Early Preplant Research Articles

Cotton Weed Management Systems in Conventional and Conservation Tillage

Weed management trials were established near Lubbock, TX in 2017 and 2018 to compare systems in both conventional and conservation tillage. Four herbicide systems were included for both the conventional and conservation tillage. Conventional tillage treatments included trifluralin preplant incorporated (PPI) followed by (fb) no preemergence (PRE) fb dicamba + glyphosate + acetochlor early postemergence (EPOST) fb dicamba + glyphosate midpostemergence (MPOST), trifluralin PPI fb prometryn PRE fb dicamba + glyphosate EPOST fb dicamba + glyphosate + acetochlor MPOST, no PPI fb prometryn PRE fb dicamba + glyphosate EPOST fb dicamba + glyphosate + acetochlor MPOST, trifluralin PPI fb prometryn PRE fb glyphosate EPOST fb glyphosate + acetochlor MPOST. Conservation tillage treatments included dicamba + glyphosate early preplant (EPP) fb paraquat + prometryn PRE fb dicamba + glyphosate EPOST fb dicamba + glyphosate MPOST, dicamba + glyphosate + flumioxazin EPP fb paraquat + prometryn PRE fb dicamba + glyphosate EPOST fb dicamba + glyphosate MPOST, glyphosate EPP fb dicamba + prometryn fb dicamba + glyphosate EPOST fb dicamba + glyphosate MPOST, no EPP fb dicamba + prometryn fb dicamba + glyphosate EPOST fb dicamba + glyphosate MPOST. Visual weed control for Russian thistle, kochia, and Palmer amaranth was recorded at cotton planting and 14 days after planting. Palmer amaranth control was recorded at 14 and 28 days after the EPOST and MPOST treatments. Effective season-long control of Palmer amaranth (>98%) was achieved using various dicamba-based herbicide systems in both conventional and conservation tillage. Glyphosate-based herbicide systems controlled Palmer amaranth <53% in 2017 and <84% in 2018 due to the number of glyphosate-resistant weeds present. All dicamba treatments controlled Palmer amaranth >83% in 2017 and >98% in 2018.

Winter Annual Weed Response to Nitrogen Sources and Application Timings prior to a Burndown Corn Herbicide

Autumn and early preplant N applications, sources, and placement may affect winter annual weed growth. Field research evaluated (1) the effect of different nitrogen sources in autumn and early preplant on total winter annual weed growth (2006–2010), and (2) strip-till and broadcast no-till N applied in autumn and early preplant on henbit (Lamium amplexicauleL.) growth (2008–2010) prior to a burndown herbicide application. Total winter annual weed biomass was greater than the nontreated control when applying certain N sources in autumn or early preplant for no-till corn. Anhydrous ammonia had the lowest average weed density (95 weeds m−2), though results were inconsistent over the years. Winter annual weed biomass was lowest (43 g m−2) when applying 32% urea ammonium nitrate in autumn and was similar to applying anhydrous ammonia in autumn or early preplant and the nontreated control. Henbit biomass was 28% greater when applying N in the autumn compared to an early preplant application timing. Nitrogen placement along with associated tillage with strip-till placement was important in reducing henbit biomass. Nitrogen source selection, application timing, and placement affected the impact of N on winter annual weed growth and should be considered when recommending a burndown herbicide application timing.

Tolerance of foxtail, proso and pearl millets to saflufenacil

Herbicide options for weed control in millets are very limited and hence there is a need for exploring potential herbicides. Field trials were conducted at three locations in Kansas and Nebraska in 2009 to evaluate foxtail millet, proso millet, and pearl millet tolerance to saflufenacil applied preemergence (PRE) at 36, 50, and 100 g ai ha−1. Foxtail millet was the most sensitive of the three millets to saflufenacil. Among experimental sites, saflufenacil at 36 g ha−1 injured foxtail millet 59–99% and reduced plant stands 41–95%; nearly all plants died at 100 g ha−1. Despite early season foliar injury and up to 36% stand reduction, fodder or grain yields of proso and pearl millets were not reduced by any rate of saflufenacil compared to untreated controls. Additional trials were conducted at four locations in Kansas, Nebraska and South Dakota in 2010 and 2011 to refine saflufenacil use rate (36 and 50 g ha−1) and application timing [14 days early preplant (EPP); 7 days preplant (PP); and PRE] for use in proso and pearl millets. Saflufenacil applied EPP or PP, regardless of rate, caused up to 21 and 6% foliar injury and up to 21 and 9% plant stand reduction in proso and pearl millets, respectively. However, yields were not reduced by EPP or PP treatments in either millet crop. PRE applications of saflufenacil caused the highest crop injury and stand reduction in both millets. Saflufenacil PRE at 36 g ha−1 caused up to 57 and 40% foliar injury and up to 42 and 24% stand reductions in proso and pearl millets, respectively; however, yields were not affected. Comparatively, saflufenacil PRE at 50 g ha−1 reduced yields of proso and pearl millets 36 and 52%, respectively, on sandy loam soils with high pH (8.3) and low organic matter content (1.1%). Overall, results indicated that foxtail millet lacks tolerance to saflufenacil, but up to 50 g ha−1 of saflufenacil may be safely applied as near as 7 days before planting proso or pearl millets. If situation demands, saflufenacil at 36 g ha−1 can also be applied PRE to either crop with risk of some crop injury.

Proso Millet Tolerance to Saflufenacil

Proso millet is an important short-season summer cereal in western Nebraska, southeast Wyoming, and eastern Colorado. The objective of this study was to evaluate proso millet tolerance to saflufenacil applied early preplant (EPP) or PRE. Field studies were conducted in Lingle, WY and Sidney, NE in 2008 and 2009. A dose–response study was conducted in the greenhouse at the University of Wyoming in Laramie, WY to determine proso millet cultivar response to saflufenacil applied at six rates from 0 to 400 g ai ha−1. In the field, saflufenacil was applied EPP and PRE at 50 and 100 g ha−1. Proso millet stands were reduced by an average of 33 and 23% by PRE and EPP treatments compared with the nontreated check; however, proso seed yields were not affected by saflufenacil timing or rate. In the greenhouse, ‘Panhandle’ and ‘Dawn’ exhibited less tolerance to saflufenacil than ‘Sunrise’, the cultivar used in the field studies.

Soybean Tolerance to Early Preplant Applications of 2,4-D Ester, 2,4-D Amine, and Dicamba

Preplant applications of two 2,4-D formulations and dicamba were evaluated for injury to no-till soybean. Herbicides applied 28 or 21 d before planting (DBP) at 0.56 kg ae/ha for the 2,4-D formulations and 0.28 kg ae/ha for dicamba did not injure soybean. At 14 DBP soybean injury was lower (< 6%) with applications of 2,4-D than with dicamba (13% to 17%). Injury increased when herbicides were applied at 7 DBP with soybean injury from both 2,4-D (< 11%) and dicamba (< 38%). When the herbicides were applied at planting soybean injury was < 18% with the 2,4-D formulations and < 73% with dicamba. Soybean yields were unaffected by the injury from herbicides applied 21, 14, and 7 DBP. However, soybean yield was decreased to 870 kg/ha in 2005 when dicamba was applied at planting compared to the nontreated check (1,950 kg/ha)

Timing and Dose of Metolachlor Affect Rigid Ryegrass (Lolium rigidum) Control in Wheat

The efficacy of metolachlor on rigid ryegrass was determined under a no-till seeding system in an experiment conducted in 2004 and 2005 in South Australia. Metolachlor at a rate of 0.48 and 0.96 kg ai/ha was applied at 40 or 46 d (very early preplant, VEPP) and 20 or 23 d before crop sowing (early preplant, EPP), and at sowing (preplant, PP) in 2004 and 2005; the herbicide was incorporated by sowing. The control of rigid ryegrass was greater than 80% when metolachlor was applied PP; however, that application resulted in phytotoxic effects on emergence and yield of wheat; metolachlor was more phytotoxic when applied at 0.96 kg/ha than at 0.48 kg/ha. Metolachlor applied EPP provided 71 to 83% rigid ryegrass control, whereas VEPP application provided only 33 to 49% control. Reduction in wheat grain yield was not observed at these application times. This study indicates that metolachlor at 0.48 kg/ha could be safely applied around 20 d before crop sowing to selectively control rigid ryegrass in wheat.

Fall and Early Preplant Application Timing Effects on Persistence and Efficacy of Acetamide Herbicides1

The persistence and efficacy of acetamide herbicides at application timings from fall to preemergence (PRE) were studied in 1998 and 1999 on mollisols (1.1 to 2.8% organic carbon). Metolachlor, s-metolachlor, acetochlor (as an emulsifiable concentrate [EC] formulation and two encapsulated formulations, capsule suspension [CS] and microencapsulated [ME]), and the combination of flufenacet metribuzin were evaluated at five application times including late fall, 60 and 30 d early preplant (EPP), preplant incorporated, and PRE. Soil bioassays 180 d after application indicated flufenacet metribuzin, metolachlor, s-metolachlor, and the acetochlor CS had 62 to 74% giant foxtail control, whereas acetochlor EC and ME had 43 to 46% control. Applications at 60 EPP of metolachlor, s-metolachlor, and acetochlor CS provided 70 to 75% giant foxtail control in greenhouse bioassays, whereas flufenacet metribuzin, acetochlor ME, and acetochlor EC provided 38 to 57% control. At the 30 EPP timing, metolachlor and acetochlor CS had 80 to 82% control, whereas acetochlor EC provided 46% control, and acetochlor ME, flufenacet metribuzin, and s-metolachlor had 65 to 74% control. Quantitative soil analysis (0 to 6 cm) 10 d after planting (DAP) indicated metolachlor, s-metolachlor, and acetochlor CS concentrations ranged from 12 to 16% and 32 to 47% of applied herbicide for the fall and PRE application timings, respectively, whereas acetochlor (ME and EC) were from 1 to 3% and 16 to 21% of applied for the fall and PRE application timings, respectively. Bioassay reduction was correlated (R2 = 0.68) with soil-herbicide concentrations at 10 DAP.Nomenclature: Acetochlor; flufenacet; metolachlor; metribuzin; s-metolachlor; giant foxtail, Setaria faberi Herrm. #3 SETFA.Additional index words: Soil dissipation.Abbreviations: CS, capsule suspension; DAP, days after planting; EC, emulsifiable concentrate; EPP, early preplant; ME, microencapsulated; OC, organic carbon; PPI, preplant incorporated; PRE, preemergence; SETFA, giant foxtail.

Weed Control with Fall and Early-Preplant Herbicide Applications in No-Till Soybean

Field studies were conducted during 1999 and 2000 to compare weed control after fall and early-preplant (EPP) herbicide applications in no-till soybean. Three residual treatments (chlorimuron plus metribuzin, chlorimuron plus sulfentrazone, and metribuzin) were applied at two rates and timings (fall and 30 d EPP) either alone or in combination with glyphosate and 2,4-D. The addition of glyphosate and 2,4-D to fall-applied residual herbicides significantly increased control of common chickweed, annual bluegrass, cressleaf groundsel, and shepherd's-purse. The effect of application rate on weed control was species dependent. Fall-applied residual herbicides were comparable with EPP treatments with respect to winter annual weed control; however, at planting control of summer annual weed species with fall treatments was less consistent compared with EPP residual herbicides.

Weed Management and Economic Returns in No-Tillage Herbicide-Resistant Corn (Zea mays)1

Field studies were conducted to evaluate corn vigor reduction, weed control, corn yield, and economic returns in a no-till system with various herbicide strategies using full and reduced rates of acetochlor and atrazine with glyphosate, glufosinate, or imazethapyr + imazapyr in their respective type of herbicide-resistant, no-tillage corn. Crop vigor reduction due to herbicide injury was 10% or less with all treatments. A burndown plus a full label rate of a residual herbicide applied early preplant (EPP) generally provided less than 80% control of giant foxtail, common waterhemp, and common cocklebur but usually greater than 85% control of common ragweed and common lambsquarters. Two-pass strategies generally provided greater than 85% control of all species evaluated. Early postemergence, mid-postemergence (MPOST), and late postemergence strategies generally provided inconsistent and poor overall weed control. EPP–MPOST strategies generally provided lower weed control than strategies using acetochlor or ...

Weed Control in Field Corn (Zea mays) with RPA 201772 Combinations with Atrazine and S-Metolachlor1

The premix atrazine 1 S-metolachlor is commonly used to control a wide range of weeds in corn, but it is weak on velvetleaf and several other broadleaf species. RPA 201772, used at reduced rates in combination with atrazine 1 S-metolachlor, may improve the weed control spectrum. In field studies at Urbana and Dekalb in 1998 and 1999, RPA 201772 was combined with a premix of atrazine at 1,820 g ai/ha and S-metolachlor at 1,408 g ai/ha to compare RPA 201772 rate effects on corn injury, weed control, and yield. RPA 201772 was applied at 0, 26, 53, 78, 105, and 132 g ai/ ha early preplant (EPP), preplant incorporated (PPI), and preemergence (PRE). Compared with at- razine 1 S-metolachlor alone, RPA 201772 combinations did not improve giant foxtail control. However, RPA 201772 at 26 or 53 g/ha increased control of redroot pigweed, common lambsquarters, ivyleaf morningglory, common ragweed, giant ragweed, and velvetleaf in some environments. At Urbana in both years, RPA 201772 at 26 g/ha in combination with atrazine 1 S-metolachlor increased velvetleaf control 15% compared with the premix alone. RPA 201722 at 26 to 78 g/ha decreased velvetleaf densities with all application methods. Greater weed control and higher corn yield occurred in treatments applied PRE or PPI compared with EPP applications, except where conditions were dry after PRE applications. This research demonstrates the benefit of RPA 201772 at low rates for broadleaf weed control with less potential for crop injury compared with high RPA 201772 rates. Nomenclature: RPA 201772 (proposed common name, isoxaflutole), 5-cyclopropyl isoxazol-4-yl-2- mesyl-4-trifluoromethylphenyl ketone; common lambsquarters, Chenopodium albumL. # 3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; giant ragweed, Ambrosia trifidaL. # AMBTR; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; redroot pigweed, Amaranthus retroflexus L. # AMARE; velvetleaf, Abutilon theophrasti Medicus # ABUTH; corn, Zea mays L. Additional index words: HPPD inhibitor, isoxaflutole, reduced herbicide rates. Abbreviations: DAE, days after emergence; DAT, days after treatment; EPP, early preplant; PPI, preplant incorporated; PRE, preemergence.

Reduced rates of sulfentrazone plus chlorimuron and glyphosate in no-till, narrow-row, glyphosate-resistantGlycine max

Abstract Field studies were conducted in 1998 and 1999 to evaluate crop response, weed control, Glycine max yield, and economic returns of labeled (1×) and one-half labeled (½×) rates of early preplant (EPP) sulfentrazone plus chlorimuron and postemergence glyphosate, compared to glyphosate-alone systems in no-till, narrow-row, glyphosate-resistant G. max. Treatments containing a 1× or ½× rate of EPP sulfentrazone plus chlorimuron with glyphosate followed by (fb) a postemergence treatment of glyphosate provided 80 to 100% control of Xanthium strumarium, Ambrosia artemisiifolia, and Polygonum pensylvanicum and 82 to 100% control of Setaria faberi and Amaranthus rudis if glyphosate was applied mid-postemergence (MPOST) or late postemergence (LPOST). Glyphosate alone EPP fb glyphosate postemergence or sequential postemergence treatments of glyphosate provided 77 to 100% control of S. faberi, A. artemisiifolia, and P. pensylvanicum. Glycine max yield did not significantly differ between treatments that contai...

Use of preplant sulfentrazone in no-till, narrow-row, glyphosate-resistantGlycine max

Abstract Field studies were conducted in 1998 and 1999 to evaluate crop response, weed control, Glycine max yield, and economic returns with sulfentrazone alone and tank-mixed with glyphosate, cloransulam, or chlorimuron at two preplant application timings in no-till, narrow-row, glyphosate-resistant G. max. No significant crop injury was observed. Setaria faberi and Polygonum pensylvanicum control 5 wk after planting (WAP) was generally greater with sulfentrazone applied early preplant (EPP) than with sulfentrazone applied at planting (AP). When applied AP, glyphosate plus sulfentrazone provided greater S. faberi control than sulfentrazone alone. Control of Amaranthus rudis, Ambrosia artemisiifolia, and Ipomoea hederacea was greater in 1998 than in 1999 because of more timely early-season precipitation. Sulfentrazone-based programs provided 80 to 100% control of A. rudis in 1998, but control in 1999 ranged from 72 to 95% at Columbia and 46 to 83% at Novelty. Cloransulam alone, at either application timin...

Application Timing Determines Giant Foxtail (Setaria faberi) and Barnyardgrass (Echinochloa crus-galli) Control in No-Till Corn (Zea mays)1

Field studies were conducted from 1996 to 1998 to evaluate grass control in no-till corn (Zea mays) with herbicides applied early preplant (EPP), preemergence (PRE), and postemergence (POST) at the Belleville Research Center at Belleville, IL. Grass control was affected by application timing rather than herbicide. The herbicides applied PRE provided more consistent giant foxtail (Setaria faberi) and barnyardgrass (Echinochloa crus-galli) control (90 to 98%) than the same herbicides applied EPP (0 to 92%). There also was no difference in giant foxtail and barnyardgrass control between the emulsifiable concentrate (EC) formulation and microencapsulated (ME) formulation of acetochlor. Rimsulfuron plus thifensulfuron applied POST provided 90 to 97% control of giant foxtail and barnyardgrass. Metolachlor, EC-acetochlor, SAN 582H, and rimsulfuron plus thifensulfuron provided 85 to 92% control of yellow nutsedge (Cyperus esculentus) compared with 63 to 74% control for BAY FOE 5043 plus metribuzin and ME-acetochlor. Corn grain yield was greater with herbicides applied either PRE or POST than applied EPP. Grass control and grain yield were greater with herbicides applied either PRE or POST compared with EPP.Nomenclature: Acetochlor, 2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide; BAY FOE 5043 (proposed name, flufenacet), N-(4-fluorophenyl)-N-(1-methylethyl)-2-[[5-(trifluoromethyl)-1,3,4-thiadiazol-2-yl]oxy]acetamide; metolachlor, 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide; metribuzin, 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one; rimsulfuron, N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]-3-(ethylsulfonyl)-2-pyridinesulfonamide; SAN 582H (proposed name, dimethenamid), 2-chloro-N-(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl) acetamide; thifensulfuron, 3-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl] amino]sulfonyl]-2-thiophenecarboxylic acid; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; giant foxtail, Setaria faberi Herrm. # SETFA; yellow nutsedge, Cyperus esculentus L. # CYPES; corn, Zea mays L. ‘Pioneer 3335’.Additional index words: Early preplant, preemergence, postemergence.Abbreviations: DAP, days after planting; EC, emulsifiable concentrate formulation; EPP, early preplant; ME, microencapsulated formulation; POST, postemergence; PRE, preemergence.

Weed Control and Corn (Zea mays) Tolerance from Soil-Applied RPA 201772

Field experiments were conducted in 1996, 1997, and 1998 to evaluate weed control and corn tolerance from soil-applied RPA 201772. Treatments alone and in tank mixtures with other corn herbicides were applied preemergence (PRE) at two locations with conventional tillage and at early preplant (EPP) and PRE application timings in no-tillage corn. RPA 201772 was applied alone and in tank mixtures with one-half the typical field rates of other PRE corn herbicides. In conventional tillage experiments in 1996, 1997, and at one location in 1998, all treatments containing RPA 201772 provided > 90% control of common lambsquarters, redroot pigweed, common ragweed, and velvetleaf. In two no-tillage experiments, common lambsquarters and velvetleaf control was > 90%, regardless of application timing. However, control of redroot pigweed and common ragweed varied among years and application timings. Weed control was more variable from herbicide treatments applied EPP compared with the PRE application timing. Giant foxtail control in both tillage systems was rate, timing, and year dependent. RPA 201772 rates higher than 79 g/ha controlled giant foxtail > 85% at three of five locations. At one location, tank mixtures with RPA 201772 increased giant foxtail control. Corn injury occurred in one of two conventional tillage locations and at the no-tillage location in both 1996 and 1997. Injury was most commonly observed in coarse-textured soils with low clay and organic matter and was more severe with higher rates of RPA 201772. Increased corn injury was also observed when RPA 201772 was combined with acetochlor plus dicloramid or BAYFOE 5043 plus metribuzin. Corn injury from RPA 201772 occurred at application rates above the proposed rate for use on corn. In some cases, severe injury to corn reduced corn yield. Injury to corn from RPA 201772 was not unique to any tillage system and was site, year, and rate dependent.

Wild Carrot (Daucus carota) Control in No-Tillage Cropping Systems

Wild carrot is becoming a serious weed problem in Michigan continuous no-tillage crop production. Greenhouse and field research was conducted to identify effective management strategies for wild carrot control in no-tillage cropping systems. In the greenhouse, PRE applications of acetochlor plus dichlormid (5.8:1 w:w), cyanazine, linuron plus chlorimuron (18:1), and metribuzin plus chlorimuron (10:1) and POST applications of bentazon, CGA-152005, clopyralid, cyanazine, and MON 12000 provided the greatest control of wild carrot seedlings. In the field, PRE and POST treatments containing chlorimuron consistently controlled overwintered wild carrot greater than 71% at 30 d after the POST application in no-tillage soybean. Atrazine, MON 12000, nicosulfuron, and primisulfuron applied POST consistently controlled overwintered wild carrot greater than 78% at 30 DAT in no-tillage corn. Glyphosate at 0.84 or 1.68 kg ae/ha applied in October to established wild carrot provided greater than 74% control the following spring. Early preplant (EPP) applications of glyphosate at 0.84 kg/ha in no-tillage soybean gave 95 and 24% control of overwintered wild carrot in St. Clair and Lenawee Counties, MI, respectively, at 70 DAT. PRE applications of glyphosate at 0.84 kg/ha controlled overwintered wild carrot less than 69% at 58 DAT in no-tillage corn and soybean. Fall applications of 2,4-D ester at 1.12 kg ae/ha provided 18 and 88% control of wild carrot the following spring in Clinton and Lenawee Counties, respectively. EPP applications of 2,4-D ester at 1.12 kg/ha provided 7 and 72% control of overwintered wild carrot in St. Clair and Lenawee Counties, respectively.

Application Timing Affects Weed Control with Metolachlor Plus Atrazine in No-Till Corn (Zea mays)

Field trials were conducted in no-till field corn in northern Missouri to compare weed control and crop response of metolachlor plus atrazine applied under five preplant herbicide management practices. The practices consisted of (1) applying the entire dose of metolachlor plus atrazine 15, 30, or 45 d early preplant (EPP), (2) applying a split application of an EPP (67%) followed by (fb) a PRE (33%), (3) applying the entire dose PRE, (4) applying metolachlor PRE fb dicamba early post (EPOST), or (5) applying atrazine alone EPOST. Weed control at 7 wk after planting was more variable with EPP treatments than with EPP fb PRE or PRE treatments. Giant foxtail and fall panicum control was greatest with treatments that included metolachlor PRE. Velvetleaf and common cocklebur control was greatest with atrazine or dicamba EPOST and was generally unacceptable (< 80%) with any soil-applied herbicide treatment. Common lambsquarters control was greater than 90% with all treatments that included metolachlor, atrazine, or dicamba, regardless of timing. Corn yields were slightly higher with EPP fb PRE and PRE fb EPOST dicamba than with EPP alone. The results suggest that herbicide applications made nearer to the date of planting provide less variable weed control and corn yield than treatments made more than 15 d EPP.

Control of Triazine-Resistant Kochia (Kochia scoparia) in Sorghum (Sorghum bicolor)

Herbicidal control of triazine-resistant (TR) kochia was evaluated in no-till grain sorghum. Herbicides were applied early preplant (EPP) or POST. In EPP experiments, herbicides plus nonionic surfactant at 0.25% v/v were applied 7, 2, or 0 wk before planting (WBP). Fluorochloridone at 0.8 kg ai/ha applied 7 or 2 WBP, pyridate at 1.0 kg ai/ha applied 2 WBP, and paraquat at 0.4 kg ai/ha applied 0 WBP controlled 94 to 99% of TR kochia; a prepackaged mixture of glyphosate plus 2,4-D at 0.3 plus 0.6 kg ae/ha and paraquat at 0.4 kg/ha applied 7 or 2 WBP controlled 71 to 82% of TR kochia; and 2,4-D ester at 0.6 kg ae/ha applied 2 WBP controlled 75% of TR kochia. Linuron at 0.8 kg ai/ha and atrazine at 2.2 kg ai/ha were ineffective. In the POST herbicide experiments, where paraquat plus metolachlor at 0.6 plus 1.7 kg ai/ha were applied 17 d before planting, various combinations and rates of bentazon plus atrazine, bromoxynil, and dicamba with adjuvants provided good control of TR kochia that was less than 8 cm tall.

Giant Foxtail (Setaria faberi) Control in Full-Season No-Till Soybeans (Glycine max)

Alachlor plus linuron tank mixed with paraquat and applied preemergence (PRE) did not control giant foxtail all season in full-season no-till soybeans. Alachlor applied early preplant (EPP) plus PRE was necessary to control (>70%) giant foxtail acceptably all season. Metolachlor applied PRE or EPP plus PRE were equally effective in controlling giant foxtail (71 to 74%). Oryzalin at 1.7 or 2.2 kg ai/ha applied fall or spring EPP controlled giant foxtail better than 70% through July. Oryzalin applied PRE did not control giant foxtail acceptably.

Herbicide Efficacy for Various Application Times in Doublecrop Wheat and Soybean

AbstractEffective weed management is essential in reduced tillage doublecrop wheat (Triticum aestivum L.) and soybean [Glycine max Merr.] production. Field experiments were conducted on a Hartsells fine sandy loam soil (fine loamy, silaceous, thermic Typic Hapludalfs) near Crossville, AL, from 1981 to 1983 to determine the influence of application time on herbicidal efficacy of oryzalin [4‐(dipropylamino)‐3,5‐dinitrobenzenesulfonamide], pendimethalin [N‐(1‐ethylpropyl)‐3,4‐dimethyl‐2,6‐dinitrobenzenamine], and oryzalin + 2,4‐D [(2,4‐dichlorophenoxy)acetic acid] for weed control. Herbicides were applied early preplant (EP) to fully tillered wheat, and preemergence (PRE) at soybean planting. Paraquat (1,1'‐dimethyl‐4,4'‐bipyridinium ion) was applied separately at 0.3 kg ha−1 at the time of PRE applications to ail plots that received other herbicide applications (EP or PRE) and alone as a check treatment. Early preplant treatments did not reduce wheat seed yields in 2 of 3 yr compared to the untreated control. Fall panicum (Panicum dichotomiflorum Michx.) and prickly sida (Sida spinosa L.) control were similar with EP and PRE applications of all herbicides. Fall panicum control ranged from 63 to 100%, and prickly sida control from 20 to 87%. Early preplant applications provided greater Pennsylvania smartweed (Polygonum pensylvanicum L.) control than PRE applications. Pennsylvania smartweed control was 5 to 70% greater with EP applications compared to PRE applications. Preemergence applications of oryzalin + 2,4‐D produced moderate (20%) soybean injury in 1982 and 1983. Soybean seed yields were similar with EP and PRE applications in 1981 and 1982; however, seed yields were from 26 to 103% greater with EP applications than PRE applications in 1983.

Early Preplant Herbicide Applications for No-Till Soybean (Glycine max) Weed Control

Several field studies were conducted during 1981 and 1982 to determine whether early preplant (EPP) applications of residual herbicides would prevent the establishment of vegetation before planting no-till soybeans [Glycine max(L.) Merr. ‘Williams’]. Early preplant applications of either cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} or cyanazine plus oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) were applied in the fall and 3, 2, and 1 month(s) before planting no-till soybeans. In all studies, the treatments prevented vegetation from becoming established before planting, and season-long weed control was achieved with several different treatments. Early preplant cyanazine plus oryzalin provided greater than 90% control for the entire season where grass densities were low. Where grass densities were high (greater than 90% ground cover), EPP cyanazine plus a preemergence application of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] plus metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] or a postemergence application of sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} controlled 90% of the weeds, which was equal to or better than the standard preemergence treatments used (80 to 98% weed control).