broccoli, cabbage and cauliflower tolerance to sulfonylurea herbicides

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Crop Protection 25 (2006) 225–229

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Broccoli, cabbage and cauliflower tolerance to sulfonylurea herbicides

Peter H. Sikkema, Nader Soltani, Kristen McNaughton, Darren E. Robinson�

Ridgetown College, University of Guelph, 120 Main Street East, Ridgetown, ON, Canada N0P 2C0

Received 23 March 2005; received in revised form 19 April 2005; accepted 25 April 2005

Abstract

Limited information exists on cole crop tolerance to post-emergence (POST) applications of sulfonylurea (SU) herbicides under

Ontario growing conditions. Broccoli, cabbage and cauliflower were evaluated for tolerance to ethametsulfuron-methyl,

foramsulfuron, nicosulfuron, rimsulfuron, thifensulfuron-methyl, and triflusulfuron-methyl in nine separate experiments conducted

from 2002 to 2004. Each of the SU herbicides was applied at the proposed and twice the proposed use dose in broccoli, cabbage and

cauliflower. Ethametsulfuron-methyl did not cause visual injury, and did not reduce head weight or yield in all nine trials conducted.

Foramsulfuron, nicosulfuron, rimsulfuron and thifensulfuron-methyl caused unacceptable injury (greater than 10%) at the

proposed use dose of each herbicide. Injury symptoms included stunting, twisting of the petioles, and malformed, chlorotic leaves.

Foramsulfuron and nicosulfuron caused complete death of broccoli, cabbage and cauliflower at the proposed use dose of each of

these herbicides. Injury was severe enough to prevent head production of broccoli, cabbage and cauliflower at twice the proposed

use dose of rimsulfuron and thifensulfuron-methyl. Though heads were formed in the triflusulfuron–methyl treatments, head weight

and yields were reduced at the proposed use dose of this herbicide. Ethametsulfuron-methyl is the only herbicide to which broccoli,

cabbage and cauliflower possessed an acceptable level of tolerance.

r 2005 Elsevier Ltd. All rights reserved.

Keywords: Cole crops; Sensitivity; Ethametsulfuron-methyl; Foramsulfuron; Nicosulfuron; Rimsulfuron; Thifensulfuron-methyl; Triflusulfuron-

methyl

1. Introduction

Cole crops are of economic importance to agriculturein Ontario. More than 43,000 tonnes of broccoli,cabbage and cauliflower with a farm gate value of over$12 million were grown on approximately 1800 hectaresin 2003 (Mailvaganam, 2004). Broadleaved weed controlis one of the most important management considerationsin cole crop. The pre-emergence herbicides registered foruse in this crop in Ontario (s-metolachlor, trifluralin,chlorthal dimethyl and napropamide) do not controlAbutilon theophrasti Medic. (velvetleaf), Polygonum

convolvulus L. (wild buckwheat), Sinapis arvensis L.(wild mustard) or Thlaspi arvense L. (field pennycress).

e front matter r 2005 Elsevier Ltd. All rights reserved.

opro.2005.04.011

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ess: [email protected]

).

The only post-emergence (POST) herbicide registeredin cole crops is clopyralid (OMAF, 2002). Clopyralidcontrols Ambrosia artemisiifolia L. (common ragweed)and Polygonum persicaria L. (ladysthumb), but doesnot provide adequate control of Abutilon theophrasti,Polygonum convolvulus, Sinapis arvensis or Thlaspi

arvense. Further research is necessary to identifyherbicides that can control these broadleaved weeds incole crops.

Abutilon theophrasti, Polygonum convolvulus andcruciferous weeds such as Sinapis arvensis and Thlaspi

arvense are of economic importance in cole crops.Abutilon theophrasti grows 1–2.5m in height and hasnumerous, wide broad leaves that prevent light reachingcrop canopies and reduce yields (Akey et al., 1990). Italso has long-lived seeds, capable of producing apersistent seed bank (Toole and Brown, 1946; Buhlerand Hartzler, 2001). Polygonum convolvulus has wirystems that wind around nearby plants and interfere with

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Table 1

Soil characteristics for study sites in 2002, 2003 and 2004

Soil texture

Crop Year pH OM

(%)

Sand

(%)

Silt

(%)

Clay

(%)

Broccoli 2002 7.5 6.4 52 30 18

Broccoli 2003 6.7 5.7 79 13 8

Broccoli 2004 6.5 5.8 46 31 23

Cabbage 2002 6.9 5.6 50 32 18

Cabbage 2003 6.7 5.7 79 13 8

Cabbage 2004 6.5 5.8 46 31 23

Cauliflower 2002 6.4 6.4 45 37 18

Cauliflower 2003 7.2 6.1 73 15 12

Cauliflower 2004 7.1 5.1 51 28 21

P.H. Sikkema et al. / Crop Protection 25 (2006) 225–229226

harvest operations (Hume et al., 1983). Polygonum

convolvulus may also act as an alternate host for theMeloidogyne hapla Chitwood (root-knot nematode)(Belair and Benoit, 1996), a serious pest of cole crops.Competition from wild mustard can reduce cole cropyields (Welbank, 1963), but this weed is more importantas an alternate host of many cole crop pests. Sinapis

arvensis hosts the Heterodera schachtii Schmidt (sugarbeet nematode) (Baker, 1941) and the causal agent ofPlasmodiophora brassicae Wor. (clubroot) (Peterson,1961), which cause significant yield losses in cole crops.Thlaspi arvense can act as an alternate host for theContarinia nasturtii Keiffer (swede midge) (Callow andFraser, 2003). Registration of a herbicide with activityon Abutilon theophrasti, Polygonum convolvulus, Sinapis

arvensis and/or Thlaspi arvense would provide cole cropgrowers with an excellent tool for the control of theseeconomically important weed species.

Sulfonylurea herbicides inhibit the activity of acet-olactate synthase, the enzyme responsible for thesynthesis of branched-chain amino acids isoleucine,leucine and valine (LaRossa and Schloss, 1984). Theyare applied at extremely low doses (less than 100 g ofactive ingredient per hectare), possess low mammaliantoxicity and are relatively soil immobile so they havelittle potential to contaminate groundwater (Vencill,2002). Ethametsulfuron-methyl controls many crucifer-ous species, such as Sinapis arvensis or Thlaspi arvense

(OMAF, 2002). Foramsulfuron controls a range ofannual grass and broadleaved weed species, includingAbutilon theophrasti and Sinapis arvensis, as well asother competitive weeds such as Chenopodium album L.(common lambsquarters) and Amaranthus retroflexus L.(redroot pigweed) (OMAF, 2002). Nicosulfuron andrimsulfuron are graminicides that control Amaranthus

retroflexus and Sinapis arvensis, respectively (OMAF,2002). Thifensulfuron-methyl controls Sinapis arvensis,Abutilon theophrasti, Chenopodium album and Amar-

anthus retroflexus, and triflusulfuron-methyl is anexcellent herbicide for control of Abutilon theophrasti

(OMAF, 2002). Sulfonylurea herbicides have lowenvironmental impact, and can provide excellent controlof weed species that are problematic in cole cropproduction.

The objective of this research was to evaluate sixsulfonylurea herbicides (ethametsulfuron-methyl, for-amsulfuron, nicosulfuron, rimsulfuron, thifensulfuron-methyl and triflusulfuron-methyl) for tolerance inbroccoli, cabbage and cauliflower.

2. Materials and methods

Field experiments were conducted at RidgetownCollege, Ridgetown, Ontario, in 2002, 2003 and 2004.The soil characteristics for each trial are described in

Table 1. Each experiment was arranged in a randomizedcomplete block design with treatments replicated fourtimes. Treatments included a non-treated weed-freecontrol, ethametsulfuron-methyl (15 and 30 g ai/ha),triflusulfuron-methyl (35 and 70 g ai/ha), thifensulfur-on-methyl (6 and 12 g ai/ha), rimsulfuron (15 and 30 g ai/ha), nicosulfuron (25 and 50 g ai/ha), and foramsulfuron(35 and 70 g ai/ha), representing once and twice theproposed use dose for each herbicide. Plots were 6mwide by 8m long.

Broccoli (cv. Paragon), cabbage (cv. Bayou Dynasty)and cauliflower (cv. Wentworth) were planted on May28, 2002, May 29, 2003 and May 21, 2004. All cropswere grown in rows spaced 1.5m apart and the in-rowspacing was 45 cm row for a population of 14,850plants/ha. Plots were maintained weed-free by inter-rowcultivation and hand hoeing, as required.

Herbicide treatments were applied POST to cole cropsin the five- to seven-leaf stage, at 21 days aftertransplanting. The foramsulfuron treatments weresprayed with 1.75 l/ha ethylated seed oil and 2.5 l/haUAN 28%. The remaining treatments were sprayed with0.2% v/v of a non-ionic surfactant. Treatments wereapplied using a CO2-pressurized backpack sprayer,calibrated to deliver 200 l/ha with XR8002VS (TeejetXR8002VS Tip, Spraying Systems Co., North Ave &Schmale Rd., Wheaton, IL 60188) flat-fan nozzles at207 kPa pressure.

Crop injury was rated on a scale of 0–100% at 7, 14and 28 days after treatment (DAT). A rating of 0% wasdefined as no visible effect of the herbicide, and 100%was defined as plant death. Stand counts were made 14DAT. The middle 6m of each plot was harvested byhand as heads of each crop reached maturity and theweight of each head and the total number of heads perplot were determined. Broccoli was harvested fromAugust 9 to 16, 2002, July 16 to 28, 2003 and July 29 toAugust 16, 2004. Cabbage was harvested on August 16,2002, August 8, 2003 and July 27, 2004. Cauliflower was

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Table 2

Effect of herbicide treatment on visual injury for broccoli, cabbage and

cauliflower at 28 days after treatment (DAT)

Visual injury

Herbicide Dose

(g ai/ha)

Broccoli

(%)

Cabbage

(%)

Cauliflower

(%)

Ethametsulfuron-methyl 15 3* 0* 2*


Triflusulfuron-methyl 35 34 30 20


Thifensulfuron-methyl 6 62 44 44


Rimsulfuron 15 90 60 79


Nicosulfuron 25 90 81 92


Foramsulfuron 35 99 94 97


SE (7) 6 8 6

*—Asterisk indicates visual injury not significantly different from the

non-treated control at p ¼ 0.05.

Table 3

Effect of herbicide treatment on number of heads produced per plot

for broccoli, cabbage and cauliflower at harvest

Number of heads produced

P.H. Sikkema et al. / Crop Protection 25 (2006) 225–229 227

harvested on October 16, 2002, September 5, 2003, andAugust 29, 2004.

For each crop species, data were subjected to analysisof variance using the PROC MIXED procedure of SAS,version 8.0 (SAS, 1999). Variances of visual injury at 7,14 and 28 DAT, head number, head weight and yieldwere partitioned into the fixed effects of herbicidetreatment and the random effects of year and the year-by-treatment interaction. Significance of random effectswas tested using a Z-test of the variance estimate andfixed effects were tested with F-tests. Error assumptionsof the variance analyses (random, homogeneous dis-tribution of error terms and normality) were confirmedusing residual plots and the Shapiro–Wilk normalitytest. As there were no significant effects of year or theyear-by-treatment interaction, data were combined overthe three years of the study for the final analysis. Tonormalize the data, visual injury were subjected to anarcsine square root transformation (Bartlett, 1947), andhead number and weight were log transformed (Kuehl,1994). Yield data were not transformed. Orthogonalcontrasts were constructed for each variable to deter-mine if there were significant differences between eachherbicide treatment and the untreated control(/¼ 0:05). Visual injury, head number and head weightwere converted back to the original scale for thepresentation of results.

Herbicide Dose

(g ai/ha)

Broccoli

(#/plot)

Cabbage

(#/plot)

Cauliflower

(#/plot)



Triflusulfuron-methyl 35 16* 16* 11*

Triflusulfuron-methyl 70 16* 14* 8*

Thifensulfuron-methyl 6 9 15* 7*








Non-treated control 23 16 11

SE (7) 4 3 2

*—Asterisk indicates head number at harvest not significantly

different from the non-treated control at /¼ 0:05.

3. Results and discussions

3.1. Visual injury

Ethametsulfuron-methyl at 15 and 30 g ai/ha did notcause more than 10% visual injury in all three cropspecies (Table 2). Triflusulfuron-methyl, thifensulfuron-methyl, rimsulfuron, nicosulfuron and foramsulfuron allcaused visual injury to transplanted broccoli, cabbageand cauliflower at all three evaluation dates (Table 2;data only shown for 28 DAT). When injury wasobserved, regardless of herbicide treatment, injurysymptoms included stunting, twisting of the petioles,and malformed, chlorotic leaves.

3.2. Marketable head number

Broccoli marketable head production was not differ-ent from the non-treated control in the ethametsulfuron-methyl (15 and 30 g ai/ha) and triflusulfuron-methyl (35and 70 g ai/ha) treatments (Table 3). In cabbage andcauliflower, marketable head production was similar tothe non-treated control in the ethametsulfuron-methyland triflusulfuron-methyl treatments (Table 3), as wellas the low dose of thifensulfuron-methyl (6 g ai/ha).Rimsulfuron, nicosulfuron and foramsulfuron all

caused a reduction in marketable head production inall three cole crop species (Table 3).

3.3. Marketable head weight

Broccoli marketable head weight was comparable tothe non-treated control in both ethametsulfuron-methyltreatments (Table 4) and the low dose of triflusulfuron-methyl (35 g ai/ha). Cabbage and cauliflower marketablehead weight was similar to the non-treated control atboth doses of ethametsulfuron-methyl. Thifensulfuron-

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Table 4

Effect of herbicide treatments on average head weight of broccoli,

cabbage and cauliflower at harvest

Average head size

Treatment Dose

(g ai/ha)

Broccoli

(g)

Cabbage

(g)

Cauliflower

(g)



Triflusulfuron-methyl 35 159* 667 834










Non-treated control 212 1787 1217

SE (7) 47 156 184

*—Asterisk indicates average head size not significantly different from

the non-treated control at /¼ 0:05.

Table 5

Effect of herbicide treatment on yield of broccoli, cabbage and

cauliflower

Yield

Herbicide Dose

(g ai/ha)

Broccoli

(t/ha)

Cabbage

(t/ha)

Cauliflower

(t/ha)

Ethametsulfuronmethyl 15 4.1* 31.1* 13.1*

Ethametsulfuronmethyl 30 3.7* 25.0* 12.2*

Triflusulfuronmethyl 35 2.2 9.6 7.7

Triflusulfuronmethyl 70 1.7 3.4 6.3

Thifensulfuronmethyl 6 1.5 2.6 4.2

Thifensulfuronmethyl 12 1.5 0.9 4.1

Rimsulfuron 15 0.1 1.1 1.0

Rimsulfuron 30 0.0 0.2 0.2

Nicosulfuron 25 0.0 0.0 0.0

Nicosulfuron 50 0.0 0.0 0.0

Foramsulfuron 35 0.0 0.0 0.1

Foramsulfuron 70 0.0 0.0 0.0

Non-treated control 3.7 27.9 14.1

SE (7) 0.7 2.7 2.6

*—Asterisk indicates yield not significantly different from the non-

treated control at /¼ 0:05.

P.H. Sikkema et al. / Crop Protection 25 (2006) 225–229228

methyl, rimsulfuron, nicosulfuron and foramsulfuron allreduced marketable head weight of all three crops,regardless of dose of application (Table 4).

3.4. Yield

The POST application of ethametsulfuron-methyl atboth doses evaluated did not cause any significantchanges in broccoli, cabbage and cauliflower (Table 5).However, the POST applications of triflusulfuron-

methyl, thifensulfuron-methyl, rimsulfuron, nicosulfur-on and foramsulfuron reduced broccoli yield by as muchas 54, 54, 100, 100 and 100%, reduced cabbage yield byas much as 88, 97, 99, 100 and 100%, and reducedcauliflower yield by as much as 55, 71, 99, 100 and100%, respectively, compared to non-treated control(Table 5).

4. Conclusions

This research was initiated to identify POST herbi-cides that can be safely applied to broccoli, cabbage andcauliflower. Broccoli, cabbage and cauliflower were alltested, as previous research has shown that the toleranceof these crops to other herbicides, such as oxyfluorfen,lactofen and ammonium nitrate, can vary (Bitterlich etal., 1996; Johnson et al., 1992). Ethametsulfuron-methylis the only herbicide to which broccoli, cabbage andcauliflower possessed an acceptable level of tolerance.This herbicide could provide cole crop growers with ameans to control certain cruciferous weeds, such asSinapis arvensis and Thlaspi arvense (OMAF, 2002), thatact as alternate hosts for economically important diseaseand insect pests of cole crops (Callow and Fraser, 2003).

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broccoli, cabbage and cauliflower tolerance to sulfonylurea herbicides

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