Agricultural Sciences
Vol.05 No.11(2014), Article ID:50063,7 pages
10.4236/as.2014.511109

Tolerance of Maize (Zea mays L.) and Soybean [Glycine max (L.) Merr.] to Late Applications of Postemergence Herbicides

Kris J. Mahoney1*, Robert E. Nurse2, Peter H. Sikkema1

1University of Guelph, Ridgetown Campus, Ridgetown, Canada

2Agriculture and Agri-Food Canada, Harrow, Canada

Email: *kmahoney@uoguelph.ca

Copyright © 2014 by authors and Scientific Research Publishing Inc.

This work is licensed under the Creative Commons Attribution International License (CC BY).

http://creativecommons.org/licenses/by/4.0/

Received 12 July 2014; revised 22 August 2014; accepted 20 September 2014

ABSTRACT

Seven maize (Zea mays L.) and three soybean [Glycine max (L.) Merr.] field experiments were conducted from 2006 to 2009 at various locations in southern Ontario, Canada to determine the tolerance of these crops to late applications of the maximum labeled herbicide dose. Single and sequential (simulating a spray overlap) applications were evaluated for visible injury, plant height, and crop yield in the absence of weed competition. Maize exhibited excellent tolerance to herbicides applied at the 9- to 10-leaf growth stage as visible injury levels for almost all tested herbicides was similar to the untreated control 7 days after treatment (DAT). However, the sequential application of dicamba/diflufenzopyr or foramsulfuron caused 6 and 8% injury 7 DAT and 8 and 14% reduction in maize height 28 DAT, respectively. The observed injury and stunting were transient as there were no differences in yield at harvest. Soybean displayed good tolerance to most herbicides applied at the 7th trifoliate leaf growth stage as visible injury levels were similar to the untreated control. However, thifensulfuron-methyl was injurious regardless of application and imazethapyr was injurious with sequential applications. For example, single thifensulfuron-me- thyl, sequential thifensulfuron-methyl, and sequential imazethapyr application treatments caused 35, 48, and 25% injury 7 DAT, respectively. Sequential thifensulfuron-methyl treatments also caused a 28 and 17% reduction in soybean height 14 and 28 DAT, respectively. Visual injury continued to be detected up to 56 DAT for single thifensulfuron-methyl, sequential thifensulfuron- methyl, and sequential imazethapyr treatments. But, soybean yields were reduced by 10% for only sequential thifensulfuron-methyl application treatments. For all other herbicides tested, the yields at harvest were similar to the untreated control. This research demonstrated that maize had exceptional tolerance to all the herbicides used in this study whereas soybean was tolerant to most of the herbicides used in this study.

Keywords:

Critical Weed-Free Period, Injury, Yield

1. Introduction

The critical weed-free period has provided Ontario growers with the knowledge of when to control the weeds that cause detrimental yield loss in maize [1] and soybean [2] for quite some time. Researchers have also recognized that the critical weed-free period can vary from year to year and location to location [3] [4] , undermining the potential utility and implementation of this integrated weed management strategy [5] . Yet, research continues to be conducted as a better understanding of some of the underlying physiological mechanisms that underpin the critical weed-free period have recently been published [6] [7] . In general, crops need to be maintained under weed-free conditions from the start of the critical weed-free period until at least the 10-leaf stage in maize [1] [3] and the R1 (early flowing) stage in soybean [2] [3] .

Ontario maize and soybean growers have numerous herbicide options [8] for managing weeds during the critical weed-free period. Unfortunately, growers can sometimes miss registered herbicide application windows due to adverse weather conditions or mechanical breakdowns which leave large, highly competitive weeds present in the crop at a point beyond the critical weed-free period when rapid yield loss occurs [1] - [3] . At this time, growers would like to apply a high dose of postemergence (POST) herbicide to ensure effective control of these large weeds, but growers also are concerned that crop injury could negatively impact yield. Regrettably, the tolerance of maize and soybean to a high herbicide dose at a late POST application timing is largely unknown. The exception to this is maize, which can tolerate over two-fold of the maximum labeled dose of glyphosate applied at the 10-leaf stage with minimal injury and little to no yield loss [9] . Furthermore, to the best of our knowledge, few studies have been conducted in the absence of confounding weed competition effects that examine both a range of herbicides comparing relative crop tolerance [10] and the tolerance of crops to a late POST herbicide application [11] . Therefore, the objective of this research was to determine the tolerance of maize and soybean to a late application of select POST herbicides in the absence of weed interference.

2. Materials and Methods

2.1. Study Establishment

A total of ten field experiments (seven for maize and three for soybean) were conducted over a four-year period (2006 to 2009) at various locations in southern Ontario, Canada (Table 1). Maize and soybean experiments were designed as a randomized complete block, replicated four times. Seven herbicides were used in maize and eight herbicides were used in soybean and all herbicides were applied in a single application of the maximum labeled dose in Ontario [8] or as sequential applications to simulate spray overlap. In the maize experiments, the herbicides used were nicosulfuron (25 g∙ai∙ha−1), foramsulfuron (70 g∙ai∙ha−1), dicamba/diflufenzopyr (200 g∙ai∙ha−1), mesotrione + atrazine (100 + 280 g∙ai∙ha−1), bromoxynil + atrazine (280 + 1500 g∙ai∙ha−1), prosulfuron + dicamba (10 + 140 g∙ai∙ha−1), and 2,4-D/atrazine (1404 g∙ai∙ha−1). Whereas in the soybean experiments, the herbicides used were glyphosate (1800 g∙ae∙ha−1), imazethapyr (100 g∙ai∙ha−1), chlorimuron-ethyl (9 g∙ai∙ha−1), thifensul- furon-methyl (6 g∙ai∙ha−1), cloransulam-methyl (17.5 g∙ai∙ha−1), fomesafen (240 g∙ai∙ha−1), bentazon (1080 g∙ai∙ha−1), and quizalofop-p-ethyl (72 g∙ai∙ha−1). In all maize and soybean experiments, an untreated weed-free control treatment was included in addition to the single and sequential application POST herbicide treatments.

In both the maize and soybean experiments, each treatment plot was 2 m wide by 8 to 10 m long. Glyphosate- resistant maize hybrids (Table 1) were seeded 4 to 5 cm deep at a rate of approximately 75,000 seeds∙ha−1 in rows spaced 0.75 m apart. Glyphosate-resistant soybean cultivars (Table 1) were seeded 2.5 to 3 cm deep at a rate of approximately 480,000 seeds∙ha−1 in rows spaced 0.75 m apart. Herbicide treatments were applied to maize at the 9- to 10-leaf growth stage and to soybean at the 7th trifoliate leaf growth stage, both application timings were later than recommended [8] . At Exeter, herbicides were applied using a CO2 pressurized backpack sprayer calibrated to deliver 200 L∙ha−1 at 240 kPa through Tee-Jet 8002 VS nozzles (Spraying Systems Co., Glendale Heights, IL). At Harrow, a CO2 pressurized backpack sprayer delivered 222 L∙ha−1 at 210 kPa through

Table 1. Seeding and emergence dates of maize hybrids and soybean cultivars and the spray date for postemergence herbicides used in ten field experiments established from 2006 to 2009 at various locations in Ontario, Canada to examine the tolerance of maize and soybean to late applications.

aExeter (43.3500˚N, 81.4833˚W), Harrow (42.0333˚N, 82.9167˚W), and Ridgetown sites A and B (42.4406˚N, 81.8842˚W).

Tee-Jet 11003 XR nozzles (Spraying Systems Co., Glendale Heights, IL). At Ridgetown, a CO2 pressurized backpack sprayer delivered 200 L∙ha−1 at 207 kPa through Ultra-Low Drift 120-02 nozzles (Hypro, New Brighton, MN). All plots were maintained weed-free for the entire growing season using preemergence herbicides and hand weeding as needed.

2.2. Data Collection and Analysis

In both the maize and soybean experiments, visible crop injury was rated 3, 7, 14, 21, 28, and 56 days after treat- ment (DAT) based on a scale of 0 (no injury) to 100% (complete plant death) relative to untreated, weed-free control plants. Average plant height was recorded 28 and 56 DAT in maize by measuring the height of the crop from the soil surface to the extended leaf height and 14 and 28 DAT in soybean by measuring the height of the crop from the soil surface to the growing point of the plant. Both crops were harvested at maturity using a small plot combine and crop moisture and weight were recorded; final yields were adjusted to 15.5 and 13% moisture content for maize and soybean, respectively. Data for crop injury, crop height, and crop yield were analyzed separately by crop using PROC MIXED (SAS Ver. 9.2, SAS Institute Inc., Cary, NC). In the individual analysis of the maize and soybean experiments, variances were divided into fixed (herbicide treatment) and random effects [block; environment (i.e., year or location-year combinations); and the herbicide treatment × environment interaction]. The significance of the fixed effect in the maize and soybean experiments was tested using an F-test and the significance of random effects was tested using a Z-test of the variance estimate. PROC UNIVARIATE in SAS was used to test data for normality and homogeneity of variance. The herbicide treatment × environment interactions in maize and soybean experiments were not significant and therefore the data for each set of experiments were pooled across environments within each crop. Means were separated using Fisher’s Protected LSD at P < 0.05.

3. Results and Discussion

3.1. Maize Experiments

Maize exhibited excellent tolerance to the POST herbicides applied at the 9- to 10-leaf growth stage. At 3 DAT, only the sequential application of 2,4-D/atrazine caused significant visible injury of 9% (Table 2). At 7 DAT, the sequential application treatments of dicamba/diflufenzopyr, foramsulfuron, and 2,4-D/atrazine caused 6, 8, and 9% injury, respectively (Table 2). Sequential applications tended to cause at least two-fold greater injury than a single application. For example, 3% injury was observed for a single foramsulfuron application whereas the sequential application treatment caused 7% injury 14 DAT (Table 2). Furthermore, a single application of

Table 2. Visible injury of maize after late applications of postemergence herbicides at three locations (Exeter, Harrow, and Ridgetown) in Ontario, Canada in 2006 and 2007.ab

aAbbreviations: DAT, days after treatment; fb, followed immediately by. bMeans followed by the same letter within a column are not significantly different according to Fisher’s Protected LSD (P < 0.05). cIncluded Agral 90 at 0.2% v/v. dIncluded 28% UAN at 2.5 L∙ha−1. eIncluded Agral 90 at 0.25% v/v and 28% UAN at 1.25% v/v.

dicamba/diflufenzopyr caused no injury, but the sequential application caused 6% injury 14 DAT (Table 2). Similar levels of injury to maize by foramsulfuron [12] - [15] and dicamba/diflufenzopyr [16] - [19] have been reported. Conversely, up to 16% injury 3 DAT has been found in maize treated with twice the labeled dose of foramsulfuron and 23% injury 7 DAT for maize treated with twice the dose of dicamba/diflufenzopyr [10] . Maize tolerance to foramsulfuron can vary considerably by application timing and maize hybrid [20] [21] . In the current study, the visible injury was transient with reduced injury observed at 21, 28, and 56 DAT. At 56 DAT, there were no differences in injury among the treated and non-treated maize (Table 2). Although little to no visible injury was detected for the foramsulfuron or dicamba/diflufenzopyr treatments 28 DAT (Table 2), maize plants at this time were shorter than the untreated control. For example, a 9% reduction in maize height was recorded for a single foramsulfuron application and the sequential application treatment caused a 14% reduction in height 28 DAT (Table 3). The height of maize plants treated with a single application of dicamba/diflufenzopyr was similar to the untreated control, whereas sequential applications caused an 8% reduction in height 28 DAT (Table 3). This is similar to other studies which demonstrated stunting or reduced growth in maize due to applications of foramsulfuron or dicamba/diflufenzopyr [10] [12] - [14] . Nevertheless, the observed reductions in height in this study were transient as no differences were detected among the treated and non-treated maize by 56 DAT. Furthermore, the excellent tolerance to the herbicides used in this study was confirmed as the final maize yields were similar to the untreated control across all treatments (Table 3), consistent with other studies [10] [16] [19] .

3.2. Soybean Experiments

Soybean displayed good tolerance to most of the POST herbicides applied in a single application at the 7th trifoliate leaf growth stage as visible injury levels 3 and 7 DAT for almost all of these treatments were similar to the untreated control. The exception to this trend was thifensulfuron-methyl, which caused 27% injury 3 DAT and 35% injury 7 DAT (Table 4), which concurs with other studies [22] [23] . Injury levels observed 7 DAT for se-

Table 3. Maize height and yield after late applications of postemergence herbicides at three locations (Exeter, Harrow, and Ridgetown) in Ontario, Canada in 2006 and 2007.ab

aAbbreviations: DAT, days after treatment; fb, followed immediately by. bMeans followed by the same letter within a column are not significantly different according to Fisher’s Protected LSD (P < 0.05). cIncluded Agral 90 at 0.2% v/v. dIncluded 28% UAN at 2.5 L∙ha−1. eIncluded Agral 90 at 0.25% v/v and 28% UAN at 1.25% v/v.

Table 4. Visible injury of soybean after late applications of postemergence herbicides at Ridgetown, Ontario, Canada in 2007 to 2009.ab

aAbbreviations: DAT, days after treatment; fb, followed immediately by. bMeans followed by the same letter within a column are not significantly different according to Fisher’s Protected LSD (P < 0.05). cIncluded Agral 90 at 0.25% v/v and 28% UAN at 2 L∙ha−1. dIncluded Agral 90 at 0.2% v/v and 28% UAN at 2 L∙ha−1. eIncluded Agral 90 at 0.1% v/v and 28% UAN at 8 L∙ha−1. fIncluded Agral 90 at 0.25% v/v and 28% UAN at 2.5 L∙ha−1. gIncluded Turbocharge at 0.5% v/v. hIncluded 28% UAN at 10 L∙ha−1. iIncluded Sure-mix at 0.5% v/v.

quential chlorimuron-ethyl, sequential imazethapyr, and sequential thifensulfuron-methyl treatments were greater than the untreated control with 19, 25, and 48% injury, respectively (Table 4). This is similar to other studies which demonstrated 15 to 20% injury from chlorimuron-ethyl [24] [25] , 16 to 30% injury from imazethapyr [22] [23] [26] - [28] , and up to 44% injury from thifensulfuron-methyl [29] . In this study, soybean injury decreased over time across all treatments. However, soybean injury continued to be detected up to 56 DAT for sequential imazethapyr, single thifensulfuron-methyl, and sequential thifensulfuron-methyl treatments with 13, 20, and 29% injury, respectively (Table 4). For sequential thifensulfuron-methyl treatments, visual injury symptoms were also coupled with decreased plant height. For example, sequential thifensulfuron-methyl treatments caused a 28 and 17% reduction in plant height 14 and 28 DAT, respectively (Table 5), similar to previous research [26] [29] . In the current study, persistent observations of injury and reduced height resulted in a 10% reduction in soybean yield for sequential thifensulfuron-methyl treatments (Table 5), consistent with other studies [22] [26] [27] [29] . For all other treatments used in this study, soybean exhibited good tolerance to these herbicides as the yields at harvest were similar to the untreated control (Table 5).

4. Conclusions

For Ontario maize and soybean growers concerned about crop injury when a high dose of herbicide is applied later than recommended [8] , this research demonstrated that maize had exceptional tolerance to all the herbicides applied at the 9- to 10-leaf growth stage. This study expands upon related work with glyphosate in maize [9] . The most injurious treatments in this study, sequential foramsulfuron and sequential 2,4-D/atrazine treatments, caused only 8 and 9% injury 7 DAT, respectively. Yet, by harvest, these and the other herbicides tested

Table 5. Soybean height and yield after late applications of postemergence herbicides at Ridgetown, Ontario, Canada in 2007 to 2009.ab

aAbbreviations: DAT, days after treatment; fb, followed immediately by. bMeans followed by the same letter within a column are not significantly different according to Fisher’s Protected LSD (P < 0.05). cIncluded Agral 90 at 0.25% v/v and 28% UAN at 2 L∙ha−1. dIncluded Agral 90 at 0.2% v/v and 28% UAN at 2 L∙ha−1. eIncluded Agral 90 at 0.1% v/v and 28% UAN at 8 L∙ha−1. fIncluded Agral 90 at 0.25% v/v and 28% UAN at 2.5 L∙ha−1. gIncluded Turbocharge at 0.5% v/v. hIncluded 28% UAN at 10 L∙ha−1. iIncluded Sure-mix at 0.5% v/v.

had no effect on yield when compared to the untreated weed-free control. Conversely, soybean growers needing a late POST application using a high dose should exercise some caution during herbicide selection as soybean was tolerant to most of the herbicides used in this study. Thifensulfuron-methyl was injurious regardless of application and imazethapyr was injurious with sequential applications as significant soybean injury was detected from 3 to 56 DAT for these herbicides. However, soybean yield were reduced by 10% for only sequential thifensulfuron-methyl treatments. For the remaining herbicides, soybean yields at harvest were similar to the untreated control, indicative of good tolerance.

Acknowledgements

The authors acknowledge Lynette Brown, Todd Cowan, Chris Kramer, Elaine Lepp, Christy Shropshire, and Josh Vyn for their technical assistance in these studies and funding support from the Grain Farmers of Ontario.

References

  1. Hall, M.R., Swanton, C.J. and Anderson, G.W. (1992) The Critical Period of Weed Control in Grain Corn (Zea mays). Weed Science, 40, 441-447.
  2. Van Acker, R.C., Swanton, C.J. and Weise, S.F. (1993) The Critical Period of Weed Control in Soybean [Glycine max (L.) Merr.]. Weed Science, 41, 194-200.
  3. Halford, C., Hamill, A.S., Zhang, J. and Doucet, C. (2001) Critical Period of Weed Control in No-Till Soybean (Glycine max) and Corn (Zea mays). Weed Technology, 15, 737-744. http://dx.doi.org/10.1614/0890-037X(2001)015[0737:CPOWCI]2.0.CO;2
  4. Knezevic, S.Z., Evans, S.P., Blankenship, E.E., Van Acker, R.C. and Lindquist, J.L. (2002) Critical Period for Weed Control: The Concept and Data Analysis. Weed Science, 50, 773-786. http://dx.doi.org/10.1614/0043-1745(2002)050[0773:CPFWCT]2.0.CO;2
  5. Swanton, C.J. and Weise, S.F. (1991) Integrated Weed Management: The Rationale and Approach. Weed Technology, 5, 657-663.
  6. Green-Tracewicz, E., Page, E.R. and Swanton, C.J. (2012) Light Quality and the Critical Period for Weed Control in Soybean. Weed Science, 60, 86-91. http://dx.doi.org/10.1614/WS-D-11-00072.1
  7. Page, E.R., Tollenaar, M., Lee, E.A., Lukens, L. and Swanton, C.J. (2009) Does the Shade Avoidance Response Contribute to the Critical Period for Weed Control in Maize (Zea mays)? Weed Research, 49, 563-571. http://dx.doi.org/10.1111/j.1365-3180.2009.00735.x
  8. Ontario Ministry of Agriculture, Food and Rural Affairs (2012) Guide to Weed Control. Publication 75, Toronto, ON, 400 p.
  9. Mahoney, K.J., Nurse, R.E., Everman, W.J., Sprague, C.L. and Sikkema, P.H. (2014) Tolerance of Corn (Zea mays L.) to Early and Late Glyphosate Applications. American Journal of Plant Science, 5, 2748-2754. http://dx.doi.org/10.4236/ajps.2014.518291
  10. VanGessel, M.J., Johnson, Q.R. and Scott, B.A. (2009) Evaluating Postemergence Herbicides for Relative Corn Safety. Crop Management, 8. http://dx.doi.org/10.1094/CM-2009-0806-01-RS
  11. Young, B.G., Young, J.M., Matthews, J.L., Owen, M.D.K., Zelaya, I.A., Hartzler, R.G., Wax, L.M., Rorem, K.W. and Bollero, G.A. (2003) Soybean Development and Yield as Affected by Three Postemergence Herbicides. Agronomy Journal, 95, 1152-1156. http://dx.doi.org/10.2134/agronj2003.1152
  12. Bunting, J.A., Sprague, C.L. and Riechers, D.E. (2004) Proper Adjuvant Selection for Foramsulfuron Activity. Crop Protection, 23, 361-366. http://dx.doi.org/10.1016/j.cropro.2003.08.022
  13. Bunting, J.A., Sprague, C.L. and Riechers, D.E. (2005) Incorporating Foramsulfuron into Annual Weed Control Systems for Corn. Weed Technology, 19, 160-167. http://dx.doi.org/10.1614/WT-04-063R1
  14. Nurse, R.E., Hamill, A.S., Swanton, C.J., Tardif, F.J. and Sikkema, P.H. (2007) Weed Control and Yield Response to Foramsulfuron in Corn. Weed Technology, 21, 453-458. http://dx.doi.org/10.1614/WT-06-071.1
  15. Soltani, N., Shropshire, C. and Sikkema, P.H. (2014) Volunteer Glyphosate and Glufosinate Resistant Corn Competitiveness and Control in Glyphosate and Glufosinate Resistant Corn. Agricultural Sciences, 5, 402-409. http://dx.doi.org/10.4236/as.2014.55042
  16. Soltani, N., Shropshire, C. and Sikkema, P.H. (2010) Control of Common Cocklebur (Xanthium strumarium L.) in Corn. Canadian Journal of Plant Science, 90, 933-938. http://dx.doi.org/10.4141/cjps10065
  17. Soltani, N., Shropshire, C. and Sikkema, P.H. (2011) Giant Ragweed (Ambrosia trifida L.) Control in Corn. Canadian Journal of Plant Science, 91, 577-581. http://dx.doi.org/10.4141/cjps2010-004
  18. Soltani, N., Vyn, J.D. and Sikkema, P.H. (2009) Control of Common Waterhemp (Amaranthus tuberculatus var. rudis) in Corn and Soybean with Sequential Herbicide Applications. Canadian Journal of Plant Science, 89, 127-132. http://dx.doi.org/10.4141/CJPS08051
  19. Vyn, J.D., Swanton, C.J., Weaver, S.E. and Sikkema, P.H. (2006) Control of Amaranthus tuberculatus var. rudis (Common Waterhemp) with Pre and Post-Emergence Herbicides in Zea mays L. (Maize). Crop Protection, 25, 1051- 1056. http://dx.doi.org/10.1016/j.cropro.2006.01.016
  20. Bunting, J.A., Sprague, C.L. and Riechers, D.E. (2004) Corn Tolerance as Affected by the Timing of Foramsulfuron Applications. Weed Technology, 18, 757-762. http://dx.doi.org/10.1614/WT-03-178R1
  21. Bunting, J.A., Sprague, C.L. and Riechers, D.E. (2004) Physiological Basis for Tolerance of Corn Hybrids to Foramsulfuron. Weed Science, 52, 711-717. http://dx.doi.org/10.1614/WS-04-008R
  22. Simpson, D.M. and Stoller, E.W. (1995) Response of Sulfonylurea-Tolerant Soybean (Glycine max) and Selected Weed Species to Imazethapyr and Thifensulfuron Combinations. Weed Technology, 9, 582-586.
  23. Simpson, D.M. and Stoller, E.W. (1996) Thifensulfuron and Imazethapyr Interaction at the ALS Enzyme Sulfonylurea-Tolerant Soybean (Glycine max). Weed Science, 44, 763-768.
  24. Johnson, B.F., Bailey, W.A., Wilson, H.P., Holshouser, D.L., Herbert Jr., D.A. and Hines, T.E. (2002) Herbicide Effects on Visible Injury, Leaf Area, and Yield of Glyphosate-Resistant Soybean (Glycine max). Weed Technology, 16, 554-566. http://dx.doi.org/10.1614/0890-037X(2002)016[0554:HEOVIL]2.0.CO;2
  25. Monks, C.D., Wilcut, J.W. and Richburg III, J.S. (1993) Broadleaf Weed Control in Soybean (Glycine max) with Chlorimuron Plus Acifluorfen or Thifensulfuron Mixtures. Weed Technology, 7, 317-321.
  26. Ivany, J.A. and Reddin, J. (2002) Effect of Post-Emergence Herbicide Injury and Planting Date on Yield of Narrow- Row Soybean (Glycine max). Canadian Journal of Plant Science, 82, 249-252. http://dx.doi.org/10.4141/P01-028
  27. Mills, J.A. and Witt, W.W. (1989) Effect of Tillage Systems on the Efficacy and Phytotoxicity of Imazaquin and Imazethapyr in Soybean (Glycine max). Weed Science, 37, 233-238.
  28. Simpson, D.M. and Stoller, E.W. (1996) Physiological Mechanisms in the Synergism between Thifensulfuron and Imazethapyr in Sulfonylurea-Tolerant Soybean (Glycine max). Weed Science, 44, 209-214.
  29. Hart, S.E. and Roskamp, G.K. (1998) Soybean (Glycine max) Response to Thifensulfuron and Bentazon Combinations. Weed Technology, 12, 179-184.

Abbreviations

DAT, days after treatment;

POST, postemergence.

NOTES

*Corresponding author.