2, and 4% (w/w) was cast into tablets of three sizes. The controlled release of the herbicide was tested by the following methods: (a) in the laboratory with eduction by soaking tablets in water, (b) in the greenhouse with azalea (Rhododendron obtuseum Planch. ‘Richardii’) stock in container, and (c) in the lathe house with azalea stock in containers. In the laboratory experiment, the quantity of herbicide educed from tablets of equivalent volumes, weights, and concentrations were similar regardless of surface area of the three tablet sizes. Successively decreasing quantitites of alachlor were educed with each of the first 10 soakings. Following these soakings, the quantity of alachlor educed per soaking stabilized for the next 30 soakings. In both greenhouse and lathe house experiments, azalea plants treated with as much as 45 kg/ha alachlor formulated in tablet(s) were not damaged. In the best greenhouse treatments, two small tablets per container, effective weed control was obtained for up to 7.5 months from a single application of alachlor at rates of 11, 22, and 45 kg/ha.

Influence of time of planting and distance from the cotton row of pitted morningglory (Ipomoea lacunosa L.), prickly sida (Sida spinosa L.), and redroot pigweed (Amaranthus retroflexus L.) on yield of seed cotton (Gossypium hirsutum L. ‘Stoneville 213’) was determined on Decatur clay loam during 1975 through 1978. Weed growth was measured in 1977 and 1978. Seeds of the three weed species were planted 15, 30, or 45 cm from the cotton row at time of planting cotton or 4 weeks later. Weeds planted 4 weeks after planting cotton grew significantly less than did weeds planted at the same time as cotton. When planted with cotton, redroot pigweed produced over twice as much fresh weight as did prickly sida or pitted morningglory. The distance that weeds were planted from the cotton row did not affect weed growth in 1978, but did in 1977. The distance that weeds were planted from the cotton row did not affect their competitiveness in any year as measured by yield of cotton. However, in each year, yields of cotton were reduced to a greater extent by weeds planted with cotton than when planted 4 weeks later. In 3 of 4 yr, there were significant differences in competitiveness of each of the three weed species with cotton.

Neither glyphosate [N-(phosphonomethyl)glycine] nor the soil metabolite aminomethylphosphonic acid were detected in the first flow of water through two canals following application of glyphosate at 5.6 kg/ha to ditchbanks when the canals were dry. Soil samples collected the day before canals were filled (about 23 weeks after treatment) contained about 0.35 ppm glyphosate and 0.78 ppm aminomethylphosphonic acid in the 0 to 10-cm layer. When glyphosate was metered into the water at a rate calculated to provide 150 ppb in the canal water at a single site on two flowing canals, about 70% of the glyphosate was accounted for 1.6 km downstream from the application site. Thereafter, the rate of disappearance diminished, and about 58% of the applied glyphosate was present at the end of the canals 8 or 14.4 km downstream from the introduction sites.

Photographic techniques and the point-frame transect method were used to study areal growth of kikuyugrass grown in the field without competition in 1990 and 1991. The effect of cutting height on plant extension was also examined in 1991. There were no differences in sward area between eight selections planted in 1990, except on the first measurement date, but selections differed in height and number of primary and secondary stolons. Expansion was irregular in all but one selection, and the patch shape of all irregular selections was defined by the direction and number of the earliest buds to sprout from the stolons. Only two of the eight selections were planted in 1991. Cutting height affected extension from the plot center, linear plant frequency, and plant biomass. The lowest height of cut, 2.5 cm, had the least extension and frequency, the higher cut, 5 cm, was intermediate, and the unmowed plots had the highest extension and frequency. There were differences between selections in number of nodes per unit area, which resulted in differences in response to mowing. Results from a greenhouse clipping experiment showed that although root weight of stolon sections used as propagules was reduced by defoliation, starch content was not affected. The spreading ability of kikuyugrass appears to be based on its ability to branch from its stolons presumably due to reallocation of resources. Based on these results, close mowing could slow the process of kikuyugrass invasion into other turf species but is inadequate to control it.

The most effective and dependable method of controlling wild cane [Sorghum bicolor (L.) Moench] in corn (Zea mays L.) was with a combination of cultivation plus herbicides. Timely cultivations were equally or more effective than preplant herbicides in controlling wild cane, but neither method was adequate by itself. The best herbicide in this study for the control of wild cane in corn was S-ethyl dipropylthiocarbamate (EPTC) alone or in combination with (2,4-dichlorophenoxy)acetic acid (2,4-D) or 2-chloro-4,6-bis-(ethylamino)-s-triazine (simazine). Residual effects of simazine at 4 lb/A in the soil reduced the yield of the following oats (Avena sativa L.) crop 1 out of 3 years.

Soybean [Glycine max (L.) Merr.] cultivars ‘UFV1’ and ‘UFV2’ grown at Viçosa and Florestal, Brazil, and ‘Bonus' and ‘Wells' at Urbana, Illinois, were sprayed at growth stages R5.5 to R6 (full-pod) or R7 (50% defoliation) with the desiccant/herbicides glyphosate [N-(phosphonomethyl)glycine], paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), or sodium chlorate:sodium borate (50:50, w/v). Desiccation of plants by paraquat significantly reduced seed weight and germination at all locations and increased the incidence of Alternaria and Phomopsis spp. at Urbana. Analysis of the combined data from the Brazilian locations showed a significant decrease in seed germination for all treatments except paraquat sprayed on the UFV2 at R7 and sodium chlorate: sodium borate sprayed on UFV1 at R7. Herbicide application at R7 did not result in consistent increases in seedborne Fusarium or Phomopsis spp. at any Brazilian location. Rainfall and temperature at seed maturation were more important variables in pod-to-seed infection by these fungi than increased rates of tissue senescence caused by the desiccants.

Methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy) phenoxy] propanoic acid} (diclofop as used herein refers to the methyl ester) added to nutrient solution inhibited adventitious root development and reduced the mitotic index in adventitious root tips of wheat (Triticum aestivum L. ‘Neepawa’) and wild oat (Avena fatua L.). Elongation of wild oat roots was significantly inhibited by 0.15 μM diclofop 24 h after treatment; whereas, wheat roots were unaffected at concentrations less than 1.5 μM even at 12 days, indicating at least a 10-fold difference in sensitivity. Initiation of new adventitious roots was reduced in both species by 0.30 μM diclofop. Mitotic index was more severely reduced at lower concentrations and after a shorter exposure in wild oat than in wheat. Histological studies showed that 24 h after wild oat roots were treated with 0.30 μM diclofop for 24 h, severe damage occurred to tissues within the developing central cylinder, close to the root apex. Disruption of cortical and epidermal cells generally was not as severe until 4 to 7 days after treatment. By 12 days the entire root tip was almost completely obliterated, with only the epidermal cell walls remaining intact.