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.

To assess the influence of long-term fertilization on weed communities of early and late rice crops, the weed species composition was investigated in experimental plots initiated in 1981 at the Key Field Experimental Monitoring Station of the Reddish Paddy Soil Eco-Environment in Wangcheng, China. The treatments were (1) a control (CK), no fertilizer; (2) N–P, no K; (3) N–K, no P; (4) P–K, no N; (5) N–P–K; (6) N–P–K + Ca, N, P, and K plus lime; (7) N–P + S, N and P plus additional rice straw return; (8) N–P–K + S, N, P, and K plus additional rice straw; (9) N–K + M, N and K plus swine manure. The results indicated that weed flora composition and density were influenced by the different fertilization treatments. Multivariate analyses indicated that changes in the weed community composition were primarily due to soil-available N, followed by light intensity on the field surface, and soil-available P. More weed species and total weed density were observed in the control and P–K plots than in plots in which N, P, and K were applied together. Omission of N application had a greater effect on the weed community than the omission of P or K applications. Nutrients derived from synthetic fertilizers and organic manure or the additional application of lime had no obvious effect on the weed community of late rice crops.

Annual sowthistle (Sonchus oleraceus L.) is a major weed of mungbean crops in Australia. Resistance in this weed to several herbicide groups is a challenging issue for its management. Hence, cultural weed management strategies, such as increasing the crop competitive ability through increased stand density, should be considered to reduce reliance on herbicides. It was hypothesized that a competitive crop stand may reduce the growth and seed production of S. oleraceus. Two pot studies were conducted, and each study was repeated once. The first study evaluated the effect of different mungbean [Vigna radiata (L.) R. Wilczek] densities (0, 82, 164, 246, and 328 plants m−2) on S. oleraceus growth and seed production, while the second study focused on glyphosate-resistant and glyphosate-susceptible biotypes of this weed in competition with densities of 0, 82, and 164 mungbean plants m−2. Although increasing mungbean density from 0 to 82 and 164 plants m−2 reduced S. oleraceus seed production by 55% and 78%, respectively, a large number of seeds were produced, even at the mungbean density of 328 plants m−2 (1,185 seeds plant−1). Both glyphosate-resistant and glyphosate-susceptible biotypes of S. oleraceus responded similarly to the increase in mungbean density. The results of the second study showed that height, leaves, number of inflorescence, and seed production per plant of both glyphosate-resistant and glyphosate-susceptible biotypes were reduced but not suppressed adequately. The glyphosate-resistant biotype produced fewer leaves and less biomass and, consequently, its seed production was 24% less compared with the glyphosate-susceptible biotype in the no-competition treatment. Both biotypes of S. oleraceus produced about 4,000 seeds plant−1 in competition with 164 mungbean plants m−2. The results suggest that crop competition alone cannot provide satisfactory control of S. oleraceus; therefore, for effective and adequate weed management, other practices such as PRE herbicides should be integrated with increased crop density.

We developed two leafy spurge bacterial artificial chromosome (BAC) libraries that together represent approximately 5× coverage of the leafy spurge genome. The BAC libraries have an average insert size of approximately 143 kb, and copies of the library and filters for hybridization-based screening are publicly available through the Arizona Genomics Institute. These libraries were used to clone full-length genomic copies of an AP2/ERF transcription factor of the A4 subfamily of DEHYDRATION-RESPONSIVE ELEMENT-BINDING PROTEINS (DREB) known to be differentially expressed in crown buds of leafy spurge during endodormancy, a DORMANCY ASSOCIATED MADS-BOX (DAM) gene, and several FLOWERING LOCUS T (FT) genes. Sequencing of these BAC clones revealed the presence of multiple FT genes in leafy spurge. Sequencing also provided evidence that two different DAM transcripts expressed in crown buds of leafy spurge during endo- and eco-dormancy result from alternate splicing of a single DAM gene. Sequence data from the FT promoters was used to identify several conserved elements previously recognized in Arabidopsis, as well as potential novel transcription factor binding sites that may regulate FT. These leafy spurge BAC libraries represent a new genomics-based tool that complements existing genomics resources for the study of plant growth and development in this model perennial weed. Furthermore, phylogenetic footprinting using genes identified with this resource demonstrate the usefulness of studying weedy species to further our general knowledge of agriculturally important genes.

Bittercress (Brassicaceae) is one of the most prolific and costly weeds of the container nursery industry. Bittercress accessions from container nurseries throughout the major production zones in the United States were examined and compared with herbarium specimens. The identity of these weedy bittercress species were further explored using sequences of the nuclear ribosomal DNA (nrDNA) internal transcribed spacer (ITS) region and the nrDNA region for the COP1-interacting protein 7 (CIP7). Four species of bittercress were detected in the nursery industry of the United States, including New Zealand bittercress, hairy bittercress, flexuous bittercress, and little bittercress. The taxon referred to here as Cardamine flexuosa With. (flexuous bittercress) likely contains two genotypes previously reported as European C. flexuosa and Asian C. flexuosa. Phylogenetic relationships between the four species we examined, particularly in relationship to flexuous bittercress, were not fully resolved by the molecular evidence generated for this study. New Zealand bittercress is nonnative and does not appear in current keys to the species for the United States. Flexuous bittercress is also an alien species, which appears in some U.S. keys but not in all. To aid nurserymen and botanists in identification of these four closely related bittercress species, a key was developed and is accompanied by detailed descriptions and illustrations.

Practical and economical weed control measures are a necessary part of tree fruit and grape production. Weeds and grasses are serious competitors of fruit plants for moisture and nutrients; they provide cover for destructive mice, and interfere with harvest of the crop.

Oats, sesbania (Sesbania macrocarpa Muhl.) and purple nutsedge (Cyperus rotundus L.) were grown as test plants in nine different soil types treated with 0, 0.5, 1, 2, 4, 8, and 16 ppm of ethyl N,N-di-n-propylthiolcarbamate (EPTC). Toxicity of EPTC was negatively correlated with the organic matter of the soil. A positive correlation was found between the sand and silt content of the soil and EPTC toxicity to oats and nutsedge. Toxicity of EPTC was not correlated with soil pH, cation exchange capacity, clay content, general reaction, or parent material. EPTC induced a dormancy of nutsedge tubers, of which the length was inversely related to the organic content of the soil.

Application of 20 to 40 lb/A dichlobenil made prior to emergence accomplished various degrees of control of pondweeds (Potamogeton diversifolius, P. foliosus, P. pectinatus, P. pusillus) and a slender naiad (Najas flexilis). Coontail (Ceratophyllum demersum) was affected only by the higher dosage. Limited control and growth inhibition was achieved on several forms of algae in early spring applications. However, applications made to rooted submersed aquatic plants and filamentous algae (Cladophora, Pithophora and Chara) at postemergence stage of development had little herbicidal effect.

Dichlobenil was not acutely toxic to fish at herbicidal concentrations. The range of median tolerance limits was 10 to 20 ppmw for pumpkinseed (Lepomis gibbosus), bluegill (L. macrochirus), redear sunfish (L. microlophus), and largemouth bass (Micropterus salmoides).