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Experiments were conducted to determine tobacco tolerance to CGA-362622 applied pretransplant (PRE-T) and postemergence (POST) to tobacco and applied the previous year preemergence (PRE) and POST to cotton. CGA-362622 applied at 3.75 or 7.5 g ai/ha PRE-T injured ‘K326’ flue-cured tobacco 1%, whereas POST treatments resulted in 4 to 5% injury. Tobacco injury was transient with no mid- or late-season injury noted. Tobacco yields from all CGA-362622 POST treatments were not different from the nontreated weed-free check. Tobacco treated with 7.5 g/ha CGA-362622 PRE-T yielded greater than nontreated weed-free tobacco or tobacco treated with CGA-362622 POST. When grown in rotation, tobacco was not injured, and yields were not influenced by CGA-362622 applied PRE or POST to cotton the previous year.
Nomenclature: CGA-362622; cotton, Gossypium hirsutum L.; tobacco, Nicotiana tabacum L.
Additional index words: Carryover, crop injury, sulfonylurea herbicide.
Abbreviations: ALS, acetolactate synthase; LAYBY, late POST-directed; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; PRE-T, pretransplant.
The persistence and efficacy of acetamide herbicides at application timings from fall to preemergence (PRE) were studied in 1998 and 1999 on mollisols (1.1 to 2.8% organic carbon). Metolachlor, s-metolachlor, acetochlor (as an emulsifiable concentrate [EC] formulation and two encapsulated formulations, capsule suspension [CS] and microencapsulated [ME]), and the combination of flufenacet metribuzin were evaluated at five application times including late fall, 60 and 30 d early preplant (EPP), preplant incorporated, and PRE. Soil bioassays 180 d after application indicated flufenacet metribuzin, metolachlor, s-metolachlor, and the acetochlor CS had 62 to 74% giant foxtail control, whereas acetochlor EC and ME had 43 to 46% control. Applications at 60 EPP of metolachlor, s-metolachlor, and acetochlor CS provided 70 to 75% giant foxtail control in greenhouse bioassays, whereas flufenacet metribuzin, acetochlor ME, and acetochlor EC provided 38 to 57% control. At the 30 EPP timing, metolachlor and acetochlor CS had 80 to 82% control, whereas acetochlor EC provided 46% control, and acetochlor ME, flufenacet metribuzin, and s-metolachlor had 65 to 74% control. Quantitative soil analysis (0 to 6 cm) 10 d after planting (DAP) indicated metolachlor, s-metolachlor, and acetochlor CS concentrations ranged from 12 to 16% and 32 to 47% of applied herbicide for the fall and PRE application timings, respectively, whereas acetochlor (ME and EC) were from 1 to 3% and 16 to 21% of applied for the fall and PRE application timings, respectively. Bioassay reduction was correlated (R2 = 0.68) with soil-herbicide concentrations at 10 DAP.
Broad-spectrum weed control options for pea are limited. Field experiments conducted from 1998 to 2000 evaluated reduced rates of imazethapyr for selective control of grass and broadleaf weed species in pea. Imazethapyr was applied preemergence (PRE) and postemergence (POST) at 20, 40, 60, 80, and 100% of the PRE rate of 75 g ai/ha currently labeled in Ontario. A rate of 45 g/ha or greater was required to maintain consistent control of common lambsquarters and wild mustard when imazethapyr was applied PRE. Green foxtail and redroot pigweed control was excellent at all PRE rates 56 d after treatment. The 75-g/ha rate was required to maintain effective and consistent control of common ragweed. No injury or yield reductions were observed for any of the PRE application rates of imazethapyr. Reduced rates as low as 30 g/ha of imazethapyr applied POST maintained high levels of weed control. Pea tolerance to low rates of imazethapyr applied POST was acceptable except when applied in a year of low rainfall when peas experienced moisture stress.
Nomenclature: Imazethapyr; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; green foxtail, Setaria viridis (L.) Beauv. # SETVI; redroot pigweed, Amaranthus retroflexus L. # AMARE; wild mustard, Sinapsis arvensis L. # SINAR; pea, Pisum sativum L. ‘Bolero’, ‘Sanchos’.
Additional index words: Herbicide efficacy, pea yields, reduced herbicide rates.
Abbreviations: DAT, days after treatment; OCHU, Ontario corn heat units; POST, postemergence; PRE, preemergence.
Based on field surveys and evaluations in the greenhouse, two fungal pathogens, Bipolaris sacchari and Drechslera gigantea, were identified as promising biological control agents for cogongrass. In greenhouse trials, the application of spore suspensions of these fungi containing 105 spores/ ml in a 1% aqueous gelatin solution to cogongrass plants and their incubation in a dew chamber for 24 h resulted in disease symptoms that ranged from discrete lesions to complete blighting of leaves. Disease severity (DS), based on a rating scale for southern corn leaf blight with 50% as the maximum DS rating, ranged from 42 to 49%. In greenhouse experiments, the application of spores formulated in an oil emulsion composed of 4% horticultural oil, 10% light mineral oil, and 86% water resulted in higher levels of foliar blight with no dew exposure or shorter periods of dew exposure (4, 8, or 12 h) as compared with the application of spores formulated in 1% gelatin. Field trials demonstrated that under natural conditions, the application of a spore and an oil emulsion mixture containing 105 spores/ml of either fungus could cause foliar injury from disease and phytotoxic damage from the oil emulsion. Depending on the application rate (100 or 200 ml/plot), the level of foliar injury ranged from 40 to 86% (based on a field assessment scale of 0 to 100% foliar injury) with B. sacchari as the test fungus. However, with D. gigantea as the test fungus, foliar injury ranged from 9 to 70% depending on the application volume and the oil concentration used. Although B. sacchari and D. gigantea were capable of causing foliar blight on cogongrass, the regenerative ability of the rhizomes allowed cogongrass to recover from the damage caused by these fungi. However, the level of injury caused by these fungi is sufficient to support their use as components for integrated management of cogongrass.
Michigan soybean producers have observed that glyphosate efficacy is sometimes reduced in tank mixtures with foliar manganese (Mn) fertilizers. The objectives of this study were to evaluate the effects of Mn formulation, Mn application timing, tank mixture adjuvants, and Mn rate on glyphosate efficacy. Three Mn formulations, manganese sulfate and ethylaminoacetate chelate (Mn-EAA), manganese sulfate and lignin sulfonate chelate (Mn-LS), and manganese sulfate monohydrate (MnSO4) reduced glyphosate efficacy in greenhouse and field bioassays, but Mn ethylenediaminetetraacetate (Mn-EDTA) did not. Mn-EAA applied less than 3 d before glyphosate reduced glyphosate efficacy on velvetleaf but not giant foxtail or common lambsquarters. The antagonism increased as the interval between treatment applications was shortened but did not appear when Mn was applied to velvetleaf 1 d or more after glyphosate. Including the adjuvants ammonium sulfate (AMS), EDTA, or citric acid in the glyphosate–Mn tank mixture increased control of giant foxtail and velvetleaf but only matched the efficacy of the glyphosate plus AMS control in three combinations: AMS with Mn-LS on velvetleaf, citric acid with MnSO4 on giant foxtail, and EDTA with Mn-EAA on giant foxtail. AMS increased the glyphosate efficacy in Mn tank mixtures as much as, or more than, citric acid and EDTA, with two exceptions: EDTA with Mn-EAA on giant foxtail and citric acid with MnSO4 on velvetleaf. Control of velvetleaf declined as the amount of Mn from Mn-EAA, Mn-LS, and MnSO4 in the tank mixture increased.
Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L. #3 CHEAL; giant foxtail, Setaria faberi Herrm. # SETFA; velvetleaf, Abutilon theophrasti Medicus. # ABUTH; soybean, Glycine max L.
Field studies were conducted in 2001 in Lewiston, NC, and in 2002 at Clayton and Lewiston, NC, to investigate the response of nontransgenic cotton to simulated glyphosate drift in a weed-free environment. Nontransgenic cotton variety ‘Fibermax 989’ was planted in a conventional seedbed at all locations. Glyphosate treatments were applied early postemergence (EPOST) at the four-leaf growth stage of cotton at 0, 8.7, 17.5, 35, 70, 140, 280, 560, and 1,120 g ai/ha and represent 0, 0.78, 1.55, 3.13, 6.25, 12.5, 25, 50, and 100% of the commercial use rate, respectively. Rates as low as 140 g/ha caused lint yield reductions depending on year and location. When averaged over all locations, lint yield reductions of 4, 49, 72, and 87% compared with nontreated cotton were observed with glyphosate rates of 140, 280, 560, and 1,120 g/ha, respectively. Visual injury and shikimic acid accumulation were evident at glyphosate rates greater or equal to 70 g/ha. Collectively, visual injury and shikimic acid accumulation at 7 d after EPOST treatment might be used as a diagnostic indicator to predict potential yield reductions from simulated glyphosate drift.
Nomenclature: Glyphosate; cotton, Gossypium hirsutum L. ‘Fibermax 989’.
Additional index words: Shikimic acid.
Abbreviations: DAT, days after early postemergence treatment; DD, degree-day; EPOST, early postemergence; EPSPS, 5-enolpyruvylshikimate-3-phosphate synthase [EC 18.104.22.168]; HPLC, high-performance liquid chromatography; PDS, postemergence-directed; POST, postemergence; PRE, preemergence.
Turfgrass managers often desire to overseed thin areas during midsummer or late summer, but seeding desirable species too soon after a preemergence herbicide application can interfere with seedling growth. This study was conducted to compare the effects of three herbicides on Kentucky bluegrass seedling growth and to determine whether seeding method affects the interval before seeding can safely occur. Dithiopyr, prodiamine, and pendimethalin were applied to ‘Kentucky 31’ tall fescue plots in late April at 0.56, 0.84, and 3.36 kg ai/ha, respectively. At 2, 4, 8, 12, and 16 wk after treatment, soil cores were extracted from each plot, the existing turf was killed, and the cores were either broadcast seeded or slit seeded with Kentucky bluegrass. Slit seeding resulted in greater and more extended seedling growth suppression than broadcast seeding for all herbicides. Prodiamine suppressed Kentucky bluegrass seedling growth longer than dithiopyr and pendimethalin. Unacceptable seedling growth suppression occurred unless broadcast seeding was delayed for about 6, 8, and 14 wk after dithiopyr, pendimethalin, and prodiamine application, respectively. The required interval between herbicide application and slit seeding was approximately 11, 10, and 16 wk, respectively. Use of dithiopyr or pendimethalin rather than prodiamine and broadcast seeding instead of slit seeding allows earlier overseeding with Kentucky bluegrass.
Chinese privet is a nonnative shrub that has invaded mesic forests throughout the southeastern United States during the past century. Foliar sprays of glyphosate and triclopyr were tested in three factorial experiments that included wide ranges of application rate, timing, and formulation to refine methods for controlling Chinese privet. For spring (April) and fall (October and December) applications, percentage control of privet cover averaged 93 to 100% and 49 to 70% for glyphosate and triclopyr treatments, respectively, whereas for summer (June and August) applications, control averaged 67 to 69% and 14 to 26%, respectively (study 1). However, privet control was not influenced by variation in herbicide rates of 1.7, 3.4, 5.0, or 6.7 kg ae/ha compared with each of the five application timings. No differences were found in August comparisons of liquid vs. dry glyphosate products or water-soluble vs. oil-soluble triclopyr products for each of the four rates (study 2). In a comparison of low rates of glyphosate applied in August with or without trenching of plot perimeters to isolate privet clumps (study 3), control increased from 12 to 65% as rate increased from 0 to 0.8 kg ae/ha, suggesting that rate responses may occur at lower values than those tested in studies 1 and 2. Isolation of privet clumps by trenching did not have a statistically detectable effect on privet susceptibility to glyphosate. Low rates of glyphosate (1.7 kg ae/ha or possibly lower) will provide effective control of privet when applied in the spring or fall.
Nomenclature: Glyphosate; triclopyr; Chinese privet, Ligustrum sinense Lour.
Greenhouse experiments were conducted to examine the effect of glyphosate on reproductive development in sicklepod. Glyphosate was applied postemergence over the top at 112 and 280 g ai/ha to sicklepod at 4-leaf stage (L), 8-L, 4-L followed by 8-L, and 12-L. A nontreated control was included. Immediately after the 12-L application, number of flowers was recorded for all treatments twice per week for 8 wk. Pollen viability was measured on 1 open flower/plant/sampling time using Alexander stain. The number of pods, pod length, seeds per plant, 50-seed weight, total seed weight, seed germination, seed viability, and dry weight of aboveground biomass were also recorded. No significant differences among the treatments were found for average pod length, 50-seed weight, seed germination, seed viability, and aboveground biomass. The nontreated had 18 flowers counted over 8 wk. Glyphosate applied at 12-L and sequentially at 4-L and 8-L, averaged over glyphosate rates, reduced cumulative flower production after 8 wk by 65 and 54%, respectively, compared with the nontreated. Similarly, glyphosate at 280 g/ha, averaged over treatment timings, reduced flower production by 58% compared with the nontreated. Because the number of flowers produced was limited by glyphosate treatment due to flower abscission, pollen viability measurements could not be analyzed because of large numbers of missing data points. The number of pods, seeds, and total seed weight were reduced by 79, 80, and 81%, respectively, with 280 g/ha of glyphosate compared with the nontreated.
Sustainable invasive weed management must address treatment effects on desired vegetation. Our objective was to determine the influence of clopyralid plus 2,4-D, glyphosate, and fosamine, at various application rates and timing, on the density and biomass of Russian knapweed and desired plant groups growing in association with this invasive weed. In a randomized complete block design with four replications, three herbicides by three herbicide rates by three herbicide application timings and a nontreated control were factorially applied to two sites located along the Missouri River riparian corridor in Montana. Clopyralid plus 2,4-D, glyphosate, and fosamine were applied during the spring rosette stage of Russian knapweed (June), the bud to bloom stage of Russian knapweed (July), or the flowering stage of Russian knapweed (August). Herbicide rates were considered low, medium, and high based on label rates of clopyralid plus 2,4-D, glyphosate, or fosamine. Density and biomass of all species were sampled 3 yr after treatment. Russian knapweed biomass decreased from 125 to about 25 g/m2 using clopyralid plus 2,4-D, irrespective of rate or timing of application. Russian knapweed density was reduced by about half by this mixture of herbicides. Nonnative grass density and biomass were maintained, whereas native grasses increased using clopyralid plus 2,4-D at medium or high rates. Neither glyphosate nor fosamine provided substantial Russian knapweed control or increases in grasses. Too few forbs were present to analyze their response to the treatments. We believe that herbicides must be combined with revegetation in areas lacking a diverse mixture of desired species capable of capturing resources made available by controlling Russian knapweed.
Recent research at Mississippi State has shown that eastern gamagrass, switchgrass, and tall fescue grown as filter strips reduce herbicide losses in runoff from cotton. Field experiments were conducted in 1997 and 1998 to evaluate the response of these perennial grasses to postemergence drift and registered rates of glyphosate and paraquat in mid-April and clethodim, fluazifop-P, glyphosate, MSMA, pyrithiobac, quizalofop-P, and sethoxydim in early June. Results indicate that filter strip implementation will not simply involve establishment and maintenance. In most instances, reductions in harvested biomass were as high or higher than visual injury assessments in mid-June. This finding suggests an inability of these perennial grasses to recover from an accidental overspray or drift, within the year of the event. Management decisions must be made to protect the filter strips from contact with herbicides used in the production system to ensure filter strip integrity and survival.
Spray drift to unintended areas is more of a concern as applications of nonselective herbicides associated with herbicide-resistant crops and the proximity of residential land to agricultural land increase. This research evaluated the benefit of three commercial drift control agents for effectiveness in reducing drift in 19 to 24 km/h wind and their potential effect on weed control. The drift control agents were added to a spray mixture of glyphosate at 0.8 kg ae/ha applied in 140 L/ ha and applied with either flat-fan or flood nozzles. None of the drift control agents reduced drift compared with the spray mixture without drift control agent over a distance of 6 m, as measured by water-sensitive cards or grain sorghum bioassay, regardless of nozzle type used. In a separate study, drift control agents did not reduce the weed control of glyphosate or acifluorfen.
The importance of spray retention to the biocontrol of green foxtail with Pyricularia setariae was characterized using airbrush and broadcast sprayers at variable application volumes. Spray retention was determined by measuring amounts of a tracer dye solution on treated plants using fluorescence spectrophotometry. Depending on the droplet size, broadcast spraying at 1,000 to 2,000 L/ha produced a level of retention equivalent to that of airbrush spraying until runoff. The trend of P. setariae spore retention on green foxtail was similar to that of liquid retention. Broadcasting P. setariae at volumes producing equivalent spray retention to that of airbrush inoculation resulted in a similar level of weed control under greenhouse conditions. Reducing broadcast volume from 2,000 to 250 L/ha lowered biocontrol efficacy only slightly, when the concentration of P. setariae was increased proportionally to keep the applied fungal dose the same. A nozzle with a fine droplet spectrum (volume median diameter [VMD] 207 μm) had a significantly greater retention efficiency than a coarse spray (VMD 325 μm), but this retention difference was not translated into consistent enhancement of biocontrol efficacy. Higher retention increases may be necessary for more substantial improvement in biocontrol of green foxtail by P. setariae.
Yellow starthistle is an aggressive annual forb that has invaded millions of hectares of California's annual range. Control efforts such as burning and herbicides have been effective for short-term management. However, recruitment from the seedbank or reinvasion of the annual grassland system results in a rapid return to yellow starthistle dominance. Establishing perennial grasses would be ideal for suppression of yellow starthistle. However, a lack of effective weed control options in California during a seeding program has limited perennial grass establishment. Clopyralid was used to control yellow starthistle annually for 1, 2, or 3 yr to provide a window of reduced competition for pubescent wheatgrass establishment. Total plant cover, yellow starthistle density, biomass, and seedhead number were quantified for 6 yr. Clopyralid treatment significantly reduced yellow starthistle and allowed pubescent wheatgrass establishment with a single treatment. Both clopyralid treatment and pubescent wheatgrass establishment significantly affected the range plant community composition. Annual grasses and forbs increased in plots only treated with clopyralid for 2 or 3 yr, whereas clopyralid-treated pubescent wheatgrass plots maintained lower annual grass and forb cover. Integrating pubescent wheatgrass seeding with clopyralid treatment provided long-term yellow starthistle suppression, whereas clopyralid treatment alone resulted in a plant community susceptible to repeated invasion. These findings support the establishment of competitive perennial grasses in annual grasslands as an important component of long-term yellow starthistle management.
Nomenclature: Clopyralid; yellow starthistle, Centaurea solstitialis (L.) #3 CENSO; pubescent wheatgrass, Thinopyrum intermedium (Host. Barkworth and Dewey) Nevski var. ‘Luna’.
Additional index words: Integrated management, revegetation.
Abbreviation: MANOVA, multivariate analysis of variance.
A 2-yr experiment repeated at five locations across the northeastern United States evaluated the effect of weed density and time of glyphosate application on weed control and corn grain yield using a single postemergence (POST) application. Three weed densities, designed to reduce corn yields by 10, 25, and 50%, were established across the locations, using forage sorghum as a surrogate weed. At each weed density, a single application of glyphosate at 1.12 kg ai/ha was applied to glyphosate-resistant corn at the V2, V4, V6, and V8 growth stages. At low and medium weed densities, the V4 through V8 applications provided nearly complete weed control and yields equivalent to the weed-free treatment. Weed biomass and the potential for weed seed production from subsequent weed emergence made the V2 timing less effective. At high weed densities, the V4 followed by the V6 timing provided the most effective weed control, while maintaining corn yield. Weed competition from subsequent weed emergence in the V2 application and the duration of weed competition in the V8 timing reduced yield on average by 12 and 15%, respectively. This research shows that single POST applications can be successful but weed density and herbicide timing are key elements.
Field trials were conducted at the Coastal Plain Experiment Station in Tifton, GA, from 2000 to 2003 to study the effects of herbicide placement on weed control and cantaloupe injury. Herbicides halosulfuron (0.036 kg ai/ha), sulfentrazone (0.14 and 0.28 kg ai/ha), clomazone (0.6 kg ai/ha), and a nontreated control were evaluated. Methods of herbicide application were preplant incorporated (PPI) under the polyethylene mulch before transplanting, posttransplanting over-the-top (POST-OTT), and posttransplanting-directed (POST-DIR) to the shoulders of polyethylene-covered seedbeds. Across all herbicide treatments, PPI and POST-DIR applications were the least injurious, with POST-OTT applications the most injurious. In general, sulfentrazone (0.28 kg ai/ha) was the most injurious herbicide and halosulfuron the least injurious, regardless of herbicide placement. Halosulfuron effectively controlled yellow nutsedge and provided versatility in methods of application, with minimal injury to transplanted cantaloupe.
Nomenclature: Clomazone; halosulfuron; sulfentrazone; yellow nutsedge, Cyperus esculentus L. #3 CYPES; cantaloupe, Cucumis melo L.
Additional index words: Clomazone, halosulfuron, plasticulture, sulfentrazone.
Greenhouse and field studies were conducted to evaluate potential interactions between glyphosate and trifloxysulfuron on barnyardgrass, browntop millet, hemp sesbania, seedling johnsongrass, pitted morningglory, prickly sida, sicklepod, and velvetleaf control as well as cotton injury and yield. In the greenhouse, glyphosate at 840 g ae/ha controlled all weed species 62 to 99%, which was better than trifloxysulfuron at 2.5 or 5 g ai/ha. Control of four-leaf pitted morningglory and hemp sesbania was 80 to 88% when glyphosate and trifloxysulfuron were mixed compared with 62 to 66% control with glyphosate alone. Mixing trifloxysulfuron with glyphosate did not affect control of other species compared with glyphosate alone. In the field, glyphosate controlled barnyardgrass, prickly sida, sicklepod, seedling johnsongrass, and velvetleaf 68 to 100%. Trifloxysulfuron controlled hemp sesbania, seedling johnsongrass, and sicklepod 65 to 88%. All other species were controlled 36 to 72% with glyphosate and 10 to 60% with trifloxysulfuron. Combinations of glyphosate (840 g/ha) and trifloxysulfuron (5 g/ha) were applied postemergence over-the-top and postemergence-directed to three-, six-, and nine-leaf glyphosate-resistant cotton in the field. Cotton injury at 2 wk after treatment (WAT) was less than 13% for all herbicide treatments and less than 5% by 3 WAT. Herbicides did not affect the percent of open bolls or nodes per plant. Seed cotton yield ranged from 1,430 to 1,660 kg/ha, and only the sequential over-the-top applications of trifloxysulfuron reduced cotton yield compared with the weed-free, nontreated cotton.
Nomenclature: Glyphosate; trifloxysulfuron; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; browntop millet, Brachiaria ramosa (L.) Stapf # PANRA; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill # SEBEX; johnsongrass, Sorghum halepense L. Pers. # SORHA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; sicklepod, Senna obtusifolia (L.) Irwin & Barnaby # CASOB; velvetleaf, Abutilon theophrasti Medik. # ABUTH; cotton, Gossypium hirsutum L.
Additional index words: CGA-362622, crop injury, glyphosate-resistant cotton, herbicide interactions, pesticide interactions, tank mixtures.
Abbreviations: ALS, acetolactate synthase; EPOST, early postemergence; fb, followed by; GRC, glyphosate-resistant cotton; LPOST, late postemergence; MPOST, midpostemergence; PD, postemergence-directed; POST, postemergence; POT, postemergence over-the-top; WAT, weeks after treatment.
Cogongrass is an aggressive perennial weed, which causes severe yield losses in major crops of the moist savanna of West Africa. Field studies were conducted from 2000 to 2002 at Alabata and Ilorin, Nigeria, to evaluate the influence of dosage and time of nicosulfuron application on the control of cogongrass and corn grain yield. Nicosulfuron dosages were 50, 100, 150, and 200 g ai/ha applied 1, 2, 3, or 4 wk after planting (WAP) corn. Hand-weeded and nonweeded treatments were the controls. Three to 4 wk after treatment and at final harvest, all plots that received nicosulfuron had significantly lower cogongrass shoot dry matter (DM) than the nonweeded control across locations in all years (P ≤ 0.01). Nicosulfuron increased corn grain yield at Alabata by 96% in 2000, 100% in 2001, and 34 to 54% in 2002, and at Ilorin by 79 to 83% in 2001 and 60 to 69% in 2002 when compared with the nonweeded control. The weeded control had corn grain yield similar to plots that received nicosulfuron at 200 g/ha at Alabata in 2001, 150 g/ha at Ilorin in 2001, 50 to 200 g/ha at Alabata in 2002, and 150 and 200 g/ha at Ilorin in 2002. There were negative linear relationships between corn DM, grain yield, and cogongrass shoot DM. Application of nicosulfuron at 1 or 2 WAP, when cogongrass was 22 to 27 cm tall, gave better grain yield and lower cogongrass shoot DM than at 3 or 4 WAP, when cogongrass was 36 to 45 cm tall. The study concludes that 150 to 200 g/ha of nicosulfuron applied at 1 or 2 WAP is effective for cogongrass control without adverse effect on corn grain yield.
Bifra is an annual noxious broadleaf weed of winter-sown crops in the Central Anatolia and Middle Black Sea regions of Turkey. This species has become more prevalent in wheat fields in the past three decades because of poor chemical control. Field experiments were conducted in Havza and Kavak, Samsun, Turkey, to evaluate the effect of cultivar and seeding rate on the competitive interaction between bifra and wheat at four bifra densities. Wheat grain yield increased with seeding rate, either in the presence or in the absence of bifra in both locations. Decreasing the seeding rate from 250 to 200 kg/ha or 150 kg/ha decreased wheat yield in the presence of bifra in all cultivars. The percentage yield decreases were different according to cultivars, although yields decreased in all cultivars. On the basis of the analysis of yield variables, data suggest that the relative competitiveness was ‘Bezostaja’ > ‘Momtchill’ > ‘Kate A-1’ = ‘Panda’. Bifra biomass and seed numbers were reduced not only by an increase in the wheat seeding rate but also by cultivars. Bifra seed production in Bezostaja, Kate A-1, Momtchill, and Panda were diminished 60, 53, 54, and 46%, respectively, at the seeding rate of 250 kg/ha compared with bifra alone at a density of 350 plants/ m2.
A study was conducted to compare the effect of 1,3-dichloropropene (1,3-D) chloropicrin (Pic) in a 83:17 ratio (C-17) used alone or in combination with herbicides on tomato. Treatments evaluated included 1,3-D (325 kg ai/ha) plus Pic (67 kg ai/ha) used either alone or with pebulate (4.5 kg ai/ha), napropamide (4.5 kg ai/ha), metolachlor (1.1 and 2.3 kg ai/ha), lactofen (2.3 kg ai/ha), or flazasulfuron (0.4 kg ai/ha). Pebulate was consistently more effective in controlling purple nutsedge than the other herbicides tested. Purple nutsedge was more effectively controlled with C-17 in combination with pebulate than with the fumigant alone. Shallow incorporation of pebulate failed to improve weed control and tomato fruit yield.
Greenhouse and growth chamber experiments were conducted to investigate the sprouting potential of rootstock; the effect of temperature, burial depth, and length of rootstock on sprouting; and the effect of shoot removal on resprouting ability of rootstock in redvine and trumpetcreeper. Glyphosate translocation along the rootstock of redvine was also measured. Higher sprouting was observed at 20 to 40 C in trumpetcreeper (60 to 73%) and at 30 to 40 C in redvine (45 to 47%) compared with other temperatures. Redvine sprouting was totally inhibited at 15 C, whereas trumpetcreeper had a sprouting of 12%. Emergence of shoot from a 28-cm planting depth was completely inhibited in redvine, whereas trumpetcreeper had 23% sprout emergence. After shoot removal treatments applied every 3 wk, redvine rootstock segments ≤2 cm long were totally depleted after fifth shoot removal treatment (15 wk after planting [WAP]). In trumpetcreeper, total depletion was not reached by 15 WAP, regardless of rootstock length. 14C-glyphosate was translocated from the treated shoot attached to the apical end of a 35-cm rootstock to the untreated end with slightly less 14C-glyphosate recovered at the untreated end compared with 5 to 10 cm from the treated shoot. These results indicated that vegetative reproduction in redvine is more sensitive to cool temperatures, deep burial depth, and short rootstock segment than trumpetcreeper. Variable control of redvine with glyphosate could be due to inadequate herbicide translocation within the rootstock.
Nomenclature: Glyphosate; redvine, Brunnichia ovata (Walt.) Shinners #3 BRVCI; trumpetcreeper, Campsis radicans (L.) Seem. ex Bureau # CMIRA.
Additional index words: Absorption, regrowth, sprout regeneration, uptake.
Abbreviations: DAT, days after treatment; WAP, weeks after planting; WAT, weeks after treatment.
Field bindweed is a major weed problem for wheat producers across the Great Plains and for Oklahoma hard red winter wheat producers. Herbicides have demonstrated limited efficacy, with retreatment often suggested on labels. However, little data are available to verify efficacy with repeated treatments in Oklahoma wheat fields. Annual treatment with dicamba 2,4-D, the prepackaged mixture (premix) glyphosate 2,4-D, premix quinclorac 2,4-D at two different rates, or picloram 2,4-D to actively growing field bindweed for three consecutive years reduced stem density up to 88% at Lahoma and up to 96% at Stillwater for several months after treatment. However, by 12 to 14 mo after the last treatment, stem densities returned to 47% or more of the nontreated. Treatments applied in June or July were not more effective than treatments applied in September. These results suggested a need to shift the intent of herbicide application from multiyear control to single-year control with treatments designed to control field bindweed throughout one growing season. To field test this approach, nine farmer cooperators in 1998 to 1999 and seven cooperators in 1999 to 2000 applied either premixed glyphosate 2,4-D or dicamba in late summer or early fall after the field bindweed was allowed to grow 5 wk or more without disturbance. Of the participants, 88% reported little field bindweed present at wheat harvest, whereas 12% reported considerable field bindweed present at harvest. Cooperators were generally satisfied with the reduction in field bindweed canopy through harvest.
Nomenclature: 2,4-D; dicamba; glyphosate; picloram; quinclorac; field bindweed, Convolvulus arvensis L. #3 CONAR; wheat, Triticum aestivum L.
Additional index words: 2,4-D, dicamba, glyphosate, weed management.
Abbreviations: DAH, days after wheat harvest; OM, organic matter; premix, prepackaged mixture.
The fate of imazamox, imazethapyr, and imazaquin in soil was evaluated at various soil moisture levels and at soil pH levels of 5 and 7. The percentage of each herbicide sorbed, desorbed, dissipated, and metabolized over time was compared. Soil was kept at its field pH (pH 7) or modified to a lower pH (pH 5) and equilibrated to field moisture contents ranging from 0.27 to 0.21 g water/ g soil, at and below the field capacity of the soil. Soil moisture in the range studied did not affect the fate of the herbicides. The percentage of applied herbicide found in soil solution was greatest for imazamox and least for imazaquin (imazamox > imazethapyr > imazaquin) and was greater at pH 7 than at pH 5 for all three herbicides. Over time, less herbicide was in the soil solution and less was desorbed. Metabolism followed the same pattern. Among the herbicides, metabolism followed the following sequence, imazamox > imazethapyr > imazaquin with metabolism greater at pH 7 than at pH 5 for all three herbicides. At pH 7, the half-life for imazamox was 1.4 wk and for imazethapyr was 16 wk, and the estimated half-life for imazaquin was 191 wk.
Field studies were conducted in 2000, 2001, and 2002 at Brownstown, DeKalb, Perry, and Urbana, IL, to evaluate weed control and corn tolerance from postemergence (POST) applications of foramsulfuron in sequential and total-POST herbicide programs. Foramsulfuron applied alone controlled giant foxtail, fall panicum, and redroot pigweed 88, 99, and 99%, respectively, 28 d after treatment (DAT), which was comparable with the standard treatment of nicosulfuron. However, control of common cocklebur, velvetleaf, and common lambsquarters was significantly higher with foramsulfuron compared with nicosulfuron. Sequential herbicide programs of atrazine, S-metolachlor, or isoxaflutole applied preemergence (PRE) followed by a POST application of foramsulfuron provided greater than 85% control of giant foxtail, fall panicum, common cocklebur, velvetleaf, common waterhemp, and redroot pigweed. Of the sequential herbicide treatments, atrazine applied PRE followed by a POST application of foramsulfuron provided the greatest Pennsylvania smartweed control. A PRE application of either atrazine or isoxaflutole was needed before a POST application of foramsulfuron to control common lambsquarters. POST tank mixtures of foramsulfuron with atrazine, dicamba, and dicamba plus diflufenzopyr improved control of Pennsylvania smartweed, common cocklebur, velvetleaf, common lambsquarters, and common waterhemp when compared with foramsulfuron applied alone. The tank mixture of foramsulfuron with mesotrione improved control of all species, except Pennsylvania smartweed, common lambsquarters, and common cocklebur. Foramsulfuron tank mixtures with carfentrazone did not improve control of any weed species to commercial acceptance. Adjuvant selection was important for POST tank mixtures. Control of giant foxtail and fall panicum was reduced when atrazine was tank mixed with foramsulfuron and crop oil concentrate (COC). However, when methylated seed oil (MSO) was added to the atrazine–foramsulfuron tank mixture instead of COC, giant foxtail and fall panicum control were similar to foramsulfuron applied alone.
Nomenclature: Atrazine; carfentrazone; dicamba; diflufenzopyr, 2-[1-[[[(3,5-difluorophenyl)amino]carbonyl]hydrazono]ethyl]-3-pyridinecarboxylic acid; foramsulfuron, 2-[[[[(4,6-dimethoxy-2-pyrimidiny)amino]carbonyl]amino]sulfonyl]-4-(formylamino)-N,N-dimethylbenzamide; isoxaflutole; mesotrione; S-metolachlor; common cocklebur, Xanthium strumarium L. #3 XANST; common lambsquarters, Chenopodium album L. # CHEAL; common waterhemp, Amaranthus rudis Sauer. # AMATA; fall panicum, Panicum dichotomiflorum Michx. # PANDI; giant foxtail, Setaria faberi Herm. # SETFA; Pennsylvania smartweed, Polygonum pennsylvanicum L. # POLPY; redroot pigweed, Amaranthus retroflexus L. # AMARE; velvetleaf, Abutilon theophrasti Medicus # ABUTH; corn, Zea mays L.
Additional index words: Antagonism, tank mixture, total-POST.
Abbreviations: ALS, acetolactate synthase (EC 22.214.171.124); COC, crop oil concentrate; DAT, days after treatment; MSO, methylated seed oil; NIS, nonionic surfactant; POST, postemergence; PRE, preemergence; UAN, urea ammonium nitrate.
Full canopy closure and light interception are critical to obtaining full yield potential of ultra-short–season soybean in the midsouthern United States. We hypothesized that herbicide applications that resulted in soybean leaf injury would reduce season-long light interception and yield of ultra-short–season soybean grown in this environment. Experiments were conducted in 2001, 2002, and 2003 at Fayetteville, AR, to determine the effect of the diphenylether herbicides acifluorfen and lactofen on light interception and yield of maturity group (MG) 0 and II soybean. Factors evaluated included soybean MG, herbicide rate, treatment timing, and soybean seeding density. When applied at soybean growth stage (GS) V3, 0.2 kg ai/ha lactofen reduced green leaf area immediately after application and final canopy closure relative to soybean treated with 0.6 or 0.2 kg/ha acifluorfen and untreated soybean. Herbicide application did not affect yield of well-watered soybean when applied at GS V3 in 2001 or at early reproductive development in 2003. In 2002, an irrigation problem resulted in a period of water-deficit stress during seed fill of MG II soybean. Under these conditions, treatment with acifluorfen at GS V3 reduced soybean yield, and treatment with lactofen during early reproductive development reduced soybean yield, relative to untreated soybean. This research indicates that diphenylether herbicides can be safely applied to well-watered ultra-short–season soybean, but yield reduction can occur when applied to soybean that is not well watered.
The objective of this study was to evaluate the feasibility of using 2-aminobutyric acid (2-aba) as a chemical marker for the detection of sulfonylurea (SU) herbicides in crop and soil environments. A bioassay, on the basis of the injury index to vegetable seedlings, showed that both field mustard and Chinese mustard were more sensitive to bensulfuron, imazosulfuron, and pyrazosulfuron than lettuce and cabbage in winter. In a similar study, field mustard was found to be the most sensitive species among six summer vegetables. After foliar application of bensulfuron at 0.487 μM, 2-aba accumulation reached the maximum in field mustard within 6 to 12 h, before any visible symptoms appeared, and this high level was maintained up to 72 h. Among all vegetables tested for differential SU sensitivities, maximum accumulation of 2-aba occurred, in coincidence with the onset of injury, in field mustard. The accumulation of 2-aba in field mustard showed a linear regression to the log-transformed concentrations, ranging from 10−2 to 102 μM, of each of the three SUs. However, no such relationship between the applied rate, especially at the lower rates, and the residue content of SUs in field mustard plant was found. In addition, with the extract of SU-treated paddy soil sprayed on field mustard, the accumulation of 2-aba in this plant was found to reflect indirectly the amount of SU residues in the soil.
Nomenclature: 2-aminobutyric acid; bensulfuron; imazosulfuron, 1-(2-chlorimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxy-pyrimidin; pyzazosulfuron; cabbage, Brassica oleracea L. var. ‘Capitata’; Chinese mustard, Brassica rapa L.; field mustard, Brassica campestris L.; lettuce, Lactuca sativa L.; rice, Oryza sativa L.
Additional index words: Bensulfuron, bioassay, imazosulfuron, pyrazosulfuron.
Abbreviations: 2-aba, 2-aminobutyric acid; ALS, acetolactate synthase (EC 126.96.36.199); DAT, days after treatment; FW, fresh weight; HAT, hours after treatment; HPLC, high-performance liquid chromatography; SUs, sulfonylureas; TLC, thin-layer chromatography.
Preemergence (PRE) and postemergence (POST) herbicides registered for large crabgrass control were evaluated for control of Japanese stiltgrass, an invasive, nonnative C4 annual grass. Benefin plus oryzalin, dithiopyr, isoxaben plus trifluralin, oryzalin, oxadiazon, pendimethalin, prodiamine, or trifluralin applied PRE controlled Japanese stiltgrass 87% or greater 8 wk after treatment. Benefin plus trifluralin, metolachlor, or napropamide applied PRE were less effective (78, 39, and 59% control, respectively). Single POST applications of clethodim, fenoxaprop-P, fluazifop-P, or sethoxydim controlled Japanese stiltgrass 50 to 88%. These herbicides applied twice provided 82 to 99% control. Single POST applications of glufosinate controlled Japanese stiltgrass 82 to 85%, whereas two applications provided complete control. Single POST applications of glyphosate were just as effective as two applications in controlling Japanese stiltgrass. Dithiopyr, MSMA, and quinclorac applied POST were ineffective on Japanese stiltgrass. All PRE and POST herbicides tested were equally or more effective on Japanese stiltgrass than on large crabgrass, with the exception of metolachlor applied PRE and dithiopyr or quinclorac applied POST.
Research is needed to develop more comprehensive integrated weed management systems that would facilitate greater adoption by farmers. A field study was conducted to determine the combined effects of seed date (April or May), seed rate (recommended or 150% of recommended), fertilizer timing (fall or spring applied), and in-crop herbicide rate (50 or 100% of recommended) on weed growth and crop yield. This factorial set of treatments was applied in four consecutive years within a barley-field pea–barley-field pea rotation in a zero-till production system. Both barley and field pea phases of the rotation were grown each year to account for variable environmental conditions over years. Weed biomass was often lower with May than with April seeding because of more weeds being controlled with preplant glyphosate. However, despite fewer weeds being present with May seeding, barley yield was only greater in 1 of 4 yr and field pea yield was actually lower with May than with April seeding in 3 of 4 yr, indicating that optimum seed date is highly dependent on crop species and environmental conditions. Higher crop seed rates reduced weed biomass and increased crop yield in 2 of 4 yr in each of barley and field pea. Fertilizer timing had little effect on weed competition in barley, but spring- compared with fall-applied fertilizer reduced weed biomass and increased field pea yield in 2 of 4 yr. In-crop herbicides applied at 50% compared with 100% rates sometimes resulted in greater weed biomass and lower crop yields with recommended crop seed rates, but few differences were noted at high crop seed rates. Indeed, the weed seed bank at the conclusion of the 4-yr study was not greater with the 50% compared with 100% herbicide rate when high crop seed rates were used. This study demonstrates the combined merits of early seeding (April), higher crop seed rates, and spring-applied fertilizer in conjunction with timely but limited herbicide use to manage weeds and maintain high yields in rotations containing barley and field pea.
Nomenclature: Glyphosate; barley, Hordeum vulgare L. ‘AC Harper’; field pea, Pisum sativum L. ‘Swing’.
Russian knapweed and perennial pepperweed are invasive to meadow and riparian habitats in the semiarid intermountain west. Seed germination was tested to determine favored seedbed characteristics. Germination was inhibited in both species when water stress was imposed using polyethylene glycol. Knapweed achieved 60% germination after 40 d in dark and alternating light/dark environments. Pepperweed germination was greatest (30% after 14 d) in light and alternating light/ dark environments. Both species showed that germination declines when exposed to salt stress but continued to germinate under salt stress as high as 16 dSm−1.
Nomenclature: Perennial pepperweed, Lepidium latifolium L. #3, LEPLA; Russian knapweed, Centaurea repens L. #3 CENRE.
Additional index words: Riparian habitats, seedbed ecology.
Field experiments were conducted in 2002 and 2003 to evaluate weed control and dry bean response to fomesafen and fomesafen tank mixtures. In the first experiment, six market classes of dry bean were treated at the first trifoliate growth stage with fomesafen nonionic surfactant (NIS) urea ammonium nitrate solution (UAN) at rates ranging from 210 to 840 g/ha. In the second experiment, fomesafen NIS UAN at 280 g/ha was applied alone or combined with imazamox at 36 g/ha, bentazon at 560 g/ha, or clethodim at 140 g/ha, and each treatment was applied postemergence at either the unifoliate, first trifoliate, or third trifoliate growth stage to six dry bean cultivars. Crop injury from fomesafen in the form of stunting and leaf crinkling was apparent 7 d after treatment (DAT), but crop injury was temporary and plants recovered. Common lambsquarters and hairy nightshade control increased from 61 to 71% and 74 to 92%, respectively, as fomesafen rate increased from 210 to 280 g/ha. Redroot pigweed, kochia, and common purslane were controlled at the ≥90% level by fomesafen at 210 g/ha. Applying fomesafen and fomesafen tank mixtures at the unifoliate growth stage caused less dry bean injury and improved redroot pigweed, common lambsquarters, and hairy nightshade control compared with treatments made at the first or third trifoliate growth stage. Decreased weed control caused by delaying herbicide application to the third trifoliate growth stage resulted in a 17% decrease in crop yield, compared with treatments where herbicides were applied at the unifoliate growth stage. Combining fomesafen with other herbicides increased crop injury 4%, 14 DAT. A tank mixture of fomesafen plus imazamox caused more crop injury than fomesafen plus bentazon. Combining fomesafen with imazamox or bentazon improved hairy nightshade control to 92 and 87%, respectively; however, common lambsquarters control was improved only with tank mixtures of fomesafen with bentazon.
Nomenclature: Bentazon; clethodim; fomesafen; imazamox; common lambsquarters, Chenopodium album L. #3 CHEAL; common purslane, Portulaca oleracea L. # POROL; hairy nightshade, Solanum sarrachoides Sendt. # SOLSA; kochia, Kochia scoparia (L.) SCHRAD. # KCHSC; redroot pigweed, Amaranthus retroflexus L. # AMARE; dry bean, Phaseolus vulgaris L. black, Great Northern, light red kidney, navy, pink, pinto, ‘Shadow’, ‘Marquis’, ‘Chinook’, ‘Schooner’, ‘Viva’, ‘Poncho’.
Additional index words: Field beans, interference, seed yield.
Abbreviations: DAT, days after treatment; NIS, nonionic surfactant; POST, postemergence; UAN, urea ammonium nitrate solution.
Field experiments were conducted at four locations (Larissa, Halkidona, Thessaloniki, and Halastra) in Greece to evaluate weed and cotton response to various pyrithiobac rates applied preplant incorporated (PPI), preemergence (PRE), or postemergence (POST). Pyrithiobac applied PPI or PRE at 0.068, 0.102, or 0.136 kg ai/ha controlled black nightshade, pigweeds, and common purslane at Larissa. However, pyrithiobac applied PRE at Thessaloniki and Halkidona was more effective against black nightshade and pigweeds than pyrithiobac applied PPI. Pyrithiobac applied PPI or PRE at 0.068 or 0.102 kg/ha did not control common lambsquarters at Thessaloniki. Weed control with trifluralin plus fluometuron applied PPI and alachlor plus fluometuron applied PRE at Larissa was slightly lower than that obtained with pyrithiobac. At Halkidona, trifluralin plus fluometuron applied PPI and alachlor plus fluometuron applied PRE provided weed control similar to that obtained with pyrithiobac. But at Thessaloniki, these treatments provided better weed control than pyrithiobac. Furthermore, pyrithiobac applied early postemergence (EPOST), midpostemergence, or in sequential systems controlled black nightshade and pigweeds, but it resulted in fair to good control of common purslane, velvetleaf, and common cocklebur. None of the POST treatments controlled common lambsquarters. Fluometuron EPOST controlled black nightshade, common lambsquarters, and common purslane ≥70, 86, and 67%, respectively. Fluometuron EPOST did not control pigweeds, velvetleaf, and common cocklebur. Cotton treated with pyrithiobac, regardless of method of application, yielded similar to the weed-free control. Cotton treated with pyrithiobac PPI at the highest rate (0.136 kg/ ha) yielded less at Halkidona, although adverse effects after its application were not visually apparent. Yield of cotton treated with herbicides was similar, with no difference among treatments.
Nomenclature: Alachlor; fluometuron; pyrithiobac; trifluralin; black nightshade, Solanum nigrum L. #3 SOLNI; common cocklebur, Xanthium strumarium L. # XANST; common lambsquarters, Chenopodium album L. # CHEAL; common purslane, Portulaca oleracea L. # POROL; prostrate pigweed, Amaranthus blitoides S. Wats AMABL; redroot pigweed, Amaranthus retroflexus L. # AMARE; velvetleaf, Abutilon theophrasti Medicus # ABUTH; cotton, Gossypium hirsutum L. ‘Stoneville 474’, ‘Hazera Vered’, ‘Deltapine 20’, ‘Deltapine 50’, ‘Stoneville Bravo’.
Abbreviations: EPOST, early postemergence; MPOST, midpostemergence; MSMA, monosodium salt of methylarsonic acid; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; WAP, weeks after planting; WAT, weeks after treatment.