Palmer amaranth and pitted morningglory are difficult to manage weeds present in South Carolina soybean production fields. Glyphosate and ALS-resistant Palmer amaranth biotypes have spread rapidly throughout South Carolina making the control of these weeds more difficult. Recently, soybean varieties with tolerance to dicamba have been introduced along with several new ultra-low volatility formulations of dicamba to help with the problem. Field experiments were conducted near Blackville, SC in 2012 and 2013 to evaluate dicamba herbicide programs for broadleaf weed management in dicamba tolerant soybean. At 2 weeks after POST1 (2 WAP1), Palmer amaranth control ranged from 93% to 100% across the PRE followed by POST treatments in 2012 and 2013. By 2 weeks after POST2 (2 WAP2), control was 95% or better. Treatments containing two or three herbicide applications (PRE, POST1 and POST2) offered good to excellent (92% - 100%) pitted morningglory control. No differences in weed control were observed among treatments with 3 application times compared to those applied twice. In general, all treatments with a PRE followed by at least one POST application provided good to excellent control of Palmer amaranth and pitted morningglory. Overall, a PRE (either dicamba or flumioxazin) followed by a dicamba or a non-dicamba containing POST treatment provided good to excellent control of Palmer amaranth and pitted morningglory when applied at the correct growth stage.
As the world’s population increases, there is an increasing pressure upon the farmers to produce enough food and fiber for the world today. In the modern era, farmers have looked to researchers to develop better crop cultivars that are superior to the traditional landrace or heirloom strains that have been cultivated before modern agriculture. These improvements in crop varieties have allowed for an increased level of crop productivity. Among these breeding advances was the development of higher yielding crops which allowed farmers to plant on the same acreage with greater yield [
Upon its introduction in 1996, Roundup® Ready soybean allowed growers to make a single postemergence application of glyphosate to fields which effectively managed most of the emerged weeds [
Palmer amaranth and pitted morningglory (Ipomoea lacunosa L.) are among the most common and troublesome weeds to manage in South Carolina soybean fields [
MonsantoTM has recently commercially released a genetically modified soybean which allows the plant to metabolize dicamba using the bacterially derived gene dicamba monooxygenase (DMO). This enzyme converts the herbicidally active dicamba (3,6-dichloro-2-methoxybenzoic acid) molecule to 3,6-dichlorosalicylic acid (DCSA) which is an inactivated form with minimal plant activity [
Dicamba is a widely used herbicide for broadleaf weed control in grass crops, such as corn, grain sorghum, small grains, pasture and rangeland [
XtendimaxTM with VaporGrip® Technology, Engenia, and FeXapan with VaporGrip® Technology are new ultra-low volatility formulations of dicamba herbicide developed by MonsantoTM, BASFTM, and DupontTM, respectively, that are labeled for dicamba-tolerant soybean [
The ability to use either dicamba, glyphosate, or a tank-mix of both herbicides before planting or at selected periods during soybean development will allow growers greater flexibility in managing troublesome weeds in their crop management practices [
Separate field studies were conducted in 2012 and 2013 on a Dothan loamy sand, (fine-loamy, siliceous, thermic Plinthic Paleudult) with a pH of 6 and organic matter of 2.1% at the Clemson University Edisto Research and Education Center (33.36˚N, −81.32˚W) located near Blackville, SC to evaluate dicamba based herbicide programs for weed control in dicamba tolerant soybean. Prior to the initiation of the field studies, soil samples were collected to a depth of 10 cm at each study site and sent for nutritional analysis to the Clemson University Agricultural Service Laboratory (Clemson, SC, USA) and based on those recommendations, phosphorus (0-46-0) and potassium (0-0-60) fertilizer blend was broadcast over the entire study area each year. Soybean variety “GM_A2205” (Monsanto Company 800 N. Lindbergh Blvd. St. Louis, MO, USA) was seeded 2.5 cm deep on 26 June 2012 and soybean variety “GM_A92205” (Monsanto Company 800 N. Lindbergh Blvd. St. Louis, MO) was seeded 2.5 cm deep on 20 June 2013 in a conventionally-tilled seed bed at 20 seeds∙m−1 using an Almaco cone plot planter (Almaco Company; Nevada, Iowa, USA). Plot dimensions were two rows wide and 9.4 m long. Cotton (Gossypium hirsutum L.) was the previous crop grown at each study location.
Study 1 conducted in both 2012 and 2013 and was arranged in a randomized complete block design with 13 treatments and 3 replications, including an untreated check. Herbicide treatments, timing and rates are listed in
Premergence (PRE) treatments were applied shortly after planting, POST1 applications were done when Palmer amaranth and pitted morningglory were 5 to 10 cm in height, and POST2 applications occurred 14 days after the POST1 application. Percent visual control weed ratings were collected using a scale of 0 to 100 percent with 0 indicating no control and 100 indicating complete control. Ratings were collected 3 weeks after the PRE application (3WAP), 2 weeks after POST1 application (2WAP1) and 2 weeks after POST2 application (2WAP2). Weed species density was assessed by randomly tossing a 0.5 m2 quadrat between the 2 treated rows, then counting and identifying each weed species present in the quadrat. By request of Monsanto, the soybean was crop destructed before entering the R1 reproductive stage to prevent production of viable seed of the regulated soybean variety; therefore, yield data was not collected in either year.
Percent visual weed control and weed population densities were analyzed using the PROC GLM procedure in SAS (SAS 9.2, SAS® Institute Inc. Cary, NC, USA). Herbicide treatments and years were considered fixed effects in the model while replicate was considered a random effect. Control and species densities were combined over trial years if no significant treatment by year interaction was observed. Whenever a significant treatment by year interaction occurred the data are presented separately by trial year. Means separations were performed with Fisher’s Protected LSD (P ≤ 0.05).
The weed control parameters in both studies showed varying levels of significance for treatment and treatment by year across the selected evaluation periods,
Treatmenta | Timingb | Ratec | Product Name |
---|---|---|---|
kg∙ai∙ha−1 or kg∙ae∙ha−1 | |||
dic. | PRE | 1.12 | Clarity |
dic. gly. + dic. | PRE POST1 | 1.12 1.12 + 0.56 | Clarity Roundup PowerMAX + Clarity |
dic. gly. + dic. + aceto. | PRE POST1 | 1.12 1.12 + 0.56 + 1.26 | Clarity Roundup PowerMAX + Clarity + Warrant |
dic. gly. + dic. + aceto. + fom. | PRE POST1 | 1.12 1.12 + 0.56 + 1.26 + 0.34 | Clarity Roundup PowerMAX + Clarity + Warrant+ Reflex |
dic. gly. + dic. gly. + dic. | PRE POST1 POST2 | 1.12 1.12 + 0.56 1.12 + 0.56 | Clarity Roundup PowerMAX + Clarity Roundup PowerMAX + Clarity |
dic. gly. + dic. + aceto. gly. + dic. | PRE POST1 POST2 | 1.12 1.12 + 0.56 + 1.26 1.12 + 0.56 | Clarity Roundup PowerMAX + Clarity +Warrant Roundup PowerMAX + Clarity |
dic. gly. + dic. + aceto. + fom. gly. + dic. | PRE POST1 POST2 | 1.12 1.12 + 0.56 + 1.26 + 0.34 1.12 + 0.56 | Clarity Roundup PowerMAX + Clarity + Warrant + Reflex Roundup PowerMAX + Clarity |
flum. | PRE | 0.07 | Valor SX |
flum. gly. + dic. | PRE POST1 | 0.07 1.12 + 0.56 | Valor SX Roundup PowerMAX + Clarity |
flum. gly. + dic. + aceto. | PRE POST1 | 0.07 1.12 + 0.56 + 1.26 | Valor SX Roundup PowerMAX + Clarity + Warrant |
flum. gly. + dic. + aceto.+ fom. | PRE POST1 | 0.07 1.12 + 0.56 + 1.26 + 0.34 | Valor SX Roundup PowerMAX + Clarity + Warrant + Reflex |
flum. gly. + dic. gly. + dic. | PRE POST1 POST2 | 0.07 1.12 + 0.56 1.12 + 0.56 | Valor SX Roundup PowerMAX + Clarity Roundup PowerMAX + Clarity |
flum. gly. + dic. + aceto. dic. | PRE POST1 POST2 | 0.07 1.12 + 0.56 + 1.26 0.56 | Valor SX Roundup PowerMAX + Clarity + Warrant Clarity |
flum. gly. + dic. + aceto. + fom. gly. + dic. | PRE POST1 POST2 | 0.07 1.12 + 0.56 + 1.26 + 0.34 1.12 + 0.56 | Valor SX Roundup PowerMAX + Clarity + Warrant +Reflex Roundup PowerMAX + Clarity |
flum. gly. + s-met. + fom. | PRE POST1 | 0.07 1.12 + 1.49 + 0.34 | Valor SX Roundup PowerMAX + Dual Magnum + Reflex |
aAll POST treatments included ammonium sulfate at 2.5 % v/v. bTreatment timing: PRE, at planting; POST1, 5 - 10 cm weeds; POST2, 2 weeks after POST1. cActive ingredients (ai) rate used for acetochlor (aceto.), fomesafen (fom.), s-metolachlor (s-met), flumioxazin (flum.). Acid equivalent (ae) rate used for dicamba (dic.) and glyphosate (gly.).
Treatmenta | Timingb | Ratec | Product Name |
---|---|---|---|
kg∙ai∙ha−1 or kg∙ae∙ha−1 | |||
flum. gly. + dic. | PRE POST1 | 0.07 1.12 + 0.56 | Valor SX Roundup PowerMAX + Clarity |
flum. gly. + dic. gly. + dic. | PRE POST1 POST2 | 0.07 1.12 + 0.56 1.12 + 0.56 | Valor SX Roundup PowerMAX + Clarity Roundup PowerMAX + Clarity |
flum. gly. + dic. + aceto. | PRE POST1 | 0.07 1.12 + 0.56 + 1.27 | Valor SX Roundup PowerMAX + Clarity + Warrant |
flum. gly. + dic. + aceto. gly. + dic. | PRE POST1 POST2 | 0.07 1.12 + 0.56 + 1.27 1.12 + 0.56 | Valor SX Roundup PowerMAX + Clarity + Warrant Roundup PowerMAX + Clarity |
dic. + aceto. gly. + dic. | PRE POST1 | 0.56 + 1.27 1.12 + 0.56 | Clarity + Warrant Roundup PowerMAX + Clarity |
aceto. + metrn. gly. + dic. | PRE POST1 | 1.27 + 0.28 1.12 + 0.56 | Warrant + Metribuzin Roundup PowerMAX + Clarity |
flum. gly. + fom. + aceto. | PRE POST1 | 0.07 0.84 + 0.42 + 1.27 | Valor SX Roundup PowerMAX + Reflex + Warrant |
s-met. + fom. gly. + lact. | PRE POST1 | 1.49 0.84 + 0.22 | Dual Magnum + Reflex Roundup PowerMAX + Cobra |
a All POST treatments included ammonium sulfate at 2.5 % v/v. bTreatment timing: PRE, at planting; POST1, 5 - 10 cm weeds; POST2, 2 weeks after POST1. cActive ingredients (ai) rate used for acetochlor (aceto.), fomesafen (fom.), metribuzin (metrn.), s-metolachlor (s-met.), flumioxazin (flum.). Acid equivalent (ae) rate used for dicamba (dic.) and glyphosate (gly.).
which was similar to what was observed by Joseph et al. [
In study 1, all PRE treatments effectively controlled Palmer amaranth (>94%) when evaluated at 3 WAP (
Treatmenta | Timing | Rateb | AMAPA controlc | AMAPA densityc | ||||||
---|---|---|---|---|---|---|---|---|---|---|
3 WAPd | 2 WAP1d | 2 WAP2d | 2 WAP2d | |||||||
kg∙ai∙ha−1 or kg∙ae∙ha−1 | % | plants∙m−2 | ||||||||
2012 | 2013 | 2012 | 2013 | 2012 | 2013 | |||||
Untreated Check | - | - | - | - | - | 22 a | 17 c | |||
dic. | PRE | 1.12 | 94 b | 58 e | 72 d | 27 d | 60 c | 18 bc | 19 b | |
dic. gly. + dic. | PRE POST1 | 1.12 1.12 + 0.56 | 99 a | 100 a | 100 a | 100 a | 100 a | 0 d | 0 d | |
dic. gly. + dic. + aceto. | PRE POST1 | 1.12 1.12 + 0.56 + 1.26 | 100 a | 100 a | 100 a | 97b | 100 a | 0 d | 0 d | |
dic. gly. + dic. + aceto. + fom. | PRE POST1 | 1.12 1.12 + 0.56 + 1.26 + 0.34 | 99 a | 98 ab | 100 a | 95 b | 100 a | 1 d | 0 d | |
dic. gly. + dic. gly. + dic. | PRE POST1 POST2 | 1.12 1.12 + 0.56 1.12 + 0.56 | 99 a | 100 a | 100 a | 100 a | 100 a | 0 d | 0 d | |
dic. gly. + dic. + aceto. gly. + dic. | PRE POST1 POST2 | 1.12 1.12 + 0.56 + 1.26 1.12 + 0.56 | 99 a | 100 a | 100 a | 100 a | 100 a | 0 d | 0 d | |
dic. gly. + dic. + aceto. + fom. gly. + dic. | PRE POST1 POST2 | 1.12 1.12 + 0.56 + 1.26 + 0.34 1.12 + 0.56 | 99 a | 100 a | 100 a | 100 a | 100 a | 0 d | 0 d | |
flum. | PRE | 0.07 | 99 a | 100 a | 100 a | 100 a | 100 a | 0 d | 0 d | |
flum. gly. + dic. | PRE POST1 | 0.07 1.12 + 1.12 | 100 a | 100 a | 98 ab | 100 a | 100 a | 0 d | 0 d | |
flum. gly. + dic. + aceto. | PRE POST1 | 0.07 1.12 + 0.56 + 1.26 | 99 a | 100 a | 98 ab | 100 a | 100 a | 0 d | 0 d | |
flum. gly. + dic. + aceto. + fom. | PRE POST1 | 0.07 1.12 + 0.56 + 1.26 + 0.34 | 99 a | 100 a | 97 b | 100 a | 100 a | 0 d | 0 d | |
flum. gly. + dic. gly. +dic. | PRE POST1 POST2 | 0.07 1.12 + 0.56 1.12 + 0.56 | 99 a | 100 a | 98 ab | 100 a | 100 a | 0 d | 0 d | |
flum. gly. + dic. + aceto. dic. | PRE POST1 POST2 | 0.07 1.12 + 0.56 + 1.26 0.56 | 100 a | 100 a | 93 c | 100 a | 100 a | 0 d | 0 d | |
flum. gly. + dic. + aceto. + fom. gly. + dic. | PRE POST1 POST2 | 0.07 1.12 + 0.56 + 1.26 + 0.34 1.12 + 0.56 | 99 a | 100 a | 98 ab | 100 a | 100 a | 0 d | 0 d | |
flum. gly. + s-met. + fom. | PRE POST1 | 0.07 1.12 + 1.49 + 0.34 | 100 a | 100 a | 98 ab | 100 a | 100 a | 0 d | 0 d | |
aAll POST treatments included ammonium sulfate at 2.5% v/v; bActive ingredients (ai) rate used for acetochlor (aceto.), fomesafen (fom.), s-metolachlor (s-met.), flumioxazin (flum.). Acid equivalent (ae) rate used for dicamba (dic.) and glyphosate (gly.); cMeans within columns with no common letter (s) are significantly different according to Fishers Protected LSD at 5%; dPalmer amaranth percent control and population density evaluation periods: 3 weeks after PRE (3 WAP), 2 weeks after POST1 (2 WAP1), 2 weeks after POST2 (2 WAP2).
Treatmenta | Timing | Rateb | AMAPA controlc | AMAPA densityc | |||
---|---|---|---|---|---|---|---|
3 WAPd | 2 WAP1d | 2 WAP2d | 2 WAP2d | ||||
kg∙ai∙ha−1 or kg∙ae∙ha−1 | % | plants∙m−2 | |||||
Untreated Check | - | - | - | 21 a | |||
flum. dic. + gly. | PRE POST1 | 0.07 1.12 + 0.56 | 100 a | 100 a | 100 a | 0 b | |
flum. gly. + dic. gly. + dic. | PRE POST1 POST2 | 0.07 1.12 + 0.56 1.12 + 0.56 | 100 a | 100 a | 100 a | 0 b | |
flum. gly. + dic. + aceto. | PRE POST1 | 0.07 1.12 + 0.56 + 1.27 | 98 a | 100 a | 97 a | 1 b | |
flum. gly. + dic. + aceto. gly. + dic. | PRE POST1 POST2 | 0.07 1.12 + 0.56 + 1.27 1.12 + 0.56 | 100 a | 100 a | 100 a | 0 b | |
dic. + aceto. gly. + dic. | PRE POST1 | 0.56 + 1.27 1.12 + 0.56 | 100 a | 100 a | 98 a | 0 b | |
aceto. + metrn. gly. + dic. | PRE POST1 | 1.27 + 0.28 1.12 + 0.56 | 100 a | 100 a | 97 a | 0 b | |
flum. gly. + fom. + aceto. | PRE POST1 | 0.07 1.12 + 0.42 + 1.27 | 100 a | 100 a | 100 a | 0 b | |
s-met. + fom. gly. + lact. | PRE POST1 | 1.22 + 0.27 1.12 + 0.22 | 100 a | 100 a | 100 a | 0 b | |
s-met. + metrn. gly. + acfln. | PRE POST1 | 1.55 + 0.37 1.12 + 0.42 | 100 a | 100 a | 97 a | 0 b | |
clorm. + flum. + thif. gly. + thif. | PRE POST1 | 0.03 + 0.08 + 0.008 1.12 + 0.004 | 100 a | 100 a | 98 a | 0 b | |
aAll POST treatments included ammonium sulfate at 2.5% v/v; bActive ingredients (ai) rate used for flumioxazin (flum.), acetochlor (aceto.), acifluorfen (acfln.), s-metolachlor (s-met.), fomesafen (fom.), metribuzin (metrn.), chlorimuron (clorm.), thifensulfuron-methyl (thif.), lactofen (lact.). Acid equivalent (ae) rate used for dicamba (dic.) and glyphosate (gly.); c Means within columns with no common letter (s) are significantly different according to Fishers Protected LSD at 5%; dPalmer amaranth percent control and population density evaluation periods: 3 weeks after PRE (3 WAP), 2 weeks after POST1 (2 WAP1), 2 weeks after POST2 (2 WAP2).
At 2 WAP1, Palmer amaranth control ranged from 93% to 100% across the PRE followed by POST treatments in 2012 and 2013. By 2 WAP2, control values were 95% or better. Palmer amaranth control in dicamba PRE followed by glyphosate POST1 and dicamba PRE followed by glyphosate + dicamba + acetochlor + fomesafen POST1 at 2 WAP2 was significantly less than the remaining treatments at 97 and 95%, respectively. In contrast, Palmer amaranth control was excellent (100%) across all treatments in 2013. In 2012, all flumioxazin PRE followed by POST treatments provided excellent Palmer amaranth control (100%) at 2 WAP1. However, flumioxazin PRE followed by glyphosate + dicamba + acetochlor POST1 followed by dicamba POST2 provided significantly less Palmer amaranth control (93%) at 2 WAP1 in 2013. At 2 WAP2 in 2013, Palmer amaranth control was excellent (100%) across all flumioxazin PRE followed by POST treatments. Previous research has shown lower levels of Palmer amaranth control in dicamba POST only treatments which ranged between 59% to 83%, depending on the dicamba rate [
In study 2, all treatments provided 97% or better Palmer amaranth control. In addition, all PRE treatments were highly effective with > 98% control (
Pitted morningglory control varied significantly within treatments in 2012 and 2013 when evaluated at 2 WAP1 and 2 WAP2 compared to Palmer amaranth in study 1. This led to a treatment by year interaction being observed for 2 WAP1 and 2 WAP2 rating periods. Some experimental or environmental factors could have contributed to the treatment by year interaction observed, mainly the difference in rainfall observed between the two trial years [
The treatments containing PRE only applications (dicamba and flumioxazin) performed differently. Unlike in Palmer amaranth, a dicamba PRE only, controlled pitted morningglory better than a flumioxazin PRE only when rated 3 WAP (
Treatments containing two or three herbicide applications (PRE, POST1 and POST2) offered good to excellent (92% - 100%) pitted morningglory control; however, the PRE followed by POST1 were slightly less effective in 2012 than 2013. In 2013, all dicamba based treatments provided excellent (100%) pitted morningglory control at 2 WAP2. The non-dicamba treatment (flumioxazin PRE followed by glyphosate + S-metolachlor + fomesafen POST1) also showed excellent control (100%). Similarly, previous studies have shown good to excellent morningglory spp. control with dicamba POST containing treatments [
In study 2, pitted morningglory control varied among treatments, unlike what was observed in Palmer amaranth. Pitted morningglory control ranged from 87% to 97% across all of the PRE treatments at 3 WAP. Dicamba + acetochlor PRE was the least effective treatment at 87% control, whereas, chlorimuron +
Treatmenta | Timing | Rateb | IPOLA controlc | IPOLA densityc | ||||||
---|---|---|---|---|---|---|---|---|---|---|
3 WAPd | 2 WAP1d | 2 WAP2d | 2 WAP2d | |||||||
kg∙ai∙ha−1 or kg∙ae∙ha−1 | % | plants∙m−2 | ||||||||
2012 | 2013 | 2012 | 2013 | 2012 | 2013 | |||||
Untreated Control | - | - | - | - | - | 22 a | 19.7 b | |||
dic. | PRE | 1.12 | 92 b | 60 e | 75 d | 28 d | 63 b | 20 ab | 11 c | |
dic. gly. + dic. | PRE POST1 | 1.12 1.12 + 0.56 | 99 a | 100 a | 100 a | 97 a | 100 a | 0.7 fg | 0 g | |
dic. gly. + dic. + aceto. | PRE POST1 | 1.12 1.12 + 0.56 + 1.26 | 99 a | 98 ab | 100 a | 92 a | 100 a | 3.3 d | 0 g | |
dic. gly. + dic. + aceto. + fom. | PRE POST1 | 1.12 1.12 + 0.56 + 1.26 + 0.34 | 98 a | 98 ab | 100 a | 92 a | 100 a | 3 de | 0 g | |
dic. gly. + dic. gly. + dic. | PRE POST1 POST2 | 1.12 1.12 + 1.12 1.12 + 0.56 | 98 a | 98 ab | 100 a | 92 a | 100 a | 2.3 def | 0 g | |
dic. gly. + dic. + aceto. gly. + dic. | PRE POST1 POST2 | 1.12 1.12 + 0.56 + 1.26 1.12 + 0.56 | 100 a | 100 a | 100 a | 95 a | 100 a | 1.3 defg | 0 g | |
dic. gly. + dic. + aceto. + fom. gly. + dic. | PRE POST1 POST2 | 1.12 1.12 + 0.56 + 1.26 + 0.34 1.12 + 0.56 | 99 a | 100 a | 100 a | 98 a | 100 a | 0 g | 0 g | |
flum. | PRE | 0.07 | 83 c | 77 d | 93 abc | 48 c | 95 a | 11.7 c | 1 efg | |
flum. gly. + dic. | PRE POST1 | 0.07 1.12 + 1.12 | 100 a | 100 a | 92 bc | 97 a | 100 a | 0 g | 0 g | |
flum. gly. + dic. + aceto. | PRE POST1 | 0.07 1.12 + 1.12 + 1.26 | 99 a | 100 a | 90 c | 100 a | 100 a | 0 g | 0 g | |
flum. gly. + dic.+ aceto. + fom. | PRE POST1 | 0.07 1.12 + 1.12 + 1.26 + 0.34 | 99 a | 100 a | 88 c | 100 a | 100 a | 0 g | 0 g | |
flum. gly. + dic. gly. + dic. | PRE POST1 POST2 | 0.07 1.12 + 1.12 1.12 + 0.56 | 99 a | 98 ab | 87 c | 93.3 a | 100 a | 1.7 defg | 0.3 fg | |
flum. gly. + dic. + aceto. dic. | PRE POST1 POST2 | 0.07 1.12 + 1.12 + 1.26 0.56 | 99 a | 100 a | 90 c | 100 a | 100 a | 0 g | 1 efg | |
flum. gly. + dic. + aceto. + fom. gly. + dic. | PRE POST1 POST2 | 0.07 1.12 + 1.12 + 1.26 + 0.34 1.12 + 0.56 | 100 a | 100 a | 93 abc | 98 a | 100 a | 0.3 fg | 0 g | |
flum. gly. + s-met. + fom. | PRE POST1 | 0.07 1.12 + 1.49 | 100 a | 100 a | 88 c | 100 a | 100 a | 0.3 fg | 0 g | |
a All POST treatments included ammonium sulfate at 2.5% v/v; b Active ingredients (ai) rate used for acetochlor (aceto.), fomesafen (fom.), s-metolachlor (s-met.), flumioxazin (flum.). Acid equivalent (ae) rate used for dicamba (dic.) and glyphosate (gly.); cMeans within columns with no common letter (s) are significantly different according to Fishers Protected LSD at 5%; dPitted morningglory percent control and population density evaluation periods: 3 weeks after PRE (3 WAP), 2 weeks after POST1 (2 WAP1), 2 weeks after POST2 (2 WAP2).
flumioxazin + thifensulfuron was the most effective PRE treatment with 97% pitted morningglory control. At 2 WAP1, pitted morningglory control ranged from 97% to 100% across all treatments. Pitted morningglory control was significantly lower (although still a high level of control at 97%) in the flumioxazin PRE followed by glyphosate + dicamba POST1 followed by glyphosate + dicamba POST2 treatment. At 2 WAP2, very little differences were observed among the treatments (97% - 100% pitted morningglory control) with the exception of chloransulam + flumioxazin + thifensulfuron-methyl PRE followed by glyphosate + thifensulfuron POST1 at 93%. Monks et al. [
Treatmenta | Timing | Rateb | IPOLA controlc | IPOLA densityc | ||||
---|---|---|---|---|---|---|---|---|
3 WAPd | 2 WAP1d | 2 WAP2d | 2 WAP2d | |||||
kg∙ai∙ha−1 or kg∙ae∙ha−1 | % | plants∙m−2 | ||||||
Untreated Check | - | - | - | 24 a | ||||
flum. gly. + dic. | PRE POST1 | 0.07 1.12 + 0.56 | 90 abc | 100 a | 97 ab | 0.1 bc | ||
flum. gly. + dic. gly. + dic. | PRE POST1 POST2 | 0.07 1.12 + 0.56 1.12 + 0.56 | 95 ab | 97 b | 98 a | 0 c | ||
flum. gly. + dic. + aceto. | PRE POST1 | 0.07 1.12 + 0.56 + 1.27 | 88 bc | 100 a | 100 a | 0 c | ||
flum. gly. + dic. + aceto. gly. + dic. | PRE POST1 POST2 | 0.07 1.12 + 0.56 + 1.27 1.12 + 0.56 | 92 abc | 100 a | 100 a | 0 c | ||
dic. + aceto. gly. + dic. | PRE POST1 | 0.56 + 1.27 1.12 + 0.56 | 87 c | 100 a | 97 ab | 0 c | ||
aceto. + metrn. gly. + dic. | PRE POST1 | 1.27 + 0.28 1.12 + 0.56 | 90 abc | 100 a | 97 ab | 0.2 bc | ||
flum. gly. + fom. + aceto. | PRE POST1 | 0.07 1.12 + 0.42 + 1.27 | 95 ab | 100 a | 100 a | 0 c | ||
s-met. + fom. gly. + lact. | PRE POST1 | 1.22 + 0.27 1.12 + 0.22 | 92 abc | 100 a | 98 a | 0.2 bc | ||
s-met. + metrn. gly. + acfln. | PRE POST1 | 1.55 + 0.37 1.12 + 0.42 | 92 abc | 100 a | 100 a | 0.1 bc | ||
clorm. + flum. + thif. gly. + thif. | PRE POST1 | 0.03 + 0.08 + 0.008 1.12 + 0.004 | 97 a | 100 a | 93 b | 0.9 b | ||
a All POST treatments included ammonium sulfate at 2.5% v/v; b Active ingredients (ai) rate used for flumioxazin (flum.), acetochlor (aceto.), acifluorfen (acfln.), s-metolachlor (s-met.), fomesafen (fom.), metribuzin (metrn.), chlorimuron (clorm.), thifensulfuron-methyl (thif.), lactofen (lact.). Acid equivalent (ae) rate used for dicamba (dic.) and glyphosate (gly.); c Means within columns with no common letter (s) are significantly different according to Fishers Protected LSD at 5%; dPitted morningglory percent control and population density evaluation periods: 3 weeks after PRE (3 WAP), 2 weeks after POST1 (2 WAP1, 2 weeks after POST2 (2 WAP2).
These studies demonstrated the effectiveness of different dicamba based herbicide programs on difficult-to-control broadleaf weeds in South Carolina. Dicamba PRE alone was not as effective on broadleaf weed control in soybean compared to flumioxazin PRE only. This can be attributed to the high water solubility of dicamba and its rapid loss in the soil profile, especially in coarse textured soils [
In the treatments evaluated, those containing 2 applications (PRE followed by POST1) were similar in effectiveness as those containing 3 applications (PRE followed by POST1 and POST2). In terms of cost, fewer herbicide applications are more efficient and will be able to benefit growers who use these programs by reducing overall input costs. Dicamba PRE alone with no additional POST treatments provided the lowest level of weed control in these studies. Non-dicamba containing POST treatments did provide good to excellent control of Palmer amaranth and pitted morningglory. Although the treatments in these research studies showed good to excellent control of broadleaf weeds in diamba tolerant soybean, more research is needed on additional broadleaf weeds across different environments not present in the selected study locations to validate their effectiveness across a larger geographic area.
Technical Contribution No. 6607 of the Clemson University Experiment Station. This material is based upon work supported by the NIFA/USDA, under project number SC-1700499. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the USDA.
Mention of a trade name does not imply endorsement of the product by Clemson University to the exclusion of others that might be available.
Joseph, D.D., Marshall, M.W. and Sanders, C.H. (2017) Palmer Amaranth (Amaranthus palmeri S. Wats.) and Pitted Morningglory (Ipomoea lacunosa L.) Control in Dicamba Tolerant Soybean (Glycine max L.). American Journal of Plant Sciences, 8, 3429-3442. https://doi.org/10.4236/ajps.2017.813230