Response of Sesame to Selected Herbicides Applied Early in the Growing Season

Growth chamber experiments were conducted to evaluate the response of sesame to PRE and POST applications of soil residual herbicides. PRE applications of acetochlor and S-metolachlor at 1.26 and 1.43 kg ai·ha showed little or no sesame injury (0 to 1%) 4wks after herbicide treatments (WAT). POST treatments of acetochlor and trifluralin made 3wks after planting (WAP) resulted in greater sesame injury (40%) compared to applications at bloom (18%). Field studies were conducted in Texas and Oklahoma during the 2014 and 2015 growing seasons to determine sesame response to clethodim, diuron, fluometuron, ethalfluralin, quizalofop-P, pendimethalin, pyroxasulfone, trifluralin, and trifloxysulfuron-sodium applied 2, 3, or 4 weeks after planting (WAP). Late-season sesame injury with the dinitroaniline herbicides consisted of a proliferation of primary branching at the upper nodes of the sesame plant (in the shape/form of a broom). Ethalfluralin and trifluralin caused more “brooming” effect than pendimethalin. Some yield reductions were noted with the dinitroaniline herbicides. Trifloxysulfuron-sodium caused the greatest injury (up to 97%) and resulted in yield reductions from the untreated check. Early-season diuron injury (leaf chlorosis and necrosis) decreased as application timing was delayed, and late-season injury was virtually nonexistent with only slight chlorosis (<4%) still apparent on the lower leaves. Sesame yield was not consistently affected by the diuron treatments. Fluometuron caused early-season injury (stunting/chlorosis), and a reduction of yield was observed at one location. Pyroxasulfone applied 2 WAP caused up to 25% sesame injury (stunting) but did not result in a yield reduction. Quizalofop-P caused slight injury (<5%) and no reduction in yield.


Introduction
Sesame production has typically occurred in China and India using dehiscent varieties that are prone to capsule shattering during harvest; therefore, hand harvesting is nearly compulsory to minimize seed loss [1].Sesame was introduced to the US from Africa and was called beni/benne/benni.Betts [2] quotes letters from omas Jefferson that document his trials with sesame between 1808 and 1824.Jefferson stated that sesame ". ..is among the most valuable acquisitions our country has ever made. . . .I do not believe before that there existed so perfect a substitute for olive oil."He talks about the rule of thumb that still exists today that sesame will do well where cotton (Gossypium hirsutum L.) does well.Nondehiscent varieties were developed in the US during the 1950's to allow mechanized harvest [3], and this development has allowed hectarage to increase substantially [1].
e presence of weeds is a major obstacle in sesame production [1,[4][5][6][7][8] and can negatively influence sesame yield.Kropff and Spitters [9] reported that the major factor influencing sesame yield loss in a competitive situation between the crop and weed is the ratio between the relative leaf area of the weed and the crop at the time of crop canopy closure.e effects of weeds on sesame establishment and growth have been well documented.Balyan [10], Gurnah [11], and Singh et al. [12] reported weed-induced reductions of sesame yield up to 74% and a need for a critical weed-free period up to 50 days after planting.Babiker et al. [13] reported that unrestricted weed growth reduced sesame grain yield by 30% and keeping the sesame crop weed free for 2, 4, 6, and 8 weeks after planting increased the grain yield by 8, 37, 40, and 43%, respectively.ey concluded that the critical period of weed control in sesame appeared to be between 2 and 6 weeks after planting.Zuhair et al. [14] found that insufficient weed control during the early growth period of sesame caused 35 to 70% yield reductions, and they added that the critical period of weed control in sesame is 2 to 3 weeks after crop emergence.
With weak seedling vigor, limited competitive ability, and a lack of inexpensive and affordable labor, the use of preemergence (PRE) and/or postemergence (POST) herbicides is essential for commercially mechanized sesame production, especially in the US [7].Also, the long growing season for sesame requires that herbicides provide seasonlong control [4,6,7].Currently, S-metolachlor is the only herbicide registered for PRE use in the US but has caused sesame injury under certain conditions [15].In Texas, S-metolachlor resulted in 9 to 29% sesame stand reduction at one location, while at another location, stand reduction was ≤8% [15].At other locations, S-metolachlor provided 99% weed control and no injury [6].Regardless of earlyseason injury issues, sesame yield from the application of S-metolachlor was often greatest of all herbicides tested [6].
Herbicide tolerance may be affected by many factors including application timing [1].S-metolachlor-applied PRE can cause up to 47% injury to cotton on sandy soils; however, applications made after cotton emergence did not affect cotton stand [16].Kendig et al. [17] reported that POST applications of S-metolachlor to cotton at the four-leaf stage caused less reduction in cotton biomass than the application at the cotyledon stage.Jefferies et al. [18] reported that, in chickpea (Cicer arietinum L.), the combination of imazethapyr plus imazamox caused a height reduction and decreased node development at all growth stages; however, an application at the 9 to 12 node stage caused the most severe delay.
All POST herbicides that control broadleaf weeds in sesame have caused some sesame injury or yield reduction [5,7].For broadleaf weed problems in sesame, the use of soil-applied herbicides still appears to be the only option [4,6,7].However, since sesame hectares are increasing in areas of the US, there is a critical need to find more herbicides which can be used in sesame cultivation to extend weed control especially during the early portion of the growing season [13,14].Studies were undertaken to determine sesame tolerance to various PRE and POST herbicides that could be applied early in the growing stage to extend weed control and cause little sesame injury.

Materials and Methods
e growth chamber and field studies were conducted to compare sesame response to commonly used PRE and POST herbicides applied up to five weeks after sesame planting.
2.1.Growth Chamber Experiments.Two growth chamber experiments to evaluate the response of sesame to PRE and POSTapplications of soil residual herbicides were conducted in 2017 at Texas A&M University Weed Science Research Facility, College Station, TX.Each PRE and POST experiment was repeated 2x under similar growth chamber conditions and data pooled over time.

Sesame Variety and Soil.
Five seeds of "S-39" sesame variety were planted in 15 cm diameter plastic pots, and the pots were watered as needed.In the POST-response experiment, three healthy sesame plants were maintained at the time of herbicide application.e soil used in this study was collected from Brazos Valley Research Farm near College Station, TX, with no history of residual herbicide use.e soil texture was silty clay loam with pH 8.0 and 1.2% organic matter.
e growth chamber was maintained at 27/21 °C day/night temperature with 14 hours of photoperiod using artificial lights.

Plot Design, Herbicides, and Application.
e growth chamber experiments were laid out in a randomized complete-block design with four replications.
e PRE herbicides were applied the day following sesame planting, while POST applications of the herbicides were made at two growth stages: 3 wks after planting (WAP) when sesame growth stage was 3-4 leaf pairs and at bloom approximately 5 WAP.e PRE applications of acetochlor (Warrant ® , Monsanto Company, St. Louis, MO, 63167) at 1.26 and 2.52 kg ai•ha −1 , pethoxamid (not commercialized yet; FMC Corp., Philadelphia, PA, 19104) at 1.12 and 2.24 kg ai•ha −1 , and S-metolachlor (Dual II Magnum ® , Syngenta Crop Protection, LLC, Greensboro, NC, 27419) at 1.43 and 2.86 kg ai•ha −1 were applied at 1x and 2x of the labeled US doses, whereas acetochlor at 1.26 kg ai•ha −1 and trifluralin (Treflan ® , Helena Chemical Company, Collierville, TN, 38017) at 1.68 kg ai•ha −1 were applied at the 1x dose in POST-response experiment.Herbicides were applied using a single-tip spray chamber (DeVries Manufacturing Corp., Hollandale, MN, 56045) fitted with an XR110015 nozzle (TeeJet ® Technologies, Spraying Systems Co., Wheaton, IL, 60139) calibrated to deliver 140 L•ha −1 spray volume at 207 kPa pressure at a speed of 4.8 km•h −1 .

Sesame Injury
Sesame injury was evaluated 6 to 9 WAP (early season) and 11 to 19 WAP (late season) based on a scale of 0 (no sesame injury) to 100 (complete sesame death).Injury consisted of stunting, leaf chlorosis and necrosis, and brooming effect.e brooming effect is a proliferation of primary branching at the upper nodes of the sesame plant (in the shape/form of a broom).Branching typically does not occur from these nodes since they are primarily flowering nodes.When branching at these nodes does occur, flowers are not formed [19].ese branches are not typically long (<25 cm) and support 5 to 10 capsules as opposed to the primary branches found lower on the plant which can be almost a meter long and support up to 10x as many capsules [19].

Data
Analysis.An analysis of variance was performed using the ANOVA procedure for SAS (SAS Institute.1998.SAS user's guide.SAS Inst., Cary, NC) to evaluate the significance of herbicides and application timing on sesame response and yield.Fishers Protected LSD at the 0.05 level of International Journal of Agronomy probability was used for separation of mean differences.e untreated check was used for sesame injury ratings and yield comparison but was only included in yield data analysis.

Sesame Injury with PRE Herbicides.
e PRE application of acetochlor, pethoxamid, and S-metolachlor at the 1x dose resulted in 10% sesame injury 2 WAT, whereas 15 to 30% injury was observed with these herbicides applied at the 2x dose (Table 1).Similarly, in a study conducted in Florida, Sperry et al. [1] reported that PRE application of S-metolachlor at 1.42 and 2.78 kg ai•ha −1 resulted in 41 and 65% reduction in sesame plant height, respectively.At 4 WAT, slight or no injury was observed with the PRE applications of S-metolachlor and acetochlor at 1.43 and 1.26 kg ai•ha −1 , respectively; however, pethoxamid at 1.12 kg ai•ha −1 resulted in 7% sesame injury (Table 1).At the 2x dose, pethoxamid and S-metolachlor caused the greatest injury (39-46%), while acetochlor was less injurious (11%).Injury symptoms consisted of sesame plant stunting and curling of the leaves.

Sesame Injury with POST Herbicides.
e POST application of trifluralin (1.68 kg ai•ha −1 ) at 3 WAP showed a higher level (≥40%) of sesame injury at 2 and 4 WAT compared to the other POST treatments (Table 1).No difference in sesame response was noted with acetochlor applied 3 WAP or at sesame bloom.Averaged across all POST herbicide treatments, when evaluated 2 and 4 WAT, sesame injury was 28 and 40%, respectively, when POST applications were made 3 WAP, compared with 5 and 18% injury, respectively, with POST applications made at sesame bloom stage.Shorter internode length of the sesame plants resulted in the stunted growth following the POST application of these herbicides.

2014 Results
(1) Herbicide Injury.Early-season clethodim injury at any location was no greater than 5% when applied 2 to 3 WAP; however, the 4 WAP application of clethodim caused 18% injury at the Hale Center location (Table 2).No late-season injury with clethodim was noted at Knippa with any application timings, while 5% injury was noted with the 4 WAP application at Hale Center.At Lane, when evaluated 12 WAP, injury ranged from 1 to 5% but was not different than the untreated check.Clethodim has proven equally good at controlling both annual and perennial grasses, particularly Johnsongrass (Sorghum halepense (L.) Pers.) in sesame [5].
ere is a label in the US for clethodim (Select Max ® ) use in sesame which allows spraying at all growth stages except flowering [19].Clethodim applied during flowering has resulted in lack of capsule formation along the main stem of the plant and is commonly referred to as "cap gap" [19].
Diuron caused considerable leaf necrosis and chlorosis at both Texas locations but little to no injury was observed at the Lane location when rated early season, while late-season injury was 4% or less at all locations (Table 2).Grichar et al. [6], in an earlier study, reported that diuron applied PRE at 1.12 kg•ha −1 reduced sesame stands and caused sesame injury in one year in the Hale Center area; however, in south Texas no adverse effects with diuron were seen in the twoyear study.Typically, diuron injury with POST applications to sesame is transient, and by late-season, only slight leaf chlorosis may be noted on lower leaves [7].Fluometuron provided similar results to diuron with 12 to 47% early-season injury in Texas but <5% injury at the Oklahoma location when evaluated early season or late season.Grichar et al. [6] reported that fluometuron at 1.12 kg•ha −1 applied PRE in the High Plains region of Texas reduced sesame stand and caused injury in one of the two years, while no stand reduction or injury was noted at the south Texas location.
Sesame injury from quizalofop-P was 5% or less at all locations.Sesame injury from this herbicide has been virtually nonexistent at any rates or application timings (author's personal observation).
Ethalfluralin injury to sesame was the greatest with the 2 WAP application at Knippa (5%) and the 3 WAP application at Hale Center (10%) with little to no injury at Lane (Table 2).
is injury is typically in the form of stunting and leaf malformation.Late-season injury was only noted with the 4 WAP application at Knippa. is injury manifested itself as the brooming effect which was mainly seen on the upper portion of the plant and is only seen late season.
Early-season trifluralin injury (stunting and leaf malformation) at Knippa was greatest with the 3 and 4 WAP application, while at Hale Center, the 3 WAP application caused the greatest injury.No significant injury was noted at Lane.Late-season injury at Knippa was 50% with the 4 WAP application with no injury noted at the other locations (Table 2).e injury at Knippa was in the form of the brooming effect noted earlier. is type of injury is only seen with the dinitroaniline herbicides.
Pendimethalin injury early season at Knippa was the greatest with the 2 WAP application, while at Hale Center, all application timings resulted in significant injury.is injury, in the form of stunting and leaf malformation, decreased as the sesame plant aged.No injury was noted at Lane.Late-season injury was virtually nonexistent (≤4%), and little to no brooming effect was noted.
Typically, the dinitroaniline herbicides are applied preplant incorporated (PPI) or PRE; however, POST applications of these herbicides may be used to extend residual weed control throughout the growing season [20].Since the dinitroaniline herbicides have lower water solubility and can volatilize and photodecompose on the soil surface over time, these herbicides need to be mechanically incorporated or need rainfall or irrigation to move these herbicides into the weed seed zone [21][22][23][24].Uptake of these herbicides is primarily through roots and emerging shoots [25].Parker [26]  International Journal of Agronomy showed that trifluralin was more inhibitory to grain sorghum (Sorghum bicolor (L.) Moench) when absorbed through roots than emerging shoots.It is possible that the dinitroaniline herbicides will be concentrated in the extreme upper portions of the soil profile and weed seed may be able to germinate below the zone where dinitroaniline herbicides are located [27].In this case, emerging shoots pass through treated soil, whereas developing roots would be below the herbicide treated soil.e effectiveness of soil-applied herbicides is dependent upon several factors, including movement of the herbicide into the soil either through water provided by rainfall or irrigation or by mechanical incorporation [28,29].
(2) Sesame Yield.At Knippa, sesame yield was reduced from the untreated check with diuron and trifluralin applied 3 WAP and fluometuron applied 3 and 4 WAP (Table 3).At Hale Center, sesame yield was reduced when compared to the untreated check with diuron applied 4 WAP, ethalfluralin applied 2 and 4 WAP, and pendimethalin applied 2 and 3 WAP.At the Lane location, only trifluralin applied 2 WAP reduced sesame yield relative to the untreated check.
e yield reductions noted with diuron at Knippa and Hale Center were probably due to the early-season injury (>13%) noted at those locations.
Grichar et al. [6] concluded that it was best if the dinitroaniline herbicides were applied PRE due to severe sesame injury when applied PPI.Of the dinitroaniline herbicides, only pendimethalin (formulated as Prowl H 2 0) can be applied PRE [41]; however, annual grass control following pendimethalin applied PRE is often poor [42].Hussien et al. [43] reported that trifluralin at rates greater than 0.84 kg•ha −1 was harmful to sesame, while Schrodter and Rawson [44] reported that pendimethalin at 1.5 and 3.0 kg•ha −1 and trifluralin at 0.84 kg•ha −1 reduced sesame plant populations.Plant selectivity by herbicide placement is influenced greatly by the movement of the herbicide in soils [45].If the dinitroaniline herbicides move, they may come in contact with the absorptive sites of sesame and cause sesame injury [6].

2015 Results
(1) Sesame Injury.Early-season sesame injury with trifluralin was noted at Hale Center but no other locations (Table 4).At the 0.85 kg•ha −1 dose, sesame injury occurred with trifluralin applied 2 and 3 WAP, while at the 1.7 kg•ha −1 dose of trifluralin, sesame injury was noted at all application timings.When evaluated late season, sesame injury at Knippa and College Station was noted with both trifluralin doses applied 4 WAP, while at Hale Center, both doses and all application timings with the exception of trifluralin at 0.85 kg•ha −1 applied 3 WAP resulted in significant injury when compared to the untreated check.e late-season injury consisted of the brooming effect.No trifluralin injury was noted at Lane.Pendimethalin injury early season at Hale Center decreased as the sesame plants aged with >40% injury when pendimethalin was applied 2 WAP and <10% injury when applied 4 WAP (Table 4).No early-season injury was noted at the other locations.When evaluated late season, sesame injury with pendimethalin at Hale Center exhibited similar trends as the early-season rating with greater injury at the early application timing.Pendimethalin applications to sesame have 6 International Journal of Agronomy resulted in less brooming effect than with other of the dinitroaniline herbicides (author's personal observation).
Early-season ethalfluralin injury to sesame was noted only at the Hale Center location (Table 4).Sesame injury with ethalfluralin at 0.84 kg•ha −1 decreased from 18 to 5% as herbicide application was delayed, but at 1.68 kg•ha −1 , this trend was not seen as injury ranged from 10 to 17%.Lateseason injury with ethalfluralin was noted at Knippa with both doses applied 4 WAP, and this injury was in the form of the brooming effect.At the later evaluation at the Hale Center location, similar trends as seen with the early-season evaluation were noted, with injury at the lower dose decreasing as herbicide application was delayed, but this was not true with the higher dose.e dose of a dinitroaniline herbicide can affect sesame stand establishment.e 1/2x dose of ethalfluralin, pendimethalin EC, and trifluralin or the 3/4x dose of pendimethalin H 2 O resulted in higher stand counts than the 1 to 2x dose of these herbicides when incorporated with rolling cultivator mixing wheels [46].Previous research by Grichar et al. [4,6] reported sesame injury following the use of dinitroaniline herbicides applied PPI using various incorporation methods.Also, Grichar et al. [4] reported that ethalfluralin, pendimethalin, and trifluralin reduced sesame stand numbers when compared with the untreated check.In that study, the dinitroaniline herbicides were incorporated 2.5 cm deep with a tractordriven power tiller.In another study, Grichar et al. [6] reported that a spring-tooth harrow, with the lack of the ability to adjust incorporation depth, caused similar problems.However, the use of rolling cultivator mixing wheels, set to a depth of less than 2.5 cm, resulted in excellent sesame stands.
erefore, only a shallow incorporation of the dinitroaniline herbicides can be done when used in sesame to ensure a good stand.

International Journal of Agronomy
Early-season fluometuron injury was noted with the 2 WAP application at Knippa and Lane, while at the Hale Center location, sesame injury decreased as application timing was delayed. is trend also was visible at the lateseason rating at Hale Center, but no late-season injury was apparent at the other locations (Table 4).
Sesame injury with pyroxasulfone early season and late season was visible at Hale Center but no other locations.Sesame injury early season was less with the 4 WAP application then the 3 WAP application; however, at the lateseason evaluation sesame injury decreased as pyroxasulfone application was delayed.
Diuron injury was noted with the 2 WAP application at Knippa, Hale Center, and Lane, but the 3 and 4 WAP applications did not cause any sesame injury at Knippa or Lane.Late-season sesame injury was 5% or less at all locations.
Trifloxysulfuron-sodium injury to early-season sesame ranged from 45 to 82% at Knippa and 67 to 97% at Hale Center, but no injury was noted at Lane (Table 4).No late-season injury at Knippa with trifloxysulfuron-sodium applied 2 WAP was noted; however, the 4 WAP application resulted in >40% injury.Sesame injury at Hale Center was inconsistent and ranged from 5% with the 3 WAP application to 97% with the 2 WAP application.In cotton, trifloxysulfuron-sodium applied POST at the one-, three-, or five-leaf stage resulted in 22, 16, and 6% injury, respectively, when evaluated 21 days after treatment; however, no effect on yield was noted [47].Tobacco (Nicotiana tabacum L.) metobilized 14 C-trifloxysulfuron-sodium rapidly, with 60.9% of the absorbed herbicide remaining in the parent herbicide form 4 h after treatment, whereas only 12.1% remained after 72 h [48].ese results show that the limited absorption and translocation, as well as rapid metabolism, are the basis for tobacco tolerance to foliar-applied trifloxysulfuron-sodium.
(2) Sesame Yield.At Knippa, only trifloxysulfuron-sodium applied 3 and 4 WAP reduced sesame yields when compared with the untreated check (Table 5).At Hale Center, the 2

Conclusion
As these results show, sesame has a great ability to compensate for injury.In these studies where some of the herbicides caused severe sesame injury, sesame yields were good because the plants can compensate for open space and poor growth by additional branches with capsules [7,15,49].However, branching can only compensate for gaps of less than 30 cm.Wider gaps not only lead to lower yields, but also let light through the canopy to encourage late-season weed emergence and growth [49].A limited number of herbicides are available that can help control weeds during the production of sesame.Increasing the number of effective herbicides without crop injury would be a welcomed addition in sesame production.Annual grasses can be easily controlled in sesame with clethodim and quizalofop-P without sesame injury; however, only clethodim is approved for use on sesame in the US.Also, the label states that clethodim should not be applied during sesame flowering as an inhabitation of blooming and/or capsule formation may result [50].e use of herbicides such as diuron or fluometuron is not without issues.ese herbicides can effectively control weeds but can also affect sesame growth and yield as seen in these studies [5,7].Also, the dinitroaniline herbicides can extend weed control when used POST but can result in sesame injury and yield reductions in some instances.
Another option that may be available to growers is the use of cultivation to control unwanted or hard-to-kill weeds.However, cultivation cannot reliably control weeds within the seed row that emerge while the sesame is emerging.Since sesame grows slowly in the first three to four weeks, many growers have waited three to four weeks to cultivate.Sesame roots follow moisture, and with rain or irrigation in the first few weeks after planting, the roots may grow laterally and stay near the surface.Cultivating too close to the plant can cut roots, and plants will wilt quickly.In times of a dry season, roots grow more vertically allowing for closer cultivation.e cultivation process can throw soil up on the base of the plant covering any small weed after sesame plants are 10 to 15 cm in height.

Data Availability
e data used to support the findings of this study are available from the corresponding author upon request.
Readers may gain access to the references by using View at Publisher, View at Google Scholar, or View at Scopus.

Table 1 :
Sesame injury with PRE and POST applications of soil residual herbicides in growth chamber experiments conducted at College Station, TX, in 2017 a .WAT, weeks after herbicide treatment; b means presented within each column with no common letter(s) are significantly different at α � 0.05; c data were arcsine square root transformed before analysis; however, back-transformed real mean values are presented based on the interpretation from the transformed data; d a priori orthogonal contrast, * * significant (P < 0.01).International Journal of Agronomy a WAP, weeks after sesame planting;

Table 2 :
Early-and late-season sesame injury with selected herbicides applied 2, 3, or 4 weeks after planting at Knippa, Hale Center (Texas), and Lane (Oklahoma) in 2014.

Table 3 :
Sesame yield at Knippa, Hale Center (Texas), and Lane (Oklahoma) as influenced by selected herbicides applied 2, 3, or 4 weeks after planting in 2014.

Table 4 :
Early-and late-season sesame injury at Knippa, Hale Center, and College Station (Texas) and Lane (Oklahoma) with selected herbicides applied 2, 3, or 4 weeks after planting in 2015.
b WAP, weeks after planting.

Table 5 :
Sesame yield at Knippa, Hale Center, and College Station (Texas) and Lane (Oklahoma) as influenced by selected herbicides applied 2, 3, or 4 weeks after planting in 2015.eithertrifluralin at 0.85 and 1.7 kg•ha −1 , pendimethalin at 1.06 and 2.12 kg•ha −1 , or ethalfluralin at 0.84 and 1.68 kg•ha −1 and trifloxysulfuron-sodium applied 2 and 4 WAP reduced the yield from the untreated check (Table5).At Lane, trifluralin at 0.85 kg•ha −1 applied 2 WAP and ethalfluralin at 1.68 kg•ha −1 applied 3 WAP reduced the sesame yield when compared with the untreated check.No yield difference from the untreated check was noted with trifluralin or pendimethalin at any application timing at the College Station location.At this location, pendimethalin at 1.06 kg•ha −1 applied 4 WAP or pendimethalin at 2.12 kg•ha −1 applied 2 WAP produced the highest yields.