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Clomazone was labeled for rice in 2001; however, that label excluded its use on coarse- (light) textured soils, including sand, loamy sand, and sandy loam with less than 1% organic matter due to rice injury. Field studies conducted in 2005, 2006, and 2007 evaluated weed control and tolerance of rice to early postemergence (EPOST) applications of clomazone alone and tank mixed with other herbicides on sandy loam and clay loam soils. At 42 d after treatment (DAT), broadleaf signalgrass (BRAPP) and barnyardgrass (ECHCG) control was > 86%. At 14 DAT, rice injury was greatest (13%) from clomazone applied preemergence (PRE) at 0.44 kg ai/ha on sandy soil. Annual sedge (CYPCP) control was > 78% on sandy loam soils at 14 DAT, but increased to > 90% by 42 DAT. On clay loam soils, CYPCP control at 42 DAT ranged from 60 to 76% from clomazone alone or tank mixed with cyhalofop or fenoxaprop. All other tank mixes provided > 80% control. Hemp sesbania (SEBEX) control was > 80% from all tank mixes. Clomazone alone provided < 77% control. Data suggest that clomazone can be used EPOST in combination with other herbicides without causing significant rice injury on sandy loam soils in Texas.
Experiments were conducted at three North Carolina research stations in 2003 to evaluate weed control and corn yield in glyphosate-resistant, glufosinate-resistant, imidazolinone-tolerant, and conventional corn weed management systems. Late-season control of common lambsquarters, large crabgrass, and yellow nutsedge increased with metolachlor PRE compared with no PRE herbicide treatment. Common lambsquarters, pitted morningglory, entireleaf morningglory, spurred anoda, and tropic croton control was improved by a single early POST (EPOST) application regardless of herbicide system. Control of common lambsquarters, pitted morningglory, entireleaf morningglory, and spurred anoda was similar for glyphosate and glufosinate systems for each POST over-the-top (POT) herbicide system. A single EPOST application of imazethapyr plus imazapyr to imidazolinone-tolerant corn controlled common lambsquarters, pitted morningglory, entireleaf morningglory, and spurred anoda and was better than a single EPOST application of glyphosate, glufosinate, or nicosulfuron. Tropic croton was controlled ≥ 95% with glufosinate or glyphosate, applied once or twice, or in mixture with metolachlor. A single EPOST application of imazethapyr plus imazapyr or nicosulfuron did not control tropic croton. Common lambsquarters, entireleaf morningglory, large crabgrass, Palmer amaranth, and yellow nutsedge control was greater with a late-POST–directed (LAYBY) of ametryn than no LAYBY. Systems that did not include a POT herbicide system had the lowest percentage in the weed-free yield and the lowest yield. Treatments that included a POT system with or without a PRE treatment of metolachlor yielded within 5% of the weed-free treatment, regardless of herbicide system.
Nomenclature:Ametryn; glufosinate; glyphosate; imazapyr; imazethapyr; metolachlor; nicosulfuron; common lambsquarters, Chenopodium album L. CHEAL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray IPOHG; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; spurred anoda, Anoda cristata (L.) Schlecht. ANVCR; tropic croton, Croton glandulosus var. septentrionalis (Muell).-Arg. CVNGS; yellow nutsedge, Cyperus esculentus L. CYPES; corn, Zea mays L. ‘DKC 67-60 RR’, ‘Pioneer 34A55 LL’, ‘Garst 8222 IT’, ‘N75-KG’ ZEAMX
Experiments were conducted from 2003 through 2006 to compare annual grass control by graminicides applied alone or with other pesticides and to determine whether graminicide formulation affected annual grass control and interactions with co-applied pesticides. Formulation and rate had no affect on broadleaf signalgrass or large crabgrass control by clethodim. The efficacy of clethodim in tank mixtures with acifluorfen plus bentazon, bentazon, chlorothalonil, imazapic, pyraclostrobin, or tebuconazole were not affected by clethodim formulation. Broadleaf signalgrass and large crabgrass control by clethodim was slightly reduced by acifluorfen plus bentazon, chlorothalonil, imazapic, and pyraclostrobin, but not by tebuconazole. Chlorothalonil and pyraclostrobin reduced broadleaf signalgrass control with quizalofop-P but did not reduce fall panicum control. Azoxystrobin, propiconazole, and tebuconazole did not affect efficacy of quizalofop-P.
Peanuts are not often used as a true oilseed crop, especially for the production of fuel. However, peanut could be a feedstock for biodiesel, especially in on-farm or small cooperative businesses, where producers can dictate the cost of making their own fuel. Field studies were conducted in 2005 and 2006 to assess low-cost weed-control systems for peanuts that would facilitate the economic viability of peanut biodiesel. Four preselected herbicide costs ranging from $25 to $62/ha and two application timings were compared with nontreated ($0/ha) and typical ($115/ha) herbicide programs for weed control and peanut oil yield. A peanut oil yield goal of 930 L/ha was exceeded with multiple low-cost herbicide systems in 3 of 4 site–yr. The main effect of application timing was only significant for a single site–year in which oil yield increased linearly with cost of the PRE and POST weed-control system. An herbicide cost of $50/ha, using PRE and POST applications, was consistently among the highest in oil yield, regardless of site–year, exceeding the typical (high value) programs in 3 of 4 site–yr. Use of reduced rates of imazapic (0.5× or 0.035 kg ai/ha) was detrimental in 2 of 4 site–yr. Weed control, and thus oil yields, were most dependent on species present at each location and not on input price. Data from this series of studies will allow researchers and entrepreneurs to more accurately assess the viability and sustainability of peanut biodiesel.
Nomenclature: Imazapic; peanut, Arachis hypogaea L
Field experiments were conducted in 1999 and 2000 to evaluate early POST (EPOST) and late POST (LPOST) control of common ragweed and giant foxtail with mesotrione at 70, 105, and 140 g ai/ha alone and in mixtures with glufosinate at 300 g ai/ha in glufosinate-resistant corn. Glufosinate-resistant corn injury was frequently higher with mixtures of mesotrione plus glufosinate than with mesotrione applied alone. Mixtures of mesotrione with glufosinate applied EPOST injured corn 6 to 21% in 1999, but in 2000, injury from mixtures was 23 to 30% from LPOST applications. Common ragweed control was above 77% with all treatments, which included 105 g/ha mesotrione. Giant foxtail control was higher at 76 to 78% by mixtures of mesotrione with glufosinate applied LPOST than by mesotrione alone. Corn yields were highest when glufosinate was included in treatments at either application timing. In the greenhouse, mixtures of mesotrione with glufosinate-injured glufosinate-resistant corn 11% or less, but corn biomass was reduced by 25% for the mixture of mesotrione at 105 g/ha plus glufosinate at 350 g/ha. Mixtures of mesotrione with glufosinate can be more effective than mesotrione alone but control of common ragweed and giant foxtail might not be commercially acceptable.
Nomenclature: Glufosinate; mesotrione; common ragweed, Ambrosia artemisiifolia L. AMBEL; giant foxtail, Setaria faberi Herrm. SETFA; corn, Zea mays L
Experiments were conducted at the Lonoke Extension and Applied Research Center greenhouse at Lonoke, AR, to evaluate the effects of urea ammonium nitrate (UAN) on bispyribac and penoxsulam efficacy on barnyardgrass, hemp sesbania, and broadleaf signalgrass. Herbicide treatments included bispyribac at 17.9 or 35.8 g ai/ha or penoxsulam at 24.4 or 48.9 g ai/ha tank mixed with (1) no adjuvant, (2) a nonionic organosilicone (OSL) adjuvant at 0.125% v/v, (3) a methylated seed oil/organosilicone (MSO/OSL) adjuvant at 0.37 L/ha, (4) a proprietary blend of MSO/OSL/UAN at 2% v/v, (5) UAN at 2% v/v, (6) OSL at 0.125% plus UAN at 2% v/v, or (7) MSO/OSL at 0.37 L/ha plus UAN at 2% v/v. In addition to these adjuvants, penoxsulam was also applied with crop oil concentrate (COC) at 2.34 L/ha and with COC at 2.34 L/ha plus UAN at 2% v/v. The addition of UAN to either herbicide plus an adjuvant increased herbicide efficacy on barnyardgrass in the greenhouse, with 95 to 99% biomass reduction of three- to four-leaf barnyardgrass and 88 to 92% biomass reduction of one- to three-tiller barnyardgrass. UAN did not generally increase efficacy on hemp sesbania, as control was 90% or higher with treatments containing either herbicide and a recommended adjuvant. Adding UAN did not increase efficacy on broadleaf signalgrass. Broadleaf signalgrass control was highly variable and no treatment provided more than 65% biomass reduction.
Bensulfuron-methyl (BSM) has been one of the most widely used herbicides in Chilean rice fields because it controls a wide spectrum of weeds and does not require field drainage for application. However, failures of BSM to control water plantain in rice fields have been noted since 2002. We assessed BSM effects on suspected resistant (CU1 and CU2) and susceptible (AN1) water plantain accessions collected in Chilean rice fields during 2004 and 2005. BSM rates resulting in 50% growth reduction (GR50) of CU2 and CU1 plants were 12- and 33-fold higher than for AN1 plants, respectively. Acetolactate synthase (ALS) activity assays in vitro suggested resistance in CU1 and CU2 was due to an ALS enzyme with reduced BSM sensitivity compared to the AN1 biotype. Resistance indices (RI), or ratios of the resistant to susceptible I50 values (BSM rate to inhibit ALS-enzyme activity by 50%), were 266 (CU2/AN1) and > 38,462 (CU1/AN1). This agreed with in vivo ALS activity assays where RI were 224 (CU2/AN1) and > 8,533 (CU1/AN1). Resistance levels detected in whole-plant or in vivo ALS activity assays were orders of magnitude lower than those detected in in vitro ALS activity studies suggesting nontarget site mechanisms may have mitigated BSM toxicity. However, a consistent ranking of BSM sensitivity levels (AN1 > CU2 > CU1) throughout all three types of assays suggests resistance is primarily endowed by low target site sensitivity. We conclude that susceptible and resistant water plantain biotypes coexist in Chilean paddies, and the use of integrated weed management involving herbicides with a different mode of action would be imperative to prevent further evolution of resistance to BSM and possibly cross-resistance to other ALS inhibitors. In vitro ALS-enzyme assays provided the best discrimination of resistance levels between biotypes.
Nomenclature: Bensulfuron-methyl; water plantain, Alisma plantago-aquatica L. ALSPA; rice, Oryza sativa L
Experiments were conducted at Manhattan, KS in 2005 and 2006 to evaluate cotton response to simulated 2,4-D and dicamba drift rates at different stages of growth and multiple applications of 2,4-D. Cotton was treated with 2,4-D and dicamba at 0, 1/200, and 1/400 of the use rate (561 g ae/ha) when plants were at the three- to four-leaf, 8-, 14-, or 18-node growth stages. Injury symptoms after 2,4-D and dicamba application were more severe at the three- to four-leaf stage compared with other stages with greatest injury from 2,4-D. In general, plants partially recovered from 2,4-D and dicamba injury symptoms, and only 2,4-D applied at the 1/200 rate reduced fiber yield. In a separate study, cotton was treated with 2,4-D at 0, 1/400, 1/800, and 1/1,200 of the use rate for one, two, or three applications. Yield reduction increased as herbicide rate increased from 1/1,200 to 1/400 and the number of applications increased from one to three. In both studies, plants partially or fully recovered from injury symptoms and recovery was greater with dicamba than 2,4-D. Correlation coefficient analysis showed that visual injury ratings later in the growing season are a good predictor of yield reduction (R2 = 0.58).
Greenhouse studies were conducted to evaluate the nature of the cotton postemergence (POST) herbicides followed by (fb) MSMA postemergence-directed (LAYBY) for foliar and tuber reduction of yellow and purple nutsedge when applied to nutsedge at two different application timings. Trifloxysulfuron at 4 and 6 g ai/ha fb MSMA LAYBY reduced 10- to 15- and 20- to 30-cm purple and yellow nutsedge root and shoot dry weights by at least 56%. However, the effect of weed size at the time of application was significant for trifloxysulfuron at 6 g/ha for percent root and shoot reductions in yellow nutsedge and percent root reduction in purple nutsedge. Significance of herbicide rate was only observed for percent shoot and root reduction of 10- to 15-cm yellow nutsedge. Trifloxysulfuron treatments reduced purple and yellow nutsedge shoot and root dry weights equivalent to treatments involving glyphosate POST fb MSMA LAYBY. MSMA at 1,120 and 2,240 g/ha and glufosinate POST fb MSMA LAYBY were effective for reducing purple and yellow nutsedge shoot dry weights, although percent reduction was influenced by nutsedge height at herbicide application. Treatments involving pyrithiobac POST fb MSMA LAYBY slightly increased 10- to 15-cm yellow nutsedge root dry weights. MSMA at either rate produced additive responses when included in tank mixtures with trifloxysulfuron at either rate or pyrithiobac POST fb MSMA LAYBY in yellow nutsedge. Other tank mixes or sequential combinations did not cause additive or synergistic responses.
Nomenclature: Glufosinate; glyphosate; MSMA; pyrithiobac; trifloxysulfuron; purple nutsedge, Cyperus rotundus L. CYPRO; yellow nutsedge, Cyperus esculentus L. CYPES;cotton, Gossypium hirsutum L
Experiments were conducted to evaluate the effect of application rate, growth stage, and tank mixing azimsulfuron, bentazon, MCPA, propanil, or cyhalofop on the efficacy of bispyribac–sodium against early watergrass and late watergrass from rice fields in northern Greece. Mixtures of bispyribac–sodium with the insecticides carbaryl, diazinon, and dichlorvos were also evaluated. Bispyribac–sodium (24 to 36 g ai/ha) applied alone at the three- to four-leaf growth stage provided 89 to 100% control of early watergrass and 84 to 100% control of late watergrass. When bispyribac–sodium was applied alone at the five- to six-leaf growth stage of early watergrass and late watergrass, control ranged from 78 to 100% and 71 to 100%, respectively. Mixtures of bispyribac–sodium with azimsulfuron provided better control of both species at any growth stage than bispyribac–sodium applied alone. On the contrary, mixtures of bispyribac–sodium with bentazon, MCPA, or propanil were less effective on both species at any growth stage than bispyribac–sodium applied alone. A slight efficacy reduction occurred on both species for the mixture of bispyribac–sodium with cyhalofop. Mixtures of bispyribac–sodium with the insecticides carbaryl or dichlorvos showed reduced efficacy on both species, whereas increased efficacy on both species was observed for mixtures of bispyribac–sodium with diazinon as compared with the single application of bispyribac–sodium.
Field studies were conducted in 2006 and 2007 to evaluate strategies for management of four glyphosate-tolerant common lambsquarters populations in glyphosate-resistant soybeans. Treatments consisted of several different preplant herbicide combinations followed by one or two postemergence applications of 0.84 to 3.36 kg ae/ha of glyphosate. Preplant application of a combination of glyphosate, 2,4-D ester and residual herbicides resulted in the most effective control of all populations, and allowed use of a single postemergence glyphosate application at the lowest rate. Late-season control of common lambsquarters ranged from 66 to 95% where no preplant herbicides were applied, 72 to 97% for preplant application of glyphosate and 2,4-D, and 96 to 100% for the combination of glyphosate, 2,4-D, flumioxazin, and cloransulam-methyl. Individual plants survived and produced seed following single postemergence glyphosate applications of 3.36 kg ae/ha, and multiple glyphosate applications totaling 2.5 kg ae/ha. Multiple postemergence treatments were more effective than single postemergence treatments for reduction of common lambsquarters population density and seed production. The progeny of plants that survived high rates of glyphosate in the field were screened for their response to glyphosate in the greenhouse. Progeny from one of three populations exhibited increased glyphosate tolerance from 1 yr of selection pressure.
Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L;soybean, Glycine max (L.) Merr
Field studies were conducted in 2004 and 2005 in Michigan to determine the effect of seeding establishment method and weed control on forage quality of glyphosate-resistant alfalfa in the establishment year. Seeding methods included alfalfa only (clear-seeding) and alfalfa with a companion crop of oat (companion-seeding). Herbicide treatments included an untreated control and glyphosate treatment for both establishment systems, and either imazamox in the clear-seeding system or imazamox clethodim in the companion-seeding system. The greatest differences among treatments in forage quality were observed at the first harvest in both establishment years. Results suggest high quality, productive alfalfa stands can be established utilizing glyphosate-resistant alfalfa in a clear seeding system.
Trials were established in 2003, 2004, and 2005 in Ontario to determine the effects of residues of mesotrione, atrazine, and mesotrione plus atrazine 1 and 2 yr after application on broccoli, carrot, cucumber, onion, and potato. One yr after mesotrione application, injury was 43, 37, 18, 24, and 0% in broccoli, carrot, cucumber, onion, and potato, respectively. The addition of atrazine to mesotrione in the year before planting increased injury to 55, 53, 30, 42, and 3% in broccoli, carrot, cucumber, onion, and potato, respectively. Plant dry weight and yield were also decreased by mesotrione residues the year after application in all crops except potato. The addition of atrazine to mesotrione accentuated the reduction in dry weight and yield in broccoli, carrot, cucumber, and onion. There was no injury, or reductions in dry weight or yield in any crop planted 2 yr after application of mesotrione alone or in tank mix with atrazine. A recropping interval of 2 yr is recommended following applications of mesotrione or mesotrione plus atrazine for broccoli, carrot, cucumber, and onion. Potato can be safely planted the year following application of mesotrione plus atrazine.
Knowledge of weed community structure in vegetable crops of the north central region (NCR) is poor. To characterize weed species composition present at harvest (hereafter called residual weeds) in processing sweet corn, 175 fields were surveyed in Illinois, Minnesota, and Wisconsin from 2005 to 2007. Weed density was enumerated by species in thirty 1-m2 quadrats placed randomly along a 300- to 500-m loop through the field, and additional species observed outside quadrats were also recorded. Based on weed community composition, population density, and mean plant size, overall weed interference level was rated. A total of 56 residual weed species were observed and no single species dominated the community of NCR processing sweet corn. Several of the most abundant species, such as common lambsquarters and velvetleaf, have been problems for many years, while other species, like wild-proso millet, have become problematic in only the last 20 yr. Compared to a survey of weeds in sweet corn more than 40 yr ago, greater use of herbicides is associated with reductions in weed density by approximately an order of magnitude; however, 57% of fields appeared to suffer yield loss due to weeds. Sweet corn harvest in the NCR ranges from July into early October. Earlier harvests were characterized by some of the highest weed densities, while late-emerging weeds such as eastern black nightshade occurred in fields harvested after August. Fall panicum, giant foxtail, wild-proso millet, common lambsquarters, and velvetleaf were the most abundant species across the NCR, yet each state had some unique dominant weeds.
Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; eastern black nightshade, Solanum ptychantum Dunal. SOLPT; fall panicum, Panicum dichotomiflorum Michx. PANDI; giant foxtail, Setaria faberi Herrm. SETFA; velvetleaf, Abutilon theophrasti Medic. ABUTH; wild-proso millet, Panicum miliaceum L. PANMI; sweet corn, Zea mays L
Volunteer potato is a major weed pest of sweet corn in regions where winter soil temperatures fail to kill tubers left in the ground after harvest. Studies were conducted in 2004 to 2005 to determine the effect of combining atrazine with mesotrione applied POST on volunteer potato control and new tuber production in sweet corn. Mesotrione at 0.035, 0.07, and 0.1 kg/ha and atrazine at 0.3, 0.6, and 1.1 kg/ha were applied alone and in all possible combinations when volunteer potato ranged from 5 to 12 cm tall. Mesotrione applied alone at all rates, atrazine at 1.1 kg/ha, or mesotrione plus atrazine combinations reduced the number of new tubers produced to ≤ 1.1 per plant compared with 11 tubers per plant in nontreated checks. Potatoes treated with atrazine alone at 0.3 or 0.6 kg/ha produced 3.3 or 1.9 tubers per plant, respectively, which could lead to volunteer potato problems in the succeeding crop. Sweet corn yield was not affected by herbicide treatment in 2004 but was reduced in 2005 when atrazine was used alone at 0.3 or 0.6 kg/ha because of poor control of volunteer potato. Additional studies were conducted from 2004 to 2006 to determine volunteer potato control in sweet corn in reduced and conventional tillage and treated with fluroxypyr, mesotrione, or no herbicide. Volunteer potato control was improved and the number and weight of tubers was reduced 79 and 91%, respectively, in conventionally tilled plots treated with fluroxypyr compared with reduced-tillage plots. Control of volunteer potato with mesotrione was greater than 98% and reduced tuber number and weight greater than or equal to all other treatments regardless of tillage level.
Field experiments were conducted in 1999, 2000, and 2001 to investigate PRE and POST applications of halosulfuron-methyl in combination with clomazone plus ethalfluralin for control of sedge and smooth pigweed in summer squash. Halosulfuron was applied PRE or POST to summer squash at 9, 18, or 27 g ai/ha in combination with a PRE application of clomazone at 175 g ai/ha plus ethalfluralin at 630 g ai/ha. Smooth pigweed control by addition of halosulfuron at 18 and 27 g/ha in combination with clomazone plus ethalfluralin PRE was greater than 89% independent of application method. Yellow nutsedge control was greater than 83% with POST applications of halosulfuron at 18 and 27 g/ha in combination with clomazone plus ethalfluralin PRE. Yellow nutsedge control was greater than 60% from all POST halosulfuron applications at 9, 18, or 27 g/ha in the greenhouse. In a separate field study without ethalfluralin PRE, rice flatsedge control was more than 85% from halosulfuron applied POST at 18 and 27 g/ha. Yellow summer squash and zucchini squash were injured as much as 52 and 47%, respectively, from inclusion of halosulfuron PRE or POST at 27 g/ha in treatments. Summer squash yields were generally not affected by halosulfuron rate, and were comparable to or higher than summer squash treated by only the mixture of clomazone plus ethalfluralin. In these studies, summer squash were injured by halosulfuron applied at 9 to 27 g/ha PRE or POST, yet rapidly recovered, making this herbicide acceptable for use in combination with clomazone and ethalfluralin for controlling several common weed species.
The use of POST herbicides has been limited in sweet corn because of the narrow spectrum of weed control or potential crop injury. Field experiments were conducted to evaluate the 4-hydroxyphenyl pyruvate dioxygenase (HPPD)-inhibiting herbicides mesotrione, tembotrione, and topramezone applied POST in sweet corn at three locations. Efficacy of mesotrione, tembotrione, and topramezone applied alone or mixed with atrazine was compared to other labeled POST herbicides following PRE S-metolachlor. Giant foxtail control was greater with tembotrione or topramezone than mesotrione alone or mixed with atrazine. Common lambsquarters, velvetleaf, and common ragweed were controlled 98% or greater with the HPPD-inhibiting herbicides when mixed with atrazine. Tolerance of six sweet corn hybrids was determined in the field when treated with 1× and 2× rates of these herbicides mixed with atrazine. Tolerance of six sweet corn hybrids to these herbicides was determined in the greenhouse when treated with 0.5, 1, 2, 4, 8, and 16 times the labeled rate. Differential hybrid tolerance to each herbicide was observed in both the field and greenhouse evaluations. Tembotrione killed ‘Merit’ in both evaluations. Excluding Merit, hybrids generally had good tolerance to tembotrione and topramezone in the field, but had differential tolerance to mesotrione. With the exception of Merit, hybrids generally had greater tolerance to tembotrione than topramezone and less tolerance to mesotrione in the greenhouse. These HPPD-inhibiting herbicides provide POST weed control, but the potential for sweet corn injury varies among the herbicides and hybrids and warrants further characterization.
Nomenclature: Atrazine; mesotrione; S-metolachlor; tembotrione; topramezone;common lambsquarters, Chenopodium album L. CHEAL; common ragweed, Ambrosia artemisiifolia L. AMBEL; giant foxtail, Setaria faberi Herrm. SETFA; velvetleaf, Abutilon theophrasti Medicus ABUTH; corn, Zea mays L
Applications of metribuzin plus MSMA have been used to control goosegrass in bermudagrass turf for over 20 yr. In 2003, two goosegrass biotypes on the island of Kauai, Hawaii were found to be resistant to applications of metribuzin plus MSMA. Metribuzin plus MSMA applied at rates of 0.28 kg ai/ha plus 2.2 kg/ha, respectively, followed by MSMA at 2.2 kg/ha 7 d later, provided 100% control of two susceptible goosegrass biotypes, but no control of two resistant biotypes. At the flowering growth stage, metribuzin applied at a rate of 0.28 kg/ha controlled both susceptible biotypes (> 92%), but did not control the two resistant biotypes. Two applications of MSMA applied at a rate of 2.2 kg/ha (7 d apart) did not control any of the four biotypes at the flowering growth stage. The two resistant biotypes were approximately 100 to 200 times less sensitive to increasing rates of metribuzin than the two susceptible biotypes. The two biotypes that were resistant to metribuzin plus MSMA were also resistant to applications of simazine plus MSMA. However, all four biotypes were susceptible to applications of glyphosate and foramsulfuron.
Diflufenzopyr is an auxin-transport inhibitor that can increase the phytotoxicity of certain auxin-mimicking herbicides such as dicamba on broadleaf species. Dicamba is commonly used alone and in combination with other auxin herbicides for broadleaf weed control in various species of turfgrass. Dicamba efficacy applied over a series of rates either alone or as an admixture with either 20 or 40% by weight of diflufenzopyr relative to the weight of dicamba was evaluated on purple cudweed and common lespedeza. The 20% admixture reduced the LD50 of dicamba on purple cudweed from 23 to 20 g/ha. Similarly, LD50 on common lespedeza was reduced from 36 and 27 g/ha. The 20% admixture was 13 and 25% more active than dicamba alone for these two weed species, respectively. However, the synergistic benefit was limited to a relatively narrow range of rates that are below the minimal registered rate of dicamba. Turfgrass injury, as expressed by the suppression of foliage growth, was similar whether dicamba was applied alone or with diflufenzopyr for all species evaluated except St. Augustinegrass. The admixture was less injurious than dicamba alone in St. Augustinegrass. The synergistic benefit with respect to weed control was obtained without a corresponding increase in injury on the turfgrasses.
Nomenclature: Dicamba; diflufenzopyr; common lespedeza, Kummerowia striata (Thunb.) Schindl. LESST; purple cudweed, Gnaphalium purpureum L. GNAPU; St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze ‘Raleigh’
Field trials were conducted at three California locations near Oxnard, Salinas, and Watsonville from 2002 to 2006 to evaluate broadleaf weed control and tolerance of strawberry to oxyfluorfen. Oxyfluorfen applied at 0.3 and 0.6 kg/ha before strawberry transplanting reduced densities of broadleaf weeds such as California burclover, hairy nightshade, little mallow, shepherd's-purse, and yellow sweetclover 70 to 100% compared with nontreated plots but did not control horseweed. Oxyfluorfen application resulted in 9% and 19% greater visible injury to strawberry for the two rates, respectively, compared with nontreated plants in 1 yr but did not reduce strawberry yield. After oxyfluorfen application at 0.6 kg/ha, strawberry plants had 5 to 48% more injury than nontreated plants in subsequent years but early-season yields were similar. Hand-weeding time was reduced 30 to 50% compared with nontreated plots regardless of oxyfluorfen rate. Both water-based and solvent-carrier formulations of oxyfluorfen resulted in similar weed control, strawberry injury, and fruit yield. Plastic mulch installation after oxyfluorfen application but before planting reduced injury to strawberry more than 50% compared with nonmulched beds. Oxyfluorfen applied 30 d before strawberry transplanting had similar crop injury and yield to applications made 15 and 7 d before planting. These results suggest that oxyfluorfen can be used safely in California plasticulture strawberry production for control of common weed species and to reduce labor inputs associated with hand weeding.
Nomenclature: Oxyfluorfen; California burclover, Medicago polymorpha L. MEDPO;hairy nightshade, Solanum physalifolium Rusby SOLSA; horseweed, Conyza canadensis L. ERICA; little mallow, Malva parviflora L. MALPA; shepherd's-purse, Capsella bursa-pastoris L. CAPBP; yellow sweetclover, Melilotus officinalis L. MEUOF;strawberry, Fragaria×ananassa
Field experiments were conducted in 2001 and 2002 to study the effect of date of planting, herbicide, and straw mulch on menthol mint yield and oil quality in northwest India. Menthol mint was planted at three dates (December 10, December 30, and January 20). Diuron was applied prior to emergence at rates of 0.0, 0.4, and 0.6 kg ai/ha, with and without rice straw mulch (6 t/ha). Menthol mint planted on December 30 and January 20 produced more plantlets and dry matter than the December 10 planting. Menthol mint planted on December 10 had higher weed density and weed biomass, and lower menthol mint herbage and oil yield than the later planting dates. Straw mulch application reduced weed density and weed biomass, and increased plantlet population, menthol mint dry matter accumulation, fresh herbage, and menthol mint oil yield. Preemergence (PRE) applications of diuron at 0.4 and 0.6 kg ai/ha increased menthol mint population and crop dry matter accumulation, and decreased weed density and weed biomass compared to the weedy check. Diuron at 0.6 kg/ha increased fresh herbage and menthol mint oil yield over the untreated weedy check, but there were no other differences between the two rates of diuron. Physicochemical properties of menthol mint oil were not affected by any of the three tested factors.
Nomenclature: Diuron; menthol mint, Mentha arvensis L
Sugarbeet varieties vary in their response to herbicides. s-Metolachlor and dimethenamid-P were recently registered for use in sugarbeet. Field trials were conducted in Michigan in 2004, 2005, and 2006 to evaluate the response of 12 sugarbeet varieties to s-metolachlor and dimethenamid-P applied PRE and POST to two-leaf and four-leaf stage sugarbeet. s-Metolachlor and dimethenamid-P reduced sugarbeet density when rainfall occurred within 7 d of the PRE applications. Dimethenamid-P PRE caused the most injury across all varieties followed by s-metolachlor PRE. Applying dimethenamid-P POST to two-leaf sugarbeet injured plants more than s-metolachlor applied POST to two- and four-leaf stage sugarbeet. The least amount of sugarbeet injury from dimethenamid-P was from POST applications at the four-leaf stage. Sugarbeet varietal differences were most pronounced from PRE applications of both herbicides and from the POST two-leaf application of dimethenamid-P. Of the 12 sugarbeet varieties evaluated, Hilleshog 2771RZ and Beta 5833R were the most tolerant, whereas Hilleshog 7172RZ was typically the most sensitive variety to these herbicides. Growers will probably not choose varieties based on herbicide tolerance alone, but instead base variety selection on sugar yield and disease resistance. However, if a grower has chosen a particular variety, this information could assist in assessing the risk of using s-metolachlor or dimethenamid-P for weed control.
Nomenclature:Dimethenamid-P; s-metolachlor; sugarbeet, Beta vularis L
Currently there are no herbicides registered for direct application to buckwheat for broadleaf weed control. This 4-yr Lithuanian study examined weed control using several rates of clopyralid alone or combined with a single rate of desmedipham. Most applications were applied at the 1-leaf stage of crop growth, however, one rate of clopyralid was applied pre-emergence (PRE) in 2 of the 4 yr. Buckwheat injury was evident within a few days after application (or emergence) with all treatments, but by harvest, no symptoms were evident. In the 2 yr with greatest weed densities, densities were reduced with increasing clopyralid rates alone or with desmediphan. However, weed biomass and density were similar to the nontreated control at harvest. Common lambsquarters, scentless mayweed, wild buckwheat, and narrowleaf hawksbeard were species that were best (> 40% density reduction) controlled with clopyralid. With few exceptions, buckwheat yield in all herbicide-treated plots was similar to the nontreated control. Because yield was not increased with these herbicides, other weed control benefits, such as reduced interference with harvesting equipment or less dockage due to weed seed contamination, must be carefully weighed against the costs of herbicide and application and crop injury that reduced early-season vigor.
An experiment was conducted to determine the utility of multispectral imagery for identifying soybean, bare soil, and six weed species commonly found in Mississippi. Weed species evaluated were hemp sesbania, palmleaf morningglory, pitted morningglory, prickly sida, sicklepod, and smallflower morningglory. Multispectral imagery was analyzed using supervised classification techniques based upon 2-class, 3-class, and 8-class systems. The 2-class system was designed to differentiate bare soil and vegetation. The 3-class system was used to differentiate bare soil, soybean, and weed species. Finally, the 8-class system was designed to differentiate bare soil, soybean, and all weed species independently. Soybean classification accuracies classified as vegetation for the 2-class system were greater than 95%, and bare soil classification accuracies were greater than 90%. In the 3-class system, soybean classification accuracies were 70% or greater. Classification of soybean decreased slightly in the 3-class system when compared to the 2-class system because of the 3-class system separating soybean plots from the weed plots, which was not done in the 2-class system. Weed classification accuracies increased as weed density or weeks after emergence (WAE) increased. The greatest weed classification accuracies were obtained once weed species were allowed to grow for 10 wk. Palmleaf morningglory and pitted morningglory classification accuracies were greater than 90% for 10 WAE using the 3-class system. Palmleaf morningglory and pitted morningglory at the highest densities of 6 plants/m2 produced the highest classification accuracies for the 8-class system once allowed to grow for 10 wk. All other weed species generally produced classification accuracies less than 50%, regardless of planting density. Thus, multispectral imagery has the potential for weed detection, especially when being used in a management system when individual weed species differentiation is not essential, as in the 2-class or 3-class system. However, weed detection was not obtained until 8 to 10 WAE, which is unacceptable in production agriculture. Therefore, more refined imagery acquisition with higher spatial and/or spectral resolution and more sophisticated analyses need to be further explored for this technology to be used early-season when it would be most valuable.
Nomenclature: Hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill SEBEX; palmleaf morningglory, Ipomoea wrightii Gray IPOWR; pitted morningglory, Ipomoea lacunosa L. IPOLA; prickly sida, Sida spinosa L. SIDSP; sicklepod, Senna obtusifolia (L.) H. S. Irwin & Barnaby CASOB; smallflower morningglory, Jacquemontia tamnifolia (L.) Griseb. IAQTA; soybean, Glycine max (L.) Merr. ‘Asgrow 4403’
Thermal weed control methods have been incorporated into weed control programs in organic and conventional production systems. Flaming is commonly used, but steaming has been proposed to increase efficiency of heat transfer to weeds and reduce the risk of fire. The objective of this research was to measure injury to leaves of plant species that differ in leaf morphology and to measure injury to plants at different stages of plant development. The study was conducted in a glasshouse and plants were exposed to steaming at 400 C for 0.36 s—equivalent to a steaming speed of 2 km/h. Overall, leaf thickness was the best morphological characteristic to predict injury (r2 = 0.51), with greater thickness resulting in less injury. For broadleaf species only, species with wider leaves were injured more than species with narrower leaves (r2 = 0.64). Injury was greatest when plants had fewer than six true leaves and when their shoots were less than 10 cm long. There was a wide range of injury across species, and the grass species bermudagrass and perennial ryegrass were injured (68 to 81%) more than other species such as common purslane and English daisy (23 to 34%). Biomass of all species tested was reduced by approximately 40%, indicating that leaf injury was not the sole effect of steaming on plant growth. These results indicated that considering both visual estimates of injury and morphological characteristics is important to properly assess thermal weed control effectiveness.
Nomenclature: Bermudagrass, Cynodon dactylon (L.) Pers.; common purslane, Portulaca oleracea L.; English daisy, Bellis perennis L.; perennial ryegrass, Lolium perenne L
The extended production of allelochemicals from a living mulch cover crop may potentially enhance weed management and crop productivity compared with traditional zucchini squash production systems. However, the efficacy of a living mulch cover crop in no-tillage (NT) systems with herbicides has not been determined for many vegetable crops. The objective of this research was to evaluate weed management and zucchini squash production using the combination of NT and a herbicide-suppressed winter rye cover crop with or without PRE herbicides. When used in combination with herbicides, the winter rye living mulch reduced the biomass of redroot pigweed compared to the herbicides applied alone, but did not influence the biomass of smooth crabgrass for any herbicide treatment. Visual estimates of weed control were similar for each herbicide treatment with and without the winter rye living mulch. The herbicide-suppressed winter rye resulted in excessive stunting of zucchini squash at 56 d after treatment which correlated with 20 and 50% squash yield reductions for the 2004 and 2005 growing seasons, respectively. Although some squash yield loss may have resulted from direct competition with the winter rye living mulch, yield reductions most likely resulted from allelopathy. The winter rye living mulch was the primary contributing factor for reduced squash yield and did not interact with herbicide treatment. All treatments containing herbicides resulted in yields similar to the weed-free treatment. Because of excessive zucchini injury, this research suggests that the use of herbicide-suppressed winter rye living mulch does not appear to be a feasible option for increased weed control in zucchini squash production regardless of the herbicide treatment.
Nomenclature: Clethodim; clomazone; dimethenamid; ethalfluralin; imazamox; redroot pigweed, Amaranthus retroflexus L. AMARE; smooth crabgrass, Digitaria ischaemum (Schreb. ex Schweig.) Schreb. ex Muhl. DIGIS; winter rye, Secale cereale L. ‘Wheeler’; zucchini squash, Cucurbita pepo L. ‘Independence II’
Weed control strategies based on conserving crop yields rather than preventing weed seed production may result in increased weed densities and management costs over the long-term, particularly in less competitive crops such as tomatoes. The effect of crop, tillage, and duration of weed control on weed seed bank size and composition was examined from spring 2001 to spring 2003 near Lafayette, IN. Main plots in 2001 and 2002 contained soybean or tomato planted in rotation (soybean-tomato, tomato-soybean). Subplots were managed with either conventional or no-till practices. Sub-subplots contrasted threshold strategies in which weeds were either controlled for four to six weeks (period threshold, PT) or throughout the growing season (no-seed-threshold, NST). Seed banks were sampled annually in the spring. Emergent weeds were counted` at four and twelve weeks after planting (WAP) in 2001 and 2002. Weed seed banks did not significantly change in the NST plots in any year. However, seed bank densities increased substantially following tomatoes in PT plots. In contrast, weed seed bank densities decreased following soybeans in PT plots. The difference in seed banks and emergent weeds between soybean and tomatoes could be attributed primarily to greater suppression of giant foxtail by the soybean canopy. Giant foxtail control was greater in PT soybeans than in PT tomatoes in both years and giant foxtail comprised most of the PT tomato seed bank in 2002 and 2003. Tillage did not affect weed seed banks in any year. This study highlights the need to control later emerging weeds in tomatoes to prevent large increases in the weed seed bank.
Nomenclature: Giant foxtail, Setaria faberi Herrm. SETFA; Soybean, Glycine max L.; Tomato, Lycopersicon esculentum L
This study measured impact of cool-season crops on seedling emergence, survival, and seed production of weeds common in corn and soybean. Weed dynamics were monitored in permanently marked quadrats in winter wheat, spring wheat, and canola. Three species, green foxtail, yellow foxtail, and common lambsquarters, comprised more than 80% of the weeds observed in the study. Seedling emergence was reduced by winter wheat, but not by spring wheat or canola, when compared with adjacent quadrats without a crop canopy. Approximately 10% of seedlings in spring wheat and canola developed into seed-bearing plants, but no seed-bearing plants were present in winter wheat at harvest. Common lambsquarters produced more than 1,100 seeds/plant, whereas a foxtail plant produced 85 seeds, averaged across spring wheat and canola. At harvest, new seedlings were present in all crops; thus, control after harvest will be required to prevent seed production in the fall. Winter wheat may provide an opportunity to disrupt population dynamics of weeds common in corn and soybean without requiring herbicides.
Nomenclature: Common lambsquarters, Chenopodium album L.; green foxtail, Setaria viridis (L.) Beauv.; yellow foxtail, Setaria glauca (L.) Beauv.; canola, Brassica napus L.; corn, Zea mays L.; soybean, Glycine max (L.) Merr.; wheat, Triticum aestivum L
Agricultural practices, other than herbicide use, can affect the rate of evolution of herbicide resistance in weeds. This study examined associations of farm management practices with the occurrence of herbicide (acetyl-CoA carboxylase or acetolactate synthase inhibitor)-resistant weeds, based upon a multi-year (2001 to 2003) random survey of 370 fields/growers from the Canadian Prairies. Herbicide-resistant weeds occurred in one-quarter of the surveyed fields. The primary herbicide-resistant weed species was wild oat, with lesser occurrence of green foxtail, kochia, common chickweed, spiny sowthistle, and redroot pigweed. The risk of weed resistance was greatest in fields with cereal-based rotations and least in fields with forage crops, fallow, or where three or more crop types were grown. Weed resistance risk also was greatest in conservation-tillage systems and particularly low soil disturbance no-tillage, possibly due to greater herbicide use or weed seed bank turnover. Large farms (> 400 ha) had a greater risk of weed resistance than smaller farms, although the reason for this association was unclear. The results of this study identify cropping system diversity as the foundation of proactive weed resistance management.
Nomenclature: Common chickweed, Stellaria media (L.) Vill. STEME; green foxtail, Setaria viridis (L.) Beauv. SETVI; kochia, Kochia scoparia (L.) Schrad. KSHSC; redroot pigweed, Amaranthus retroflexus L. AMARE; spiny sowthistle, Sonchus asper (L.) Hill SONAS; wild oat, Avena fatua L. AVEFA
Field-scale experiments were conducted at several western Canada locations to determine the importance of early weed removal over variable landscapes. In eight of 10 cases, imidazolinone-resistant (IR) canola yield decreased linearly as herbicide application (15/15 g/ha imazamox/imazethapyr or 15/15 g/ha imazamox/imazethapyr plus 150 g/ha clopyralid) was delayed beyond the one- to two-leaf stage. In two of 10 cases, canola oil content also decreased as herbicide treatment was delayed. Canola yields at all environments (location by year combinations) averaged 2,073, 1,872, or 1,650 kg/ha when treated at the one- to two-, three- to five-, or six- to seven-leaf stage, respectively. Assuming canola prices from a low of $250/t to a high of $650/t, growers could lose $50 to $131/ha, respectively, by delaying herbicide application from the one- to two- to the three- to five-leaf stage, or $106 to $275/ha, respectively, by delaying herbicide application from the one- to two- to the six- to seven-leaf stage.
Nomenclature: Clopyralid; imazamox; imazethapyr; canola, Brassica napus L. ‘46A73’
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