In the discipline of Weed Science, nuclear magnetic resonance (NMR) has been used extensively for obtaining structural information on herbicide compounds in the areas of herbicide synthesis, metabolism, and environmental degradation. However, little research has been published with regard to the utilization of NMR in determining molecular interactions in the spray solution. The molecular influence of citric add and an organosilicone adjuvant on glyphosate was analyzed with NMR spectrometry. 14C-glyphosate absorption studies showed a decrease in glyphosate absorption by sunflower when Ca2+ was added to the spray solution. This absorption antagonism was overcome with the inclusion of an organosilicone adjuvant. 1H-NMR was used to stow that the organosilicone adjuvant did not directly interact with the glyphosate molecule nor did it prevent the formation of Ca-glyphosate. Citric add was effective in overcoming the Cat2+ antagonism of glyphosate activity when the citric add concentration was 2× or 4× the Ca2+ molar concentration based on plant fresh weight and plant height, respectively. 1H-NMR was utilized to show that citric acid reacted with Ca2+ in solution to produce Ca-citrate and prevent the formation of Ca-glyphosate. NMR was an effective technique for characterizing chemical interactions among the spray solution components.

Autoradiography and radioassay results indicated that 14C-picloram (14C-4-amino-3,5,6-trichloropicolinic acid) was absorbed and translocated rapidly in Canada thistle [Cirsium arvense (L.) Scop.], soybean [Glycine max (L.) Merr. ‘Harosoy 63’], and barley (Hordeum vulgare L. ‘Parkland’) following foliar or root application. Foliar absorption was much faster and more complete in soybean and Canada thistle than in barley. The radioactivity from 14C-picloram accumulated in shoot meristems in Canada thistle and soybean, whereas in barley it was distributed throughout the plant following uptake by foliage or roots. Decarboxylation of 14C-picloram by foliarly-treated Canada thistle, soybean, and barley plants did not occur in appreciable amounts. Chromatographic analysis of ethanol extracts of plants treated with 14C-picloram up to 20 days revealed no evidence of picloram metabolism by these plant species. It is concluded that differences in absorption and in distribution patterns of picloram after shoot or root uptake contribute greatly to the expression of its selective action in the species studied.

Roller-applied picloram (4-amino-3,5,6-trichloropicolinic acid) at a concentration of 30 to 60 g ae/L gave similar control to leafy spurge (Euphorbia esula L. ♯ EPHES) as spray-applied picloram at 1.1 to 2.2 kg ae/ha. Leafy spurge control was most effective when the roller applicator was adjusted to treat a maximum amount of stem tissue with a 60 g/L picloram solution. Control was not improved by including a petroleum oil or surfactant additive. Fall applications of roller-applied picloram tended to provide better control than spring applications. When used on dense leafy spurge stands, the roller applicator applied only 40% as much picloram as spray treatments of 2.2 kg/ha. However, picloram residues in soil following roller application were similar to those from picloram at 0.3 to 1.1 kg/ha applied as a spray.

The influence of several factors on the injury to corn (Zea mays L.) seedlings from high rates of EPTC (S-ethyl dipropylthiocarbamate) + R-25788 (N,N-diallyl-2,2-dichloroacetamide) was determined in growth chambers. This herbicide combination severely injured 6% of the corn seedlings at rates as low as 14 ppm if the herbicide was poorly incorporated into the soil. If thoroughly incorporated, severe injury did not occur unless the rate of application exceeded 56 ppm. Decreased injury resulted when seed were placed so as to insure rapid shoot emergence. Seed planted at 2 cm with its coleoptile pointed upward or horizontally (with posterior facing upward) was injured less than in other positions, Corn cultivars differ in their susceptibility to EPTC + R-25788 at 30 but not at 20 C. Of the several corn cultivars tested at 30 C, SX-98 was the least injured by EPTC + R-25788. Corn injury was progressively reduced as leaching volumes were increased and as the time from herbicide application to corn planting was increased.

Rough-rice yield of drill-seeded paddy rice (Oryza sativa L. ‘Lebonnet’ and ‘Starbonnet’) at stands of 215 to 270 plants/m2 at Stuttgart, Arkansas were reduced 18% by season-long competition of spreading dayflower (Commelina diffusa Burm. f. ♯3 COMDI) at a density of 22 plants/m2. Competition durations of 20, 40, 60, or 80 days did not reduce rice yields. None of the durations of competition affected head-rice yields (percent whole milled kernels) or germination of rice seed.

A set of universal and degenerate primers has been designed to clone (by polymerase chain reaction [PCR]) the conserved domains of the acetolactate synthase (ALS) gene where mutations confer resistance to ALS herbicides in plants. These primers were successful in cloning conserved domains of ALS in all monocotyledonous and dicotyledonous plants tested to date, as well as that of bacteria. Total genomic DNA was used as the source of target DNA because no introns were found in the sequences to be amplified. The design of the universal primers was performed after subtle modifications of the consensus degenerate hybrid oligonucleotide primers approach, which implies the synthesis of hybrid oligonucleotide primers containing fixed clamp 5′ and degenerate core 3′ sequences. Optimizations of PCR reactions were done according to a Taguchy approach described for the first time with degenerate oligonucleotides. This method optimizes a PCR reaction using four variables (deoxynucleoside triphosphate, DNA, primers, and Mg2+) under three different concentrations per variable using just nine reactions. The ALS herbicide-binding domains from many susceptible and resistant plants can be cloned and sequenced in a few hours by using only 100 mg of starting plant material, like one leaf or several small seedlings or seeds.

Analysis of soil in which corn (Zea mays L.) has been grown annually for 9 yr with or without yearly applications of 3.4 kg/ha atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] indicated that long-term atrazine use had little effect upon soil microbes or biochemical processes. With the exception of a transient inhibition of bacterial growth during the first week after field application, repeated applications did not affect the numbers of viable bacteria or fungi, relative abundance of bacteria producing hydrolytic enzymes, or soil enzyme levels.

Research was conducted to determine the competitiveness and fitness of a protoporphyrinogen oxidase (protox)-resistant common waterhemp biotype. Protox-resistant and protox-susceptible biotypes were grown under noncompetitive and competitive arrangements in the greenhouse. In the noncompetitive study, a single plant of each biotype was planted separately in 15-cm-diam pots. Photosynthesis, leaf area, and plant biomass were measured 10, 20, 30, and 40 d after transplanting (DATP). In general, photosynthesis rate and plant biomass were similar between biotypes. However, the protox-resistant biotype had higher leaf area than the susceptible biotype at 20, 30, and 40 DATP. A replacement series study was conducted in the greenhouse to evaluate the relative competitiveness of protox-resistant and protox-susceptible common waterhemp. Photosynthesis, leaf area, plant height, and plant biomass were measured 7, 14, 21, and 28 DATP. Protox-resistant and -susceptible common waterhemp were equally competitive 28 DATP. Relative crowding coefficient values 28 DATP were 0.86, 0.89, 1.09, and 1.13 for photosynthesis, leaf area, plant height, and plant biomass, respectively. This suggests protox-resistant and -susceptible common waterhemp were equally competitive and the frequency of protox-resistant biotype is unlikely to decrease in the absence of protox–herbicide selection pressure.

Field and laboratory experiments were conducted in 1983 and 1984 to compare the degradation of dichlormid (2,2-dichloro-N,N-di-2-prophenylacetamide), dietholate (O,O-diethyl O-phenylphosphorothioate), EPTC (S-ethyl dipropyl carbamothioate), and butylate [S-ethyl bis(2-methylpropyl) carbamothioate] in soils that had or had not been previously treated with each chemical. EPTC + dichlormid, butylate + dichlormid, EPTC + dichlormid + dietholate, or butylate + dichlormid + dietholate were applied annually for 4 yr to field plots to establish treatment histories. Butylate and EPTC degradation was enhanced in soils with previous histories of butylate and EPTC, respectively. Degradation rates of dietholate were equivalent in untreated soils or soils previously treated with EPTC + dietholate or butylate + dietholate.

Emergence of tall morningglory [Ipomoea purpurea (L.) Roth] seedlings was delayed and reduced as planting depths increased from 1.3 to 5.0 cm. Development of seedlings emerging from 3.8 cm or greater depth was delayed for up to 4 weeks as indicated by dry weight accumulation. In both greenhouse and field studies, chemical control of tall morningglory was generally greater when seedlings emerged from planting depths of 2.5 cm or greater. The competitive ability of tall morningglory, as indicated by yield reduction of cowpea [Vigna sinensis (L.) Endl], was dependent upon both planting depth and duration of infestation. Cowpea yields were reduced more by the tall morningglory plants that emerged from 1.3 cm than by those that emerged from greater planting depths for a given infestation period.

Five rice (Oryza sativa L.) cultivars were evaluated in the greenhouse for tolerance to fenoxaprop {(±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoic acid}. Rice was more tolerant to fenoxaprop when flooded at 7 days after spraying, based on trends in reduction of weight of seedling topgrowth. ‘Lebonnet’ was the only cultivar that responded differently when five cultivars were compared. In the field, rice yield was not adversely affected by fenoxaprop applied at 168 g ai/ha and flooded 1 to 10 days after treatment, but yield increased as the time interval between application of 336 g ai/ha and flooding increased. Yield data suggested that flooding should be delayed at least 5 days when rice is treated with the high rate. The cultivar ‘Newbonnet’ was slightly less tolerant than 'Starbonnet’ in the field.

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.

Responses of weeds and sugarbeets (Beta vulgaris L.) to postemergence treatments of methyl m-hydroxycarbanilate m-methylcarbanilate (phenmedipham) and two analogues were evaluated in six field studies. Phenmedipham at 1.7 kg/ha controlled foxtail millet (Setaria italica (L.) Beauv.) and kochia (Kochia scoparia (L.) Schrad.) better than 2.2 kg/ha of methyl m-hydroxycarbanilate carbanilate and ethyl m-hydroxycarbanilate carbanilate. Pigweed (Amaranthus spp.) was controlled better by the analogues at 1.1 kg/ha than by phenmedipham. The foliar growth of sugarbeets was generally suppressed more by the analogues than by phenmedipham, but injury was not considered detrimental at 1.1 kg/ha. Yield of sugarbeet roots and sugar was reduced by 7% or less by phenmedipham at rates of 1.1 to 4.5 kg/ha, but these yield reductions were associated primarily with the failure of phenmedipham to completely control all weeds for 5 to 9 weeks after treatment.

Research was conducted to determine the influence of soil fertilization and mowing on persistence of Indian mockstrawberry and common blue violet in an old, weakened tall fescue lawn. Fertilization treatments included: F0 = none applied; F1 = spring and fall application of 0.49 kg N, 0.21 kg P, and 0.41 kg K 100 m-2; and F2 = spring and fall application of twice the F1 rate. Mowing treatments were: M0 = not mowed; and M1 and M2 = mowing heights of approximately 4 and 6 cm, respectively, at biweekly intervals. Persistence of both weeds was influenced more by mowing than by fertilization. Survival of Indian mockstrawberry was greatest when mowed at 6 cm and not fertilized and lowest when highly fertilized and not mowed. Blue violets were virtually eliminated by either mowing treatment and did not respond to fertilization. Mowing and fertilization effectively reduced survival of Indian mockstrawberry and common blue violet in the tall fescue lawn.

Weed control, yield, quality, and net return in reduced-cost and standard weed control systems were studied in “Sunbelt runner’ peanuts (Arachis hypogaea L.) planted in a twin-row pattern in 1982 to 85 at Tifton, GA, and 1982 to 84 at Headland, AL. Reduced herbicide rates and/or less expensive herbicides were used to decrease weed control costs. In years and locations where weed populations were low there were no differences in weed control, crop yield, or quality. The lowest cost treatment, which included three applications of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), caused reduced weed control at both locations in 1982 and reduced yield in 1982 and 1984. None of the systems consistently resulted in the highest weed control, crop yield, or quality. A system including reduced rates of preplant-incorporated herbicides followed by two applications of paraquat performed as well as the standard system but cost about 40% less. Due to low cost and generally high yields this system resulted in consistently high net returns. Results indicate that the potential exists for reducing herbicide inputs without sacrificing yield or quality.

Pennsylvania smartweed (Polygonum pensylvanicum L.) achenes were harvested from plants growing either free from competition or in competition with corn (Zea mays L. ‘Pioneer 3780′) plants. Seeds were dormant when harvested. After 15 weeks of prechilling, 4 and 35% of the seeds germinated from plants with and without corn competition, respectively; after 30 weeks of prechilling, more than 92% of all seeds germinated. Scanning electron microscopy revealed that the carpel walls of achenes from plants with corn competition were porous with many channels. Carpel walls of achenes from plants without corn competition were without pores and channels. Transmission electron microscopy showed more lipid bodies in the embryo epidermal cells of seeds from plants with corn competition. Cell walls of embryos from non-prechilled seeds from plants with corn competition contained lipoidosomes that traversed cell walls. Lipoidosomes did not occur in cells of prechilled seeds.

Viable cutleaf groundcherry (Physalis angulata L. var. angulata) seed were produced 4 weeks after flowering began. Constant temperatures of 10 and 40 C totally inhibited germination. Varying photoperiods had no effect on the germination. Seedling emergence decreased (89% to 0%) as planting depth increased (0 to 10 cm). Greater than 97% preemergence control of cutleaf groundcherry was obtained with metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea], alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2 -1,3,4-oxadiazolin-5-one], oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene], and bifenox [methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate]. Postemergence applications of dinoseb (2-sec-butyl-4,6-dinitrophenol), chloroxuron {3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea}, naptalam (N-1-naphthylphthalamic acid) plus dinoseb, oxyfluorfen, and acifluorfen {sodium 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate} linuron plus 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid], metribuzin plus 2,4-DB, and bifenox resulted in 96 to 100% control of cutleaf groundcherry. When confined to the soybean [Glycine max (L.) Merr.] drill, no significant reductions in soybean leaf area index (LAI), plant height, dry weight accumulation, crop growth rate (CGR), or seed yield were obtained from cutleaf groundcherry competition at densities as high as 60 plants/m of row. Presently, cutleaf groundcherry does not appear to be a major weed problem in soybean production.

Handweeding sugarbeets (Beta vulgaris L. ‘Mono Hy D2’) for 8 weeks after planting prevented sugarbeet yield losses. Weeds invading sugarbeet plots at the two-leaf stage (4 weeks after planting) reduced sugarbeet yields 26%. Cycloate (S-ethyl N-ethylthiocyclohexanecarbamate) caused more visual sugarbeet injury and stand reduction than did ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate]. Broadleaf and grass weeds differed in their response to cycloate and ethofumesate, but overall, total weed yields were lower in plots treated with cycloate. Ethofumesate injured sugarbeets more when applied before planting and incorporated into the soil than when applied preemergence. Herbicides applied when sugarbeets had four to six leaves generally injured sugarbeets less, but controlled weeds less effectively, than when sugarbeets had two to four leaves. None of these herbicide treatments were as effective as handweeding in providing season-long weed control. Every 1120 kg/ha of oven dry weeds present in sugarbeet fields corresponded to a decrease in sugarbeet root yields of 10 000 to 11 500 kg/ha.

Controlled burning during winter reduced densities of common goldenweed [Isocoma coronopifolia (Gray) Greene] by 33 to 44% and suppressed canopy cover and height of surviving common goldenweeds for 2 yr. Applied to an unburned infestation, 2,4-D [(2,4-dichlorophenoxy) acetic acid] or dicamba (3,6-dichloro-o-anisic acid) granules only partially controlled common goldenweed at rates of 2 kg/ha or less. Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} or picloram (4-amino-3,5,6-trichloropicolinic acid) pellets provided excellent control of common goldenweed if applied at 2 kg/ha during March and at 1 kg/ha if applied after burning in February. The burning pretreatment appeared to synergistically enhance effectiveness of herbicides applied at relatively low rates. Increases in standing crop of buffelgrass (Cenchrus ciliaris L.) following burning were usually small and temporary, but effective herbicide treatments and burn-herbicide combinations increased buffelgrass standing crop by as much as three-fold.

The susceptibility of sweet pepper (Capsicum annuum L. ‘Keystone Resistant Giant’) and tolerance of hot pepper (Capsicum chinense L. ‘Bohemian Chili’) to bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] was demonstrated under greenhouse and field conditions. Sweet pepper growth and fruit production were inhibited by foliar applications of bentazon at rates of 0.6 to 6.7 kg ai/ha. Severity of injury increased with application rate. Injury symptoms in sweet pepper were leaf chlorosis, with necrosis and death of shoot apices. Foliar applications of bentazon to hot pepper resulted in little or no injury. Bentazon inhibited Hill reaction activity of isolated chloroplasts from both species to a similar extent, suggesting that selectivity of this compound in hot pepper is not due to resistance at the chloroplast level.