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Studies were conducted from 1992 to 1995 to determine the effect of rimsulfuron on corn spurry, wild radish, narrowleaf goldenrod, and quackgrass and potato cultivars. Rimsulfuron alone gave 100% control of wild radish, 68 to 70% control of corn spurry, and 75 to 90% control of narrowleaf goldenrod. Rimsulfuron plus metribuzin gave 99 to 100% control of wild radish and 85 to 100% control of corn spurry. Quackgrass control varied from 51 to 90% between experiments, indicating that environmental and plant factors affected the activity of the herbicide. Tank mixes with metribuzin slightly reduced the control of quackgrass but resulted in greater foliar injury than that of rimsulfuron to potato. Slight injury to potato plants disappeared within 2 to 3 wk, and tuber yields were not reduced. Russet Burbank, Shepody, and Kennebec potato cultivars had slight (2 to 8%) injury from rimsulfuron. Injury to Shepody (14 to 20%) and Russet Burbank (11%) increased when rimsulfuron was applied with metribuzin. Rimsulfuron had no effect on the number or the fresh weight of sprouts on daughter tubers tested the next spring after application.
Nomenclature: Metribuzin; rimsulfuron; corn spurry, Spergula arvensis L. #3 SPRAR; narrowleaf goldenrod, Solidago canadensis L. # SOLCA; quackgrass, Elytrigia repens Nevski # AGRRE; wild radish, Raphanus raphanistrum L. # RAPRA; potato, Solanum tuberosum L. # SOLTU ‘Russet Burbank’, ‘Shepody’, ‘Kennebec’.
Additional index words: Daughter tuber sprouting, DPX E-9636.
Abbreviations: GC, ground crack; lf, leaf; PEI, Prince Edward Island; POST, postemergence; PRE, preemergence; RH, relative humidity.
Field trials were conducted at two sites in both 1997 and 1998 to evaluate soybean response and weed control with glufosinate alone or combined with quizalofop, lactofen, imazethapyr, flumiclorac, or bentazon plus acifluorfen in narrow-row, glufosinate-resistant soybean. Soybean injury ranged from 0 to 21% at 2 wk after treatment (WAT) and from 0 to 5% by 4 WAT. Glufosinate alone at 0.29 and 0.4 kg ai/ha controlled velvetleaf, common waterhemp, common ragweed, morningglory species, and giant foxtail greater than 85% in all studies. Mixtures containing glufosinate and other herbicides controlled these species greater than 81% but did not improve control over glufosinate alone. Estimates of weed biomass closely reflected visual control evaluations. However, giant foxtail biomass was higher for mixtures of glufosinate plus lactofen, flumiclorac, or bentazon and acifluorfen, indicating possible antagonism of glufosinate activity. At both locations, soybean yields were similar among most treatments, but that of the glufosinate plus lactofen treatment was lower when compared with other treatments. Additional trials evaluated soybean response and weed control with a preemergence herbicide followed by glufosinate postemergence (POST), glufosinate applied once or twice POST, and mixtures of glufosinate plus imazethapyr or flumiclorac POST in wide-row soybean. Glufosinate applied twice controlled common waterhemp, morningglory species, prickly sida, common cocklebur, and giant foxtail up to 39% greater than did glufosinate applied once. The addition of imazethapyr, but not flumiclorac, to glufosinate improved weed control when compared with glufosinate alone.
Nomenclature: Acifluorfen; bentazon; flumiclorac; glufosinate; imazethapyr; lactofen; quizalofop; common cocklebur, Xanthium strumarium L. #3 XANST; common ragweed, Ambrosia artemisiifolia L. # AMBEL; common waterhemp, Amaranthus rudis Sauer # AMATA; giant foxtail, Setaria faberi Herrm. # SETFA; morningglory species, Ipomoea spp. # IPOSS; prickly sida, Sida spinosa L. # SIDSP; velvetleaf, Abutilon theophrasti Medik. # ABUTH; soybean, Glycine max (L.) Merr. ‘Asgrow 2704 LL’.
Additional index words: Herbicide mixtures, herbicide-resistant crop, soybean injury.
Abbreviations: COC, crop oil concentrate; EPOST, early postemergence; LPOST, late postemergence; MPOST, midpostemergence; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.
Weed management strategies are needed to control weeds in corn that emerge after postemergence (POST) application of glyphosate or glufosinate. Field trials were conducted from 1996 to 1999 to determine if residual herbicides could be used with glyphosate or glufosinate to provide season-long weed control in glyphosate-resistant or glufosinate-resistant corn. Preemergence (PRE) applications of several residual herbicides followed by POST applications of glyphosate or glufosinate were compared with POST tank mixtures of glyphosate or glufosinate with residual herbicides. All residual herbicides used in combination with glyphosate, when compared with glyphosate alone, increased control of redroot pigweed and common lambsquarters by an average of 20% and resulted in a 4 to 19% increase in control of giant foxtail. Each residual herbicide tank mixture with glufosinate, when compared with glufosinate alone, increased control of common ragweed and giant foxtail. In most instances, weed control was similar for total POST and for PRE followed by POST systems. Velvetleaf control was reduced by 12% when glyphosate was tank mixed with a half rate of atrazine compared with a full rate of atrazine. Common lambsquarters control was reduced by 13% when glyphosate was tank mixed with a half vs. a full rate of acetochlor. Glufosinate tank mixed with half rates of acetochlor atrazine, flumetsulam, or pendimethalin reduced control of velvetleaf compared with the full rate of these products. Corn yields were not affected by residual herbicide application timings or rates of residual herbicides.
Nomenclature: Acetochlor; atrazine; flumetsulam; glufosinate; glyphosate; pendimethalin; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi L. # SETFA; redroot pigweed, Amaranthus retroflexus L. # AMARE; velvetleaf, Abutilon theophrasti Medik. # ABUTH; corn, Zea mays L. ‘DK 493GR’, ‘DK 493RR’.
Field and greenhouse studies were conducted to evaluate herbicides in pumpkin. Field experiments at three Illinois locations determined weed control and crop injury from clomazone, dimethenamid, ethalfluralin, sulfentrazone, imazamox, RPA 201772, flumiclorac, and halosulfuron applied preemergence. Clomazone plus sulfentrazone controlled redroot pigweed 78 to 99%, ivyleaf morningglory 80 to 97%, common lambsquarters 97%, common purslane 84 to 99%, and velvetleaf 55 to 99%. Imazamox plus clomazone commonly provided more consistent broadleaf weed control than did ethalfluralin plus clomazone. RPA 201772 when used on sandy soils killed the pumpkin. Sulfentrazone initially caused chlorosis and necrosis on pumpkin seedlings when soil organic matter was low (< 1%) or when soil moisture was high. However, plants recovered rapidly, and yields were not affected. In a greenhouse study pumpkin was more tolerant to clomazone plus sulfentrazone than to sulfentrazone.
Nomenclature: Clomazone; dimethenamid; ethalfluralin; flumiclorac; halosulfuron, imazamox; RPA 201772 (proposed name, isoxaflutole), 5-cyclopropyl-4-(2-methylsulphonyl)-4-trifluoromethyl-benzoyl isoxazole; sulfentrazone; common lambsquarters, Chenopodium album L. #3 CHEAL; common purslane, Portulaca oleracea L. # POROL; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; redroot pigweed, Amaranthus retroflexus L. # AMARE; velvetleaf, Abutilon theophrasti Medicus # ABUTH; pumpkin, Cucurbita pepo var. pepo L. ‘Howden’.
Additional index words: Herbicide combinations, herbicide interactions.
Abbreviations: DAT, days after treatment; PRE, preemergence.
Field studies were conducted at three sites in Delaware from 1997 to 1999 to evaluate fall glyphosate applications followed by postemergence (POST) field corn herbicides on horsenettle control and shoot densities. The fall treatments were either no fall treatment or 2.2 kg ai/ha glyphosate as a preharvest treatment in soybean at least 2 wk prior to frost. POST treatments were applied the following spring in no-tillage field corn 4 wk after planting (WAP) and included glyphosate, CGA 152005 plus primisulfuron plus dicamba, halosulfuron plus dicamba, atrazine plus dicamba, nicosulfuron plus rimsulfuron plus atrazine plus dicamba, or nicosulfuron plus dicamba. The fall glyphosate application delayed horsenettle shoot emergence in the spring and resulted in > 90% control at the time of POST in-crop applications. At 11 WAP, the highest horsenettle control was observed with a fall glyphosate application followed by POST in-crop treatments of CGA 152005 plus primisulfuron plus dicamba, halosulfuron plus dicamba, or nicosulfuron plus rimsulfuron plus dicamba and no fall treatment followed by CGA 152005 plus primisulfuron plus dicamba.
Nomenclature: Atrazine; CGA 152005, 1-(4-methoxy-6-methyl-triazin-2-yl)-3-[2-(3,3,3-trifluoropropyl)-phenylsulfonyl]-urea, proposed common name prosulfuron; dicamba; glyphosate; halosulfuron; nicosulfuron; primisulfuron; rimsulfuron; horsenettle, Solanum carolinense L. #3 SOLCA; corn, Zea mays L.; soybean, Glycine max (L.) Merr.
Two field studies evaluating horsenettle control were conducted from 1997 to 1999 to examine the efficacy of various fall-applied herbicides and rates and to evaluate the effect of the stage of horsenettle senescence on the effectiveness of fall glyphosate applications. The herbicides and rates evaluated in the fall herbicide efficacy study included 1.1, 2.2, or 3.4 kg ai/ha glyphosate, 1.7, 2.2, or 3.4 kg ai/ha glyphosate-trimesium, 0.6, 1.1, or 2.2 kg ai/ha dicamba, 0.06 plus 0.16, 0.09 plus 0.2, or 0.17 plus 0.44 kg ai/ha BAS 654 plus dicamba, respectively, or 2.2 kg ai/ha glyphosate plus 0.6 kg ai/ha dicamba. The highest horsenettle control in the following spring was observed with all rates of glyphosate or glyphosate-trimesium, the highest rate of BAS 654 plus dicamba, or glyphosate plus dicamba. In the study on the horsenettle stage of senescence, 2.2 kg ai/ha glyphosate was applied at stages of senescence in the fall. The presenescence stage reduced horsenettle shoot density from fall to spring and provided the highest level of control in June and July of the following year compared with plants that had already begun leaf color change and leaf drop.
Nomenclature: BAS 654, 2-(1-[([3,5-difluorophenylamino]carbonyl)-hydrazono]ethyl)-3-pyridinecarboxylic acid, proposed common name diflufenzopyr; dicamba; glyphosate; horsenettle, Solanum carolinense L. #3 SOLCA.
Additional index words: Fall herbicide applications, perennial weed management.
Abbreviations: COC, crop oil concentrate; NIS, nonionic surfactant; POST, postemergence; UAN, urea ammonium nitrate; WAP, weeks after planting.
Diminished control of goosegrass was observed in tomato fields located in Manatee County, FL, after years of repeated paraquat use. Tolerance of the Manatee biotype to paraquat was confirmed by its comparison in greenhouse studies with a susceptible biotype from the Alachua County, FL. A 30-fold increase in paraquat rate was required to reach the 50% growth reduction level of the resistant biotype over the susceptible biotype. The Manatee biotype was not tolerant to clethodim, metribuzin, or sethoxydim. These herbicides provided adequate control of all the goosegrass biotypes tested.
Crop response to carfentrazone–ethyl can be affected by environmental conditions. Field research was initiated to determine the effect of irrigation and light intensity prior to herbicide treatment on crop response to carfentrazone–ethyl. Wheat, corn, and soybean response was evaluated in 1996 and 1997, 2 yr that differed significantly in rainfall. It was difficult to distinguish differences in visible crop injury between irrigated and nonirrigated crops within the same year; however, injury was much higher in 1996 than in 1997. In 1996, the study area received timely rainfall prior to treatment of each crop, but in 1997, no precipitation was recorded during the treatment period. Overall, irrigated plants appear to be slightly more sensitive than nonirrigated plants. In contrast, crop injury was significantly higher in response to low light intensity prior to herbicide treatment. Soybean plants covered with 80% shade cloth for 5 d prior to carfentrazone–ethyl application were injured 24 to 41% more than nonshaded plants. Corn was relatively insensitive to either condition. Soybean plants were very sensitive to carfentrazone–ethyl and were highly influenced by both light intensity and irrigation. Wheat response to carfentrazone–ethyl was not influenced within 1 yr by irrigation, but injury in 1996 was four times higher than in 1997. Light intensity prior to treatment influenced wheat response to carfentrazone–ethyl, where shading before treatment increased visible injury in wheat, but by less than 10%. The risk of crop injury increases when carfentrazone–ethyl is applied to irrigated plants or to crops following several cloudy days.
Nomenclature: Carfentrazone–ethyl; corn, Zea mays L. ‘Pioneer 3655’; soybean, Glycine max (L.) Merr. ‘Conrad'; spring wheat, Triticum aestivum L. ’Blanca'.
Field experiments were conducted in 1998 and 1999 at two locations in Mississippi to determine weed control efficacy of postemergence soybean herbicides alone or following pendimethalin imazaquin preemergence in glufosinate-tolerant soybean planted in 38- or 76-cm rows. Glufosinate applications controlled pitted morningglory better than conventional herbicide treatments, regardless of row spacing. Pendimethalin imazaquin did not increase the efficacy of glufosinate on pitted morningglory. Pitted morningglory control was increased in narrow rows when compared to wide rows with all treatments. Sicklepod control ranged from 90 to 100% in narrow rows with glufosinate, regardless of rate. Residual herbicides alone controlled sicklepod 54%, regardless of row spacing. With grass species, two applications of 420 g ai/ha glufosinate controlled weeds 82 to 100%. Residual herbicides followed by 420 g/ha glufosinate controlled grass species 80% or more, regardless of row spacing. Hemp sesbania control ranged from 80 to 92% in 76- and 38-cm rows with one application of 560 g/ha glufosinate. Glufosinate at 420 g/ha used as sequential applications controlled hemp sesbania better than the conventional treatment in 76-cm rows. Residual herbicides in combination with glufosinate did not increase hemp sesbania control. There were no differences in yield due to row spacing at Stoneville in either year due to extremely dry growing conditions during pod set. At Starkville, two applications of 420 g/ha glufosinate resulted in higher yields than pendimethalin imazaquin followed by 420 g/ha glufosinate in both years. Pendimethalin imazaquin followed by 420 g/ha glufosinate increased yield in narrow rows compared to wide rows at Starkville in 1998.
Nomenclature: Glufosinate; imazaquin; pendimethalin; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex. A. W. Hill #3 SEBEX; pitted morningglory, Ipomoea lacunosa L. # IPOLA; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby # CASOB; soybean, Glycine max (L.) Merr.
Additional index words: Glufosinate-tolerant soybean.
Abbreviations: POST, postemergence; POST-3, POST application 3 wk after planting; POST-5, POST application 5 wk after planting; PRE, preemergence; WAP, weeks after planting.
Field studies were conducted in 1998 and 1999 to evaluate the efficacy of glufosinate on Palmer amaranth, redroot pigweed, and common waterhemp at different growth stages in soybean planted at early, normal, and late dates. At 2, 4, and 8 wk after treatment, common waterhemp control was greater than Palmer amaranth and redroot pigweed control with single glufosinate applications of 410 g ai/ha at 2- to 5-, 7- to 10-, or 15- to 18-cm Amaranthus height or with two sequential applications of 293 g/ha at 2- to 5-cm height and 2 wk later. Only the sequential applications of 410 and 293 g/ha resulted in more than 80% control of Palmer amaranth and redroot pigweed, but all five treatments controlled common waterhemp more than 80%. All glufosinate treatments reduced the dry weight of all Amaranthus species by more than 65%. However, the sequential applications resulted in the greatest dry weight reductions.
Nomenclature: Glufosinate; common waterhemp, Amaranthus rudis Sauer #3 AMATA; Palmer amaranth, Amaranthus palmeri S.Wats. # AMAPA; redroot pigweed, Amaranthus retroflexus L. # AMARE; soybean, Glycine max (L.) Merr.
Additional index words: Environmental conditions, herbicide-tolerant soybean, postemergence herbicide.
Abbreviations: ALS, Acetolactate synthase (EC 126.96.36.199); OM, organic matter; RH, relative humidity; WAT, weeks after treatment.
Field observations in Ohio suggested a possible interaction between soybean cyst nematode (SCN) and glyphosate in Countrymark 316 soybean, a transgenic glyphosate-resistant (R) variety that also expresses SCN resistance derived from ‘PI88788’ soybean. To investigate this possible interaction under controlled conditions, greenhouse experiments were conducted in which Countrymark 316 (R) and Corsoy 79 (S = susceptible to glyphosate and SCN) soybean root and shoot weights were measured in response to three concentrations of race 3 SCN inoculum and five glyphosate doses. Experiments were conducted in which glyphosate was applied 9, 18, or 27 d after inoculation (DAI). Data from SCN treatments in the (S) soybean experiments were regressed on glyphosate dosage and fit to a log-logistic dose–response model. SCN–glyphosate interaction in the (S) soybean variety reduced root dry weight of SCN-inoculated plants 6% compared with noninoculated plants when 1.0 kg/ha glyphosate was applied 18 DAI. The most significant interaction of SCN and glyphosate in the (S) variety occurred when glyphosate was applied 27 DAI; the glyphosate dose required to reduce shoot fresh weight 25% was 0.55 kg/ha in the noninoculated control compared with 0.32 kg/ha in plants inoculated with 1,000 SCN eggs/200 cm3 soil. Glyphosate rates of 0.84 and 1.69 kg/ha reduced root dry weights of Countrymark 316 (R) soybean 10 to 13% at the 18 DAI application timing only. Inoculation with SCN reduced shoot fresh weight of (R) soybean 8 to 29% across all experiments, but there was no interaction of glyphosate and SCN in (R) soybean.
Nomenclature: Glyphosate; soybean, Glycine max (L.) Merr. ‘Countrymark 316’ and ‘Corsoy 79’; soybean cyst nematode, Heterodera glycines Ichinohe.
Additional index words: Herbicide–nematode interaction, integrated pest management.
Abbreviations: DAI, days after inoculation; EPSPS, 5-enolpyruvylshikimate-3-phosphate synthase (EC 188.8.131.52); GR25, dose required to reduce root or shoot growth by 25%; I50, dose corresponding to biomass halfway between upper- and lower-response limits; POST, postemergence; R, glyphosate SCN resistant; S, glyphosate SCN susceptible; SCN, soybean cyst nematode.
A 2-yr field study was conducted to evaluate the response of rice to rotational crop herbicides in combination with rice herbicides in water-seeded culture. Fluometuron, imazethapyr, metolachlor, and norflurazon were applied at 0.5, 0.25, 0.125, and 0.063 times the recommended use rates preplant incorporated (PPI) to simulate herbicide carryover from previous crops. Molinate and thiobencarb at 4.5 kg ai/ha were applied PPI, and quinclorac at 0.43 kg ai/ha postemergence. No interaction between rice herbicides and rotational crop herbicides was observed for rice injury at 4 wk after planting (WAP), plant dry weight, stand, and height at 8 WAP, or rice grain yield. However, rice heading was delayed with some rotational crop herbicide and rice herbicide combinations. Fluometuron at the 0.5 and 0.25× rates injured rice 64 and 21% at 4 WAP, and reduced rice yield 96 and 20%, respectively. At 4 WAP, metolachlor at the 0.5 and 0.25× rates injured rice 93 to 29%, and reduced rice yield 85 to 20%, respectively. An 84 to 100% rice injury at 4 WAP and a 81 to 100% rice yield reduction were observed with norflurazon at the 0.5 and 0.25× rates, respectively. Imazethapyr caused 15 to 26% rice injury 4 WAT and 22 to 41% yield reduction.
Field trials were conducted during 1998 and 1999 to evaluate the effects of sequential herbicide treatment, herbicide application timing, and mowing on mugwort control. In the first field trial dicamba, triclopyr, clopyralid, picloram, metsulfuron, glufosinate, glyphosate, and the dimethylamine salt and the isooctyl ester of 2,4-D were applied to mugwort at 7-wk intervals to evaluate mugwort control after one, two, and three herbicide applications. When applied in three sequential applications, all herbicides except triclopyr, metsulfuron, and glufosinate provided at least 70% mugwort control 1 yr after treatment (YAT). At least 70% mugwort control was also achieved with just two sequential applications of dicamba, and only one application of picloram or clopyralid provided 100 and 84% mugwort control 1 YAT, respectively. In the second field trial the influence of application timing was investigated by applying herbicides to mugwort in the vegetative and the flowering stages of growth. Additionally, the effect of sequential mowing was evaluated by applying herbicides to mugwort regrowth after either one or two mowings. Generally, there was no difference in the level of mugwort control achieved with applications of these herbicides to mugwort in the flowering vs. the vegetative stage of growth. However, when averaged over all the herbicides included in these trials, two sequential mowings conducted before herbicide application enhanced the control of mugwort compared with either unmowed mugwort or mugwort that had been mowed once before herbicide application. Additionally, with the exception of picloram and glyphosate, all the herbicides evaluated in these trials provided higher mugwort control when applied to unmowed mugwort compared with mugwort that had been mowed only once. The results from these trials indicate that sequential herbicide treatment and sequential mowing are strategies that will enhance the control of mugwort when used with the majority of herbicides evaluated in these trials.
Sclerotinia stem rot is an important soybean disease. An increase in phytoalexin production with herbicide treatments may reduce the incidence of this disease in soybean. Research was conducted to determine soybean response, Sclerotinia sclerotiorum lesion development, and phytoalexin production in glyphosate-resistant and -susceptible soybean cultivars treated with protoporphyrinogen oxidase–inhibiting herbicides. Necrosis of soybean leaves 7 d after postemergence application of oxyfluorfen at 17.5 g ai/ha, carfentrazone at 1.8 g ai/ha, sulfentrazone at 9.0 g ai/ha, fomesafen at 280 g ai/ha, acifluorfen at 425 g ai/ha, flumiclorac at 30 g ai/ha, CGA-248757 at 4 g ai/ha, and oxadiazon at 280 g ai/ha was equal to or less than lactofen at 70 g ai/ha. In a detached leaf bioassay, S. sclerotiorum lesion diameter was reduced by oxyfluorfen, carfentrazone, sulfentrazone, lactofen, fomesafen, flumiclorac, and oxadiazon compared with the untreated control. Furthermore, lesion diameter on untreated leaves of soybean treated with oxyfluorfen, carfentrazone, sulfentrazone, lactofen, fomesafen, acifluorfen, flumiclorac, CGA-248757, and oxadiazon was reduced compared with the untreated control. Lactofen and sulfentrazone increased leaf phytoalexin production similarly, but neither herbicide affected stem phytoalexin production compared with the untreated control. Glyphosate-resistant and near-isogenic–susceptible cultivars responded similarly when inoculated with S. sclerotiorum in the detached leaf bioassay. Glyphosate-resistant S20-B9 and P93B01 produced more phytoalexins than glyphosate-susceptible S 19-90 and P9281. Herbicide treatments may increase phytoalexin production in leaves of treated plants, but levels in the stem do not explain protection from Sclerotinia stem rot.
Greenhouse and field research was conducted to determine the effect of glufosinate, glyphosate, and glyphosate plus additional adjuvant on yellow nutsedge control and tuber production. Glyphosate at 0.84 kg/ha reduced yellow nutsedge dry weight 64%, whereas glufosinate at 0.4 kg/ha reduced dry weight only 22% when averaged over diammonium sulfate (DAS) and spray volume. Furthermore, yellow nutsedge dry weight was reduced 53% in the presence and 34% in the absence of DAS; however, dry weights were similar when spray volumes of glufosinate or glyphosate ranged from 140 to 1038 L/ha. Yellow nutsedge control with glyphosate and glufosinate increased to 88 and 68%, respectively, when the herbicides were injected into the plant. In the field, glufosinate at 0.4 kg/ha and glyphosate at 0.84 kg/ha controlled yellow nutsedge 19 and 53%, respectively. Glyphosate reduced yellow nutsedge tuber density 51%, tuber fresh weight 59%, and tuber sprouting 17% 42 wk after treatment in the field. The addition of nonionic surfactant, methylated seed oil, or crop oil concentrate to glyphosate plus DAS did not increase yellow nutsedge control with glyphosate in the greenhouse or field.
Competition from annual grasses and yellow starthistle can severely reduce perennial grass forage production and quality in pasture and rangeland. The purpose of this study was to determine yellow starthistle and weedy annual grass control by imazapic applied alone or in combination with picloram, and smooth brome tolerance to these treatments. Sixty days after treatment (DAT) imazapic applied at 70 and 140 g ae/ha reduced annual grass (downy brome, medusahead, and annual bluegrass) plant density and biomass by 66 to 76% compared with the untreated control. Picloram applied at 280 and 420 g ae/ha reduced yellow starthistle plant density and biomass by over 93%. Imazapic applied at 70 and 140 g/ha reduced smooth brome biomass by 79 to 95% at 60 DAT. Picloram did not affect the density or the biomass of annual grasses or smooth brome, whereas imazapic did not markedly affect the density or the biomass of yellow starthistle. Downy brome control increased to a maximum of 97% with increasing imazapic dose (maximum of 280 g/ha) at 30, 60, and 90 DAT.
Nomenclature: Ammonium salt of imazapic; potassium salt of picloram; annual bluegrass, Poa annua L. #3 POAAN; downy brome, Bromus tectorum L. # BROTE; medusahead, Taeniatherum caput-medusae (L.) Nevski. # ELYCM; smooth brome, Bromus inermis Leyss. # BROIN; yellow starthistle, Centaurea solstitialis L. # CENSO.
Additional index words: Herbicide tolerance.
Abbreviations: DAT, days after treatment; OM, organic matter; POST, postemergence.
Field studies were conducted in 1999 and 2000 at Belleville, IL, to compare herbicide efficacy and economic return on investment (EROI) for various herbicide systems in conventional, imidazolinone-resistant, glufosinate-resistant, and glyphosate-resistant corn hybrids. Corn injury 14 d after RPA 201772 preemergence (PRE) treatments ranged from 0 to 10%. Treatments with nicosulfuron rimsulfuron atrazine injured corn 5 to 24% at 7 d after treatment (DAT); however, no injury was visible at 14 DAT. Corn injury by all herbicide treatments dissipated by 28 DAT. All treatments controlled giant foxtail at least 88%. Common waterhemp was controlled at least 94% with all treatments, except for imazethapyr imazapyr postemergence (POST), which did not control common waterhemp. All treatments controlled at least 92% of common cocklebur, giant ragweed, and ivyleaf morningglory, with the exception of the total PRE herbicide system of S-metolachlor atrazine in 2000. Average grain yield ranged from 7,290 to 9,180 kg/ha in 1999, with the yield of the glyphosate-resistant hybrid lower than that of all other hybrids. In 2000, average grain yield ranged from 8,440 to 11,520 kg/ha, with the grain yield of the glyphosate-resistant hybrid greater than that of all other hybrids. There were no differences in economic return in 1999 because of the treatment, the herbicide system, or the hybrid. In 2000 EROI was greater with the glyphosate-resistant hybrid than with the other hybrids. EROI was influenced more by the grain yield of the corn hybrid than by the associated weed control costs. It has been demonstrated by this research that effective and economical weed control can be achieved in all hybrids, with minimal injury.
Potassium azide (PA) (112 kg/ha), oxadiazon 1,3-dichloropropene (1,3-D) (168 kg/ha 140 L/ha), dazomet (392 kg/ha), dazomet chloropicrin (392 168 kg/ha), dazomet 1,3-D (392 kg/ha 140 L/ha), iodomethane (IM) (336 kg/ha), metam-sodium (MS) (748 L/ha), MS chloropicrin (748 L/ha 168 kg/ha), and MS 1,3-D (748 140 L/ha) were evaluated at Jay and Arcadia, FL, in 1998 and 1999 as alternatives to methyl bromide (MeBr) fumigation for the management of common turfgrass weeds. Potassium azide was as effective as MeBr in controlling ‘Coastal’ bermudagrass, yellow and purple nutsedges, alexandergrass, broadleaf signalgrass, tall and sharppod morningglories, and various winter annual broadleaf weeds, but it failed to provide acceptable control of redroot pigweed. 1,3-Dichloropropene oxadiazon did not control yellow nutsedge, purple nutsedge, or Coastal bermudagrass. Similarly, this combination treatment failed to control carpetweed but did provide 83% control of the winter annual weed species, 71% control of alexandergrass and broadleaf signalgrass, and ≥ 80% control of tall morningglory, sharppod morningglory, and redroot pigweed. Dazomet combination treatments provided control of Coastal bermudagrass at Jay; however, control of common bermudagrass, alexandergrass, and broadleaf signalgrass was not acceptable at Arcadia. Sedge species control with dazomet combinations was poor (< 63%) at both sites. Iodomethane, a treatment not yet registered by the U.S. Environmental Protection Agency (EPA), controlled weedy grass species, sedge species, and broadleaf weeds present at the two locations under different environmental conditions. Metam-sodium alone and MS chloropicrin, tarped and untarped, and MS 1,3-D provided acceptable weed control; however, MS chloropicrin covered with a plastic tarp for 48 h was the best MS treatment. Metam-sodium chloropicrin, with plastic tarp, controlled weedy grass and broadleaf species equal to MeBr; however, unacceptable sedge species control at Jay and Arcadia was 56 and 79%, respectively. Metam-sodium applied alone failed to control redroot pigweed; however, MS combinations provided control. These studies confirm that no EPA-registered fumigant alternative to MeBr, applied alone or in combination for preplant turf soil fumigation, exists. Consequently, until such time that an effective alternative is identified, turf managers will be forced to forego fumigation, or they will have to choose a less-effective alternative and accept the consequences of contamination.
Field studies were conducted in 1999 and 2000 at Belleville, IL, to evaluate herbicide efficacy, grain yield, and economic return on investment (EROI) from various herbicide systems in conventional, sulfonylurea-tolerant, glufosinate-resistant, and glyphosate-resistant soybean varieties. Several grower-oriented herbicide systems were developed within each soybean variety using current weed control options. These herbicide systems included herbicides with soil-residual, herbicides with different modes of action, and combinations of preemergence (PRE) followed by (fb) postemergence (POST) herbicides. Soybean injury ranged from 1 to 16% 28 d after (DA) PRE applications of sulfentrazone plus chlorimuron plus pendimethalin. Injury 7 DA POST treatments ranged from 2 to 39%, with the greatest injury occurring from the conventional herbicide combination of fomesafen plus fenoxaprop plus fluazifop-P. No injury symptoms persisted through soybean harvest. Control of giant foxtail was the most consistent (97% or greater) in the PRE broadleaf fb POST herbicide system 56 DA planting. Common waterhemp control was at least 85% for all treatments, with the exception of the single POST herbicide systems of chlorimuron plus thifensulfuron plus quizalofop-P, and glufosinate and the standard sequential herbicide system of pendimethalin fb chlorimuron plus thifensulfuron. All treatments provided at least 87% control of common ragweed and ivyleaf morningglory. Soybean grain yield was similar between varieties in the weed-free control plots in 1999. In 2000, grain yield of the glyphosate- and glufosinate-resistant soybean varieties was greater than for the conventional and sulfonylurea-tolerant varieties. Overall, soybean grain yield and EROI were less for some treatments because of poor control of common waterhemp. Weed control had a greater influence than herbicide-related costs on EROI.
Greenhouse studies verified that smooth crabgrass from a golf course tee in southern New Jersey was resistant to fenoxaprop-P, although smooth crabgrass from a nearby untreated rough was susceptible to this herbicide. Fenoxaprop-P-resistant plants were injured, however, when fenoxaprop-P was applied at levels above the maximum use rate for turf. Fenoxaprop-P applied postemergence at 0.76 kg ai/ha, four times the maximum rate, reduced shoot weight of the resistant biotype by 35%, whereas application of 1.52 kg/ha, eight times the maximum rate, reduced shoot weight by 64%. Large crabgrass and the susceptible biotype of smooth crabgrass were controlled by fenoxaprop-P applied at 0.1 kg/ha. Fenoxaprop-susceptible and -resistant biotypes of smooth crabgrass had a similar response to MSMA, dithiopyr, and quinclorac applied postemergence. The fenoxaprop-P–resistant smooth crabgrass biotype was controlled by the cyclohexanedione herbicides sethoxydim and clethodim, but the aryloxyphenoxypropionate herbicides fluazifop and quizalofop reduced shoot weight by only 15 to 66% depending on herbicide and rate.
A replacement series study was conducted in a greenhouse in 1998 and 1999 to evaluate the interference interactions among two rice cultivars and two red rice ecotypes. Plants were established in proportions of 3:0, 2:1, 1:2, and 0:3 (rice–red rice) plants/pot. Relative yield of Kaybonnet based on the shoot dry weight was lower than that of KatyRR or LA3, whereas PI 312777 was comparable to that of KatyRR and LA3. These results indicate that Kaybonnet was less competitive than PI 312777 when contrasted with KatyRR and LA3 red rice ecotypes. Kaybonnet (commercial rice cultivar) was dominated by both KatyRR (suspected rice × red rice cross) and LA3 (tall red rice ecotype) in tiller production, whereas PI 312777 (weed-suppressive cultivar) was comparable to either KatyRR or LA3. Both KatyRR and LA3 considerably reduced the leaf area of Kaybonnet. In contrast, PI 312777 reduced the growth of KatyRR, and its leaf area was comparable to that of LA3. The data suggest that high tillering capacity, as demonstrated by PI 312777, should be considered when breeding for rice cultivars that are competitive against weeds. This agronomic characteristic of rice may improve the success of reduced herbicide rate application programs.
Nomenclature: Red rice, Oryza sativa L. #3 ORYSA ‘KatyRR’, ‘LA3’; rice, Oryza sativa L. ‘Kaybonnet’, ‘PI 312777’.
Additional index words: Leaf area, red rice growth, relative yield, rice growth, strawhull.
Abbreviations: DAE, days after emergence; RY, relative yield; RYT, relative yield total.
“Pesta” is a granular, extruded product made from a cereal grain flour and any biological control agent. A strain of Pseudomonas fluorescens, BRG100, which is a pathogen of green foxtail, has been formulated into a Pesta product. P. fluorescens BRG100 survived processing best in oat flour, and the addition of 20% (wt/wt) maltose extended the shelf life of the product to more than 32 wk. Field studies of 8-wk duration showed that a Pesta product containing BRG100 suppressed green foxtail emergence by as much as 90%. An optimally formulated and processed Pesta product has potential for the biocontrol of green foxtail.
Nomenclature:Pseudomonas fluorescens; green foxtail, Setaria viridis (L.) Beauv. #3 SETVI; oats, Avena sativa L. # AVESA.
Additional index words: Biological control, encapsulation, lactose, maltose.
Field experiments were conducted in 1999 and 2000 to determine the influence of mesotrione postemergence application rate, application timing, and addition of atrazine on corn injury, weed control, and corn grain yield. Corn injury in the form of leaf bleaching ranged from 0 to 15% at 7 d after treatment (DAT). In general, most of the bleaching injury rapidly dissipated with slight (≤ 8%) to no corn injury observed at 28 DAT. Control of common cocklebur with mesotrione at 14 DAT ranged from 79 to 98% for all treatments over both years. Applying mesotrione at 140 g/ha, at the early postemergence (EPOST) timing, or in combination with atrazine provided the greatest control of common cocklebur at 14 DAT. Application rate of mesotrione was the only factor that was significant in both years for control of common cocklebur later in the season at 56 DAT. Control of ivyleaf morningglory with mesostrione at 14 DAT ranged from 60 to 90% for all treatments in both years. Control of ivyleaf morningglory at 14 DAT was enhanced by the addition of atrazine to mesotrione. Control of ivyleaf morningglory at 56 DAT was greater with mid-postemergence and late postemergence than with EPOST applications, and was generally enhanced by the addition of atrazine. Yellow nutsedge control with mesotrione was inconsistent, ranging from 40 to 87% at 14 DAT for all treatments over both years. The addition of atrazine to mesotrione increased yellow nutsedge control from 47 to 87% at 14 DAT in 2000. Increasing the rate of mesotrione from 70 to 140 g/ha, as well as the addition of atrazine, improved control of yellow nutsedge at 56 DAT. Corn grain yield was not affected by corn injury or weed control as there were no significant differences in grain yield between herbicide-treated plots and handweeded plots.
Nomenclature: Atrazine; mesotrione; common cocklebur, Xanthium strumarium L. #3 XANST; ivyleaf morningglory, Ipomoea hederacea L. Jacq. # IPOHE; yellow nutsedge, Cyperus esculentus L. # CYPES; corn Zea mays L. ‘DK 592SR’, ‘DK 683SR’.
Abbreviations: COC, crop-oil concentrate; DAT, days after treatment; EPOST, early postemergence; MPOST, mid-postemergence; LPOST, late postemergence; PRE, preemergence; UAN, 28% urea ammonium nitrate.
Field studies were conducted in 1999 and 2000 at Simcoe, Ridgetown, and Exeter, Ontario, to evaluate the tolerance of nine sweet corn cultivars to mesotrione, applied preemergence (PRE) at 140 and 280 g ai/ha and postemergence (POST) at 100 and 200 g ai/ha. Urea ammonium nitrate fertilizer (28%) at 2.5% (v/v) and crop oil concentrate at 1% (v/v) were added to POST applications of mesotrione only. All cultivars were tolerant to mesotrione applied PRE. There was no injury, or reductions in plant height or yield with PRE applications of mesotrione at any location in either year. POST applications of mesotrione, particularly at 200 g/ha, caused significant phytotoxicity to ‘Calico Belle’ and ‘Del Monte 2038’. Other cultivars also showed phytotoxic symptoms; however, this injury was much reduced and did not occur at all locations each year. Sweet corn injury by mesotrione increased as rate increased. Del Monte 2038 also had significantly reduced plant height and yields. Other cultivars had no plant height or yield reductions because of POST applications of mesotrione.
Nomenclature: Mesotrione; sweet corn, Zea mays L.
Additional index words: Crop injury, plant height, triketone.
Abbreviations: DAP, days after planting; DAT, days after treatment; HPPD, p-hydroxy-phenylpyruvate dioxygenase; OM, organic matter; PRE, preemergence; POST, postemergence; SU, sulfonylurea.
Failure to detect noxious weeds with current survey methods prevents their control and has contributed to their ability to establish and spread in remote range and forest sites. Techniques used in remote sensing can classify plant occurrence on maps, offering a method for surveying invasive species in remote locations and across extensive areas. An imaging hyperspectral spectrometer recorded images on July 19, 1998 in Farragut State Park near Bayview, ID, in the reflected solar region of the electromagnetic spectrum ranging from 440 to 2,543 nm to detect spotted knapweed. The sensor records 128 spectral bands in 12- to 16-nm intervals at a spatial resolution of 5 m. A spectral angle mapper (SAM) algorithm was used to classify the data. Infestations in Idaho with 70 to 100% spotted knapweed cover that were 0.1 ha were detected regardless of the classification angle. However, narrow angles (2 to 8°) did not completely define the extent of the infestation, and the widest angle tested (20°) falsely classified some areas as infested. The overall image error for all classes was lowest (3%) when SAM angles ranged from 10 to 11°. Specific errors for the spotted knapweed class for the 10 to 11° angles showed that omissional and commissional errors were less than 3%. Areas with as little as 1 to 40% spotted knapweed cover were detected with an omissional error of 1% and a commissional error of 6%. Further verification sites were established on August 11, 1998 near Bozeman, MT, using the algorithms developed for Idaho. The omissional error for the Montana sites was 0%, and the commissional error was 10%. The hyperspectral sensor, Probe 1, proved an effective detection tool with the ability to detect spotted knapweed infestations.
Nomenclature: Spotted knapweed, Centaurea maculosa Lam. #3 CENMA syn C. stoebe L. and C. biebersteinii DC.
Abbreviations: Ĉi, commissional error; DGPS, differentially corrected global positioning system; GPS, global positioning system without differential correction; L95, lower bounds expressed as 95% probability interval; Ôi, omissional error; SAM, spectral angle mapper; U95, upper bounds expressed as 95% probability interval.
The presence of volunteer canola is becoming a significant agro-ecological concern, given the large-scale use of herbicide-tolerant varieties in some areas. Our goal was to estimate the frequency and persistence of volunteer canola in Québec cropping systems by surveying fields that included a single canola crop since 1995. A survey was conducted in 131 fields in the main canola-growing areas of Québec: in the Saguenay-Lac Saint-Jean region and the Québec City–La Pocatière area. Volunteer canola plants were counted in 0.25-m2 quadrats every 10 m along a W pattern, and every 15 m along the margins of 88 fields. Volunteer canola plants were found in 90% of the fields surveyed and in a wide range of crops, including cereal, corn, and soybean. Average densities of 4.9 and 3.9 plants/m2 were found 1 yr after canola production in fields and field margins, respectively. Volunteer canola densities decreased significantly over time. However, volunteer plants were still present at low densities 4 and 5 yr after production. Dense stands of volunteer canola were found before postemergence herbicide application in no-till fields (9.8 ± 4.1 plants/m2), suggesting that, contrary to what was suggested in the literature, seeds could become dormant in no-till as well as in tilled systems. A small proportion of the volunteer canola plants observed in no-till fields near Québec City and Ottawa included plants that had overwintered, either originating from fall-germinated seedlings, harvested adult plants that had grown new leaves before the onset of winter, or spring regrowth from the base of unharvested adult plants from experimental plots. The presence and persistence of low densities of volunteer canola may not have been a cause of concern until now. However, producers should be made more aware of the potential short-and long-term problems associated with potential gene flow between different herbicide-tolerant canola (HT canola) varieties and also between HT canola and related weed species.
Midwest growers rely heavily on agrichemical retailers and crop consultants for making pest management decisions. A survey was mailed to 793 fertilizer and agricultural chemical dealers in Illinois to help understand their basis for pesticide recommendations, sources of information, and water quality concerns. Survey response rate was approximately 55%, and results indicated that agrichemical retailers use several sources of information, including manufacturers, universities, and company training programs. Newsletters and fact sheets were recognized as the most useful types of university resources, whereas videos were deemed the least useful. Product effectiveness was identified by 85% of the respondents as being the most important factor affecting pesticide selection. Soil erosion was listed as the greatest threat to water quality. Filter strips and best management practices were suggested as being the most likely to succeed in protecting water quality.
Additional index words: Agrichemical retailer survey, pest management decisions, water quality concerns.
The sugarcane varieties ‘LCP 85-384’, ‘HoCP 85-845’, and ‘LCP 82-089’ were treated in the plant cane crop (first production year) with various combinations of azafeniden preemergence (PRE) at 0.56 or 0.84 kg ai/ha after planting in September/October, postemergence (POST) at 0.56 kg/ha in spring (March), and semidirected at 0.42 kg/ha after the final cultivation at layby in May. In the first ratoon crop (second production year) azafeniden was reapplied in spring and at layby. Herbicide programs were compared with the standard program of atrazine plus pendimethalin PRE after planting, POST applications of diuron plus pendimethalin in spring, and atrazine plus pendimethalin semidirected at layby. Crop injury was negligible for all herbicide treatments applied after planting. Azafeniden injured sugarcane 30 to 33% when applied POST in spring, and injury was most severe in plant cane and first ratoon HoCP 85-845 when they were considerably taller and had more foliage at application compared with the other varieties. Injury from azafeniden following layby application ranged from 9 to 19% in plant cane and first ratoon crops. Multiple applications of azafeniden during the plant cane and first ratoon years did not reduce stalk height, population, sugarcane yield, or sugar yield for any of the varieties when compared with the standard herbicide program.
Abbreviations: DAL, days after layby application; DAP, days following after-planting application; DAS, days after spring application; FR99, 1999 first ratoon experiment; FR00, 2000 first ratoon experiment; PC98, 1998 plant cane experiment; PC99, 1999 plant cane experiment; POST, postemergence; PRE, preemergence; TRS, theoretical recoverable sugar.
Purple starthistle is one of the numerous species of Centaurea that have been accidentally introduced to western North America where most have become pernicious noxious weeds. Purple starthistle is not nearly as widely distributed as its close relative, yellow starthistle, but it is more undesirable because of its growth characteristics and the number, length, and persistence of its spines. Purple starthistle reproduces only by seeds. Knowledge of the seed and seedbed ecology of weeds is important in all suppression strategies and especially for purple starthistle, which has potential biological control agents that suppress seed production. Our purpose was to determine the germination of purple starthistle seeds at a wide range of constant or alternating incubation temperatures from 0 through 40 C. The maximum observed germination ranged from 94 to 100%. Some germination occurred at least 75% or above of the 55 temperature regimes tested. Optimum germination, defined as not less than the maximum observed minus one-half of the confidence interval at the 0.01 level of probability, averaged 88 to 96%. Only one accession of purple starthistle had germination at what we classify as very cold seedbed temperatures. All accessions had near 50% germination at cold seedbed temperatures. Germination was highest at moderate seedbed temperatures and declined at warmer temperatures. The only constant incubation temperature that supported optimum germination was 20 C, and that was for only one accession. The only temperature regime that always supported optimum germination was 15/25 C (15 C for 16 h and 25 C for 8 h in each 24-h period).
Nomenclature: Purple starthistle, Centaurea calcitrapa L. #3 CENCA; yellow starthistle, Centaurea solstitialis L.
Additional index words: Invasive weeds, seed and seedbed ecology.
Our objective was to maximize Canada thistle control and plant community diversity in a waterfowl production area administered by the U.S. Fish and Wildlife Service. We tested three rates (1.5, 3.0, and 4.5 ai/ha) of glyphosate applied during spring, summer, or fall using two application methods. The lowest rate of glyphosate decreased the Canada thistle density by about 30% relative to the control. Glyphosate applied in the fall decreased Canada thistle density below that of the control more consistently than when applied in spring or summer. Wick application generally resulted in less Canada thistle biomass than did broadcast application. Species richness was generally higher when glyphosate was wick applied, and all rates of this application method increased species richness when compared with the control. We recommend fall wick application of glyphosate at 1.5 kg ai/ha to control Canada thistle near the riparian areas. This application provided optimum Canada thistle control, while maintaining species richness important for waterfowl.
Nomenclature: Glyphosate; Canada thistle, Cirsium arvense L. #3 CIRAR.
Repeated application of acetyl-coA carboxylase–inhibiting herbicides, such as sethoxydim, may select for resistant (R) weed populations, making a rapid and reliable seedling bioassay a useful tool. Such a bioassay was developed to determine shoot and root responses of giant foxtail seedlings to sethoxydim. Root and shoot elongation of susceptible (S) and R giant foxtail seedlings was measured at 3 and 6 d after exposure to 0.1 to 100 mg/L sethoxydim. A bioassay concentration of 10 mg/L sethoxydim easily discriminated between S and R biotypes of giant foxtail at 6 d after exposure, with R:S shoot and root growth ratios of 3 and 10, respectively.