Early Postemergence Treatments Research Articles

HPPD-resistant cotton response to isoxaflutole applied preemergence and postemergence

AbstractStudies were conducted in 2019 and 2020 in Lewiston, NC, to determine the crop response of 4-hydroxyphenylpyrivate dioxygenase (HPPD)-resistant cotton to isoxaflutole (IFT) and other cotton herbicides as part of a cotton weed management program that included herbicides applied preemergence, early postemergence (EPOST), and mid-postemergence (MPOST). IFT was applied PRE at 105 g ha−1 alone and in various combinations with acetochlor, diuron, fluometuron, fluridone, fomesafen, pendimethalin, and pyrithiobac. EPOST treatments included IFT at 53 or 105 g ha−1 alone or in combination with glyphosate or glufosinate, or dimethenamid-P + glufosinate. Glyphosate + glufosinate was applied MPOST to all treatments except the nontreated control. Cotton injury from IFT applied PRE was minimal (0% to 3%). Injury following EPOST application of dimethenamid-P + glufosinate ranged from 3% to 5% and 6% to 9% in 2019 and 2020, respectively. In both years, injury from IFT applied PRE followed by IFT applied EPOST never exceeded injury from IFT applied PRE followed by dimethenamid-P + glufosinate. Isoxaflutole applied PRE followed by IFT applied EPOST at 105 g ha−1 resulted in 0% to 2% cotton injury, indicating that IFT can be applied either PRE or EPOST with minimal risk to cotton. Late-season cotton height and cotton lint yield were not affected by any herbicide treatment. The experimental HPPD-resistant cotton cultivar was minimally injured by IFT applied PRE and EPOST, it tolerated standard cotton herbicides, and yield loss was not observed. Given these results, HPPD-resistant cotton and IFT may be integrated into cotton weed management systems with minimal risk for cotton injury and provide an additional effective mechanism of action for managing troublesome weeds in cotton.

Phytotoxicity levels in a wet year in an experiment on maize sensitivity to herbicides

The phytotoxic effects of herbicides applied pre-, early post- and post-emergence were studied in maize in a herbicide sensitivity experiment were set up in Martonvásár and Törökszentmiklós. The herbicides were applied in normal and in double doses to 37 Martonvásár inbred lines and to six parental single crosses. The small-plot experiments were set up in two replications. The wet weather that followed the pre- and early post-emergence treatments promoted the appearance of phytotoxic symptoms on maize. The degree of phytotoxicity was recorded on the 14th day after post-emergence treatment and on the 14th and 28th days after the pre- and early postemergence treatments. Herbicides applied pre-emergence only caused slight symptoms on maize. Although the double dose increased the damage, it was still not more than 5% on average. The symptoms caused by herbicides applied in the early post-emergence stage were more intensive than those detected in the pre-emergence treatments. However, the damage caused by the double dose of isoxaflutol + thiencarbazone-methyl and by the split treatment with nicosulfuron remained below 10%. The symptoms became somewhat more severe at the 2nd scoring date. Among the post-emergence treatments the maize genotypes had the least tolerance of the mesotrione + nicosulfuron combination of active ingredients, where the double quantities resulted in 13–14% damage in average.

Johnsongrass (Sorghum Halepense) Control and Economics of Using Glyphosate-resistant Soybean in Fallowed Sugarcane Fields

Johnsongrass control in fallowed sugarcane fields was evaluated with glyphosate and the graminicides quizalofop, fluazifop, and clethodim applied in soybean compared with nonsoybean tillage and glyphosate programs. Glyphosate was applied to glyphosate-resistant soybean as a single early postemergence (EPOST) treatment around 30 d after planting (DAP) at rates of 840, 1,120, or 2,240 g ai/ha; as sequential treatments EPOST and late postemergence (LPOST) around 60 DAP at 560 followed by (fb) 560 or 1,120 fb 1,120 g/ha; or as a single LPOST treatment at 2,240 g/ha. Quizalofop at 77 g ai/ha, fluazifop at 420 g ai/ha, and clethodim at 280 g ai/ha were also evaluated as single EPOST treatments. In 1996 johnsongrass control 7 d after EPOST treatment (DAT) was at least 90% for glyphosate treatments but control was 73 to 77% for the graminicides. In 1997 johnsongrass control 7 DAT was at least 82% for all herbicide treatments. Excellent johnsongrass control approximately 50 DAT was achieved both years with all the glyphosate and graminicide treatments. In the nonsoybean fallow weed control programs where plots were tilled twice or three times fb one or two glyphosate applications, complete control of johnsongrass was obtained both years. In 1996 when glyphosate was applied EPOST or EPOST fb LPOST, soybean yields were equivalent and averaged 3.3 times that of the single LPOST glyphosate application. Soybean yields where the graminicides were used and where glyphosate was applied as a single LPOST treatment were no greater than the nontreated control. Economic analysis on the basis of soybean yield data and variable costs of herbicides, seed, field application, seedbed preparation, tillage, labor, fuel, repairs, and custom harvest expense in 1996 showed a positive net return only for glyphosate applied EPOST at 840 g/ha ($99.82/ha) or 1,120 g/ha ($46.94/ha) and for glyphosate applied at 560 g/ha EPOST fb LPOST ($10.41/ha). Although showing a negative net return, glyphosate applied EPOST at 2,240 g/ha ($−8.32/ha) or EPOST fb LPOST at 1,120 g/ha ($−50.97/ha), the loss was less than that for nonsoybean fallow tillage and glyphosate programs ($−155.70/ha and $−157.78/ha). In 1997, when soybean was not harvested because of environmental conditions, variable costs exceeded those of the nonsoybean programs, indicating that planting soybean strictly as a cover crop would not be economically advantageous. Sugarcane growth and yield the year following the fallow programs was not negatively affected by production of soybean regardless of herbicide program.

Herbicide Programs for the Control of ALS-Resistant Shattercane (Sorghum bicolor) in Corn (Zea mays)

Growers from three counties in Virginia have recently experienced difficulty controlling shattercane in corn with acetolactate synthase (ALS)–inhibiting herbicides. Seed was collected from these locations and from a susceptible biotype and tested for resistance to imazethapyr, imazapyr, and nicosulfuron in greenhouse trials. Seedlings from these locations were also treated with glufosinate and glyphosate. Greenhouse experiments indicated that one of the four shattercane biotypes was resistant to ALS-inhibiting herbicides. Effective control of the resistant biotype was possible with glufosinate or glyphosate. Field experiments were conducted in 2003 and 2004 to determine the most effective herbicide program utilizing herbicide-tolerant/-resistant corn hybrids for the control of shattercane. Early postemergence (EP) and late postemergence (LP) applications of imazethapyr plus imazapyr or EP nicosulfuron did not control shattercane, and yield from the imidazolinone-tolerant (IT) hybrid was equivalent between these treatments and was equivalent to yield from the weedy control (WC). At 23 wk after planting (WAP), EP applications of glyphosate controlled shattercane 71 and 75% compared to only 21 and 66% with EP applications of glufosinate in 2003 and 2004, respectively. In both years, LP applications of glufosinate or glyphosate controlled shattercane better than did EP applications of glufosinate or glyphosate. Treatment timing with respect to corn yield within either the glufosinate-resistant (LL) or glyphosate-resistant (RR) corn hybrid was critical. EP treatments of glufosinate or glyphosate resulted in yields that were equivalent to yield from the weed-free control (WFC) of each hybrid. LP treatments of glufosinate or glyphosate, however, resulted in yields that were equivalent to only 90 and 91% of yield from the WFC of each hybrid, respectively.

Time of Weed Removal with Glyphosate Affects Corn Growth and Yield Components

Growers need to be aware that corn (Zea mays L.) develops leaf area slowly and competes poorly with early emerging weeds in the northeastern USA when planning a total postemergence program in glyphosate‐resistant corn. We applied glyphosate at early postemergence (EPOST), third to fourth leaf stage (V3–V4) of corn growth; mid‐postemergence (MPOST), V5 to V6 stage; and late postemergence (LPOST), V7 to V8 stage, in New York in 2003 and 2004 to determine how initial glyphosate timing affects growth, development, yield, and yield components of corn. The EPOST treatment, which received glyphosate when weeds were 10 cm or less in height, and a weed‐free treatment silked on the same date, had similar dry matter (DM) accumulation (738 g m−2) and leaf area index (LAI) at silking (∼3.50), kernels per plant (528–549), and grain yield (11.1 Mg ha−1). The MPOST treatment, which received glyphosate when some weeds were 18 to 35 cm tall, silked 2 d later, had 35% less LAI and 39% less DM accumulation at silking, 21% less kernels per plant, and 25% less grain yield. Although the LPOST and untreated control, which had 1363 and 653 weeds m−2 at the V5–V6 stage in 2003 and 2004, respectively, had the same LAI at silking (1.75–1.87), the LPOST treatment yielded higher (6.4 vs. 3.2 Mg ha−1). Results from this study indicate that growers in the northeastern USA should apply glyphosate by the V3–V4 stage to avoid yield losses from early season weed competition.

Weed Management withS-Metolachlor and Glyphosate Mixtures in Glyphosate-Resistant Strip- and Conventional-Tillage Cotton (Gossypium hirsutumL.)

Five studies were conducted at Clayton, Rocky Mount, and Lewiston-Woodville, NC, in 2001 and 2002, to evaluate weed management, crop tolerance, and yield in strip- and conventional-tillage glyphosate-resistant cotton. Cotton was treated with two glyphosate formulations; glyphosate-IP (isopropylamine salt) or glyphosate-TM (trimethylsulfonium salt), early postemergence (EPOST) alone or in a mixture withS-metolachlor. Early season cotton injury was minimal (3%) with either glyphosate formulation alone or in mixture withS-metolachlor. Weed control and cotton yields were similar for both glyphosate formulations. The addition ofS-metolachlor to either glyphosate formulation increased control of broadleaf signalgrass, goosegrass, large crabgrass, and yellow foxtail 14 to 43 percentage points compared with control by glyphosate alone.S-metolachlor was not beneficial for late-season control of entireleaf morningglory, jimsonweed, pitted morningglory, or yellow nutsedge. The addition ofS-metolachlor to either glyphosate formulation increased control of common lambsquarters, common ragweed, Palmer amaranth, smooth pigweed, and velvetleaf 6 to 46 percentage points. The addition of a late postemergence-directed (LAYBY) treatment of prometryn plus MSMA increased control to greater than 95% for all weed species regardless of EPOST treatment, and control was similar with or withoutS-metolachlor EPOST. Cotton lint yield was increased 220 kg/ha with the addition ofS-metolachlor to either glyphosate formulation compared with yield from glyphosate alone. The addition of the LAYBY treatment increased yields 250 and 380 kg/ha for glyphosate plusS-metolachlor and glyphosate systems, respectively.S-metolachlor residual activity allowed for an extended window for more effective LAYBY application to smaller weed seedlings instead of weeds that were possibly larger and harder to control.

Pre and Early Postemergence Herbicide Phytotoxicity and Yield Effects in Transplanted Peppers

Field research was conducted to evaluate pre-transplant (PRE) applications of sulfentrazone (0.20 or 0.41 kg·ha-1 a.i.) and flufenacet (0.045 kg·ha-1 a.i.), or early postemergence (EPOST) halosulfuron (0.027, 0.036 or 0.054 kg·ha-1 a.i.) on phytotoxicity and yield of field-grown chili (var. Sonora), jalapeño (var. Grande) and bell (var. Giant Belle) peppers (Capiscum annuum) in Texas. Crop injury recorded 15 days after sulfentrazone treatments (DAT) showed minor stunting at the low rate, but moderate stunting and temporary leaf malformation when applied at 0.41 kg·ha-1 a.i. Increased stunting occurred 37 DAT at both rates; however, new leaf growth was not affected. Flufenacet did not result in crop injury to any of the three types grown. Phytotoxicity from halosulfuron recorded 7 DAT gave significantly higher ratings for stunting/chlorosis for broadcast EPOST treatments when compared to EPOST-directed applications. Injury from halosulfuron was temporary and considered minor with all EPOST treatments by 22 DAT. Pepper yield data showed that EPOST halosulfuron treatments were statistically equivalent to the untreated controls for each of the three types, but there was a trend for lower yields with rates higher than 0.027 kg·ha-1 a.i. All peppers treated with flufenacet gave excellent yields. Sulfentrazone applied at the high rate gave the greatest yield losses in all three types, and this was significant in the jalapeños. The results indicate that all three herbicides have potential for use in commercial pepper production in Texas. However, more research is needed to evaluate these and other herbicides for improved crop safety in peppers.

Effect of Application Rate and Timing of AE F130060 03 plus AE F107892 for Control of Italian Ryegrass (Lolium multiflorum) in Barley (Hordeum vulgare)1

Experiments were conducted in 2000 and 2001 to evaluate efficacy of AE F130060 03 plus AE F107892 applied postemergence for the control of Italian ryegrass in barley. AE F130060 03 plus AE F107892 controlled Italian ryegrass when applied at two application rates and at three timings. Barley successfully recovered from initial injury caused by early-postemergence (EP) and middle-postemergence (MP) application timings. The late-postemergence (LP) timing resulted in lower yield than the EP or MP application timings. AE F130060 03 plus AE F107892 applied EP controlled Italian ryegrass similar to flufenacet plus metribuzin applied delayed preemergence (DPRE) when rainfall was received. Barley yields were also similar. However, with insufficient rainfall, AE F130060 03 plus AE F107892 provided superior Italian ryegrass control. EP treatments of AE F130060 03 plus AE F107892 after a DPRE application of flufenacet plus metribuzin or chlorsulfuron plus metsulfuron completely controlled Italian ryegrass and resulted in excellent yields.Nomenclature: AE F107892, diethyl 1-(2,4-dichlorophenyl)-5-methyl-2-pyrazoline-3, 5-dicarboxylate; AE F115008 00, [methyl 4-iodo-2-[3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-ureidosulfonyl]benzoate, sodium salt]; AE F130060 00, methyl-2-[3-(4,6-dimethoxypyrimidin-2-yl)ureidosulfonyl]-4-methane-sulfonamidomethylbenzoate; chlorsulfuron; flufenacet; metribuzin; metsulfuron; Italian ryegrass, Lolium multiflorum (Lam.) #3 LOLMU; barley, Hordeum vulgare (L.) # HORVX ‘Nomini’; wheat, Triticum aestivum (L.) # TRZAW.Additional index words: Crop tolerance, diclofop resistance.Abbreviations: DAT, days after treatment; DPRE, delayed preemergence; EP, early postemergence; LP, late postemergence; MP, middle postemergence; POST, postemergence; PRE, preemergence.

Weed management with pyrithiobac preemergence in bromoxynil-resistant cotton

An experiment was conducted at two locations in Georgia and one location in North Carolina during 1994 and 1995 to evaluate weed management systems utilizing pyrithiobac applied preemergence (PRE) in conventional-tillage bromoxynil-resistant cotton. Weed management systems evaluated included different combinations of pyrithiobac PRE, bromoxynil or bromoxynil plus MSMA applied early postemergence (EPOST), bromoxynil applied postemergence (POST), and cyanazine plus MSMA applied late postemergence-directed (LAYBY). Pyrithiobac PRE improved control of Florida beggarweed, pitted morningglory, prickly sida, sicklepod, and spurred anoda compared with systems that did not include pyrithiobac PRE. Averaged across locations, pyrithiobac PRE increased cotton lint yields 330 kg ha−1. Bromoxynil applied EPOST or POST increased weed control and cotton lint yield. Bromoxynil EPOST, POST, or EPOST plus POST did not control sicklepod. The addition of MSMA to bromoxynil EPOST improved sicklepod control. Two applications of bromoxynil controlled more pitted morningglory and sicklepod than one application. Control of all dicotyledonous weeds was increased by cyanazine plus MSMA LAYBY, and this treatment increased yields at all locations. Cotton was not injured by pyrithiobac PRE or by bromoxynil applied EPOST or POST, but temporary visual injury was observed with EPOST treatments of MSMA.

Flood Depth, Application Timing, and Imazethapyr Activity in Imidazolinone-Tolerant Rice (Oryza sativa)1

A study was conducted in 1999 to evaluate weed control and imidazolinone-tolerant (IMI-tolerant) rice response to 140 g ai/ha imazethapyr at different application timings and to flood depths of 5, 10, and 20 cm at the Rice Research Station near Crowley, LA, and at the Northeast Research Station near St. Joseph, LA. Barnyardgrass control, rice injury, and rice yield were not influenced by flood depth; therefore, data were averaged over flood depths. Season-long barnyardgrass control was greater than 80% at both locations with imazethapyr applied preplant incorporated (PPI), early postemergence (EPOST), and mid-postemergence (MPOST). IMI-tolerant rice injury at 7 d after late postemergence (LPOST) treatment (DAT) was less than 5% for all imazethapyr treatments at Crowley and 1 to 8% for PPI, preemergence (PRE), delayed preemergence (DPRE), and EPOST timings at St. Joseph. However, IMI-tolerant rice injury was 5% or less at 42 DAT for all treatments at Crowley and St. Joseph. IMI-tolerant rice yield at Crowley was 2,780 to 3,000 kg/ha following applications of imazethapyr at PPI, PRE, DPRE, and EPOST, and these yields were higher than the yields of the MPOST and LPOST treatments. At St. Joseph, IMI-tolerant rice yields were equal for imazethapyr applied PPI, DPRE, and EPOST treatments compared with Crowley.Nomenclature: Imazethapyr; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; rice, Oryza sativa L. imidazolinone-tolerant ‘93 AS 3510’.Additional index words: ALS, acetolactate synthase, Clearfield rice, soil-applied herbicide, water depth.Abbreviations: DAT, days after LPOST treatment; DPRE, delayed preemergence; EPOST, early postemergence; IMI-tolerant, imidazolinone-tolerant; LPOST, late postemergence; MPOST, mid-postemergence; PPI, preplant incorporated; PRE, preemergence; power take-off (PTO).

Woolly Cupgrass (Eriochloa villosa) Management in Corn (Zea mays) by Sequential Herbicide Applications and Cultivation1

Field experiments were conducted in southern Wisconsin from 1996 to 1998 to evaluate the effects of acetochlor applied preemergence (PRE) followed by nicosulfuron or sethoxydim applied postemergence (POST) and of cultivation on woolly cupgrass control, corn grain yield, and woolly cupgrass seed production. Sethoxydim treatments provided greater woolly cupgrass control than nicosulfuron treatments in 1997 and similar control to nicosulfuron treatments in 1996 and 1998. However, neither herbicide killed all emerged woolly cupgrass plants, regardless of herbicide rate or POST application timing. Late postemergence treatments provided greater season-long control than early postemergence treatments in 1996 and 1998, but there was no difference in control between timings in 1997. Acetochlor applied PRE at 1,800 g ai/ha (1×) followed by nicosulfuron (35 g ai/ha) or sethoxydim (213 g ai/ha) at the registered rate (1×) or at one half of the registered rate (0.5×) consistently provided sufficient woolly cupgrass control to maximize corn yield, regardless of cultivation or POST herbicide application timing. Acetochlor PRE treatments, cultivated and noncultivated, followed by sethoxydim POST and cultivated acetochlor PRE treatments followed by nicosulfuron POST treatments provided sufficient control in each year to limit woolly cupgrass seed production to a level that decreased the predicted future seedbank density, regardless of herbicide rate or POST herbicide application timing. However, noncultivated acetochlor treatments followed by nicosulfuron applied at 1× followed by 0.5× or at 0.5× followed by 0.5× did not consistently reduce seed production to a level that decreased the predicted future seedbank density. These results suggest that the rate of sethoxydim can be reduced to 0.5× if a full rate of acetochlor is applied PRE with little effect on corn yield or woolly cupgrass seedbank density. However, reducing the rate of nicosulfuron to 0.5× following an application of acetochlor at the full rate or reducing both the acetochlor and nicosulfuron or sethoxydim rate to 0.5× is recommended only if a cultivation is planned.Nomenclature: Acetochlor; nicosulfuron; sethoxydim; woolly cupgrass, Eriochloa villosa (Thunb.) Kunth #3 ERBVI; corn, Zea mays L. ‘DeKalb SR404’, ‘DeKalb DK493SR’.Additional index words: Acetochlor, herbicide rate, herbicide application timing, nicosulfuron, sethoxydim, sethoxydim-resistant corn, woolly cupgrass seed production.Abbreviations: COC, crop oil concentrate; DAT, days after treatment; EPOST, early postemergence; LPOST, late postemergence; OM, organic matter; POST, postemergence; PRE, preemergence; UAN, urea ammonium nitrate.

Weed Control and Economic Comparisons of Glyphosate-Resistant, Sulfonylurea-Tolerant, and Conventional Soybean (Glycine max) Systems1

Abstract: A field study was conducted over 2 yr to compare efficacy and economics of glyphosate-resistant, sulfonylurea-tolerant, and conventional soybean (Glycine max) weed control programs. Herbicide programs in the three soybean systems provided at least 90% control of browntop millet (Brachiaria ramosa), prickly sida (Sida spinosa), yellow nutsedge (Cyperus esculentus), pitted morningglory (Ipomoea lacunosa), and hemp sesbania (Sesbania exaltata) in most cases and postemergence (POST)-only programs were as effective as preemergence (PRE) followed by POST programs. Control of hyssop spurge (Euphorbia hyssopifolia) ranged from 93 to 100% in glyphosate-resistant soybean and from 88 to 100% in conventional soybean, but control was 60 to 100% in sulfonylurea-tolerant soybean. Sicklepod (Senna obtusifolia) control was at least 91% in glyphosate-resistant and sulfonylurea-tolerant soybean but was 81% for the standard SAN 582 plus imazaquin PRE and acifluorfen plus bentazon early POST treatment in conventiona...

Managing Purple Nutsedge (Cyperus rotundus) Populations Utilizing Herbicide Strategies and Crop Rotation Sequences

Field experiments were conducted in North Carolina from 1994 through 1998 to evaluate the effects of five weed management strategies and four corn (Zeamays)–peanut (Arachis hypogaea) rotation sequences on purple nutsedge (Cyperus rotundus) population development. Effects of these weed management programs on cotton (Gossypium hirsutum) and peanut production in following years were also investigated. Herbicide programs included a nontreated control, a carbamothioate preplant incorporated (PPI) combination treatment utilizing vernolate in peanut and butylate in corn, an early postemergence (EPOST) acetolactate synthase (ALS) inhibitor combination treatment utilizing imazapic in peanut and halosulfuron in corn, and EPOST treatments of imazapic and imazethapyr in both peanut and imidazolinone-resistant corn. Crop rotation sequences for the 3 yr included continuous corn (CCC), corn–peanut–corn (CPC), peanut–corn–peanut (PCP), and continuous peanut (PPP). The imazapic and ALS inhibitor combination treatments both provided excellent shoot and tuber control. After 3 yr, imazapic and the ALS inhibitor combination treatment reduced shoot and tuber population densities to less than 10% of the nontreated control. Imazethapyr provided variable but better control than the carbamothioate treatment with tuber densities (measured from 0 to 15 cm soil depth) and shoot densities increasing from 733 to 2,901 tubers/m3of soil and 16 to 43 shoots/m2, respectively, after 3 yr. Tuber densities increased in the nontreated control from 626 to 9,145 tubers/m3of soil and from 962 to 5,466 tubers/m3of soil in the carbamothioate treatment during this same period. Also, shoot densities increased in the nontreated control from 22 to 159 shoots/m2and from 8 to 92 shoots/m2in the carbamothioate treatment. There was a 31% peanut yield reduction from 1994 to 1996 when peanut was continuously planted or rotated to corn for only 1 yr. Herbicide carryover effects were not observed in cotton during 1997.

Weed Control Using Reduced Rates of Postemergence Herbicides in Narrow and Wide Row Soybean

Field studies were conducted in 1994 and 1995 to examine the effects of soybean [Glycine max (L.) Merr.] row spacing and application rate and timing of four postemergence herbicide tank mixtures on weed control and soybean yield. Weed control and soybean yield were greater in narrow rows (7.5 in.) than wide rows (30 in.). Herbicide tank mixtures applied at 25% of the full recommended rate at an early postemergence timing followed by a second 25% application at a standard postemergence timing (1/4x E Post + 1/4x Post) resulted in weed control and soybean yield equal to that of herbicide tank mixtures applied at the full recommended rate at a standard postemergence timing (lx Post). Three of four tank mixtures in 1994 and two of four in 1995, applied at 50% of the full rate applied at a standard postemergence timing (1/2x Post) resulted in weed control and soybean yield equal to that of 1x Post applications. All tank mixtures applied at 50% of the full rate at an early postemergence timing (1/2x E Post) resulted in poor weed control and low soybean yield. In most cases it was more profitable to plant soybean in narrow rows than wide rows regardless of application rate or timing, based on economic gross margin calculations. Gross margins of tank mixtures applied at 1/4x E Post + 1/4x Post were similar to or greater tban tbe gross margin of the same tank mixture applied at the full rate in 13 of 16 cases. Gross margins of tank mixtures applied at 1/2x Post were similar to or greater than the gross margin of the same tank mixture applied at the full rate in eight of 16 cases.

Eclipta (Eclipta prostrata L.) Control in Peanuts (Arachis hypogaea L.)1

Abstract Field experiments were conducted from 1991 to 1993 to evaluate eclipta, Eclipta prostrata L., control and peanut, Arachis hypogaea L., response to herbicide treatments. Fomesafen {5-[2-chloro-4-(trifluoro-methyl)phenoxy]-N-(methylsulfonyl)-2-nitrobenzamide} applied at cracking was the only preemergence-applied herbicide which provided season-long control (>84%). Herbicides applied postemergence were more effective when the eclipta was less than 5 cm in height. The most consistent early postemergence treatments were bromoxynil (3,5-dibromo-4-hydroxybenzonitrile), bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazm-4(3H)-one 2,2-dioxide], and bentazon + acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} + 2,4-DB [4-(2,4-dichloro-phenoxy)butanoic acid]. Various other early postemergence followed by late postemergence sequential treatments also were equally effective. Minor peanut injury was observed at the early season rating from several herbicides; however, all injury had disappeared by the late season rating. Eclipta control did not consistently improve peanut pod yield.

Experimental Foliar Treatments for Control of Tobacco Thrips in Peanut, 1992:

Abstract Efficacy of foliar insecticide treatments was evaluated against TT injury in Virginia-type peanut in Suffolk, VA. Peanuts were planted 4 May with 36-inch row spacing. Foliar treatments were applied 2 x, either broadcast at late ground cracking and again at early postemergence (broadcast, LGC + EPO), or banded at late ground cracking and again at early postemergence (band, LGC + EPO). The late ground cracking treatments were applied about 4 wk (2 Jun) after planting and the early postemergence treatments were applied about 7 wk (24 Jun) after planting. Broadcast treatments were applied with a CO2 pressurized backpack sprayer calibrated to deliver 20 gal/acre at 17 psi through 8003 VS flat fan nozzles spaced 18 inches apart on the spray boom. Band treatments were applied in a 12-inch band over the row with a CO2 pressurized backpack sprayer calibrated to deliver 17 gal/acre at 22 psi through 1,8004 E flat fan nozzle per row. A RCB experimental design was used with 4 replicates; plots were 4 rows by 35 ft. Treatments were evaluated by determining plant injury based on a 0-10 scale where 0 = no TT injured leaves and 10 = 100 percent injured leaves. Data were analyzed using ANOVA and LSD procedures.

Weed Control in Water- and Dry-seeded Rice,Oryza sativa

Herbicides were applied as single, sequential, or tank mixture treatments at different growth stages and rates and were compared with standard treatments for control of barnyardgrass, bearded sprangletop, elipta, spreading dayflower, and aquatic weeds in water- or dry-seeded rice. In water-seeded rice, thiobencarb granules applied alone or sequentially selectively controlled bearded sprangletop and aquatic weeds in the 1- to 4-leaf stages better than standards of propanil alone or mixed with bentazon. Fenoxaprop plus bentazon selectively controlled 1- to 4-leaf bearded sprangletop but failed to control 1- to 4-leaf aquatic weeds. In dry-seeded rice, treatments of fenoxaprop applied to tillering rice after earlier applications of preemergence thiobencarb or postemergence applications of propanil selectively controlled barnyardgrass, bearded sprangletop, eclipta, or spreading dayflower better than standards of propanil alone or mixed with thiobencarb. Fenoxaprop alone or in tank mixtures with other herbicides applied early postemergence either injured rice or failed to control weeds. Esprocarb applied preemergence controlled weeds but injured rice while early postemergence treatments of propanil plus esprocarb performed better than standard herbicide treatments.

Control of Woolly Croton (Croton capitatus) in Soybean (Glycine max)

Field studies were conducted in 1981 to 1983 to evaluate selected herbicides for control of a natural infestation of woolly croton (Croton capitatusMichx. ♯ CVNCP) in soybean [Glycine max(L.) Merr.]. Ineffective woolly croton control was obtained with all preemergence herbicides evaluated. Early postemergence treatments of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} and lactofen {1-(carboethoxy)ethyl) 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate} provided excellent woolly croton control. Postdirected applications of oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] applied at the V4 stage of soybean growth and tank mixes of cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile}, linuron [N′-(3,4-dichlorophenyl)-N-methoxy-N-methylurea], or metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] plus 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] applied at the V4 and repeated at the V6 stage of soybean growth also provided effective control.

Effect of Herbicides on the Production of Common Buffelgrass (Cenchrus ciliaris)

Dicamba (3,6-dichloro-o-anisic acid), 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], 3,6-dichloropicolinic acid, picloram (4-amino-3,5,6-trichloropicolinic acid), triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] were applied at rates of 0.3, 0.6, 1.1, and 2.2 kg/ha pre- and postemergence to greenhouse-grown common buffelgrass (Cenchrus ciliarisL. ♯3PESCI). Buffelgrass tolerated preemergence sprays of 3,6-dichloropicolinic acid up to and including 1.1 kg/ha. All other treatments except picloram and 2,4,5-T at 0.3 kg/ha were phytotoxic to emerging buffelgrass. Buffelgrass tolerated early postemergence applications of 2,4-D, picloram, and tebuthiuron at 0.3 kg/ha; dicamba and 2,4,5-T at 0.6 kg/ha; and 3,6-dichloropicolinic acid at 2.2 kg/ha based on oven-dry shoot production 1 month after treatment. Regrowth of buffelgrass from stubble 1 month after original harvest of the early postemergence treatment occurred only with all rates of 3,6-dichloropicolinic acid and 2,4,5-T at 0.3 kg/ha. When treated at 45 days after planting, buffelgrass tolerated dicamba, 2,4-D, 2,4,5-T, 3,6-dichloropicolinic acid, and picloram at 2.2 kg/ha, but top growth production was significantly reduced by most rates of hexazinone and tebuthiuron. Relative differences in regrowth of buffelgrass 1 month after the original harvest were similar to those of the original harvest. Mature buffelgrass (90 or 150 days old) responded similarly to herbicides as the 45-day-old buffelgrass.

Commelinaceae-A Review of the Distribution, Biology and Control of the Important Weeds Belonging to this Family

Abstract The Commelinaceae is chiefly a tropical family, present in all the major continents and extending into the temperate zone in parts of America, E. Asia and Europe. The review includes the three major weed species in this family, Commelina benghalensis L., C. diffusa Burm. f. and Murdannia nudiflora (Linn. Brenan. The synonymy of each species is listed and the importance of the weeds discussed in relation to their biology. The results of trials in cereals, broadleaved and plantation crops are summarised. The most successful methods of herbicide application are pre-emergence or early post-emergence. Herbicides should be applied in the early stages of the growth cycle as single or sequential applications. Bentazone applied as an early post-emergence treatment, either alone or in mixtures is one of the most successful herbicides in controlling Commelina species. Metribuzin applied pre-emergence alone or in mixtures is another chemical giving satisfactory control in many parts of the world. Esters or a...