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Abstract: Glyphosate was compared with other commonly used corn herbicides at three locations in Kentucky in 1998 and 1999. Sequential glyphosate treatments provided greater than 87% control of common cocklebur, ivyleaf morningglory, common lambsquarters, and giant ragweed. Control of these species with glyphosate treatments was similar to the control with atrazine plus other postemergence (POST) herbicides. Generally, treatments containing s-triazines and chloracetamides applied to the soil surface were not as effective as sequential glyphosate or atrazine plus POST herbicides. Corn yield was not significantly different at any location or for any year, whereas differences in net return occurred at one location in 1998.
Nomenclature: Atrazine; chloracetamides; glyphosate; s-triazines; common cocklebur, Xanthium strumarium L. #3 XANST; common lambsquarters, Chenopodium album L. # CHEAL; giant ragweed, Ambrosia trifida L. # AMBTR; ivyleaf morningglory, Ipomoea hederacea L. Jacq. # IPOHE; corn, Zea mays L. ‘DeKalb 626RR’.
Additional index words: Acetochlor, dicamba, Digitaria sanguinalis L. Scop. DIGSA, dimethenamid, giant foxtail, large crabgrass, 1-(4-methoxy-6-methyl-triazin-2-yl)-3-[2-(3,3,3-trifluoropropyl)-phenylsulfonyl]-urea, metolachlor, net return, primisulfuron, prosulfuron, Roundup Ready® corn, Setaria faberi Herrm. SETFA, simazine.
Abbreviations: ASN, as needed; MP, mid-postemergence; POST, postemergence; PRE, preemergence; REG, regrowth.
Abstract: Field experiments were conducted in 1997 and 1998 to evaluate the effect of mowing followed by hexazinone for West Indian dropseed/giant smutgrass (Sporobolus indicus var. pyramidalis) (hereafter referred to as dropseed) control. The experimental design was a split plot, with mowing (nonmowed [mature] and 35-cm regrowth) as the whole plot and hexazinone rate (0.0 [control], 0.56, 0.84, 1.12, 1.40, and 1.68 kg ai/ha) as the subplot treatments. The application of 0.84 kg/ha hexazinone provided 94 and 81% dropseed control, 365 d after treatment (DAT) during 1997 and 1998, respectively. Increasing application rate to 1.12 kg/ha hexazinone provided 87 and 88% dropseed control, 365 DAT during 1997 and 1998, respectively. Both the 0.84 and 1.12 kg/ha rates provided the same average control (87.5%); however, the 1.12 kg/ha rate provided consistent control over years. Mowing dropseed, followed by hexazinone application at 35-cm regrowth, provided no additional control when compared with no mowing treatments. Rates of hexazinone at 1.40 and 1.68 kg/ha caused phytotoxicity to bahiagrass and increased bare soil surface area, especially 90 and 120 DAT. Phytotoxic effect on bahiagrass and on bare soil decreased 365 DAT, resulting in 75 to 80% total forage cover. Concentration and yield of total nonstructural carbohydrates were significantly lower for the mowed 35-cm regrowth treatment than for the nonmowed plants; however, even in its weakened condition this reduction had no effect on dropseed control.
Nomenclature: Hexazinone; West Indian dropseed/giant smutgrass, Sporobolus indicus (L.) R. Br. var. pyramidalis (P. Beauv.) Veldkamp; S. indicus (L.) R. Br. var. indicus #3 SPZIN; S. jacquemontii Kunth.; S. poiretii (Roem. & Schult.) A. S. Hitchc. # SPZIN; bahiagrass, Paspalum notatum Fluegge # PASNO.
Abstract: Field studies were conducted at two locations in North Carolina in 1999 and 2000 to evaluate weed and bromoxynil-resistant cotton response to bromoxynil, pyrithiobac, and MSMA applied early postemergence (EPOST), alone or mixtures in all combinations (two way and three way), and to prometryn plus MSMA applied late postemergence directed (LAYBY). Trifluralin preplant incorporated followed by fluometuron preemergence controlled common lambsquarters, eclipta, and smooth pigweed at least 90%. These herbicides also provided greater than 90% common ragweed control at two locations but only 65% control at a third location. Pyrithiobac and pyrithiobac plus MSMA EPOST increased sicklepod control more than did bromoxynil or bromoxynil plus MSMA EPOST. Bromoxynil and pyrithiobac were more effective for sicklepod control when applied in mixture with MSMA. Bromoxynil plus pyrithiobac EPOST or with MSMA controlled (≥ 90%) common lambsquarters, common ragweed, entireleaf morningglory, prickly sida, and smooth pigweed early season. But the LAYBY treatment of prometryn plus MSMA frequently improved late-season control of entireleaf morningglory, large crabgrass, prickly sida, and sicklepod. A tank mixture of MSMA plus bromoxynil or pyrithiobac and the three-component tank mixture (bromoyxnil, MSMA, plus pyrithiobac) provided a broader weed control spectrum than did either bromoxynil or pyrithiobac alone. Cotton lint yields were increased with all postemergence systems, and the LAYBY treatment of prometryn plus MSMA increased cotton yields in 13 out of 16 comparisons. High cotton yields were indicative of high levels of weed control.
Nomenclature: Bromoxynil, fluometuron, MSMA, prometryn, pyrithiobac, trifluralin, common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; eclipta, Eclipta prostrata L. # ECLAL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; prickly sida, Sida spinosa L. # SIDSP; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; smooth pigweed, Amaranthus hybridus L. # AMACH; cotton, Gossypium hirsutum L. ‘Stoneville BXN 47’.
Additional index words: Crop injury, herbicide-resistant cotton, Brachiaria platyphylla, BRAPP.
Abbreviations: EPOST, early postemergence; fb, followed by; LAYBY, late postemergence directed; PDS, postemergence directed; PRE, preemergence; PPI, preplant incorporated.
Abstract: Woolly cupgrass seeds are dormant at physiological maturity and lose dormancy while afterripening in winter. Field experiments were conducted with the seeds collected from the locations across Iowa in the fall of 1991 and 1992. The seeds were buried in mid-November 0, 5, and 15 cm below the soil surface. Seeds were extracted biweekly until mid-February and germination tests conducted. Seeds buried below the soil surface were less dormant when compared with seeds on the soil surface. There were also dormancy differences between locations. Differences observed between locations and variations from 1991 to 1992 indicated that the parent plant environment, and the likely genotype, had a significant effect on woolly cupgrass seed dormancy.
Abstract: Field experiments were conducted at three locations in North Carolina in 1998 and 1999 and one location in Virginia in 1998 to evaluate weed management systems in peanut. Treatments consisted of diclosulam alone preemergence (PRE), or diclosulam plus metolachlor PRE alone or followed by (fb) bentazon plus acifluorfen postemergence (POST). These systems were also compared with commercial standards of metolachlor PRE fb bentazon plus acifluorfen POST or imazapic POST. Our data indicate that diclosulam PRE plus metolachlor PRE in conventional tillage peanut production usually controlled common lambsquarters, common ragweed, prickly sida, and entireleaf morningglory. But control of spurred anoda, goosegrass, ivyleaf morningglory, large crabgrass, and pitted morningglory by this system was inconsistent and may require additional POST herbicide treatments. Systems that included diclosulam plus metolachlor PRE consistently provided high yields and net returns.
Nomenclature: Acifluorfen, bentazon, diclosulam, imazapic, metolachlor; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; entireleaf morningglory, Ipomoea hederacea var. integruiscula Grey # IPOHG; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq # IPOHE; large crabgrass, Digitaria sanguinalis L. Scop. # DIGSA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; spurred anoda, Anoda cristata L. # ANVCR; peanut, Arachis hypogaea L. ‘NC 10C’, ‘NC 12C’.
Additional index words: Economic analysis.
Abbreviations: fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.
Abstract: Field studies were conducted over 2 yr in Louisiana to evaluate entireleaf morningglory and hemp sesbania control by glyphosate isopropylamine salt applied alone at 420, 560, and 700 g ae/ha and in combination with chlorimuron at 4, 6, 9, and 11 g ai/ha. Comparison treatments included glyphosate alone at 840 g/ha, glyphosate at 1,400 g/ha plus chlorimuron at 13 g/ha, and sethoxydim at 210 g ai/ha plus chlorimuron at 11 g/ha. Entireleaf morningglory and hemp sesbania were controlled no more than 77% with glyphosate rates as high as 840 g/ha. Chlorimuron added to glyphosate increased entireleaf morningglory control in two of the three experiments to 83 to 88% and hemp sesbania control to 86 to 98%. Response to chlorimuron was not rate dependent. In most cases, glyphosate–chlorimuron mixtures did not antagonize barnyardgrass control, and increasing rate of glyphosate did not always increase control. Soybean was injured no more than 6% by chlorimuron at one location, but injury was as great as 30% at another location, which was possibly due to smaller soybean size. Differences in weed control and soybean injury among the glyphosate and glyphosate–chlorimuron combinations were not reflected in soybean yields. Because injury occurred early season, sufficient time remained for soybean to recover and produce acceptable yields. Weed control by sethoxydim plus chlorimuron was less consistent than that by glyphosate plus chlorimuron, and soybean yield in most cases was inferior to the glyphosate treatments.
Nomenclature: Chlorimuron; glyphosate; sethoxydim; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex. A. W. Hill # SEBEX; soybean, Glycine max (L.) Merr.
Additional index words: Herbicide mixtures, transgenic soybean.
Abstract: Field studies were conducted in 1995 and 1996 at three locations in North Carolina to evaluate weed control and soybean injury with postemergence (POST) treatments of cloransulam-methyl alone or in tank-mixture with acifluorfen, fomesafen, or lactofen compared with a commercial standard of acifluorfen plus bentazon. Soybean injury was 2 to 3% 7 d after treatment with cloransulam-methyl applied alone and 11 to 46% when applied with fomesafen, lactofen, acifluorfen, or acifluorfen plus bentazon. Cloransulam-methyl applied alone controlled 95% of entireleaf morningglory and ivyleaf morningglory. Control was not increased by the addition of acifluorfen, fomesafen, or lactofen. Cloransulam-methyl improved the control of common lambsquarters to at least 81% compared with dimethenamid applied preemergence alone (69% control). All diphenyl ether herbicide treatments controlled common lambsquarters at least 91%. Prickly sida control by cloransulam-methyl ranged from 14 to 73% 8 wk after treatment. Control of prickly sida was varied by diphenyl ether herbicides (73 to 100% control). Tank-mixtures of cloransulam-methyl fomesafen and cloransulam-methyl acifluorfen increased the control of prickly sida over either herbicide applied alone. Soybean yield was greater for all tank-mixtures than for any diphenyl ether herbicide or for cloransulam-methyl treatment applied alone. But only the acifluorfen cloransulam-methyl treatment had higher economic returns than the cloransulam-methyl treatment alone. All other POST systems, with the exception of lactofen applied alone, had similar economic returns. Tank-mixtures of cloransulam-methyl and diphenyl ether herbicides increased the spectrum of control and soybean yield compared with these herbicides applied alone.
Nomenclature: Acifluorfen; bentazon; cloransulam-methyl; dimethenamid; fomesafen; lactofen; common lambsquarters, Chenopodium album L. #3 CHEAL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; prickly sida, Sida spinosa L. # SIDSP; soybean, Glycine max (L.) Merr.
Additional index words: Economic analysis, tank-mixtures.
Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; WAT, wk after POST treatment.
Abstract: A study was conducted to evaluate flumioxazin preemergence (PRE) at 71 and 105 g ai/ha, when used with dimethenamid PRE, dimethenamid preplant incorporated (PPI), or ethalfluralin PPI, for crop injury, weed control, and yield. Peanut injury from treatments including flumioxazin 2 wk after soil-applied treatment (WAST) was less than 2% at two locations and 50 to 67% at a third location. Peanut injury increased with flumioxazin rate. Soil-applied treatments that included flumioxazin at either rate controlled common lambsquarters and prickly sida at least 96 and 89%, respectively. Addition of postemergence (POST) herbicides to any soil-applied program controlled prickly sida and ivyleaf morningglory at least 94 and 98%, respectively. Treatments that included ethafluralin or dimethenamid controlled goosegrass at least 82%. With a few exceptions, peanut yields were not improved by use of POST herbicides. Where peanut injury occurred, increased flumioxazin rate resulted in lower peanut yield when averaged over PPI and POST herbicide treatments.
Nomenclature: Dimethenamid; ethalfluralin; flumioxazin; common lambsquarters, Chenopodium album L. #3 CHEAL; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; prickly sida, Sida spinosa L. # SIDSP; peanut, Arachis hypogaea L. ‘NC 7’, ‘NC 10C’.
Additional index words: Acifluorfen, bentazon, 2,4-DB, imazapic.
Abbreviations: fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; WAPT, weeks after POST treatment; WAST, weeks after soil-applied treatment.
Abstract: Field and greenhouse experiments were conducted to evaluate clethodim, CGA-362622, mixtures thereof, and sequential treatments for control of broadleaf signalgrass, fall panicum, goosegrass, and large crabgrass. In greenhouse experiments, clethodim alone provided 93 and 100% control of three- to four-leaf goosegrass at the low (105 g ai/ha) and high (140 g/ha) rates, respectively, whereas CGA-362622 did not control grasses in greenhouse or field experiments. Control of six- to eight-leaf goosegrass in the greenhouse with clethodim was 75% for the low rate and 89% for the high rate. Control of goosegrass in greenhouse studies was reduced at least 43 percentage points with CGA-362622 and clethodim at the high rate in mixture compared with control provided by clethodim at the high rate alone. When CGA-362622 and clethodim were applied in mixture in field studies, the effectiveness of the graminicide was decreased from > 97 to < 57% control for all annual grasses. Antagonism of clethodim activity was greater than that of the tank mixture when clethodim was applied 1 d after CGA-362622 on large crabgrass, goosegrass, and fall panicum. Clethodim applied 7 d before or after CGA-362622 controlled the four grass species as well as did clethodim applied alone. When CGA-362622 was applied to goosegrass alone, fresh weight accumulation stopped for a period of 4 d compared with untreated plants. Normal growth resumed after 4 d.
Abstract: Control of common waterhemp in corn with chloroacetamide and dinitroaniline herbicides can be inconsistent. Common waterhemp control by dimethenamid, S-metalochlor, pendimethalin, and three formulations of acetochlor, applied alone or with atrazine as single preemergence (PRE) or sequential PRE followed by postemergence (POST) treatment, was determined. The manufacturer's suggested use rate (1 time) of PRE herbicides was compared with sequential applications (0.66 time PRE followed by 0.34 time POST) of herbicides. POST applications included dicamba to control emerged common waterhemp. Single and sequential herbicide applications controlled common waterhemp at least 98%, 28 d after planting (DAP). But herbicides applied sequentially were more effective than PRE treatments by 56 DAP. Encapsulated acetochlor formulations controlled common waterhemp at least 85% by 56 DAP regardless of application method. Sequential applications of S-metolachlor controlled common waterhemp greater than 83%. Atrazine improved common waterhemp control regardless of herbicide or application method 56 DAP. Sequential applications of dimethenamid or S-metolachlor alone or with atrazine were more effective than single PRE applications of these herbicides.
Abstract: Experiments were conducted at two locations in North Carolina from 1999 to 2000 to evaluate flumioxazin preplant (PP) for weed management in strip-tillage cotton planted in winter-wheat cover. Flumioxazin PP was evaluated at two rates alone and in mixture with two commonly used PP herbicides and one experimental PP herbicide. Flumioxazin PP at 71 or 105 g ai/ha tank mixed with the isopropylamine salt of glyphosate at 1.12 kg ai/ha, paraquat at 1.05 kg ai/ha, or the trimethylsulfonium salt of glyphosate at 1.12 kg ai/ha controlled common chickweed, common lambsquarters, common ragweed, Palmer amaranth, and smooth pigweed ≥ 96% 29 to 43 d after treatment (DAT). Both glyphosate formulations and paraquat alone provided ≥ 91% control of common chickweed and henbit 29 to 43 DAT, but control of common lambsquarters, common ragweed, large crabgrass, Palmer amaranth, and smooth pigweed was ≤50%. Treatments including flumioxazin injured cotton (≤ 5%) at one location. In all comparisons within a location, cotton treated with flumioxazin PP at 71 or 105 g/ha in mixture with either glyphosate formulation or with paraquat provided equivalent or higher yields than did cotton not treated with flumioxazin PP.
Nomenclature: Flumioxazin; glyphosate; paraquat; common chickweed, Stellaria media L. Vill. #3 STEME; common lambsquarters, Chenopodium album L. CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; henbit, Lamium amplexicaule L. # LAMAM; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; Palmer amaranth, Amaranthus palmeri L. # AMAPA; smooth pigweed, Amaranthus hybridus L. # AMACH; cotton, Gossypium hirsutum L. ‘Paymaster 1218 RRBG’, ‘Paymaster 1220 RRBG’; wheat, Triticum aestivum L.
Additional index words: Burndown treatment, cover crops.
Abbreviations: COC, crop-oil concentrate; DAT, days after treatment; glyphosate-IP, isopropylamine salt of glyphosate; glyphosate-TM, trimethylsulfonium salt of glyphosate; PDS, postemergence-directed spray; POST, postemergence; PP, preplant; PRE, preemergence; WAP, weeks after planting.
Abstract: Greenhouse studies were initiated in 2001 to evaluate the effect of V-10029 applications on shoot and root growth of rice cultivars. V-10029 applications did not affect the shoot and root weight or shoot–root ratio of Cocodrie. Tolerance of Bengal was less than that of Cocodrie and was growth stage dependent. V-10029 treatments at the one- to two-leaf rice growth stage reduced shoot growth but had no effect on root, resulting in a lower shoot–root ratio compared with that of the nontreated 1 wk after treatment (WAT). At 2 and 3 WAT, both shoot and root growth were reduced by V-10029, with shoot–root ratio being greater than that of the nontreated, indicating a greater inhibition of roots than of shoots. V-10029 treatments at the two- to three-leaf rice growth stage reduced both shoot and root growth of Bengal across all three sampling dates. V-10029 treatments at the three- to four-leaf rice growth stage did not affect shoot growth but reduced root growth 2 and 3 WAT with no difference in shoot–root ratio. There was no difference in shoot and root weight or shoot–root ratio between the propanil comparison treatment and the nontreated. These results indicate that rice cultivars may differ in their tolerance to V-10029 and tolerance may be growth stage dependent.
Abstract: Current environmental concerns demand intensive research on conservation tillage for cotton production. Studies were conducted in 1994 and 1995 at Florence, SC, to evaluate weed and cotton response to various weed management systems in cotton with reduced tillage. Broadcast application of pendimethalin at 1.1 kg ai/ha and fluometuron at 2.2 kg ai/ha preemergence (PRE) followed by pyrithiobac at 0.07 kg ai/ha early postemergence (EPOST) was more effective than was a 38-cm band of these herbicides in controlling naturally occurring populations of sicklepod, Palmer amaranth, goosegrass, and southern crabgrass and in providing cotton yields equal to yields under weed-free conditions. With the 38-cm band of PRE and EPOST herbicides, two supplemental weed treatments at 3 and 7 wk after planting using glyphosate applied at 0.84 kg ae/ha POST with a hooded sprayer or a no-till cultivator was required to achieve acceptable weed control, but cotton yields were less than yields for the broadcast treatment alone. Glyphosate- or cultivation-only systems were generally ineffective in reducing weed interference and precluding cotton yield reductions. Optimum cotton production with reduced tillage can be achieved with broadcast application of PRE and EPOST herbicides but alternative methods offer promise for reducing costs and environmental effects and deserve additional study.
Nomenclature: Fluometuron; glyphosate; pendimethalin; pyrithiobac; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; Palmer amaranth, Amaranthus palmeri L. #3 AMAPA; sicklepod, Senna obtusifolia L. Irwin and Barneby # CASOB; southern crabgrass, Digitaria ciliaris L. # DIGSP; cotton, Gossypium hirsutum L. ‘KC 311’.
Abbreviations: EPOST, early postemergence; fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; WAP, weeks after planting.
Abstract: The unimbibed crush test, in which seed viability is evaluated by crushing and visual inspection of dry seeds, was compared with tetrazolium staining, an established method of testing seed viability. The unimbibed crush test potentially provides an immediate and rapid method for determining seed viability. Six sets of seed lots, involving the four weed species, velvetleaf, common lambsquarters, redroot pigweed, and smooth pigweed, were tested by each method. For four of the six sets, results from the crush test were statistically indistinguishable from those of the tetrazolium test. For the other two sets of seed lots, the crush test indicated higher viability than did the tetrazolium test. The crush test may be most useful for seed bank surveys in which many samples are typically processed, and most of the variation in density of viable seeds is associated with number of seeds present rather than percentage viability. Its use in more exacting circumstances like seed survival studies requires caution.
Nomenclature: Tetrazolium, 2,3,5 triphenyl tetrazolium chloride; common lambsquarters, Chenopodium album L. #3 CHEAL; redroot pigweed, Amaranthus retroflexus L. # AMARE; smooth pigweed, Amaranthus hybridus L. # AMACH; velvetleaf, Abutilon theophrasti Med. # ABUTH.
Abstract: Field experiments were conducted to determine the effect of shattercane interference on corn grain yield and nitrogen uptake in central Missouri. A glyphosate-resistant corn variety was planted, and atrazine was used to control all weeds except shattercane. Glyphosate was applied when shattercane was 8, 15, 23, 31, 38, or 46 cm tall, and plots were hand weeded weekly thereafter. Season-long shattercane interference resulted in an 85% yield loss in 1999 and a 43% yield loss in 2000. Yield reductions occurred when shattercane was allowed to remain with corn until it was 31 cm tall. In both years, late-season corn biomass N content was highly correlated (r = 0.95 and 0.84, respectively) with corn yield. When shattercane was allowed to reach the maximum recommended height for nicosulfuron or primisulfuron application (31 cm), significant yield losses occurred, and shattercane accumulated 10 and 20 kg N/ha, whereas corn accumulated 10 and 16 kg N/ha, respectively, in 1999 and 2000. Corn grain yield was reduced 0.66% (r2 = 0.71) for each day of interference before a postemergence (POST) application of glyphosate.
Abstract: Field experiments were conducted on the Eastern Shore of Virginia from 1999 to 2001 to evaluate the effects of tank mixture applications of isopropylamine or trimethylsulfonium salts of glyphosate with two liquid formulations of manganese (Mn lignin or Mn chelate) on spray solution pH and weed control in glyphosate-resistant soybean. Additions of manganese to herbicide solutions resulted in a reduction in the acidifying effects of the herbicides as well as in the control of common lambsquarters, large crabgrass, morningglory spp., and smooth pigweed. Reduced control caused by manganese could be overcome with higher rates of the herbicides on some species, but reduced control of common lambsquarters was seen when manganese was included with any herbicide application rate. For most species, Mn chelate caused a greater reduction in control than did Mn lignin. Although manganese caused significant decreases in weed control, soybean yield was not influenced by glyphosate salt, application rate, or manganese. Reduced weed control caused by the addition of manganese to herbicide solutions may be due to the complexing of the herbicide formulations, which could result in the formation of insoluble salt complexes that are not readily absorbed through the plant cuticle, resulting in decreased glyphosate phytotoxicity.
Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L. #3 CHEAL; large crabgrass, Digitaria sanguinalis L. # DIGSA; morningglory spp., Ipomoea spp. # IPOSS; smooth pigweed, Amaranthus hybridus L. # AMACH; soybean, Glycine max (L.) Merr. ‘Asgrow 5401 RR’.
Additional index words: pH, reduced weed control, tank mixture.
Abbreviations: Ipa, isopropylamine; POST, postemergence; Tms, trimethylsulfonium; WAP, weeks after planting; WAT, weeks after treatment.
Abstract: Field experiments were conducted at four locations in Kansas and Wyoming during the 1998 to 1999, 1999 to 2000, or 2000 to 2001 winter wheat–growing seasons to compare BAY MKH 6561 and MON 37500 at four postemergence timings for weed control and crop response. BAY MKH 6561 at 45 g ai/ha and MON 37500 at 35 g ai/ha controlled cheat 95% or more when applied early-fall postemergence (EFP), late-fall postemergence (LFP), early-spring postemergence (ESP), or late-spring postemergence (LSP) at Hays, KS, in 1999 and 2001. At Manhattan, KS, in these years, cheat control was 98 to 100%, except for MON 37500 (83 to 90%) applied LSP. Downy brome control with BAY MKH 6561 or MON 37500 declined as application timing was delayed at Hays, Archer, WY, and Torrington, WY. Averaged over herbicides, downy brome was controlled 38 to 95% when herbicides were applied EFP and 10 to 79% when applied LSP. Late-season wheat stunting was 11% or less, regardless of herbicide treatment, at Manhattan each year; no late-season injury was visible at Hays, Archer, or Torrington. Yields did not differ between treated and untreated wheat at Manhattan in 1999 or 2001, at Archer in 2000, or at Hays in 1999. Wheat receiving BAY MKH 6561 EFP yielded 8% more grain than did wheat treated with MON 37500 LSP at Hays in 2001 and at Torrington. At these two locations, all herbicide-treated wheat yielded 10 to 20% more grain than did the untreated wheat.
Nomenclature: BAY MKH 6561, methyl 2-({[(4-methyl-5-oxo-3-propoxy-4,5-dihydro-1H-1,2,4-triazol-1-yl)carbonyl]amino}sulfonyl)benzoate sodium salt; MON 37500, 1-(4,6-dimethoxypyrimidin-2-yl)-3-(2-ethanesulfonyl-imidazo[1,2-a]pyridine-3-yl)sulfonylurea; cheat, Bromus secalinus L. #3 BROSE; downy brome, Bromus tectorum L. # BROTE; winter wheat, Triticum aestivum L. ‘2137’, ‘Akron’, ‘Jagger’, ‘Pronghorn’, ‘Vista’.
Additional index words: Propoxycarbazone-sodium, stunting, sulfosulfuron, yield.
Abstract: Field studies were conducted at Lewiston and Rocky Mount, NC, in 1996 and 1997 to evaluate weed control and peanut response to preplant incorporated (PPI) treatments of diclosulam alone and in systems with postemergence (POST) commercial standard herbicides. All plots received ethalfluralin PPI at 840 g ai/ha. In both years, ethalfluralin plus diclosulam PPI at 17 or 26 g ai/ha followed by (fb) acifluorfen plus bentazon POST, paraquat plus bentazon POST, or imazapic POST controlled common lambsquarters, ivyleaf morningglory, pitted morningglory, prickly sida, smooth pigweed, spurred anoda, and yellow nutsedge in a manner similar to or better than did the commercial standards of ethalfluralin PPI fb metolachlor preemergence (PRE) fb acifluorfen plus bentazon or ethalfluralin PPI fb acifluorfen plus bentazon POST. Yield from peanut treated with diclosulam systems that included POST herbicides was equivalent to or higher than that from peanut treated with ethalfluralin PPI fb metolachlor PRE fb acifluorfen plus bentazon POST or ethalfluralin PPI fb acifluorfen plus bentazon POST. Peanut exhibited excellent tolerance to diclosulam PPI at all rates.
Nomenclature: Acifluorfen; bentazon; diclosulam; ethalfluralin; imazapic; metolachlor; paraquat; common lambsquarters, Chenopodium album L. #3 CHEAL; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; smooth pigweed, Amaranthus hybridus L. # AMACH; spurred anoda, Anoda cristata (L.) Schlecht. # ANVCR; yellow nutsedge, Cyperus esculentus L. # CYPES; peanut, Arachis hypogaea L. ‘NC 7’, ‘NC 10C’.
Additional index words: Herbicide injury.
Abbreviations: fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.
Abstract: Three studies were conducted in 1999 and 2000 to determine whether acetolactate synthase (ALS)–resistant common ragweed and giant ragweed biotypes were present in Ohio. Results of field studies indicated that biotypes of both species had cross-resistance to three chemical families of ALS-inhibiting herbicides. Cloransulam-methyl applied postemergence at 9, 18, and 36 g/ha controlled more than 85% of two susceptible populations of common and giant ragweed 28 d after treatment, whereas less than 35% control of resistant populations was achieved at the same rates. Fomesafen, lactofen, and glyphosate applied alone at the recommended rates provided the most effective control of ALS-resistant common and giant ragweed. Mixtures of cloransulam-methyl with either fomesafen or lactofen did not significantly increase ALS-resistant common and giant ragweed control compared with each diphenylether herbicide used alone. Dose–response bioassays conducted in the greenhouse indicated that susceptible common and giant ragweed tended to be more sensitive to cloransulam-methyl and chlorimuron than to imazamox. ALS-resistant common ragweed demonstrated a high level of resistance to all the herbicides tested because GR50 values were not reached with rates 1,000 times higher than the recommended rate. ALS-resistant giant ragweed treated with 13,000 g/ha of chlorimuron and 18,000 g/ha of cloransulam-methyl was not inhibited enough to obtain a GR50 value, thus also demonstrating a high level of resistance. The GR50 for ALS-resistant giant ragweed treated with imazamox was 1,161 g/ha. Results of these studies confirmed the presence of ALS–cross-resistant populations of common and giant ragweed in Ohio and suggest that herbicides with different mechanisms of action will be required to manage these weeds effectively.
Nomenclature: Chlorimuron; cloransulam-methyl; fomesafen; glyphosate; imazamox; lactofen; common ragweed, Ambrosia artemisiifolia L. #3 AMBEL; giant ragweed, Ambrosia trifida L. # AMBTR.
Additional index words: Acetolactate synthase, herbicide resistance.
Abbreviations: ALS, acetolactate synthase; COC, crop oil concentrate; DAT, days after treatment; NIS, nonionic surfactant; POST, postemergence; PPF, photosynthetic photon flux; PRE, preemergence; UAN, urea ammonium nitrate; 1× rate, the recommended label rate; 2× rate, twice the recommended label rate.
Abstract: Outside its native range, smooth cordgrass is a noxious weed in estuaries throughout the world. Trials were conducted to evaluate smooth cordgrass control with imazapyr at various timings, rates, and spray volumes, and with several surfactants; comparisons were made with glyphosate, the sole herbicide registered in the United States for estuarine use. Across years, all sites, application dates, and experiments, it was found that smooth cordgrass control with imazapyr at 1.68 kg/ha was better and more consistent than with glyphosate at 8.4 kg/ha. Control with imazapyr at 0.84 kg/ha was comparable to control with glyphosate at 8.4 kg/ha. The time between application and tidal inundation over the canopy affected the efficacy of imazapyr less than that of glyphosate. There was a lack of consistent effects across dates of application. For imazapyr, a higher application volume (467 L/ha) usually provided better control than did the low volume (93 L/ha), but excellent control was achieved using ultra-low application volumes (23 and 47 L/ha) if the dry time was greater than 12 h. Several surfactants provided comparable efficacy for imazapyr.
Additional index words: Aquatic weed management, estuary, surfactant, ultra-low volume.
Abbreviations: MAT, months after treatment; MHHW, mean higher high water; MLLW, mean lower low water; RCB, randomized complete block design; SE, standard error.
Abstract: Field studies were conducted to determine if varying carrier volume proportionally with herbicide dosage, thus maintaining constant herbicide concentration in the carrier, would change the response of sweet corn to glyphosate and of cotton to 2,4-D when compared with using a constant carrier volume where herbicide concentration would vary and be more dilute. For all the parameters measured, more sweet corn injury occurred if the concentration of glyphosate was constant in all volumes of spray. The glyphosate no-effect level for sweet corn was determined to be 0.046 kg/ha when using the variable carrier volume but was over four times greater (0.185 kg/ha) when applied at the constant carrier volume of 281 L/ha. Cotton response to 2,4-D was similar, with the constant herbicide concentration in the carrier at the lower volumes causing greater injury. The response of seed cotton yield was not different when comparing constant to variable carrier volume. The highly sensitive growth stage of cotton at the time of application (bud formation before blooming) may explain this result. These studies demonstrate the need to use carrier volumes that are proportional to the herbicide dosage, thus maintaining constant herbicide concentration in the carrier, when conducting simulated herbicide drift research. Failure to do so could underestimate the potential for injury.
Nomenclature: Glyphosate; 2,4-D; cotton, Gossypium hirsutum L. ‘Acala 1517-95’; sweet corn, Zea mays L. ‘Sweetie 82’.
Additional index words: Crop injury, nontarget crops, off-site movement.
Abbreviations: DAT, days after treatment; OM, organic matter; NMSU-PSRC, New Mexico State University Plant Sciences Research Center.
Abstract: Studies were conducted at Clayton, Lewiston, and Rocky Mount, NC, to evaluate weed and cotton response to herbicide systems in bromoxynil-resistant Stoneville BXN 47 cotton. Herbicide systems that included clomazone preemergence (PRE) controlled broadleaf signalgrass, common lambsquarters, common ragweed, goosegrass, large crabgrass, and prickly sida greater than 88%. Inconsistent Palmer amaranth control was observed with the addition of fomesafen PRE to clomazone PRE and pendimethalin preplant-incorporated (PPI) herbicide systems. Addition of bromoxynil early postemergence (EPOST) to clomazone and pendimethalin systems increased ivyleaf morningglory control to greater than 84% and provided higher yields than did the same systems without bromoxynil. Bromoxynil EPOST followed by (fb) cyanazine MSMA late postemergence directed (LAYBY) improved weed control in clomazone and pendimethalin systems. Clomazone PRE and pendimethalin PPI with or without fomesafen PRE fb bromoxynil EPOST fb LAYBY herbicides controlled weeds and yielded equivalent to the standard herbicide system of pendimethalin PPI fb fluometuron PRE fb bromoxynil EPOST fb LAYBY.
Nomenclature: Bromoxynil; clomazone; cyanazine; fluometuron; fomesafen; MSMA; pendimethalin; broadleaf signalgrass, Brachiaria platyphylla (Griseb) Nash. #3 BRAPP; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; large crabgrass, Digitaria sanguinalis L. # DIGSA; Palmer amaranth, Amaranthus palmeri S. Wats. # AMAPA; prickly sida, Sida spinosa L. # SIDSP; cotton, Gossypium hirsutum L. ‘Stoneville BXN 47’.
Additional index words: Herbicide-tolerant crops.
Abbreviations: EPOST, early postemergence; fb, followed by; LAYBY, late postemergence directed; PD, postemergence directed; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.
Abstract: In 1998, Indian regulatory agencies approved the registration of CGA 184927, MON 37500, and fenoxaprop for postemergence control of isoproturon-resistant littleseed canarygrass. Herbicides used in rice and wheat before 1998 were generally mixed with sand or urea and were applied by hand. Foliar pesticide spray applications consisted primarily of insecticides and fungicides that were applied to high-value crops. These pesticides were often sprayed to runoff with backpack sprayers that were equipped with single hollow-cone or flood nozzles. Applicators walked through the fields, swinging the wands in sweeping motions resulting in uneven pesticide distribution and overapplication. The newly registered postemergence herbicides were applied with the same equipment and in the same fashion. After these applications, control of littleseed canarygrass was strikingly inconsistent, and the growers blamed the lack of control on the manufacturers. It was later clear that basic understanding of the application techniques was lacking. In response to this, an application training workshop was organized and conducted in India and Nepal in 2000. The workshops focused on teaching the participants how to use and fabricate multiple-nozzle booms, the importance of flat-fan nozzles, calibration, drift avoidance, and applicator safety. To date, approximately 3,000 farmers, extension agents, scientists, and industry representatives have attended more than 30 workshops. The participants were unanimously enthusiastic about the value of the workshops. Although simplistic, the adoption of this technology will significantly decrease the amounts of herbicides applied and will increase efficacy and efficiency.
Nomenclature: CGA 184927 (proposed common name, clodinafop), 2-propynyl R-2-[4-[(5-chloro-3-fluoro-2-pyrdinyl)oxy]phenoxyl]-propanoate propynyl ester; fenoxaprop; isoproturon; MON 37500 (proposed common name, sulfosulfuron), 1-(4,6-dimethoxypyrimidin-2-yl)-3-[(2-ethanesulfonyl-imidazo[1,2-a]pyridine)sulfonyl]urea; littleseed canarygrass, Phalaris minor Retz. #3 PHAMI; rice, Oryza sativa L.; wheat, Triticum aestivum L.
Additional index words: Backpack sprayers, pesticide application method, technology transfer.
Abbreviation: I-HRAC, The Herbicide Resistance Action Committee of India.
Abstract: Glyphosate is the only herbicide used for controlling illicit coca (Erythroxylum coca and E. novogranatense), a source of cocaine. Because commercially available formulations of glyphosate were inconsistent in controlling coca, research was conducted in a large-scale aerial eradication program, greenhouse (in Maryland) and field (Hawaii), to develop more effective control systems. Sixteen surfactants (cationic, nonionic, or mixed) were tested with two commercial glyphosate herbicide formulations, in aqueous or oil-based carrier systems, for coca control. Ultimately, two glyphosate–surfactant systems (COC/OSI-U [a mixture of crop-oil concentrate, Agri-Dex® and organosilicone, Silwet L-77®] and CAT/ANA [cationic surfactant/anionic surfactant, Optima®]) were found that increased glyphosate phytotoxicity fourfold: 1.1 kg ae/ha of glyphosate surfactant was equivalent to 4.4 kg ae/ha glyphosate without added surfactant, for both species. In consequence, the glyphosate mixture used in Colombia for coca eradication was modified with substantially improved results.
Nomenclature: Glyphosate; coca, selected taxa of the genus Erythroxylum, especially E. coca var. coca Lam, E. novogranatense var. novogranatense (Morris) Hieron, E. coca var. ipadu Plowman, and E. novogranatense var. truxillense (Rusby) Plowman.
Abstract: Studies were conducted from 1998 to 2001 in Tifton, GA, on weed management systems in transplanted cantaloupe and watermelon grown on polyethylene-covered seedbeds. Soil fumigants were metham (748 L/ha) and a nonfumigated control. All metham applications were sprayed in a 61-cm band and incorporated with a modified power tiller. Herbicide treatments were ethalfluralin (0.8 kg ai/ha) premergence (PRE), ethalfluralin plus halosulfuron (36 g ai/ha) PRE, ethalfluralin PRE followed by glyphosate (1.1 kg ai/ha) postemergence POST-SHIELDED, ethalfluralin plus halosulfuron PRE followed by glyphosate POST-SHIELDED, and a nontreated control. Premergence herbicides were directed to row middles not covered in polyethylene, without contacting the transplants. Glyphosate was applied to row middles using a hooded sprayer, just before vine running. Overall weed control was not improved with soil fumigation in either cantaloupe or watermelon, and there was no yield response in either crop. There may be minimal benefit in transplanted cantaloupe and watermelon on polyethylene-covered seedbeds from preplant soil fumigation for weed control, in the absence of other pests. Herbicide systems that included halosulfuron PRE or glyphosate applied POST-SHIELDED improved control of yellow nutsedge compared with ethalfluralin alone. Control of Texas panicum, southern crabgrass, Florida pusley, and smooth pigweed was not improved by halosulfuron or glyphosate. Polyethylene-covered seedbeds provide a mechanical barrier to weed infestation for many species. Integration of these weed control practices gives cantaloupe and watermelon growers effective options for weed management, particularly for a troublesome species such as yellow nutsedge.
Abstract: Research was conducted to evaluate structure–function relationships of citric acid esters that varied in alkyl chain number (mono-, di-, and tri-), ethylene oxide number (EO 4,7,9,25,35,52), and alkyl chain length (C8, C12/14, C16/18). Adjuvant efficacy was evaluated on two weed species for each of the four herbicides. The experimental adjuvants were applied with glyphosate and glufosinate on giant foxtail and common lambsquarters, imazamox on velvetleaf and common lambsquarters, and nicosulfuron on giant foxtail and large crabgrass. Adjuvant efficacy was weed and herbicide specific. EO number and alkyl chain length and number influenced adjuvant efficacy with the effectiveness of various combinations dependent on both herbicide and weed species. EO numbers as high as 52 were shown to be effective for glyphosate, glufosinate, and imazamox.
Nomenclature: Glufosinate; glyphosate; imazamox ammonium salt; nicosulfuron; common lambsquarters, Chenopodium album L. #3 CHEAL; giant foxtail, Setaria faberi Herrm. # SETFA; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; velvetleaf, Abutilon theophrasti Medicus. # ABUTH.
Additional index words: Adjuvant, surfactant.
Abbreviations: DAT, days after treatment; EO, ethylene oxide.
Abstract: Catchweed bedstraw, common hempnettle, wild buckwheat, and wild oat are serious competitors to arable crops in many parts of the world where cutting implements may be used to control weeds. After cutting, regrowth may become a problem. In greenhouse experiments, weed species were cut at different stages of development (wild oat had two or three leaves, and the dicot weed species were 10 or 15 cm high) and at different heights aboveground (5 and 8 cm). Three weeks after sowing, biomass was measured and compared with that of uncut plants. Cutting height had a significant effect on the regrowth of all species. Common hempnettle was the most sensitive to cutting height followed by wild oat, wild buckwheat, and catchweed bedstraw. Increasing cutting height from 5 to 8 cm above the soil surface increased biomass production by 100 to 400% for all species. Cutting catchweed bedstraw at 8 cm resulted in larger biomass production than that of uncut plants (about 30%). For this species, weed control by cutting once in the growing season, 8 cm aboveground, may result in increased weed biomass production when compared with no cutting. The stage of development when the plants were cut did not have a significant effect on the regrowth ability of any of the species, probably because the two growth stages were relatively close in time.
Nomenclature: Catchweed bedstraw, Galium aparine L. #3 GALAP; common hempnettle, Galeopsis tetrahit L. # GAETE; wild buckwheat, Polygonum convolvulus L. # POLCO; wild oat, Avena fatua L. # AVAFA.
Additional index words: Alternative weed control, compensatory growth, mechanical weed control, mowing, overcompensation, ranking weeds.
Abstract: Field experiments were conducted from 1994 through 1996 to evaluate the effects of imazapic applied postemergence (POST) at 0.05 and 0.07 kg ai/ha, imazethapyr applied preplant incorporated (PPI) or POST at 0.07 kg ai/ha, and metolachlor applied PPI at 1.7 kg ai/ha on yellow nutsedge control, nutsedge tuber density, and peanut yield. All herbicides controlled yellow nutsedge at least 75% after 3 yr. Imazapic at 0.05 and 0.07 kg/ha controlled yellow nutsedge more consistently than did imazethapyr or metolachlor. Imazethapyr applied POST controlled yellow nutsedge more effectively than did imazethapyr applied PPI. Yellow nutsedge tuber densities in herbicide-treated plots were 51 to 75% less than in untreated control plots. Plots treated with imazapic, imazethapyr applied POST, and metolachlor resulted in higher peanut yields than did untreated control plots.
Nomenclature: Imazapic; imazethapyr; metolachlor; yellow nutsedge, Cyperus esculentus L. #3 CYPES; peanut, Arachis hypogaea L. ‘GK-7’.
Additional index words: ALS inhibitors, efficacy, tuber density.
Abbreviations: EPOST, early postemergence; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.
Abstract: Glyphosate-resistant spring wheat is being developed and may soon be available to growers. Field experiments were conducted to examine the effect of various rates and application timings of glyphosate on the tolerance of glyphosate-resistant spring wheat and the level of weed control attained with glyphosate in wheat. Glyphosate-resistant wheat exhibited excellent tolerance to glyphosate applied at the one- to two- or four- to five-leaf stages at rates up to 1,780 g ae/ha, representing a fourfold safety margin to the proposed field use rate. Glyphosate at 445 g/ha reduced shoot biomass of green foxtail, wild oat, redroot pigweed, and wild mustard > 95% in glyphosate-resistant wheat in all years, but wild buckwheat biomass was only reduced 67 to 75% at doses up to 890 g/ha. Glyphosate applied in-crop at 667 g/ha reduced quackgrass biomass by 97 to 99%. Comparison of glyphosate with other spring wheat herbicides indicated that glyphosate provided similar or better in-crop control of several weed species. Yield of weed-infested glyphosate-resistant spring wheat responded positively to glyphosate in all years.
Nomenclature: Glyphosate; green foxtail, Setaria viridis (L.) Beauv. #3 SETVI; quackgrass, Elytrigia repens (L.) Nevski # AGRRE; redroot pigweed, Amaranthus retroflexus L. # AMARE; wild buckwheat, Polygonum convolvulus L. # POLCO; wild mustard, Brassica kaber (DC.) L.C. Wheeler # SINAR; wild oat, Avena fatua L. # AVEFA; spring wheat, Triticum aestivum L. ‘Bobwhite’, ‘BW251’.
Additional index words: Herbicide resistance, wheat tolerance, wheat yield.
Abstract: Sericea lespedeza is an invasive weed in the tallgrass prairies of the Southern Great Plains. Field experiments were initiated in 1995 at three locations in central Oklahoma to evaluate control of sericea lespedeza for several years after treatment with herbicide. Herbicide treatments included triclopyr at 560 and 840 g ae/ha, fluroxypyr at 210 and 560 g ae/ha, and metsulfuron at 13 and 21 g ai/ha applied at simple-stem (SS), branched-stem (BS), and flowering (FL) growth stages of sericea lespedeza. At all three locations, applications of triclopyr and fluroxypyr at the BS growth stage resulted in less than 4% of the pretreatment sericea lespedeza stem density remaining in the first growing season after treatment (GSAT). Metsulfuron applied at the FL growth stage resulted in 0 to 9% of the pretreatment stem density remaining in the first GSAT. Regardless of rate, triclopyr and fluroxypyr applied at the BS growth stage provided the most consistent long-term control of sericea lespedeza. Percentage of pretreatment stem density remaining with these treatments was 0 to 20% at two locations in the third GSAT, and 4 to 15% at one location in the fifth GSAT. Aboveground biomass yields of desirable grasses (bermudagrass, indiangrass, and little bluestem) at two locations were greater than that of the untreated check in the second and third GSAT in all herbicide treatments. But biomass yield of bermudagrass did not increase when sericea lespedeza was controlled at the location with eroded soil conditions.
Nomenclature: Fluroxypyr; metsulfuron; triclopyr; bermudagrass, Cynodon dactylon L. #3 CYNDA; indiangrass, Sorghastrum nutans (L.) Nash; little bluestem, Shizachyrium scoparium (Michx.) Nash; sericea lespedeza, Lespedeza cuneata L. # LESCU; western ragweed, Ambrosia psilostachya DC. # AMBPS.
Additional index words: Pasture, tallgrass prairie.
Abbreviations: BS, branched stem; FL, flowering; GSAT, growing season after treatment; SS, simple stem.
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