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Field experiments were conducted in 2001, 2002, and 2003 to evaluate PRE applications of mesotrione at 150, 230, and 310 g ai/ha alone, and in mixtures with S-metolachlor at 1,070 g ai/ha and atrazine at 560 and 1,120 g ai/ha in corn. Corn injury was 11 to 18% with all treatments in 2002 when 3.2 cm of rainfall occurred within 10 d after PRE applications, but no injury was observed in 2001 and 2003 when rainfall was 0 and 1.1 cm within 10 d after PRE applications, respectively. Rainfall following PRE herbicide applications also influenced weed control, where weed control was generally poor with all herbicide treatments in 2001. Mesotrione at 150 g/ha controlled common lambsquarters and smooth pigweed at least 95% in 2002 and 2003, but control was 70% or less in 2001. PRE mesotrione at rates of 230 or 310 g/ha controlled common ragweed at least 83% in 2002 and 2003, but control exceeded 88% with mixtures of mesotrione at rates greater than 150 g/ha plus S-metolachlor plus atrazine at 560 g/ha. Morningglory species (ivyleaf morningglory, pitted morningglory, and tall morningglory) were not consistently controlled by mesotrione alone. In 2002 and 2003, mixtures of all mesotrione rates plus S-metolachlor plus atrazine at 1,120 g/ha controlled morningglory species at least 90%. Corn treated with mesotrione at any rate plus S-metolachlor plus atrazine at 1,120 g/ha consistently produced high yields. It is concluded that control with this three-way mixture would be most consistent with a minimum rate of mesotrione at 230 g/ha and atrazine at 1,120 g/ha.
Nomenclature: Atrazine; mesotrione; S-metolachlor; common lambsquarters, Chenopodium album L. CHEAL; common ragweed, Ambrosia artemisiifolia L. AMBEL; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE; morningglory species, Ipomoea spp. IPOSS; pitted morningglory, Ipomoea lacunosa L. IPOLA; smooth pigweed, Amaranthus hybridus L. AMACH; tall morningglory, Ipomoea purpurea (L.) Roth PHBPU; corn, Zea mays L. ‘Dekalb DKC64-10 (RR2)’, ‘Pioneer 33B51’, ‘Pioneer 33G26’.
Field studies conducted from 2005 to 2007 in Kansas compared the effects of KIH-485 and flufenacet to acetochlor and s-metolachlor applied PRE in grain sorghum. All treatments were combined with 1.12 kg/ha of atrazine for broadleaf weed control. KIH-485 and flufenacet, each at one time (1×) and two times (2×) the labeled rates, controlled large crabgrass 55 to 76% in 2005 and 94% or more in 2006 and 2007. In 2005, all herbicides controlled shattercane less than 20%, and only KIH-485 at the 2× rate controlled shattercane more than 70% in 2006 and 2007. Averaged over herbicides, green foxtail was controlled 98% in 2005, 77% in 2006, and 79% in 2007. Most herbicides controlled foxtail 86% or more when averaged over experiments, however, s-metolachlor at 1×, flufenacet at either rate, or atrazine alone did not. Sorghum was not stunted with KIH-485 or flufenacet in two of seven experiments. However, sorghum growth was reduced 23 to 54% with the 2× rates of KIH-485, flufenacet, or acetochlor in four experiments. Compared to the weed free control, sorghum stand establishment was reduced 18% with the 2× rate of flufenacet at Colby in 2006. At Hays in 2005, stand reductions occurred with acetochlor or KIH-485 at the 2× rates and either rate of flufenacet. Averaged over experiments, grain yields were reduced 9 and 10% with KIH-485 and flufenacet at the 2× rates, respectively. Where precipitation was greatest during the 2 wk following herbicide application, weed control was the best with these herbicides, but sorghum injury was also greatest.
Southern Great Plains wheat growers typically apply either sulfosulfuron or propoxycarbazone-sodium for selective control of cheat. Although astute growers apply herbicides early in the growing season, herbicide application is often delayed until mid-winter or later. The effects of application timing of propoxycarbazone-sodium on cheat efficacy and on injury to the following grain sorghum crop have not been documented. Application of each herbicide at 17 intervals throughout the growing season indicated that cheat control with propoxycarbazone-sodium was greater than or equal to 90% even when application was delayed for several months after seeding. In contrast, cheat control with sulfosulfuron was variable when application was delayed more than 6 wk after wheat was seeded. Delaying sulfosulfuron application decreased wheat yield. Grain sorghum was not affected by propoxycarbazone-sodium residues regardless of application timing to wheat. Conversely, grain sorghum was severely injured by sulfosulfuron residues regardless of herbicide application timing.
Nomenclature: Propoxycarbazone-sodium; sulfosulfuron; cheat, Bromus secalinus L. BROSE; grain sorghum, Sorghum bicolor L.; wheat, Triticum aestivium L.
Field experiments were conducted in Oklahoma to quantify the wheat grain yield losses and price discounts resulting from season-long interference with cheat, feral rye, Italian ryegrass, jointed goatgrass, and wild oat. Plots were seeded to individual weeds at one of seven seeding rates, and wheat was planted in all plots at a uniform rate. Maximum weed densities were 89 (cheat), 80 (feral rye), 158 (Italian ryegrass), 170 (jointed goatgrass), and 120 plants/m2 (wild oat). Wheat grain yield losses caused by interference from the maximum density of each weed species were 19 (cheat), 55 (feral rye), 20 (Italian ryegrass), 21 (jointed goatgrass), and 28% (wild oat). Wheat grain total price discounts caused by interference from the maximum density of each weed species were 22 (cheat), 368 (feral rye), 26 (Italian ryegrass), 36 (jointed goatgrass), and 64 cents/hectoliter (wild oat). Of the five weed species included in this research, interference from feral rye had the greatest effect on wheat grain yield and price.
Nomenclature: Cheat, Bromus secalinus L. BROSE; feral rye, Secale cereale L. SECCE; Italian ryegrass, Lolium perenne L. ssp. multiflorum (Lam.) Husnot LOLMU; jointed goatgrass, Aegilops cylindrica Host AEGCY; wild oat, Avena fatua L. AVEFA; wheat, Triticum aestivum L. ‘Jagger’.
Palmer amaranth resistance to acetolactate synthase (ALS)–inhibiting herbicides was first identified in Georgia in 2000. Since then, complaints from peanut producers have increased concerning failure of ALS herbicides in controlling Palmer amaranth. Because efficacy of ALS herbicides can be compromised under adverse conditions, seeds from Palmer amaranth plants that escaped weed control were collected across the peanut-growing region in Georgia to investigate the cause of these reported failures. Greenhouse and growth-chamber studies were conducted using these seeds to evaluate whether weed escapes were a result of Palmer amaranth resistance to ALS herbicides. Each of the 61 accessions collected across Georgia exhibited varying levels of resistance to imazapic applied POST (< 55% control, relative to ALS-susceptible Palmer amaranth). Subsamples of the accessions were evaluated for their response to imazapic rates, which indicated variable levels of resistance across Palmer amaranth accessions. The rate of imazapic that provided 50% reduction in Palmer amaranth plant biomass (I50) for the known susceptible biotype was 0.9 g/ha of imazapic. Of the 10 accessions evaluated, 8 of them had I50 values that ranged from 3 to 297 g/ha of imazapic. The other two accessions could not be fit to the log-logistic dose–response curve and had undeterminable I50 values because of high levels of ALS resistance (> 1,400 g/ha of imazapic). Herbicide cross-resistance experiments indicated that 30 accessions were resistant to the ALS herbicides imazapic, chlorimuron, pyrithiobac, and diclosulam at the recommended field-use rates. However, each of these 30 accessions was susceptible to glyphosate. These data demonstrate that ALS-resistant Palmer amaranth occurs throughout the peanut-growing region of Georgia. Growers in Georgia will need to alter their weed-control programs in peanut to include herbicides with multiple modes of action that do not rely on ALS herbicides for effective Palmer amaranth control.
Field experiments were conducted from 2004 through 2006 to evaluate cressleaf groundsel control following fall or early-spring preplant herbicide applications. Glyphosate, glyphosate imazethapyr, glyphosate 2,4-D ester, paraquat, paraquat simazine, chlorimuron tribenuron, and pendimethalin glyphosate 2,4-D ester applied in the fall controlled at least 93% of the cressleaf groundsel. Glyphosate, glyphosate imazethapyr, glyphosate 2,4-D ester, chlorimuron tribenuron, and pendimethalin glyphosate 2,4-D ester applied in the spring provided at least 94% control of the cressleaf groundsel. Chlorimuron tribenuron provided at least 98% control, regardless of application timing. These results indicate that herbicides applied in the fall or early spring can control cressleaf groundsel. However, certain herbicides provide greater control when applied in the fall compared with spring.
Two field studies were conducted in 2007 and 2008 to evaluate at-planting burndown and POST herbicide applications targeting volunteer glyphosate-resistant (GR) soybean in rice. In the burndown study, paraquat, glufosinate, and a thifensulfuron plus tribenuron mixture were applied immediately after rice seeding. Paraquat controlled volunteer GR soybean at least 95% at all evaluations both years. Control with glufosinate was greater in 2007 than 2008 due to rainfall that occurred following application the second year. The thifensulfuron plus tribenuron mixture provided similar control in both years, but control never exceeded 71%. Additionally, a study was conducted evaluating POST-applied rice herbicides including propanil (4,480 and 2,240 g ai/ha), triclopyr (420 and 210 g ai/ha), bispyribac-sodium (38 and 19 g ai/ha), penoxsulam (40 and 20 g ai/ha), and halosulfuron (70 and 35 g ai/ha). Control across all POST herbicides and application rates was equivalent (> 95%) 28 and 56 d after application except for propanil, which controlled volunteer GR soybean less than other treatments. Volunteer GR soybean can be effectively managed in a rice production system with at-planting burndown or POST herbicide applications in rice.
Research was conducted in North Carolina to determine peanut response to flumioxazin as influenced by rate and timing of application and cultivar. Delaying application of flumioxazin from 1 d after planting until peanut emergence increased injury regardless of rate. The Virginia market-type cultivar ‘NC-V 11’ was injured more by flumioxazin than the cultivars ‘Gregory’ or ‘Perry’. However, pod yield was not affected by flumioxazin even though significant injury was observed early in the season regardless of flumioxazin rate, application timing, or cultivar. Diclosulam was more effective than flumioxazin in controlling eclipta when these herbicides were applied PRE with metolachlor or following pendimethalin PPI. However, control by flumioxazin prevented yield loss when compared with metolachlor alone.
Experiments were conducted during 2000 and 2001 at a total of 13 locations throughout Alabama, Georgia, Florida, North Carolina, and Texas to evaluate efficacy of herbicides at or below the manufacturer's suggested use rate. Herbicide applications included diclosulam and flumioxazin applied PRE alone or followed by imazapic applied early postemergence (EPOST). All possible combinations of diclosulam at 0, 13.5, or 27 g ai/ha and flumioxazin at 0, 53, or 105 g ai/ha applied PRE were included. Imazapic was applied at 35 g ai/ha. Ivyleaf morningglory was controlled more than 87% when imazapic was applied EPOST regardless of PRE herbicide. Pitted morningglory control > 67% was observed with applications of diclosulam (27 g/ha) followed by imazapic, diclosulam (13.5 g/ha) plus flumioxazin (53 g/ha), diclosulam (13.5 g/ha) plus flumioxazin (105 g/ha), and diclosulam (27 g/ha) plus flumioxazin (105 g/ha). Sicklepod was controlled more than 74% with flumioxazin (53 g/ha) followed by imazapic and diclosulam (27 g/ha) plus flumioxazin (105 g/ha) followed by imazapic. Florida beggarweed was controlled more than 84% by all PRE herbicide combinations except flumioxazin (53 g/ha) alone or diclosulam (27 g/ha) alone or with imazapic. Yellow nutsedge was controlled at least 90% with diclosulam at either rate followed by imazapic and by diclosulam plus flumioxazin followed by imazapic regardless of rate. Pod yield was generally higher when herbicides were applied regardless of herbicide combination or rate. Peanut yield was maximized with the lowest rates of flumioxazin or diclosulam PRE followed by imazapic EPOST.
In the spring of 2007, a widespread freeze occurred that led to the replanting of about 81,000 hectares of corn in Tennessee. Limited research was available on effective herbicide options to control failed stands of glyphosate-tolerant corn where replanting to corn was desired. Therefore, in 2007 on three failed freeze-damaged corn stands (27,000 plants/ha) and in 2008 on two non–freeze-damaged corn stands (81,000 plants/ha), studies were initiated to determine how to control the failed stand while not harming subsequent replant corn. The results from this research clearly show that producers have several effective options to manage undesirable glyphosate-tolerant corn before replanting to corn. Clethodim at 0.14 kg/ha, paraquat at 0.84 kg/ha, or paraquat at 0.70 kg/ha plus a photosystem II (PSII) inhibitor provided very good control of the original corn stand without affecting the yield of the replanted corn. Moreover, the addition of a PSII inhibitor could provide residual weed control in the replanted corn. Paraquat should be applied at rates of 0.70 kg/ha or greater to obtain consistent control of an undesirable corn stand.
Nomenclature: Glyphosate; corn, Zea mays L. ‘DeKalb 69-71’.
Dogfennel is one of the most problematic weeds in Florida pasturelands and its control can become inconsistent as the plant matures. A premix of triclopyr fluroxypyr has been recently introduced for weed control in pastures and rangeland; however, little published information exists concerning the control of dogfennel in pastures with this herbicide combination. Therefore, experiments were initiated to determine the efficacy of triclopyr fluroxypyr compared with commonly used pasture herbicides on dogfennel at three heights. All herbicides utilized in this study are commonly used for dogfennel control. Dogfennel control was affected by both herbicide treatment and dogfennel height. In general, 0.80 0.28 kg ai/ha of 2,4-D amine dicamba resulted in inconsistent control, especially as dogfennel plants increased in size. Increasing the rate of 2,4-D amine dicamba to 1.21 0.42 kg/ha increased the consistency. Triclopyr fluroxypyr provided similar levels of control as that of 1.21 0.42 kg/ha 2,4-D amine dicamba. In all locations, control of 154-cm dogfennel was signficanatly lower than that of 38-cm dogfennel. These data indicate that triclopyr fluroxypyr is an effective option for dogfennel control, but dogfennel height at the time of application is an important factor for optimizing control.
Nomenclature: 2,4-D Amine; dicamba; fluroxypyr; triclopyr; Dogfennel, Eupatorium capillifolium L.
Sourgrass is a stoloniferous perennial grassy weed found on golf courses throughout Hawaii. No herbicides are currently labeled for selective control of sourgrass in seashore paspalum turf, a species used regularly on golf courses throughout the tropics. A single granular application of fine salt (99% sodium chloride, 1% sodium silicoaluminate, 83% of particles 0.5 to 0.25 mm in diameter) at a rate of 1,464 kg/ha provided 84 and 23% control of sourgrass 6 wk after initial treatment (WAIT) in 2007 and 2008, respectively. Sequential granular applications of fine salt at 488 kg/ha provided 92 and 96% control of sourgrass in 2007 and 2008, respectively, at 6 WAIT. Granular applications of a coarse salt (100% sodium chloride, 75% of particles 2.0 to 1.0 mm in diameter) provided a lower level of control than fine salt at both the 1,464- and 488-kg/ha rates on three out of four rating dates in 2008; a similar trend was observed in 2007, but no significant differences were observed between these treatments. All salt treatments led to higher soil sodium adsorption ratios (SAR) and electrical conductivity (ECe) than the untreated check; however, levels reported in this study were significantly lower than the threshold SAR and ECe levels that have been associated with reduced seashore paspalum growth. Sequential applications of MSMA at 1.12 kg/ha and MSMA plus metribuzin at 1.12 kg/ha and 0.28 kg/ha, respectively, provided greater than 90% control in 2008, but less than 40% control in 2007. Greater seashore paspalum injury was observed following applications of MSMA and MSMA plus metribuzin than following salt applications. Additional research is needed to evaluate strategies for controlling sourgrass in seashore paspalum turf that do not induce phytotoxic injury after application.
A field trial was conducted for 3 yr (2005 through 2007) near Scottsbluff, NE, to examine weed control, crop safety, forage production, and economics of glyphosate-tolerant and conventional alfalfa establishment systems. Glyphosate applied to alfalfa at the unifoliate growth stage provided 67% weed control and was similar to imazamox applied at the two-trifoliate leaf stage. Delaying glyphosate application until alfalfa had reached the two-trifoliate growth stage improved weed control to 83%, and weed control was similar to imazamox plus 2,4-DB and imazethapyr plus 2,4-DB. Imazamox and imazethapyr caused minor crop injury, and the addition of bromoxynil or 2,4-DB to both herbicides further decreased crop safety. Weeds were most competitive with the first forage harvest and reduced relative feed value, crude protein, and value (dollars per t) of forage compared to forage that had been treated with herbicides. The total forage yield for the season consisted of three forage harvests and was greatest when no herbicides were applied. The total forage yield of plots treated with glyphosate at the two-trifoliate growth stage was greater than that of plots treated with imazamox or imazethapyr in combination with bromoxynil. When glyphosate was applied at the two-trifoliate growth stage, seasonal forage yield was similar to forage treated with imazamox, imazethapyr, or both herbicides in combination with 2,4-DB. When herbicide was applied to alfalfa at the two-trifoliate growth stage, the net return from using glyphosate with a glyphosate-tolerant alfalfa variety or utilizing imazamox with a conventional alfalfa variety were similar at $742 and $743/ha, respectively.
Field trials were conducted to determine if tillage and soil-applied herbicides had an effect on weed control and sugarbeet growth with a micro-rate herbicide program. Sugarbeet emergence was earlier in the moldboard plowed system compared with the chisel plowed system at three of four sites. Conditions were dry and sugarbeets emerged 5 d later in the moldboard plowed system compared with the chisel plowed system at the fourth site. Even though the rate of sugarbeet emergence differed between tillage systems at all four sites, final sugarbeet populations did not differ at two of the four sites. Sugarbeet injury from PRE treatments of S-metolachlor, ethofumesate, and ethofumesate plus pyrazon, followed by four POST micro-rate applications, ranged from 11 to 27% and 1 to 18% in the chisel and moldboard plowed systems, respectively, 6 wk after planting (WAP). Under wet conditions, sugarbeet stand was reduced and injury was greatest from PRE applications of S-metolachlor. Common lambsquarters, pigweed (redroot pigweed and Powell amaranth), and giant foxtail control in mid-August was consistently higher when a PRE herbicide was applied prior to micro-rate herbicide treatments. Even though there were differences between PRE and no-PRE treatments with respect to sugarbeet injury and weed control, recoverable white sucrose yield did not differ between herbicide treatments. However, recoverable white sucrose yield was greater in the moldboard plowed treatments compared with the chisel plowed treatments at three out of the four sites.
Nomenclature: Ethofumesate; S-metolachlor; pyrazon; common lambsquarters, Chenopodium album L. CHEAL; giant foxtail, Setaria faberi Herrm. SETFA; Powell amaranth, Amaranthus powellii S. Wats. AMAPO; redroot pigweed, Amaranthus retroflexus L. AMARE; sugarbeet, Beta vulgaris L.
Herbicide applications prior to turf renovation often fail to provide complete control of perennial warm-season turfgrass species like seashore paspalum. Surface applications of dazomet at 506 kg/ha provided > 90% POST control of ‘SeaDwarf’ seashore paspalum turf in 2008. Although applications of glyphosate at 5.6 kg/ha or fluazifop-P-butyl at 0.42 kg/ha induced significant injury, these treatments provided < 40% POST control of SeaDwarf seashore paspalum turf 10 wk after initial treatment (WAIT) in 2008. A similar response was noted following applications of glyphosate plus fluazifop-P-butyl at rates of 5.6 kg/ha and 0.42 kg/ha, respectively. POST control following applications of glyphosate at 5.6 kg/ha plus fluazifop-P-butyl at 0.42 kg/ha, prior to applying dazomet at 506 kg/ha, was not different from that which was observed following applications of dazomet alone at 506 kg/ha. These data suggest that granular applications of dazomet alone, at 506 kg/ha, can be used to provide effective control of SeaDwarf seashore paspalum prior to renovation.
During the summer fallow period of the sugarcane production cycle, glyphosate in conjunction with frequent tillage is used to destroy sugarcane regrowth and reduce perennial weed infestations. For tillage to be reduced or eliminated in fallowed fields, weed control must be maintained and sugarcane must be completely destroyed so as not to interfere with the subsequent planting operation. Field studies were conducted to evaluate glyphosate rates and formulations for control of sugarcane, bermudagrass, and johnsongrass. Glyphosate (isopropylamine salt) applied in April at 1.68, 2.24, and 2.80 kg ai/ha controlled 15-cm sugarcane at least 95% 42 d after treatment (DAT). Control of 25- and 40-cm sugarcane was maximized at 1.68 kg/ha (91 and 86% control, respectively). In another study, 25-cm sugarcane was controlled equally with isopropyl amine and potassium salt glyphosate formulations. Bermudagrass control 40 d after glyphosate was applied at 1.12 kg/ha was 86% and increased to 98% when the same rate was applied sequentially. In fallowed sugarcane fields, conventional-tillage, reduced-tillage, and no-tillage programs were implemented from mid-April through mid-August to evaluate weed control and economics. When a glyphosate application was substituted for a tillage operation, bermudagrass and johnsongrass control was increased compared with the conventional tillage alone program, but differences in sugarcane and sugar yield among the various programs the following year were not observed. Based on 2006 costs, elimination of a single tillage operation reduced cost $18.49/ha and addition of glyphosate (2.8 kg/ha plus application cost) increased cost $43.47/ha. Total cost for the conventional tillage–alone fallow program was $110.94/ha; where herbicide was used in the reduced-tillage and no-tillage programs, total cost was $19.47 to $77.38/ha more.
Weeds are a major constraint in tomato production, especially in the absence of methyl bromide. Field trials were conducted in 2006 and 2007 to evaluate the integrated use of a mustard ‘Caliente’ (a blend of brown and white mustard) cover crop with one-half and full rate PRE/POST herbicides for weed control and crop response in polyethylene-mulched tomato. Caliente was flail mowed and incorporated into the soil prior to forming beds. PRE herbicides were applied under polyethylene mulch, and POST herbicides were sprayed over the top of tomato. Full rates for S-metolachlor, halosulfuron, and trifloxysulfuron were 1,600, 27, and 7.9 g ai/ha, respectively. Caliente had no effect on weed control or tomato injury and yield. Except for large crabgrass control and tomato injury and yield, only the main effect of herbicide selection and application rate affected these parameters. Tomato injury was minimal (< 6%) from PRE- and POST-applied herbicides. S-metolachlor applied PRE provided 66% purple nutsedge, 67% yellow nutsedge, and 77% Palmer amaranth control at 4 wk after transplanting (WATP). S-metolachlor–treated plots at the full rate produced the highest marketable fruit yield among herbicide treatments, with jumbo fruit yield equivalent to the hand-weeded treatment. Trifloxysulfuron was the best POST-applied herbicide based on marketable yield and weed control. POST-applied trifloxysulfuron provided 41% purple nutsedge, 58% yellow nutsedge, and 55% Palmer amaranth control at 8 to 9 WATP. Halosulfuron applied PRE controlled purple and yellow nutsedge 70 and 78%, respectively, at 4 WATP, and POST-applied halosulfuron controlled purple nutsedge 74% and yellow nutsedge 78% at 8 to 9 WATP. Halosulfuron applied either PRE or POST failed to control Palmer amaranth and large crabgrass. Greater weed control and marketable tomato yield were achieved with full rates of herbicides. This research demonstrates no additional advantage of Caliente mustard when used with herbicides in tomato. None of the PRE or POST herbicides applied alone were sufficient to maintain season-long, broad-spectrum weed control and optimum marketable yield in tomato. Therefore, integration of PRE and POST herbicides at full rates is suggested.
Nomenclature: Halosulfuron; S-metolachlor; trifloxysulfuron; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; purple nutsedge, Cyperus rotundus L. CYPRO; yellow nutsedge, Cyperus esculentus L. CYPES; brown mustard, Brassica juncea L.; tomato, Lycopersicon esculentum Mill. ‘Amelia’; white mustard, Sinapis alba L.
Potato producers rely heavily on herbicides for the majority of weed control. However, recent occurrences of herbicide-resistant weed populations and the lack of new herbicide registrations have stimulated interest in alternative strategies. The choice of potato cultivars that can suppress or tolerate weed competition could be a component of an integrated weed management system to reduce reliance on herbicides. The competitive ability of 10 potato cultivars—‘Atlantic’, ‘Bannock Russet’, ‘Dark Red Norland’, ‘Goldrush’, ‘Rodeo’, ‘Russet Burbank’, ‘Russet Norkotah’, ‘Snowden’, ‘Superior’, and ‘Villetta Rose’—was evaluated in 2006 and 2007 in Hancock, WI. Weed competition treatments included (1) weedy throughout the season, (2) weed-free from emergence to 4 wk after emergence (WAE) by hand-weeding, and (3) weed-free by hand-weeding for the entire season. Potato cultivars did not differ in ability to reduce weed biomass. Early-season time of potato emergence and canopy closure, as well as weed competition treatments, were strongly related to potato tuber yield. In general, Bannock Russet yield relative to weed-free controls of the same cultivar was less than that of most other cultivars. Overall, Atlantic, Russet Burbank, Snowden, and Superior yields (relative to weed-free control yields) usually were greater than the yields of other cultivars under weedy conditions. Although the ability to suppress weeds was similar among cultivars, differences in yield among cultivars grown in the presence of weeds suggest differential tolerances of weed competition.
Weed management can be difficult and expensive in organic agricultural systems. Because of the potentially high cost of the natural product herbicides vinegar and clove oil, their efficacy with regard to weed species growth stages needs to be determined. A further objective was to identify anatomical and morphological features of redroot pigweed and velvetleaf that influence the effectiveness of vinegar and clove oil. Research was conducted on greenhouse-grown cotyledon, two-leaf, and four-leaf redroot pigweed and velvetleaf. Dose–response treatments for vinegar included 150-, 200-, 250-, and 300-grain vinegar at 318 L/ha and at 636 L/ha. Clove oil treatments included 1.7, 3.4, 5.1, and 6.8% (v/v) dilutions of a clove oil product in water (318 L/ha), and a 1.7% (v/v) dilution in 200-grain vinegar (318 L/ha). An untreated control was included. Separate plantings of velvetleaf and pigweed were treated with vinegar or clove oil and were used to study anatomical and morphological differences between the two species. Redroot pigweed was easier to control with both products than velvetleaf. Whereas 200-grain vinegar applied at 636 L/ha provided 100% control (6 d after treatment [DAT]) and mortality (9 DAT) of two-leaf redroot pigweed, this same treatment on two-leaf velvetleaf provided only 73% control and 18% mortality. The obtuse leaf blade angle in velvetleaf moved product away from the shoot tip, whereas in pigweed, the acute leaf blade angle, deep central leaf vein, and groove on the upper side of the leaf petiole facilitated product movement toward the stem axis and shoot tip. For both species, and at all application timings, 150-grain vinegar at 636 L/ha provided control equal to that of 300-grain vinegar at 318 L/ha. As growth stage advanced, control and biomass reduction decreased and survival increased. Application timing will be critical to maximizing weed control with vinegar and clove oil.
Researchers interested in describing or understanding agroecological systems have many reasons to consider on-farm research. Yet, despite the inherent realism and pedagogical value of on-farm studies, recruiting cooperators can be difficult and this difficulty can result in so-called “convenience samples” containing a potentially large and unknown bias. There is often no formal justification for claiming that on-farm research results can be extrapolated to farms beyond those participating in the study. In some sufficiently well-understood research areas, models may be able to correct for potential bias; however, no theoretical argument is as persuasive as a direct comparison between a randomized and a convenience sample. In a 30-cooperator on-farm study investigating weed community dynamics across the state of Wisconsin, we distributed a written survey probing farmer weed management behaviors and attitudes. The survey contained 59 questions that overlapped a large, randomized survey of farmer corn pest management behavior. We compared 187 respondents from the larger survey with the 18 respondents from our on-farm study. For dichotomous response questions, we found no difference in response rate for 80% of the questions (α = 0.2, β > 0.5). Differences between the two groups were logically connected to the selection criteria used to recruit cooperators in the on-farm study. Similarly, comparisons of nondichotomous response questions did not differ for 80% of the questions (α = 0.05, β > 0.9). Exploratory multivariate analyses failed to reveal differences that might have been hidden from the marginal analyses. We argue that our findings support the notion that the convenience samples often associated with on-farm research may be representative of the more general class of farms, despite lack of bias protection provided by truly randomized designs.
William G. Johnson, Micheal D. K. Owen, Greg R. Kruger, Bryan G. Young, David R. Shaw, Robert G. Wilson, John W. Wilcut, David L. Jordan, Stephen C. Weller
A survey of farmers from six U.S. states (Indiana, Illinois, Iowa, Nebraska, Mississippi, and North Carolina) was conducted to assess the farmers' views on glyphosate-resistant (GR) weeds and tactics used to prevent or manage GR weed populations in genetically engineered (GE) GR crops. Only 30% of farmers thought GR weeds were a serious issue. Few farmers thought field tillage and/or using a non-GR crop in rotation with GR crops would be an effective strategy. Most farmers did not recognize the role that the recurrent use of an herbicide plays in evolution of resistance. A substantial number of farmers underestimated the potential for GR weed populations to evolve in an agroecosystem dominated by glyphosate as the weed control tactic. These results indicate there are major challenges that the agriculture and weed science communities must face to implement long-term sustainable GE GR-based cropping systems within the agroecosystem.
Greenhouse dose–response studies were conducted to determine the effectiveness of PRE and POST applications of saflufenacil on blue mustard, flixweed, Palmer amaranth, redroot pigweed, and tumble pigweed. Weed species did not differ in their responses to saflufenacil applied PRE. Averaged across species, PRE application of saflufenacil at 6 to 30 g/ha reduced weed biomass 82 to 98%, but biomass did not differ among rates of 12 g/ha or higher. POST application of saflufenacil reduced weed biomass by 92%, averaged across species and rates. On the basis of regression analysis, the 90% plant biomass reduction for saflufenacil applied PRE and POST was 9 and 6 g/ha, respectively. Saflufenacil applied PRE reduced population density by 77 to 98%, averaged across weed species; a rate of 9 g/ha reduced population density 90% (DR90) on the basis of regression analysis. Averaged across species, POST application of 6 to 30 g/ha reduced population density by 63 to 93%, but regression analysis indicated that the DR90 value was greater than 30 g/ha. Averaged across rates, saflufenacil reduced the population density of flixweed, Palmer amaranth, redroot pigweed, tumble pigweed, and blue mustard by 49, 64, 67, 73, and 78%, respectively.
Novel forms of selective weed control are needed by many types of growers, but especially by organic growers who are restricted from using synthetic herbicides. Abrasive grit made from corn cobs was expelled from a sand blaster at 517 kPa pressure and aimed at plants of common lambsquarters and corn positioned 300 mm distant. Most small weed plants were killed by one split-second blast of grit, but corn plants suffered little damage by the same treatment. Air-propelled grit made from agricultural residues possibly could be used for selective nonchemical weed control without the need for soil tillage.
Nomenclature: Common lambsquarters, Chenopodium album L.; corn, Zea mays L.
Soft rush is a perennial, tussock-forming plant that often infests low-lying grazing areas in Florida. Experiments were conducted to determine the most effective herbicides for control of soft rush. Herbicide treatments included triclopyr fluroxypyr at 0.43 0.15 and 0.86 0.30 kg/ha, 2,4-D amine at 1.12 and 2.24 kg/ha, 2,4-D amine carfentrazone at 1.12 0.02 and 2.24 0.02 kg/ha, aminopyralid at 0.12 kg/ha, and 2,4-D amine dicamba at 1.61 0.56 kg/ha and were applied to soft rush with and without mowing to a 15-cm stubble height. Aminopyralid and triclopyr fluroxypyr did not control soft rush with or without mowing 1 and 12 mo after treatment (MAT). When mowing occurred prior to application, treatments containing 2,4-D provided at least 81% control of soft rush 1 MAT. In contrast, control was no greater than 59% when treatments were applied without mowing soft rush. Mowing had no impact on soft-rush control with herbicides 12 MAT. Applications of 2.24 kg/ha 2,4-D provided at least 90% control 12 MAT, but this was not significantly different from the premix of 2,4-D dicamba or 2.24 0.02 kg/ha 2,4-D carfentrazone treatments. Therefore, effective control of soft rush can be obtained with the use of 2,4-D amine or products that contain 2,4-D amine.
The interactive effects of nitrogen rate (0, 28, 56, and 112 kg/ha), vine density (0, 1.8, 3.6, and 5.4 t/ha of the cultivar ‘Stevens’), and weed management (preemergence herbicide, postemergence control, inoculation with weed seeds, and untreated) were determined on the recolonization of open spaces caused by localized biomass removal in a newly planted commercial cranberry bed. To assess the effect of the 64 treatment combinations on initial colonization, all cranberry and weed biomass was removed from a randomly selected 930-cm2 area in each plot in Year 1. To quantify recolonization of the disturbed area, the same quadrat was resampled and all plant biomass was collected in Year 2. Cranberry biomass production in the disturbed area increased in a quadratic fashion with increasing N rates for all vine densities except zero. Cranberry biomass in the year after disturbance was positively correlated with cranberry biomass present in the previous year. Weed stem biomass in the year after disturbance was positively correlated with weed stem biomass from Year 1 and negatively correlated with percentage cranberry biomass from Year 1 and Year 2. Less than one-third of the treatment combinations recovered enough to produce at least 200 g/m2 1 yr postdisturbance (a reasonable expectation of biomass production). Growers who have low weed pressure and extensive cranberry cover on their farms can expect that disturbed areas will be recolonized by cranberry vines when they utilize adequate, but not excessive, nitrogen regimes.
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