bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of glyphosate application timings and methods on glyphosate-resistant cotton
Authors: Viator Ryan P. , Jost Phil H. , Senseman Scott A. , Cothren J. T.
Published: July 2006

Under certain conditions, application of glyphosate to glyphosate-resistant (GR) cotton can lead to fruit shedding and yield reductions. Field studies were conducted at the Texas Agricultural Experiment Station using GR cotton, cv. ‘DeltaPine 5690RR’, to determine if application method and timing affect cotton fruit retention. Glyphosate at 1.12 kg ai ha−1was precisely postdirected (PD), postdirected with 25% foliage coverage (PDFC), or applied over the top (OT) at the 8- or 18-leaf stage after an initial topical application of 1.12 kg ha−1glyphosate at the four-leaf stage. In one of the years of this study, 8 PD, 18 PDFC, and 18 OT reduced yield. In 1999 and 2000, 8 PDFC and 8 OT applications of glyphosate caused yield loss, mainly due to lower mean boll weight. Glyphosate applied topically at the eight-leaf stage also affected the Position 1 boll retention throughout the plant in both years. Glyphosate contact with leaves and stems should be avoided when applying glyphosate after the four-leaf stage to prevent possible yield loss.
Influence of pine bark and gravel on degradation of isoxaben in retention basins
Authors: Jameson Gretchen L. , Briggs Jeanne A. , Whitwell Ted , Fernandez R. Thomas , Riley Melissa B.
Published: July 2006

Herbicides applied to container plants in nurseries are transported in runoff water to on- and off-site ponds and retention basins. This study was conducted to determine biotic and abiotic effects on isoxaben dissipation in model flow-through retention basins to maximize aqueous isoxaben degradation. Field studies were conducted in 1999 and 2000 to evaluate the effects of gravel and pine bark amendments and water retention times on isoxaben persistence in holding basins. In 1999, total isoxaben discharge into flow-through gravel-filled basins was greater than isoxaben losses from gravel and nongravel basins in which water was retained. Photodegradation appeared to be greater in basins without gravel, indicating that gravel protected isoxaben from photolysis. Further studies determined the effect of water retention time and the presence of aged pine bark amendment on isoxaben discharge from basins. Isoxaben discharge level was reduced when water retention time was increased from 3 to 5 d. In the 3-d retention time treatment, added pine bark reduced peak isoxaben discharge by 45% and total isoxaben by 53% at 14 d after treatment. In treatments containing pine bark within the retention basins, isoxaben was released over a longer period of time. No differences were observed in 5-d water retention time treatments with and without pine bark. Analysis of gravel from isoxaben-treated retention basins indicated the presence of several genera of bacteria includingPseudomonas, Arthrobacter, andCellulomonas. Some isolates ofPseudomonas, Rahnella, Methobacterium, andPaenibacillusfrom the basins grew on M9 medium with isoxaben as the sole carbon and energy source, indicating their ability to metabolize isoxaben. Results indicate that retention basins are helpful in reducing isoxaben levels before release or reuse of runoff water from a container nursery, and that retention time of runoff water in basins is the most important factor in reducing isoxaben discharge.
Effect of weed growth stage and adjuvant on the efficacy of fomesafen and bentazon
Authors: Bellinder Robin R. , Arsenovic Marija , Shah Denis A. , Rauch Bradley J.
Published: July 2006

The efficacies of bentazon and fomesafen in controlling annual weeds in dry and edible pod beans in New York State were investigated in greenhouse and field experiments. Dose responses to bentazon and fomesafen were studied for four weed species (ragweed, velvetleaf, eastern black nightshade, and hairy nightshade) under greenhouse conditions. Herbicides were applied at cotyledon to two-, two- to four-, and four- to six–true leaf stages, both with and without a crop oil concentrate (bentazon) or a nonionic surfactant (fomesafen). Field studies were conducted for 2 yr for all weed species except eastern black nightshade, for which no adequate field populations were found. Field studies confirmed greenhouse results, indicating that weed control could be improved by the use of an adjuvant, but there were exceptions. In general, adjuvant usage improved the efficacy of fomesafen more than it did with bentazon. The minimum rates of herbicide required for effective and consistent control was dependent on the particular combination of weed species, herbicide and its rate of application, growth stage at which the application was made, and adjuvant usage.
Response of nonglyphosate-resistant cotton to reduced rates of glyphosate
Authors: Miller Donnie K. , Downer Robert G. , Leonard B. Roger , Holman E. Merritt , Kelly Steve T.
Published: July 2006

Field research was conducted in 1999 and 2000 to determine the effect of reduced glyphosate rates on growth and yield of nonglyphosate-resistant cotton. Rates of 9, 18, 35, 70, 140, and 280 g ha−1, representing 0.008, 0.016, 0.031 0.063, 0.125, and 0.25, respectively, of the maximum use rate per application (1,120 g ha−1), were applied to cotton at the two-, five-, or nine-node growth stage. On the basis of visual injury estimates, cotton was more tolerant to glyphosate at the nine-node than at earlier growth stages. Plant dry weight was reduced with 70 g ha−1of glyphosate or higher, when applied at the two- and five-node growth stages in two of three experiments. Dry weight was not affected by glyphosate at the nine-node stage. Plant height also was unaffected by glyphosate rates below 70 g ha−1, but height reduction was noted for all growth stages by experiment combinations, with the exception of the nine-node application for both experiments in 2000, with herbicide rates of 70 g ha−1or higher. Cotton maturity delay, as noted by an increase in node above white flower number, was observed only at the highest glyphosate rate applied to two- and five-node cotton in one of three experiments. Percent open boll data analysis indicated a decreased opportunity of observing an open boll with increasing glyphosate rate, and this effect was greater at the five-node compared with the two- and nine-node stages in two of three experiments. Seedcotton yield after all glyphosate applications was equivalent to that for the nontreated control.
Cropping system effects on giant foxtail (Setaria faberi) demography: II. Retrospective perturbation analysis
Authors: Davis Adam S. , Dixon Philip M. , Liebman Matt
Published: July 2006

Cropping system characteristics affect weed management by altering key demographic rates of weeds, including recruitment, seedling survival, fecundity, and seed survival. To facilitate the design and improvement of cropping systems that limit weed population growth, analytical methods are needed to identify weed management “choke points” (weed life stages that vary in response to management and whose variation strongly affects weed population growth rate). The objectives of this study were to (1) determine whether wheat–red clover green manure can limit giant foxtail population growth rate (λ) in a wheat–corn–soybean crop sequence and (2) identify choke points in the giant foxtail life cycle with respect to the green manure treatment. Demographic data were used to construct a periodic matrix model of giant foxtail population growth in a wheat–corn–soybean crop sequence, with either a wheat sole crop (W) or a wheat–red clover intercrop (R) in the wheat phase. Identification of choke points was accomplished by adapting the life-table response experiment (LTRE) design for retrospective perturbation analysis of the periodic matrix model. The difference inλ(Δλ) between the two treatments was decomposed into contributions from each parameter in each rotation phase of the periodic model. Each LTRE contribution was equal to the product of the sensitivity ofλto changes in a given parameter by the treatment difference in that parameter. Those parameters making large contributions to Δλrepresented weed management choke points. Giant foxtail population growth rate in the simulation was more than twice as great in the W treatment (λ= 2.54) than in the R treatment (λ= 1.16). Retrospective perturbation analysis indicated that the proportion of seeds surviving predation in the wheat phase made the largest LTRE contribution (0.55) to Δλ, followed by seedling recruitment in the soybean (0.41) and corn (0.20) phases. By identifying weed management choke points within a given system, retrospective perturbation analysis can target research and management efforts for greater reductions in weed population growth.
Isolation of acetolactate synthase homologs in common sunflower
Authors: White Anthony D. , Graham Michelle A. , Owen Micheal D. K.
Published: July 2006

A common sunflower population from Howard, SD (HSD) was previously determined to be cross-resistant to imazethapyr and chlorimuron-ethyl, both acetolactate synthase–inhibiting (ALS) herbicides. Experiments were conducted to determine if target-site polymorphisms could act as a mechanism of ALS-inhibitor herbicide resistance in the HSD common sunflower. Approximately 1,600 nucleotides were amplified by polymerase chain reaction and sequenced from putativeALSgene(s) in common sunflower and Jerusalem artichoke. In sunflower, two different amplification products were detected that differed by a nine-basepair deletion. This suggested the presence of at least two ALS genes in common sunflower that could contribute to the herbicide resistance phenotype. In addition, an Ala205to Val205substitution was observed in several clones from resistant common sunflower (amino acid position is relative to the full-length mouse-ear cress ALS protein). Previously documented mutations at this position in other species indicated that it might play a vital role in conferring resistance to one or more ALS-inhibitor herbicides.
Leafy spurge (Euphorbia esula) seed dormancy
Authors: Foley Michael E.
Published: July 2006

Leafy spurge is a herbaceous perennial weed that reproduces asexually through adventitious vegetative buds and sexually by seeds. Seeds can remain viable in the soil for up to 8 yr. The objectives of this research were to determine whether the seed coat and endosperm restrict germination and to assess whether afterripening treatments affect germinability. Germination of nonafterripened intact seeds was 30% after 28 d of incubation. Afterripening seeds for 12 wk under warm moist conditions provided a twofold stimulation to 58% germination after 21 d compared with the control and three other afterripening treatments. Afterripening under warm moist conditions for an additional 12 wk provided nearly complete germination within 7 to 21 d, but seeds harvested in year 2000 also responded in the same way to cool moist conditions. The removal of seed coat (dehulled) and removal of endosperm surrounding the embryonic axis in dehulled seeds led to rapid germination, approaching 80 to 90% in 5 d. Fructose did not enhance germination of dehulled seeds or embryonic axes. Thus, leafy spurge displays coat-imposed seed dormancy that can be overcome by afterripening under moist conditions.
Analysis of competition between wet-seeded rice and barnyardgrass (Echinochloa crus-galli) using a response–surface model
Authors: Ni Hanwen , Moody Keith , Robles Restituta P.
Published: July 2006

Competition between wet-seeded rice and barnyardgrass under two distinct environments was analyzed using a two-parameter response–surface model at the International Rice Research Institute in the Philippines. The findings showed that this model could predict crop yield loss due to weed competition over a wide range of crop and weed densities. The low-tillering, new plant–type cultivar was a weaker competitor and had a higher yield loss than high-tillering cultivar ‘IR72’ and a hybrid. Increasing the crop density could reduce yield loss due to weed competition. This effect was greater for the new plant type than for IR72 and the hybrid when barnyardgrass density was low. In contrast, this effect was less for the new plant type than for IR72 and the hybrid when the weed density was high. Competitiveness of the three rice cultivars was also affected by season. Crop yield loss was higher in the wet season than in the dry season.
Influence of spotted knapweed (Centaurea maculosa) management treatments on arbuscular mycorrhizae and soil aggregation
Authors: Lutgen E. R. , Rillig M. C.
Published: July 2006

Spotted knapweed is an invasive mycorrhizal weed prevalent in the Pacific Northwest of the United States. Little is known about the effects of spotted knapweed or its management methods on soil quality and soil structure. This study compared soils from spotted knapweed–infested areas with areas where spotted knapweed is being managed using several herbicides and mechanical treatments. We measured concentrations of glomalin, a glycoprotein produced by arbuscular mycorrhizal fungi (AMF), that is correlated with soil aggregate stability, AMF hyphal length, and percent water-stable aggregates (WSA) in soils from managed and unmanaged areas. Areas with high knapweed density (unmanaged areas) generally had lower glomalin concentrations and AMF hyphal lengths compared with areas receiving chemical and combined mechanical–chemical management treatments. Total glomalin was significantly negatively correlated with percent knapweed cover. However, WSA was high (70 to 80%) in soils from all management treatments and was not affected by knapweed cover. Our results suggest that spotted knapweed does not have negative effects on soil quality from our study site, likely because of the high aggregate stability of the soils in the area. However, Centaurea maculosa may have negative effects on soil quality in soils with lower aggregate stability.
Multiple herbicide–resistant canola can be controlled by alternative herbicides
Authors: Beckie Hugh J. , Séguin-Swartz Ginette , Nair Harikumar , Warwick Suzanne I. , Johnson Eric
Published: July 2006

Unintentional herbicide resistance gene stacking in canola may alter the sensitivity of volunteers to herbicides of alternative modes of action commonly used for their control. Greenhouse experiments were conducted to investigate the response of three single-herbicide–resistant (HR) cultivars (glyphosate, glufosinate, imidazolinone), one non-HR cultivar, and seven multiple (double or triple)–HR experimental lines to 2,4-D (amine and ester), MCPA ester, and metribuzin applied at the two- to three-leaf stage and of one non-HR and four HR cultivars (glyphosate, glufosinate, imidazolinone, bromoxynil) to 2,4-D amine applied at two growth stages (two- to three-leaf stage and five- to six-leaf stage). All canola cultivars or lines treated at the two- to three-leaf stage responded similarly to increasing doses of each of the three herbicides. At the five- to six-leaf stage, however, the bromoxynil HR cultivar was less sensitive to 2,4-D than the other cultivars. The results of this study suggest that canola with multiple-herbicide–resistance traits does not differ from cultivars that are non-HR or single HR in its sensitivity to herbicides commonly used to control volunteers. All volunteers, whether non-HR, single HR, or multiple HR, should be treated when plants are most sensitive to herbicides (two- to four-leaf stage) to reduce their interference against crops and their perpetuation of gene flow.
Physiological characterization of auxinic herbicide-resistant biotypes of kochia (Kochia scoparia)
Authors: Goss Gina A. , Dyer William E.
Published: July 2006

Auxin-mediated responses of kochia biotypes resistant to dicamba (HRd) or resistant to dicamba and fluroxypyr (HRdf) were compared with those of two susceptible biotypes. Rates of shoot and root gravitropic response and patterns of apical dominance, as determined by lateral bud sprouting after decapitation, were determined in the absence of herbicide treatment. Shoots of susceptible plants reoriented toward vertical at a rate of 23.4° h−1, whereas the rates of HRd and HRdf shoot reorientation were significantly slower at 7.2° and 14.4° h−1, respectively. Root gravitropic responses were not different between resistant and susceptible biotypes. In contrast to susceptible biotypes, both apical and basal lateral buds on HRd plants elongated after decapitation, although differences between HRd and susceptible biotypes became smaller during succeeding weeks. The elongation pattern of HRdf lateral buds was intermediate to that of susceptible and HRd plants. Inhibition assays of root growth by natural and synthetic auxins showed that HRd root growth was less sensitive to dicamba, 2,4-D, naphthalene-1-acetic acid, and indole-3-acetic acid than was root growth of HRdf or the susceptible biotypes. Collectively, results support the hypothesis that auxin binding or signal transduction pathways are impaired in resistant biotypes and that HRd may contain different lesions than does HRdf.
Evaluation of yield loss in field sorghum from a C3and C4weed with increasing CO2
Authors: Ziska L. H.
Published: July 2006

Dwarf sorghum (C4) was grown at ambient and at projected levels of atmospheric carbon dioxide (250 mol mol−1above ambient) with and without the presence of a C3weed (velvetleaf) and a C4weed (redroot pigweed), to quantify the potential effect of rising atmospheric carbon dioxide concentration [CO2] on weed–crop interactions and potential crop loss. In a weed-free environment, increased [CO2] resulted in a significant increase in leaf weight and leaf area of sorghum but no significant effect on seed yield or total aboveground biomass relative to the ambient CO2condition. At ambient [CO2] the presence of velvetleaf had no significant effect on either sorghum seed yield or total aboveground biomass; however, at elevated [CO2], yield and biomass losses were significant. The additional loss in sorghum yield and biomass was associated with a significant (threefold) increase in velvetleaf biomass in response to increasing [CO2]. Redroot pigweed at ambient [CO2] resulted in significant losses in total aboveground biomass of sorghum but not in seed yield. However, as [CO2] increased, significant losses in both sorghum seed yield and total biomass were observed for sorghum–redroot pigweed competition. Increased [CO2] was not associated with a significant increase in redroot pigweed biomass (P = 0.17). These results indicate potentially greater yield loss in a widely grown C4crop from weedy competition as atmospheric [CO2] increases.
Spring wheat seed size and seeding rate effects on yield loss due to wild oat (Avena fatua) interference
Authors: Stougaard Robert N. , Xue Qingwu
Published: July 2006

The development of competitive cropping systems could minimize the negative effects of wild oat competition on cereal grain yield, and in the process, help augment herbicide use. A 3-yr field experiment was conducted at Kalispell, MT, to investigate the effects of spring wheat seed size and seeding rate on wheat spike production, biomass, and grain yield under a range of wild oat densities. Wheat plant density, spikes, biomass, and yield all increased as seed size and seeding rates increased. Averaged across all other factors, the use of higher seeding rates and larger seed sizes improved yields by 12 and 18%, respectively. Accordingly, grain yield was more highly correlated with seed size than with seeding rate effects. However, the combined use of both tactics resulted in a more competitive cropping system, improving grain yields by 30%. Seeding rate effects were related to spike production, whereas seed size effects were related to biomass production. As such, plants derived from large seed appear to have greater vigor and are able to acquire a larger share of plant growth factors relative to plants derived from small seed.
Seasonal variation of picloram metabolism in broom (Gutierrezia sarothrae) and threadleaf (Gutierrezia microcephala) snakeweed populations in a common garden
Authors: Gibbs Larissa A. , Sterling Tracy M.
Published: July 2006

Broom and threadleaf snakeweed are major rangeland weeds in the western United States, and picloram is the major herbicide used for their management. Previous work has shown that these species are most susceptible to picloram applied in autumn or when precipitation is high and that differences in herbicide absorption and tissue sensitivity as measured by picloram-induced ethylene production do not fully explain variation in seasonal response. Therefore, the role of picloram metabolism in seasonal susceptibility to picloram was examined. Because snakeweed is characterized as highly genetically variable, picloram metabolism was evaluated monthly for 3 yr among populations from two species as well. Picloram metabolism was examined monthly for 3 yr among two populations of threadleaf and nine populations of broom snakeweed grown in a common garden. Metabolism ranged from 30 to 70% of picloram applied, and picloram was converted to two metabolites more polar than picloram regardless of species or population. Although metabolism was greatest in the year with the most precipitation, rate of metabolism was unrelated to precipitation received in the 7-d period before treatment. Application timing as defined by a given month or specific phenological stage was not related to the level of metabolism. We conclude that variation in picloram metabolism is not involved in differential susceptibility across season or population.
Multiple-herbicide resistance across four modes of action in wild radish (Raphanus raphanistrum)
Authors: Walsh Michael J. , Powles Stephen B. , Beard Brett R. , Parkin Ben T. , Porter Sally A.
Published: July 2006

Populations of wild radish were collected from two fields in the northern Western Australian wheatbelt, where typical herbicide-use patterns had been practiced for the previous 17 seasons within an intensive crop production program. The herbicide resistance status of these populations clearly established that there was multiple-herbicide resistance across many herbicides from at least four modes of action. One population exhibited multiple-herbicide resistance to the phytoene desaturase (PDS)–inhibiting herbicide diflufenican (3.0-fold), the auxin analog herbicide 2,4-D (2.2-fold), and the photosystem II–inhibiting herbicides metribuzin and atrazine. Another population was found to be multiply resistant to the acetolactate synthase–inhibiting herbicides, the PDS-inhibiting herbicide diflufenican (2.5-fold), and the auxin analog herbicide 2,4-D amine (2.4-fold). Therefore, each population has developed multiple-herbicide resistance across several modes of action. The multiple resistance status of these wild radish populations developed from conventional herbicide usage in intensive cropping rotations, indicating a dramatic challenge for the future control of wild radish.
Production of Pleospora papaveracea biomass in liquid culture and its infectivity on opium poppy (Papaver somniferum)
Authors: Bailey B. A. , Hebbar K. P. , Lumsden R. D. , O'Neill N. R. , Lewis J. A.
Published: July 2006

The fungus Pleospora papaveracea is a potential biocontrol agent for opium poppy. The objective of this study was to characterize the growth and production of propagules of P. papaveracea on various substrates and determine their infectivity on opium poppy. Pleospora papaveracea was grown on agar media containing wheat bran, corn cobs, soy fiber, cottonseed meal, rice flour, cornstarch, pectin, dextrin, or molasses, all with the addition of brewer's yeast (BY). Maximum radial growth of P. papaveracea occurred on molasses, soy fiber, and wheat bran media. Pleospora papaveracea produced chlamydospores on dextrin–BY and cornstarch–BY only. Pleospora papaveracea growth in liquid media with 1% (wt/v) dextrin, cornstarch, soy fiber, or wheat bran resulted in the production of greater than 106 colony-forming units (cfu) ml−1 within 3 to 5 d of incubation. Pleospora papaveracea produced less than 105 chlamydospores ml−1 after 10 d of incubation in wheat bran–BY and soy fiber–BY liquid media compared with the production of greater than 105 chlamydospores ml−1 after 5 d of incubation in dextrin–BY or cornstarch–BY liquid media. Fewer cfu were produced by P. papaveracea in 0.25% dextrin or 0.25 and 0.50% soy fiber liquid media than with 1 or 2% substrate. Greater than 107 chlamydospores g−1 dry weight and 108 cfu g−1 dry weight of P. papaveracea were produced in dextrin–BY liquid media in a commercial bench-top fermentor. After air drying biomass for 6 d, propagules of P. papaveracea remained infective on opium poppy. Mycelia and chlamydospores of P. papaveracea grew and formed appressoria during the infection process. Air-dried biomass, when rehydrated in 0.001% Tween 20, caused necrosis within 48 h after application to detached opium poppy leaves. At least 94% of the propagules from air-dried biomass that germinated and infected detached opium poppy leaves were of mycelial origin.
Effects of the fungal protein Nep1 andPseudomonas syringaeon growth of Canada thistle (Cirsium arvense), common ragweed (Ambrosia artemisiifolia), and common dandelion (Taraxacum officinale)
Authors: Gronwald John W. , Plaisance Kathryn L. , Bailey Bryan A.
Published: July 2006

The effects of the fungal protein Nep1 andPseudomonas syringaepv.tagetis(Pst) applied separately or in combination on Canada thistle, common ragweed, and common dandelion were examined in growth chamber experiments. Experiments examined five treatments: (1) untreated control, (2) Silwet L-77 (0.3%, v/v) control, (3) Nep1 (5 μg ml−1) plus Silwet L-77 (0.3%, v/v), (4) Pst (109colony-forming units [cfu] ml−1) plus Silwet L-77 (0.3%, v/v), and (5) Pst (109cfu ml−1) and Nep1 (5 μg ml−1) plus Silwet L-77 (0.3%, v/v). Foliar treatments were applied at 28, 26, and 21 d after planting for Canada thistle, common dandelion, and common ragweed, respectively. For all three species, foliar application of Nep1 alone or in combination with Pst caused rapid desiccation and necrosis of leaves, with the greatest effect on recent, fully expanded (RFE) leaves. Within 4 to 8 h after treatment (HAT), 60 to 80% of RFE leaves of all three species were necrotic. Measured 72 HAT, Pst populations in Canada thistle leaves treated with Nep1 plus Pst were approximately 105cfu cm−2compared with 107cfu cm−2for leaves treated with Pst alone. Measured 2 wk after treatment, foliar application of Nep1 reduced shoot dry weight of the three weeds by 30 to 41%. Treatment with Pst reduced shoot growth of common ragweed, Canada thistle, and common dandelion by 82, 31, and 41%, respectively. The large suppression of common ragweed shoot growth caused by Pst treatment was associated with a high percentage (60%) of leaf area exhibiting chlorosis. Treatment with Pst plus Nep1 did not result in significant decreases in shoot dry weight for Canada thistle and common dandelion compared with either treatment alone. For common ragweed, shoot growth reduction caused by applying Pst and Nep1 together was not greater than that caused by Pst alone.
Infiltration and adsorption of dissolved metolachlor, metolachlor oxanilic acid, and metolachlor ethanesulfonic acid by buffalograss (Buchloe dactyloides) filter strips
Authors: Krutz Larry J. , Senseman Scott A. , Dozier Monty C. , Hoffman Dennis W. , Tierney Dennis P.
Published: July 2006

Vegetative filter strips (VFS) potentially reduce herbicide transport from agricultural fields by increasing herbicide mass infiltrated (Minf) and herbicide mass adsorbed (Mas) compared with bare field soil. However, there are conflicting reports in the literature concerning the contribution of Masto herbicide trapping efficiency (TE). Moreover, no study has evaluated TE among metolachlor and metolachlor metabolites in a VFS. This experiment was conducted to compare TE,Minf, andMasamong metolachlor, metolachlor oxanilic acid (OA), and metolachlor ethanesulfonic acid (ESA) in buffalograss filter strips. Runoff was applied as a point source upslope of a 1- × 3-m microwatershed at a rate of 750 L h−1. The point source was fortified with metolachlor, metolachlor OA, and metolachlor ESA, each at 0.12 μg ml−1. After moving through the plot, water samples were collected at 5-min intervals and stored at 5 C until analysis. Water samples were extracted using solid-phase extraction and analyzed by high-performance liquid chromatography–photodiode array detection. TE was significantly greater for metolachlor (25.3%) as compared with the OA (15.5%) and ESA metabolites (14.2%). The averageMinfwas 8.5% and was not significantly different among compounds. Significantly more metolachlor (17.3%) was retained as Mascompared with either metolachlor OA (7.0%) or metolachlor ESA (5.5%). Moreover,Masaccounted for 68 and 42% of the total TE for metolachlor and metolachlor metabolites, respectively. These results demonstrate that adsorption to the VFS grass, grass thatch, or soil surface (or all) is an important retention mechanism for metolachlor and metolachlor metabolites, especially under saturated conditions. Moreover, the Masdata indicate that metolachlor is preferentially retained by the VFS grass, grass thatch, or soil surface (or all) compared with the OA and ESA metabolites. Greater metolachlor retention in VFS compared with the OA and ESA metabolites may partially explain why metolachlor metabolites are frequently measured at higher concentrations than metolachlor is in surface water.
Physiological basis for cotton tolerance to flumioxazin applied postemergence directed
Authors: Price Andrew J. , Pline Wendy A. , Wilcut John W. , Cranmer John R. , Danehower David
Published: July 2006

Previous research has shown that flumioxazin, a herbicide being developed as a postemergence-directed spray (PDS) in cotton, has the potential to injure cotton less than 30 cm tall if the herbicide contacts green stem tissue by rain splash or misapplication. In response to this concern, five-leaf cotton plants with chlorophyllous stems and older cotton, 16-leaf cotton plants, with bark on the lower stem were treated with a PDS containing flumioxazin plus crop oil concentrate (COC) or nonionic surfactant (NIS). Stems of treated plants and untreated plants at the respective growth stage were cross-sectioned and then magnified and photographed using bright-field microscopy techniques. More visible injury consisting of necrosis and desiccation was evident in younger cotton. Also, there was a decrease in treated-stem diameter and an increase in visible injury with COC compared with NIS in younger cotton. The effects of plant growth stage and harvest time on absorption, translocation, and metabolism of14C-flumioxazin in cotton were also investigated. Total14C absorbed at 72 h after treatment (HAT) was 77, 76, and 94% of applied at 4-, 8-, and 12-leaf growth stages, respectively. Cotton at the 12-leaf stage absorbed more14C within 48 HAT than was absorbed by four- or eight-leaf cotton by 72 HAT. A majority (31 to 57%) of applied14C remained in the treated stem for all growth stages and harvest times. Treated cotton stems at all growth stages and harvest times contained higher concentrations (Bq g−1) of14C than any other tissues. Flumioxazin metabolites made up less than 5% of the radioactivity found in the treated stem. Because of the undetectable levels of metabolites in other tissues when flumioxazin was applied PDS, flumioxazin was foliar applied to determine whether flumioxazin transported to the leaves may have been metabolized. In foliar-treated cotton, flumioxazin metabolites in the treated leaf of four-leaf cotton totaled 4% of the recovered14C 72 HAT. Flumioxazin metabolites in the treated leaf of 12-leaf cotton totaled 35% of the recovered14C 48 HAT. These data suggest that differential absorption, translocation, and metabolism at various growth stages, as well as the development of a bark layer, are the bases for differential tolerances of cotton to flumioxazin applied PDS.
Genetic diversity of biennial wormwood
Authors: Mengistu Lemma W. , Christoffers Michael J. , Kegode George O.
Published: July 2006

Biennial wormwood is native to North America and has become an important weed problem in soybean and dry bean fields of North Dakota, South Dakota, and Minnesota in the United States and in the prairie provinces of Canada. Intersimple sequence repeat (ISSR) markers were used to study the genetic diversity among six biennial wormwood and one annual wormwood populations. Deoxyribonucleic acid (DNA) sequences from internal transcribed spacer (ITS1 and ITS2) regions of ribosomal DNA and morphological diversity among the biennial and annual wormwood populations were also studied. High levels of genetic diversity were evident with Nei's gene diversity statistic (h) = 0.40 for biennial wormwood andh= 0.36 for annual wormwood. Total diversity of six biennial wormwood populations wasHT= 0.40, and 22% of this diversity was among populations (GST= 0.22). Estimated gene flow among biennial wormwood populations was low (Nm= 0.9), and high levels of differentiation may be due in part to low levels of genetic exchange among biennial wormwood populations. Although biennial wormwood behaves more like an annual than a biennial, the ISSR, ITS, and morphological studies show that the two species are dissimilar.
Suppression of cogongrass (Imperata cylindrica) by a bioherbicidal fungus and plant competition
Authors: Yandoc Camilla B. , Charudattan Raghavan , Shilling Donn G.
Published: July 2006

The possibility of using the fungusBipolaris saccharias a bioherbicide to suppress cogongrass and to allow the establishment of bahiagrass in cogongrass–bahiagrass mixed plantings was investigated under greenhouse conditions. The bioherbicide was prepared by mixingB. saccharispore suspension containing 105spores ml−1with an oil emulsion composed of 16% horticultural oil plus 10% light mineral oil and 74% sterile water. The bioherbicide caused severe foliar blight in cogongrass and slight phytotoxic damage on bahiagrass. In the first experiment, the bioherbicide reduced cogongrass biomass without affecting bahiagrass biomass. In the second experiment, the bioherbicide caused a 64% reduction in fresh weight, a 74% reduction in the number of rhizomes, and a 47% reduction in the height of cogongrass. The latter experiment also showed an increase in bahiagrass fresh weight in the presence of cogongrass when the bioherbicide was applied. This study indicates the potential of combining bioherbicide application with competition from a desirable grass species as a strategy for the integrated management of cogongrass.
Physiological basis for differential tolerance of tomato and pepper to rimsulfuron and halosulfuron: site of action study
Authors: Buker Richard S. , Rathinasabapathi Bala , Stall William M. , MacDonald Greg , Olson Steven M.
Published: July 2006

Tomato and pepper differ in their whole-plant tolerance to sulfonylurea (SU) herbicides rimsulfuron and halosulfuron despite both being members of the Solanaceae family. This study examined whether tomato's tolerance to SU herbicides rimsulfuron and halosulfuron was due to insensitivity of the target enzyme acetolactate synthase (ALS). Rimsulfuron and halosulfuron inhibited ALS from both tomato and pepper leaves. Enzyme inhibition and kinetic analyses showed that extractable ALS from tomato was more sensitive to rimsulfuron and halosulfuron than ALS from pepper. ALS from both species were inhibited with a mixed inhibition pattern. Thus, results indicate that enzyme insensitivity is not the reason why tomato is more tolerant than pepper to these herbicides. Tomato tolerance to rimsulfuron at the whole-plant level was reduced in the presence of terbufos, a known inhibitor of cytochrome P450 enzymes. Rimsulfuron applied at 0.018 and 0.035 kg ha−1with 1.1 kg ha−1of terbufos reduced tomato shoot weight 69 and 66%, respectively, compared with a 4 and 29% reduction when rimsulfuron was applied alone. The reduction of tomato tolerance to rimsulfuron by terbufos suggests that the sensitivity differences between these species may reflect their differences in SU herbicide metabolism.
Fertilizer nitrogen rate and the response of weeds to herbicides
Authors: Cathcart R. Jason , Chandler Kevin , Swanton Clarence J.
Published: July 2006

Differences in plant community composition have been attributed to abiotic field characteristics, crop type, localized predation, farm implement traffic, and natural dispersal mechanisms. Nitrogen (N) fertilizer rates and herbicides also are known to influence weed community structure, although their interaction has not been reported in the literature. A growth room experiment was conducted using three weed species (green foxtail, redroot pigweed, and velvetleaf) and five herbicides (nicosulfuron, atrazine, glufosinate, glyphosate, and mesotrione) differing in their mode of action and efficacy to the selected species. The experiment was conducted in growth chambers with two levels of N fertilization (low: 0.7 mM N and high: 7.7 mM N). Weeds were grown to the two- to five-leaf stage (depending on species), treated with the appropriate herbicide, and harvested approximately 2 wk after treatment. The herbicide dose at which a 50% reduction in biomass occurred (GR50) was determined using log-logistic analysis. Herbicide susceptibility of the different weed species was influenced by N level. Green foxtail grown under low N required approximately six times the dose of nicosulfuron compared with plants grown under high N. Similarly, higher doses of nicosulfuron, glufosinate, mesotrione, and glyphosate were required to achieve a 50% reduction in redroot pigweed biomass grown under low N. In contrast, N did not influence the efficacy of mesotrione, glufosinate, or atrazine when applied to velvetleaf. This indicated specificity among herbicide–species combinations. Differences in herbicide efficacy resulting from soil N levels may alter weed community structure and may potentially explain possible weed control failures on farm fields.
Influence of corn on common waterhemp (Amaranthus rudis) growth and fecundity
Authors: Nordby Dawn E. , Hartzler Robert G.
Published: July 2006

Four experiments were conducted in central Iowa during 2001 and 2002 to determine the effects of weed emergence time and corn row spacing on common waterhemp growth and fecundity. Four common waterhemp emergence cohorts were established in each experiment and corresponded to the VE, V3, V5, and V8 stages of corn grown in rows spaced 38 and 76 cm apart. Common waterhemp mortality averaged 20, 56, 97, and 99% for the first, second, third, and fourth cohorts, respectively. Mean mature common waterhemp height for the first cohort was 140 cm, whereas plants emerging at the V8 corn stage were only 5 cm tall. Biomass of the first cohort was 20% less in 38-cm rows than in 76-cm rows, but later cohorts were not affected by row spacing. Biomass and seed production of waterhemp emerging at the V3, V5, and V8 corn stages decreased 80, 97, and 99%, respectively in comparison with the first cohort. Overall results indicate that common waterhemp biomass, survival, and fecundity decline sharply with delayed emergence relative to corn, but weeds emerging at or before the V5 corn stage may still contribute significantly to the seed bank.
Predicting timing of downy brome (Bromus tectorum) seed production using growing degree days
Authors: Ball Daniel A. , Frost Sandra M. , Gitelman Alix I.
Published: July 2006

Downy brome in dryland winter wheat presents a major constraint to the adoption of reduced tillage cropping systems in the Pacific Northwest of the United States. Effective suppression of downy brome during fallow periods depletes seed in the soil and reduces infestations in subsequent winter wheat crops. Delayed tillage operations or delayed herbicide applications in the spring increase the risk for production of viable downy brome seed during fallow periods. In a series of studies, downy brome panicles were sequentially sampled at Pendleton, OR, and Pullman, WA, in 1996 and 1997, and at nine locations around the winter wheat growing region of the western United States in 1999 and 2001. Cumulative growing degree days (GDD) were calculated using local, daily maximum, and minimum air temperature data. A simple GDD model based on the formula GDD = (daily maximum temperature [C] + daily minimum temperature [C])/2, with a base temperature of 0 C and a starting point of January 1, was used to calculate cumulative GDD values for panicle sampling dates. Number of seed germinating per collected panicle was recorded in greenhouse germination tests. Estimations of degree days required for production of viable downy brome seed were made using nonlinear regression of germination on GDD. The GDD value at which viable seed can be found on plants (i.e., when seed germination > 0) was of interest. Estimates of the GDD values at which viable seed could be found in the three studies ranged from 582 GDD at Bozeman, MT, to 1,287 GDD at Stillwater, OK, with a group of GDD values for Pendleton and Pullman around 1,000. Variation in seed-set GDD among locations may be attributed to differing climatic conditions that control vernalization at the various locations or to differences in vernalization requirements among downy brome biotypes (or both).
Effects of three herbicides on whole-plant carbon fixation and water use by yellow nutsedge (Cyperus esculentus)
Authors: Earl Hugh J. , Ferrell Jason A. , Vencill William K. , van Iersel Marc W. , Czarnota Mark A.
Published: July 2006

Three herbicides were compared for their ability to reduce both carbon fixation and soil water depletion by yellow nutsedge in a growth chamber study. Whole-plant CO2exchange and water use were measured for 11 d after herbicide application. MSMA reduced carbon assimilation relative to the untreated control 1 d after treatment, and by 5 d after treatment respiration exceeded carbon assimilation during the photoperiod; however, MSMA had no significant effect on whole-plant water use during the measurement period. Halosulfuron reduced gross carbon assimilation to 30% of the pretreatment rate by the end of the experiment, but in contrast to MSMA it also strongly suppressed water use. Mesotrione never reduced carbon assimilation below 59% of the pretreatment rate and had no measurable effect on water use. Halosulfuron and MSMA reduced shoot regrowth to between 0 and 5% of the control, whereas mesotrione treatment allowed some 58% regrowth. These results indicate that whereas both MSMA and halosulfuron should provide effective control of yellow nutsedge, halosulfuron may be better able to rapidly suppress the weed's ability to compete for available soil water.
Combined effects ofAceria malherbaeand herbicides on field bindweed (Convolvulus arvensis) growth
Authors: Boydston Rick A. , Williams Martin M.
Published: July 2006

The effects of a gall mite (Aceria malherbae) and sublethal doses of either 2,4-DB or glyphosate on field bindweed growth were evaluated under laboratory conditions. Mite feeding reduced field bindweed shoot biomass 37 to 48% and root biomass 46 to 50%. 2,4-DB at 0.07 to 0.14 kg ae ha−1or glyphosate at 0.14 to 0.28 kg ai ha−1reduced field bindweed root biomass 25 to 52%. CombiningA. malherbaefeeding with either 2,4-DB or glyphosate application reduced root biomass of field bindweed plants more than mites or either herbicide alone. LiveA. malherbaewere present on field bindweed 3 wk after treatment with either herbicide. Combination ofA. malherbaewith sublethal herbicide doses may allow for field bindweed suppression while reducing potential herbicide injury to crops and maintainingA. malherbaepopulations.
Detection of pitted morningglory (Ipomoea lacunosa) with hyperspectral remote sensing. II. Effects of vegetation ground cover and reflectance properties
Authors: Koger Clifford H. , Shaw David R. , Reddy Krishna N. , Bruce Lori M.
Published: July 2006

Field research was conducted to determine the potential of hyperspectral remote sensing for discriminating plots of soybean intermixed with pitted morningglory and weed-free soybean with similar and different proportions of vegetation ground cover. Hyperspectral data were collected using a handheld spectroradiometer when pitted morningglory was in the cotyledon to two-leaf, two- to four-leaf, and four- to six-leaf growth stages. Synthesized reflectance measurements containing equal and unequal proportions of reflectance from vegetation were obtained, and seven 50-nm spectral bands (one ultraviolet, two visible, and four near-infrared) derived from each hyperspectral reflectance measurement were used as discrimination variables to differentiate weed-free soybean and soybean intermixed with pitted morningglory. Discrimination accuracy was 93 to 100% regardless of pitted morningglory growth stage and whether equal or unequal proportions of reflectance from vegetation existed in weed-free soybean and soybean intermixed with pitted morningglory. Discrimination accuracy was 88 to 98% when using the discriminant model developed for one experiment to discriminate soybean intermixed with pitted morningglory and weed-free soybean plots of the other experiment. Reflectance in the near-infrared spectrum was higher for weed-free soybean compared with soybean intermixed with pitted morningglory, and this difference affected the ability to discriminate weed-free soybean from soybean intermixed with pitted morningglory.
Design and optimization of degenerated universal primers for the cloning of the plant acetolactate synthase conserved domains
Authors: Prado Mario Duran , De Prado Rafael , Franco Antonio R.
Published: July 2006

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.