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Crop Protection 26 (2007) 715–720

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Responses of three types of winter wheat (Triticum aestivum L.) tospring-applied post-emergence herbicides

Peter H. Sikkema, Lynette Brown, Christy Shropshire, Nader Soltani�

University of Guelph Ridgetown Campus, 120 Main Street East, Ridgetown, Ont., Canada N0P 2C0

Received 22 June 2006; accepted 23 June 2006

Abstract

Field studies were conducted over a three-year period (2002–2004) to evaluate the tolerance of recently developed varieties of winter

wheat representing soft white winter wheat (SWWW), soft red winter wheat (SRWW), and hard red winter wheat (HRWW) to four

spring-applied post-emergence (POST) herbicides. Bromoxynil plus MCPA, 2,4-D amine, dichlorprop plus 2,4-D, and dicamba plus

MCPA plus mecoprop were applied at one and two times the manufacturers’ recommended dose. Bromoxynil plus MCPA and 2,4-D

amine did not cause any visual injury. Dichlorprop plus 2,4-D did not cause injury in 2002 or 2003, but did injure all the three types of

winter wheat 7 days after treatment (DAT) in 2004, but no injury was seen at 14, 28, and 42 DAT. Dicamba plus MCPA plus mecoprop

caused injury in all the three types of winter wheat each year. Dicamba plus MCPA plus mecoprop at 600 g ai/ha reduced height 7% in

SWWW and SRWW, while at 1200 g/ha reduced height 10% and 11% in SWWW and SRWW, respectively. Generally, winter wheat

yield was not affected by 2,4-D amine, bromoxynil plus MCPA, or dichlorprop plus 2,4-D. In 2003, dicamba plus MCPA plus mecoprop

at 600 g/ha decreased SWWW yield, however, when applied at 1200 g/ha, yield was decreased in all three years for both the SWWW and

SRWW. The yield of HRWW was not affected by any of the herbicides evaluated. Overall, of the four herbicides evaluated, only the

dicamba plus MCPA plus mecoprop POST caused unacceptable crop injury and yield loss in SWWW and SRWW.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: Hard red winter wheat; Height; Herbicide sensitivity; Soft red winter wheat; Soft white winter wheat; Tolerance; Yield

1. Introduction

In recent years, winter wheat (Triticum aestivum L.)production has increased in Ontario as growers added thiscrop to their rotations because of new and improvedvarieties and competitive pricing. Winter wheat is a veryeffective crop to include in the rotation for the control ofannual, biennial, and perennial weeds while at the sametime the crop residues improve soil structure.

Herbicides registered for weed control in winter wheathave not changed, while the varieties have changed over thepast 10 years. Depending on the weed species present,products such as 2,4-D, MCPA, and dicamba are still beingused, either alone or in combination (Ivany et al., 1990).Commonly used herbicides include 2,4-D amine, bromox-

e front matter r 2006 Elsevier Ltd. All rights reserved.

opro.2006.06.010

ing author. Tel.:+1519 674 1645; fax +1519 674 1600.

ess: nsoltani@ridgetownc.uoguelph.ca (N. Soltani).

ynil plus MCPA, dichlorprop plus 2,4-D, and dicamba plusMCPA plus mecoprop. Although these herbicides providebroadleaf weed control, there may be crop injury withsensitive varieties. Tottman (1980) has suggested thatvarietal differences in the tolerance of herbicides arecommon in cereals. Injury may be due to herbicide choice,application dose, application timing, variety tolerance, andenvironmental conditions (Lemerle et al., 1986). Thegrowth stage of the wheat at the time of herbicideapplication also affects crop tolerance (Tottman, 1980).MCPA amine, 2,4-D amine, dichlorprop, and mecoprop

are phenoxy herbicides that are effective for the control ofa wide spectrum of annual, biennial, and perennialbroadleaf weeds. These are growth regulating herbicidesaffecting respiration, translocation, and cell division(Lemerle et al., 1986). Swan (1975) reported that winterwheat may be sensitive to 2,4-D if applied prior to tillering.MCPA and 2,4-D were also reported to reduce grain yield

ARTICLE IN PRESSP.H. Sikkema et al. / Crop Protection 26 (2007) 715–720716

when double the recommended spring dose was applied inautumn (Derksen et al., 1989).

Bromoxynil is often combined or tank mixed withMCPA and/or dicamba. Bromoxynil inhibits photosynth-esis, respiration, and causes uncontrolled cell division andgrowth in sensitive weeds (Lemerle et al., 1986). Mostwinter wheat varieties have not shown sensitivity tobromoxynil. However, Derksen et al. (1989) showed thatwhen bromoxynil was applied at twice the recommendeddose to winter wheat in the autumn, it had the lowest yield,but when applied in the spring at the same rate, it had thehighest yield and was significantly better than the check.

Dicamba is primarily mixed with 2,4-D, MCPA, and/orbromoxynil. This herbicide modifies the nucleic acidmetabolism which causes distorted growth of sensitiveweeds (Lemerle et al. 1986). In the past, studies have showndicamba injury on more sensitive wheat varieties. Schroe-der and Banks (1989) and Rinella et al. (2001) reportedcultivars of soft red winter wheat (SRWW) with sensitivityto dicamba. Robison and Fenster (1973) found that thegrain yield of one out of five cultivars of winter wheattested was affected by a typical use dose of dicamba.

Many variables affect the extent of herbicide injury.With the wide range of winter wheat varieties availabletoday, it is important to determine if a specific variety ofwinter wheat is more sensitive to damage from commonlyused herbicides. There is no published information ontolerance of recently developed varieties of soft whitewinter wheat (SWWW), SRWW, and hard red winterwheat (HRWW) to bromoxynil plus MCPA, 2,4-D amine,dichlorprop plus 2,4-D, and dicamba plus MCPA plusmecoprop under environmental conditions of Ontario.More research is needed to determine tolerance of newlydeveloped varieties of winter wheat to commonly usedherbicides.

The objective of this research was to evaluate thetolerance of recently developed varieties of winter wheatrepresenting SWWW, SRWW, and HRWW to four spring-applied post-emergence (POST) herbicides under environ-mental conditions of Ontario.

2. Materials and methods

Field experiments were initiated each year in the autumnof 2001–2003 at the Huron Research Station, Exeter,Ontario. The soil type in 2001 was a Brookston clay loamwith 26% sand, 37% silt, 37% clay, 4.5% OM, pH of 8,and a CEC of 32. In 2002, the soil type was a Brookstonclay loam with 32% sand, 41% silt, 27% clay, 4% OM, pHof 7.9, and a CEC of 38. The soil type in 2003 was aBrookston clay loam with 34% sand, 33% silt, 33% clay,3.8% OM, pH of 8, and a CEC of 32. Seedbed preparationconsisted of moldboard plowing and cultivating twice.

The experimental design was a two-way factorialestablished as randomized complete block design with fourreplications. Main plots were herbicide treatment and sub-plots were market class of winter wheat. Plots were 2m

wide by 10m long. Winter wheat was planted in rows17.5 cm apart at a depth of 4 cm. In 2001, varieties usedwere ‘Pioneer 25W60’ (SWWW), ‘Pioneer 2540’ (SRWW),and ‘Maxine’ (HRWW). In 2002 and 2003, ‘Pioneer25W60’ (SWWW), ‘Vienna’ (SRWW), and ‘AC Morley’(HRWW) varieties were used. Winter wheat was seededwith a double disc drill at 140 kg/ha on November 1, 2001,September 26, 2002, and October 21, 2003.Experimental treatments consisted of a weed-free check

and 2,4-D amine at 550 and 1100 g/ha, bromoxynil plusMCPA at 560 and 1120 g/ha, dichlorprop plus 2,4-D at1017 and 2034 g/ha, or dicamba plus MCPA plusmecoprop at 600 and 1200 g/ha applied POST in thespring. The low dose was the maximum manufacturer’srecommended dose and the high dose simulated a sprayoverlap. Herbicides were applied with a CO2 pressurizedbackpack sprayer calibrated to deliver 200L/ha at 241 kPa.The boom was 1.5m long with four 8002 flat-fan nozzlestips (Spraying Systems Co., Wheaton, IL) spaced 50 cmapart. Herbicide applications were made when wheat wasat Zadoks stage 22–25. All plots including the non-treatedcheck were kept weed free by hand weeding.Visual crop injury was rated 7, 14, 28, and 42 days after

treatment (DAT) on a scale of 0–100%. A rating of 0%indicated no visible crop injury and a rating of 100%indicated plant death. At 42 DAT, plant height wasmeasured to the tip of the uppermost leaf when extendedfrom 10 randomly selected plants. Yield was measured atcrop maturity by harvesting the middle 1.5m of each plotwith a plot combine. Winter wheat was harvested on July22, 2002, July 25, 2003, and July 26, 2004. Yields wereadjusted to 14.5% moisture.All data were subjected to analysis of variance, and

analysed using the PROC MIXED procedure of SAS(Statistical Analysis Systems (SAS) software, Version 8.Statistical Analysis Systems Institute Inc., Cary, NC).Variances were partitioned into the random effects ofyears, blocks within years, and the interactions with fixedeffects (herbicide treatment and winter wheat types). Tomeet the assumptions of variance analyses, means of injuryratings were square root/log transformed when necessary.Means were converted back to the original scale forpresentation of results. The random effect of years andtheir interactions with herbicide treatments and winterwheat types were significant for several of the variablesanalysed. As a result, data sometimes had to be separatedby year and/or variety. Means were separated usingFisher’s protected LSD at P ¼ 0.05.

3. Results and discussion

3.1. Visual injury

In 2002, 2,4-D amine, bromoxynil plus MCPA, anddichlorprop plus 2,4-D applied POST did not cause visualinjury at 7, 14, 28, and 42 DAT (Table 1). Dicamba plusMCPA plus mecoprop applied POST resulted in minimal

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Table 1

Percent visual injury at 7, 14, 28, and 42 days after treatment (DAT) with spring post-emergence herbicide applications for three varieties of winter wheat

in 2002a

Treatment Dose (g

ai/ha)

Visual injury

7 DAT

(%)

14 DATc

(%)

28 DAT 42 DATb

SWWW

(%)

SRWW

(%)

HRWW

(%)

SWWW

(%)

SRWW

(%)

HRWW

(%)

Weed-free check 0 0 a 0 a 0 a 0 a 0 a 0 a 0

2,4-D amine 550 0 0 a 0 a 0 a 0 a 0 a 0 a 0

2,4-D amine 1100 0.2 0.1 ab 0 a 0 a 0 a 0 a 0 a 0

Bromoxynil+MCPA 560 0 0 a 0 a 0 a 0 a 0 a 0 a 0

Bromoxynil+MCPA 1120 0 0.1 ab 0 a 0 a 0 a 0 a 0 a 0

Dichlorprop+2,4-D 1017 0 0 a 0 a 0 a 0 a 0 a 0 a 0

Dichlorprop+2,4-D 2034 0 0 a 0 a 0 a 0 a 0 a 0 a 0

Dicamba+MCPA+

mecoprop

600 0 0.2 b 4.5 b 3.2 b 0 a 5.7 b 3.2 b 0.2

Dicamba+MCPA+

mecoprop

1200 0 1.1 c 6.8 c 5.8 c 2.0 b 8.1 c 7.6 c 0.4

SE 0 0.1 0.5 0.4 0.1 0.6 0.5 0.1

Means for injury at 14 and 42 DAT have been transformed back to original scale. Means followed by the same letter in each column are not significantly

different according to Fisher’s protected LSD test (Po0.05).aWheat varieties are SWWW: Pioneer 25W60, SRWW: Pioneer 2540, HRWW: Maxine.bAnalysis performed on square root-transformed data.cAnalysis performed on log-transformed data.

Table 2

Percent visual injury at 7, 14, 28, and 42 DAT with spring post-emergence herbicide applications for three varieties of winter wheat in 2003a

Treatment Dose (g

ai/ha)

Visual injury

7 DAT 14 DATb 28 DAT 42 DATb

SWWW

(%)

SRWW

(%)

HRWW

(%)

SWWW

(%)

SRWW

(%)

HRWW

(%)

SWWW

(%)

SRWW

(%)

HRWW

(%)

Weed-free check 0 0 0 a 0 0 0 a 0 0 a 0 a 0

2,4-D amine 550 0 0 0 a 0 0 0 a 0 0 a 0 a 0

2,4-D amine 1100 0 0 0 a 0 0 0 a 0 0 a 0 a 0

Bromoxynil+MCPA 560 0 0 0 a 0 0 0 a 0 0 a 0 a 0

Bromoxynil+MCPA 1120 0 0 0 a 0 0 0 a 0 0 a 0 a 0

Dichlorprop+2,4-D 1017 0 0 0 a 0 0 0 a 0.2 0 a 0 a 0

Dichlorprop+2,4-D 2034 0 0 0 a 0 0 0 a 0 0 a 0 a 0

Dicamba+MCPA+

mecoprop

600 0 0 0 a 0 0 1.4 b 0 0.6 b 1.3 b 0

Dicamba+MCPA+

mecoprop

1200 0 0 3.0 b 0 0 3.9 c 0 2.4 c 5.0 c 0

SE 0 0 0.2 0 0 0.3 0 0.2 0.3 0

Means for injury at 14 and 42 DAT have been transformed back to original scale. Means followed by the same letter in each column are not significantly

different according to Fisher’s protected LSD test (Po0.05).aWheat varieties are SWWW: Pioneer 25W60, SRWW: Vienna, HRWW: AC Morley.bAnalysis performed on square root-transformed data.

P.H. Sikkema et al. / Crop Protection 26 (2007) 715–720 717

wheat injury 7 and 14 DAT. At 28 DAT, dicamba plusMCPA plus mecoprop at 600 g/ha resulted in 5%, 3%,and 0% injury in SWWW, SRWW, and HRWW,respectively, while at 1200 g/ha there was 7%, 6%, and2% injury in SWWW, SRWW, and HRWW, respectively.A similar trend was observed at 42 DAT.

In 2003, only the dicamba plus MCPA plus mecoprop at600 and 1200 g/ha applied POST resulted in visual injury

in winter wheat (Table 2). Initially (7 and 14 DAT), greaterinjury was observed in the HRWW but by 42 DAT therewas greater injury in the SWWW and SRWW, similar tothe results observed in 2002.In 2004, injury was apparent at 7 DAT with 2,4-D amine

(growth distortion), bromoxynil plus MCPA (leaf tipburn), dichlorprop plus 2,4-D (growth distortion), anddicamba plus MCPA plus mecoprop (growth distortion)

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Table 3

Percent visual injury at 7 and 14 DAT with spring post-emergence herbicide applications for three varieties of winter wheat in 2004a

Treatment Dose (g ai/ha) Visual injury

7 DATb (%) 14 DAT (%)

Weed-free check 0 a 0 a

2,4-D amine 550 0 a 0 a

2,4-D amine 1100 0.4 ab 0 a

Bromoxynil+MCPA 560 0.4 ab 0 a

Bromoxynil+MCPA 1120 0.8 bc 0 a

Dichlorprop+2,4-D 1017 0.7 bc 0 a

Dichlorprop+2,4-D 2034 1.2 c 0 a

Dicamba+MCPA+ mecoprop 600 2.0 d 0 a

Dicamba+MCPA+ mecoprop 1200 6.9 e 2.3 b

SE 0.2 0.1

There was no injury at 28 and 42 DAT. Means for injury at 7 DAT have been transformed back to original scale. Means followed by the same letter in

each column are not significantly different according to Fisher’s protected LSD test (Po0.05).aWheat varieties are SWWW: Pioneer 25W60, SRWW: Vienna, HRWW: AC Morley.bAnalysis performed on square root-transformed data.

Table 4

Plant height 42 days after treatment (DAT) with spring post-emergence herbicide applications for three varieties of winter wheat in 2002–2004a

Treatment Dose (g ai/ha) Plant height

SWWW (cm) SRWW (cm) HRWW (cm)

Weed-free check 92 a 91 a 103 a

2,4-D amine 550 91 a 91 a 103 a

2,4-D amine 1100 92 a 87 abc 100 a

Bromoxynil+MCPA 560 91 a 89 abc 103 a

Bromoxynil+MCPA 1120 92 a 89 abc 103 a

Dichlorprop+2,4-D 1017 91 a 86 bc 103 a

Dichlorprop+2,4-D 2034 91 a 87 abc 101 a

Dicamba+MCPA+ mecoprop 600 86 b 85 c 101 a

Dicamba+MCPA+ mecoprop 1200 83 b 81 d 102 a

SE 1 1 1

Means followed by the same letter in each column are not significantly different according to Fisher’s protected LSD test (Po0.05).aWheat varieties for 2002 are SWWW: Pioneer 25W60, SRWW: Pioneer 2540, HRWW: Maxine; 2003 and 2004 are SWWW: Pioneer 25W60, SRWW:

Vienna, HRWW: AC Morley.

P.H. Sikkema et al. / Crop Protection 26 (2007) 715–720718

(Table 3). Dicamba plus MCPA plus mecoprop applied at1200 g/ha resulted in visual injury at 14 DAT.

Over the three years of this study, dicamba plus MCPAplus mecoprop consistently resulted in crop injury. Tott-man (1977) indicated similar results in which under-developed seeds were observed with this combination andtiming of herbicides. Schroeder and Banks (1989) alsofound that earlier applications of treatments containingdicamba and dicamba plus 2,4-D, contributed to wheatinjury.

3.2. Height

There was no year by herbicide treatment interaction soplant height data were combined across years. However,there was a significant herbicide by variety type interaction,so results are shown by variety type in Table 4. Plant heightwas not affected by 2,4-D amine, bromoxynil plus MCPA,or dichlorprop plus 2,4-D. Dicamba plus MCPA plusmecoprop applied at 600 g/ha reduced height by 7% in

SWWW and SRWW, while at 1200 g/ha it reduced heightby 10% and 11% in SWWW and SRWW, respectively. Theheight of HRWWwas not affected by dicamba plus MCPAplus mecoprop. In contrast, Martin et al. (1989) reportedthat dicamba plus 2,4-D amine and dicamba plus MCPAreduced plant height by 11% and 10%, respectively, whenapplied on HRWW at Zadoks Growth Stage 13. Quimbyand Nalewaja (1966) also reported a decrease in plantheight from an application of dicamba.

3.3. Yield

Generally, winter wheat yield was not affected by 2,4-Damine, bromoxynil plus MCPA, or dichlorprop plus 2,4-Dapplied POST in the spring (Table 5). There was a slightdecrease in yield of the SWWW with the bromoxynil plusMCPA applied at 560 g/ha in 2002 and a decrease in theyield of SRWW with 2,4-D amine at 550 g/ha in 2004. In2003, dicamba plus MCPA plus mecoprop at 600 g/hareduced yield in the SWWW. Dicamba plus MCPA plus

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Table 5

Yield with spring post-emergence herbicide applications for three varieties of winter wheat in 2002–2004a

Treatment Dose (g ai/

ha)

2002 2003 2004

SWWW

(T/ha)

SRWW

(T/ha)

HRWW

(T/ha)

SWWW

(T/ha)

SRWW

(T/ha)

HRWW

(T/ha)

SWWW

(T/ha)

SRWW

(T/ha)

HRWW

(T/ha)

Weed-free check 6.49 ab 6.41 a 5.53 5.88 a 5.82 a 4.75 6.15 a 6.20 a 5.63 ab

2,4-D amine 550 6.10 abc 5.94 a 5.56 5.72 a 5.80 a 5.10 6.07 ab 5.88 b 5.63 ab

2,4-D amine 1100 6.61 a 6.43 a 5.12 5.75 a 5.57 a 4.63 6.16 a 6.04 ab 5.54 ab

Bromoxynil/MCPA 560 5.74 cd 5.95 a 5.42 5.71 a 5.59 a 5.02 5.96 ab 6.18 ab 5.78 a

Bromoxynil/MCPA 1120 6.49 ab 6.48 a 5.31 5.91 a 5.67 a 4.77 6.25 a 6.12 ab 5.55 ab

Dichlorprop/2,4-D 1017 6.32 ab 6.29 a 5.58 5.89 a 5.64 a 4.87 6.16 a 6.22 a 5.64 ab

Dichlorprop/2,4-D 2034 6.29 abc 6.07 a 5.39 5.82 a 5.55 a 4.68 6.19 a 6.17 ab 5.64 ab

Dicamba/MCPA/

mecoprop

600 5.99 bc 6.07 a 5.53 4.30 b 5.53 a 4.65 5.98 ab 6.14 ab 5.44 b

Dicamba/MCPA/

mecoprop

1200 5.20 d 4.96 b 5.38 2.70 c 4.95 b 4.77 5.82 b 5.87 b 5.32 b

SE 0.13 0.14 0.10 0.19 0.07 0.05 0.04 0.04 0.04

Means followed by the same letter in each column are not significantly different according to Fisher’s protected LSD test (Po0.05).aWheat varieties for 2002 are SWWW: Pioneer 25W60, SRWW: Pioneer 2540, HRWW: Maxine; 2003 and 2004 are SWWW: Pioneer 25W60, SRWW:

Vienna, HRWW: AC Morley.

P.H. Sikkema et al. / Crop Protection 26 (2007) 715–720 719

mecoprop applied at 1200 g/ha reduced yield in all threeyears for both the SWWW and SRWW. The yield ofHRWW was not affected by any of the herbicidesevaluated. Martin et al. (1989) found that dicamba aloneas well as in combination with a phenoxy herbicide,reduced yields by 12–39%. Tottman (1978) also found thatwhen tank mixes containing dicamba, 2,3,6-TBA, MCPA,and mecoprop were applied to winter wheat at twice thenormal dose, grain yield was severely affected. Theseresults are consistent with those found by Ivany et al.(1990), Rinella et al. (2001), and Tottman (1982) who alsonoted yield losses from use of dicamba.

4. Conclusions

Differential sensitivity to POST herbicides was observedin winter wheat varieties evaluated. Other studies haveshown similar differential tolerances with other varieties ofwinter wheat (Derksen et al., 1989; Ivany et al., 1990;Rinella et al., 2001; Robison and Fenster, 1973; Schroederand Banks, 1989; Swan, 1975; Tottman, 1980). Bromoxynilplus MCPA and 2,4-D amine did not cause any visualinjury in winter wheat. Dichlorprop plus 2,4-D injuredsome winter wheat types 7 DAT, but this injury wastransient with no injury observed after 14 DAT. Dicambaplus MCPA plus mecoprop caused visual injury in all thethree types of winter wheat each year. Dicamba plusMCPA plus mecoprop caused a height reduction inSWWW and SRWW. Generally, winter wheat yield wasnot affected by the application of 2,4-D amine, bromoxynilplus MCPA, or dichlorprop plus 2,4-D. Dicamba plusMCPA plus mecoprop caused a yield decrease in all thethree years for both the SWWW and SRWW winter wheattypes. The yield of HRWW was not affected by any of theherbicides evaluated.

Based on these results, 2,4-D amine, bromoxynil plusMCPA, and dichlorprop plus 2,4-D applied POST in thespring have an adequate margin of crop safety for weedmanagement in recently developed varieties of SWWW,SRWW, and HRWW in Ontario. Dicamba plus MCPAplus mecoprop has an adequate margin of crop safety inHRWW, but causes unacceptable visual injury, heightreduction, and yield loss in SWWW and SRWW underOntario environmental conditions.

Acknowledgements

The authors would like to acknowledge Todd Cowan forhis expertise and technical assistance in these studies.Funding for this project was provided in part by theOntario Wheat Producers.

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