Weed Control and Yield Response to Foramsulfuron in Corn

Weed Science Society of America

Weed Control and Yield Response to Foramsulfuron in CornAuthor(s): Robert E. Nurse, Allan S. Hamill, Clarence J. Swanton, François J. Tardif and PeterH. SikkemaSource: Weed Technology, Vol. 21, No. 2 (Apr. - Jun., 2007), pp. 453-458Published by: Weed Science Society of America and Allen PressStable URL: http://www.jstor.org/stable/4495875 .

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Weed Technology 2007 21:453-458

Weed Control and Yield Response to Foramsulfuron in Corn

Robert E. Nurse, Allan S. Hamill, Clarence J. Swanton, Frangois J. Tardif, and Peter H. Sikkema*

Foramsulfuron has recently been registered for weed control in corn in Ontario, but there is very little information on the rate of foramsulfuron required to obtain at least 90% weed control. Our objective was to determine the foramsulfuron rates giving at least 90% weed control while maintaining crop yield loss due to weed interference and injury at less than 5%. Ten field trials were conducted at five Ontario locations (Exeter, Harrow, Ridgetown, Woodslee, and Woodstock) in 2001 and 2002 to evaluate the effectiveness of foramsulfuron at rates ranging from 8.75 to 140 g ai/ha. To obtain a reduction in biomass of 90% (o90) at 78 d after treatment (DAT), foramsulfuron must be applied to common lambsquarters at 68 g/ha and to common ragweed at 86 g/ha, respectively. For green foxtail a foramsulfuron rate of 25 g/ha was required to achieve 90% control. The application of foramsulfuron caused injury to corn at 7 DAT at Ridgetown and Woodstock only, but did not exceed a rating of 10%; by 14 and 28 DAT no corn injury was recorded at any location. Corn yield of at least 95% of a weed-free check was obtained at Woodstock when foramsulfuron was applied at 70 g/ha. At Exeter and Woodslee yield was 90% of the weed-free check at a foramsulfuron rate of 35 g/ha. Finally, at Harrow and Ridgetown, corn yield was lowered at all foramsulfuron rates because of broadleaved weed interference. Tank-mixing foramsulfuron with dicamba plus prosulfuron improved common lambsquarters and common ragweed control and final corn yield was improved by more than 20% when compared with an application of foramsulfuron alone. Thus, these results show that weed control with foramsulfuron is species specific and that tank mixtures with a broadleaf herbicide may be required for broad- spectrum weed control and to protect the full yield potential of corn. Nomenclature: Foramsulfuron; common ragweed, Ambrosia artemisiifolia L. AMBEL; common lambsquarters, Chenopodium album L. CHEAL; green foxtail, Setaria viridis (L.) Beauv. SETVI; corn, Zea mays L. Key words: Integrated weed management, dicamba, nicosulfuron, prosulfuron, rimsulfuron.

Foramsulfuron is a sulfonylurea herbicide that has recently been registered for weed control in corn. In Ontario, foramsulfuron is registered for application at a rate of 35 g ai/ha up to the eight-leaf stage of corn (OMAF 2004). Susceptible plants are controlled through inhibition of the acetolactate synthase enzyme, preventing the production of branched-chain amino acids (Vencill 2002). Foramsulfuron

provides adequate control of many grass and broadleaved weeds. If applied before early tillering, foramsulfuron will control annual grasses such as barnyard grass [Echinochloa crus-galli (L.) Beauv.], large crabgrass [Digitaria sanguinalis (L.) Scop.], Panicum spp. and Setaria spp., as well as the perennial, quack grass [Elytrigia repens (L.) Nevski]. The spectrum of broadleaved weeds controlled include: redroot pigweed [Amaranthus retroflexus L.], velvetleaf [Abutilon theophrasti Medic.], Brassica spp., eastern black nightshade [Solanum ptycanthum Dun.], common lambsquarters, and common ragweed (Anonymous 2003).

To reduce the environmental impact of a herbicide, the rate at which 90% weed control is obtained without reducing crop safety is an important component in the development of an integrated weed management program (Dieleman et al. 1996; Streibig and Kudsk 1993). The rate of the herbicide must also be low enough to minimize the amount of the chemical being introduced into the environment. In corn, early-season weed control is important and weed interference must be reduced

below a threshold level at which interspecific interference with the crop does not affect yield (Cox et al. 2005; Rajcan et al. 2004; Swanton et al. 1999).

When developing herbicides, agricultural products companies and regulatory agencies must consider a broad spectrum of weed species to decide upon the registered rate for application. Therefore, the registered rate may be higher than the rate required for control of the most economically important weed species depending on location. For example, Soltani et al. (2005) demonstrated that the herbicide flufenacet plus metribuzin applied at a rate of 670 g/ha (170 g/ha lower than registered rate) provided greater than 90% control of redroot pigweed, common lambsquarters, and common ragweed in soybean fields in southwestern Ontario. Therefore, by testing the effectiveness of a herbicide over a wide range of rates, growers will have better information to determine the appropriate weed management program that maximizes net returns and minimizes loading of herbicides into the environment.

Currently, there is little information on the foramsulfuron rate required to obtain acceptable control of several weed species in corn. Therefore, the specific objectives of this study were (1) to develop dose-response curves of foramsulfuron for weed control and yield in corn; and (2) to determine from the dose-response curves the rate of foramsulfuron required for greater than 90% control of selected weed species that offers the best crop safety in corn due to reduced early-season weed interference.

Materials and Methods

Experimental Sites. Field experiments were conducted in 2001 and 2002 at the Huron Research Station, University of

DOI: 10.1614/WT-06-071.1 * Research Scientist and Research Scientist, Agriculture and Agri-Food Canada,

2585 County Rd. 20 R.R. #2 Harrow, ON NOR 1GO, Canada; Professor and Associate Professor, University of Guelph, Guelph, ON N1G 2W1, Canada; Assistant Professor, Ridgetown College, University of Guelph, Ridgetown, ON NOP 2C0, Canada. Corresponding author's E-mail: [email protected]

Nurse et al.: Foramsulfuron in corn * 453



Table 1. Corn hybrids, planting dates, application date, crop stage, and average weed height at application across years and locations.

Weed height at application cm

Location Hybrid Year Planting date Spray date Broadleaf Grasses

Exeter Pioneer 37R71 2001 3 May 18 June 5 3 Pioneer 37H26 2002 22 May 11 June 5 4

Harrow Pioneer 34G81 2001 23 May 31 May 8 3 Pioneer 34G13 2002 8 May 13 June 4 4

Ridgetown DK520 RR 2001 7 May 13 June 6 2 DKC53-33 2002 15 May 12 June 5 3

Woodslee Pioneer 36B08 2001 9 May 13 June 4 4 NK 58-01 2002 28 May 18 June 5 2

Woodstock DKC35-50AF 2001 7 May 8 June 4 2 DKC35-50AF 2002 7 May 10 June 4 3

Guelph, Exeter, ON; Agriculture and Agri-Food Canada, Harrow, ON; Ridgetown College, University of Guelph, Ridgetown, ON; Eugene F. Whelan Experimental Farm, Agriculture and Agri-Food Canada, Woodslee, ON, and the Woodstock Research Station, University of Guelph, Wood- stock, ON. The soil at Exeter was a Brookston clay loam (Orthic Humic Gleysol, mixed, mesic, and poorly drained) with 3.8% organic matter and pH of 8.0. The soil at Harrow was a Fox sandy loam (Brunisolic Gray Brown Luvisol) with 2.6% organic matter and pH of 6.1. The soil at Ridgetown was a Wattford/Brady loam (Gleyed Brunisolic Gray Brown Luvisol) with 4.5% organic matter and pH of 6.7. The soil at Woodslee was a Brookston clay loam (Orthic Humic Gleysol, mixed, mesic, and poorly drained) with 4.1% organic matter, and pH 6.5. The soil at Woodstock was a Guelph silt loam (Gray Brown Podzolic) with 4.8% organic matter and pH 7.7.

Experimental Procedures. Procedures at all sites were the same unless otherwise noted. The soil at Exeter, Harrow, Woodslee, and Woodstock was moldboard plowed in the fall and chisel plowed in the following spring of each year. The soil at Ridgetown was maintained as no-till in 2001 and 2002. Glyphosate was sprayed at 900 g ae/ha before corn planting to control emerged weeds at the no-till Ridgetown location. Corn hybrids at all locations were seeded at approximately 76,000 seeds/ha in rows 76 cm apart. Each plot was 10 m long by 3 m wide and consisted of four corn rows, except at Woodstock where each plot was 7 m long and 3 m wide. Hybrid selection and planting date are presented in Table 1.

The experiment was organized as a randomized complete block design with 11 treatments and 4 replications. Six application rates of foramsulfuron (8.75, 17.5, 35, 70, 105, and 140 g ai/ha) were applied POST with a methylated seed oil (MSO) at 1.75 L/ha and 28% urea ammonium nitrate (UAN) at 2.5 L/ha at the four- to six-leaf stage of corn. Three tank-mix treatments were also applied: foramsulfuron (35 g ai/ha) + nicosulfuron (12.5 g/ha) + rimsulfuron (12.5 g ai/ha) + nonionic surfactant (0.2% v/v) POST; foramsulfuron (35 g ai/ha) + prosulfuron (10 g ai/ha) + dicamba (140 g ai/ha) + MSO (1.75 L/ha) + 28% UAN (2.5 L/ha) POST; and nicosulfuron (12.5 g/ha) + rimsulfuron (12.5 g/ha) + prosulfuron (10 g/ha) + dicamba (140 g/ ha) + nonionic surfactant (0.2% v/v) POST. A weed-free control was established by applying either S-metolachlor/

atrazine/benoxacor at 2,880 g ai/ha PRE or glyphosate at 900 g ae/ha POST and maintaining with hand weeding as needed. The final treatment was maintained as a weedy control. Herbicide application dates, carrier volumes, and spray pressures are reported in Table 1.

Crop injury, weed dry matter, and crop yield were measured at all sites. Weed dry matter harvests were made approximately 75 d after the application of foramsulfuron from a 1-m2 area within each plot. Plants were removed at the soil surface, separated by species, and dried to a constant weight at 80 C. Injury of corn was recorded on a scale ranging from 0 (no visible injury) to 100 (total plant death) 7, 14, and 28 d after foramsulfuron application. Corn was mechanically harvested at physiological maturity using a plot combine at all sites. Corn yields were adjusted to a 15.5% moisture level. The corn yields from the weed-free control were used as a base for calculating percentage of crop yield in all plots treated with foramsulfuron.

Statistical Analysis. All data were subjected to ANOVA using SAS statistical software.' The data were analyzed as a mixed model using the MIXED procedure of SAS. The variances were partitioned into the fixed effects of foramsulfuron rate and into the random effects of year, location, year by location, their interactions with the fixed effects, and blocks nested within year by location. The assumptions of the variance analysis were tested by ensuring that the residuals were random, homogeneous, and with a normal distribution about a mean of zero using residual plots and the Shapiro-Wilk normality test. When the effect of location, year, and their interactions with foramsulfuron rate were not significant after analysis, data presented were pooled by location or year.

To assess weed control and estimate the rate of foramsulfuron required for 90% (190) weed control, regression of weed dry matter over herbicide rate was performed using the log- logistic model described by Seefeldt et al. (1995) and modified by Schabenberger et al. (1999)

Y = A +([D - A]/[1 + {K/100 -

K} exp(B{X/Ik}]),

where Y is the response (e.g., weed dry matter), A is the lower limit, D is the upper limit, Kis percentage reduction in weed dry matter, B is the slope of the line, Ik is the dose giving Kresponse,

454 * Weed Technology 21, April-June 2007



and X is the herbicide rate. The rates of foramsulfuron required to obtain a 90% reduction of weed dry matter and the regression parameters were estimated using the NLIN procedure in SAS and were performed separately for each weed species. The dose-

response curves that were generated describe the relation of the herbicide rate (on a logarithmic scale) against the percentage reduction (linear scale) of weed dry matter as a percentage of weed dry matter in a nontreated check.

Corn yield data were subjected to an ANOVA using the MIXED procedure in SAS. The interactions of year by treatment and year by location were nonsignificant (P > 0.05); however, the interaction of location by treatment was significant (P < 0.05). Therefore, data were analyzed separately by location but pooled by year for each location. Corn yields for each location were converted to a percentage of the yield obtained in the weed-free control. An ANOVA was performed on the transformed data and confirmed that the location-by-treatment interaction still existed. A regression of the transformed corn yield data against herbicide rate was then performed using a hyperbolic model described by Cousens (1985)

Y = I *d/(1 + I *d/A) [2]

where Y is corn yield as a percentage of yield obtained using a standard herbicide, d is herbicide rate, I is the slope, and A is the

asymptote of the hyperbolic line. The regression parameters were obtained using the NLIN procedure in SAS and the graphical representation was generated using Sigma Plot. The curve was used to determine the rate of foramsulfuron required to obtain at least 95% of the corn yield that would be obtained in the weed- free plots. The 95% corn yield was designated as a yield that must be obtained to maintain optimal annual crop yields. Previous research in corn has also designated that acceptable corn yield is at least 95% of a weed-free control or a standard herbicide treatment (Knezevic et al. 1998; Sikkema et al. 1999).

Results and Discussion Common Lambsquarters. The control of common lambsquarters with foramsulfuron increased with increasing foramsulfuron rate (Figure 1). Common lambsquarters populations were abundant at all locations in both years with densities before foramsulfuron application as high as 300 plants/m2. The

100 -

90-

8 80-

70

o 60

o0

0 CHEAL

. 50 - O AMBEL V SETVI

E 40

30 -

" 20

10

8.75 17.5 35 70 105 140

Foramsulfuron (g ai/ha)

Figure 1. Weed dry matter (expressed as a percentage of the nontreated control) as influenced by various rates of foramsulfuron. Data points represent mean values (t SE) of pooled data for CHEAL, AMBEL, and SETVI. The regression lines were calculated using Eq. I and the parameter values are recorded in Table 2.

foramsulfuron rate, required to reduce dry matter by 90%

(190), was 68 g/ha. The percentage control of common lambsquarters was similar to that estimated by the log-logistic regression, with 76% weed control being recorded at foramsulfuron rates of 35 g/ha (Table 2). These results are similar to those reported by Bunting et al. (2005), who obtained 81% common lambsquarters control when foramsulfuron was applied alone at either 32 or 37 g/ha in Illinois. Arnold et al. (2005) reported 97% common lambsquarters control with a 33 g/ha application of foramsulfuron in New Mexico. The higher level of control obtained by Arnold et al. (2005) may be partially explained by their relatively low initial populations (20 plants/m ) and the application of foramsulfuron at an early (< 5-cm height) common lambsquarters growth stage. Larger initial common lambsquarters populations in this study and an average seedling height greater than 5 cm may have contributed to the comparatively lower common lambsquarters control in this study. Common Ragweed. Common ragweed control increased with increasing foramsulfuron rate (Figure 1). Populations of common ragweed were present at all locations except Harrow and initial populations ranged from 3 to 75 plants/m2. An

Table 2. Rate of foramsulfuron required to obtain a 90% reduction weed dry matter and regression parameters for selected weed species pooled across locations and years.a

Foramsulfuron rate (? SE)b Weed control 28 DATc Regression parameters ( SE)d

Weed species o90 35 g/ha B D A R2

g/ha Common lambsquarters 68 (13.7) 76 1.4 (0.27) 74 (19.3) 0.74 (0.20) 0.99 Common ragweed 86 (15.5) 85 1.5 (0.34) 91 (18.9) 0.91 (0.19) 0.99 Green foxtail 25 (1.5) 95 4.6 (6.2) 16 (3.0) 8.5 (1.5) 0.81

a Interactions of location and year with foramsulfuron rate were nonsignificant. b Rate of foramsulfuron resulting in a weed dry matter reduction of 90%.

cAbbreviation: DAT, days after treatment. d Regression parameters were calculated using Eq. 1.




120

110

100 >" - . --

0 80

10

70 / S- -Harrow

8.760 - 1 ------ Exeter 0 50m n g Ridgetown

50 .............. Woodslee o 40

.. .. Woodstock

>- 30-

0 20 O

10

8.7517.50 35.00 70.00 105.00 140.00

Foramsulfuron (g ai/ha)

Figure 2. Corn yield (expressed as a percentage of a weed-free treatment) as influenced by various rates of foramsulfuron at five Ontario locations. The regression lines were calculated using Eq. 2 and the regression parameters are presented in Table 3.

86 g/ha rate of foramsulfuron was required to obtain the o90 level of weed control (Table 2). Ragweed control was 85% at 35 g/ha foramsulfuron (Table 2). This result suggests that lower rates of foramsulfuron were required to reduce populations of common ragweed on a plant/m2 basis. Our data suggest that 190 common ragweed control is not possible when foramsulfuron is applied at the registered rate (35 g/ha); however, it is possible to obtain greater than 80% population reductions.

Green Foxtail. Green foxtail control increased with increasing foramsulfuron rate up to a rate at 35 g/ha, after which the level of control reached a plateau (Figure 1). Populations of green foxtail were present at Exeter, Ridgetown, and Woods- lee at an average density of 40 plants/m2. To obtain an o90 level of control a rate of 25 g ai/ha foramsulfuron was needed (Table 2). Greater than 95% reductions in green foxtail populations were observed with rates of foramsulfuron 35 g/ ha and above (Table 2). Bunting et al. (2004a) reported comparable control of a similar species, giant foxtail (Setaria faberi Herrm.), when foramsulfuron (37 g/ha) + MSO (1.0% v/v) + 28% UAN (2.5% v/v) were applied in Illinois. Bunting et al. (2004a) showed that 37 g/ha of foramsulfuron provides weed control of 98% as well as a 98% reduction in giant foxtail biomass relative to the nontreated control.

Additional Weed Species Controlled in This Study. Redroot pigweed (Amaranthus retroflexus L.) and velvetleaf (Abutilon theophrasti Medic.) were also among the prominent weed species present at the locations tested in our study. The data for dry weight reductions were similar across all treatments for both species; therefore, the log-logistic regression failed to converge and it was not possible to estimate 190 values for these weed species (data not shown). The recommended registered rate of foramsulfuron (35 g/ha) provided greater than 90% control of both species (data not shown). These results are similar to the > 98% redroot

Table 3. Mean corn yield in a weed-free treatment and regression parameters (Eq. 2 and Figure 3) used to calculate rate of foramsulfuron required to achieve 95% of the yield in a weed-free check across location and years.

Regression parameters (? SE) Weed-free

Location Yeara corn yield I A R2

t/ha

Exeter 2001-2002 9.8 33 (8.6) 97 (2.9) 0.82 Harrow 2001-2002 8.0 8 (1.5) 95 (4.8) 0.94 Ridgetown 2001-2002 6.9 5 (0.7) 104 (5.3) 0.97 Woodslee 2001-2002 6.7 62 (16.5) 95 (1.8) 0.79 Woodstock 2001-2002 6.7 7 (1.3) 127 (8.3) 0.95

aYear-by-main effects interaction was nonsignificant. Therefore, yield data for each location were pooled by year.

pigweed and 84% velvetleaf control reported by Arnold et al. (2005) and Bunting et al (2005). Foramsulfuron Effect on Corn Tolerance and Yield. Corn tolerance was excellent at all rates of foramsulfuron tested. At Ridgetown and Woodstock, 7 d after treatment (DAT), up to 10% visual corn injury was observed at foramsulfuron rates above 105 g/ha (data not shown). The crop injury symptoms caused by foramsulfuron included growth reduction in comparison to the nontreated control, purpling of the leaf veins and margins, a yellow flash in the whorl and patchy chlorosis of corn leaves four to six. By 14 DAT corn plants did not exhibit any visual injury symptoms, but it remains unclear if the early-season injury was reflected in the final yield. There was no rate-dependent association between foramsulfuron rate and corn injury. This is similar to corn injury levels at 7, 14, and 28 DAT reported by Bunting et al. (2004b, 2005).

Increasing foramsulfuron rate reduced early-season interference with weeds and increased corn grain yield at all locations (Figure 2). The corn grain yields in the weed-free check ranged from 6.7 to 9.8 t/ha depending on location (Table 3). At Woodstock, 95% of the corn yield relative to the weed-free check was obtained at a foramsulfuron rate of approximately 70 g/ha. To achieve 90% grain yield at Exeter and Woodslee, foramsulfuron rates of approximately 35 g/ha were required (Figure 2). Corn grain yield as a percentage of the weed-free control at Harrow and Ridgetown did not exceed 75 and 85% of the yield in the weed-free control at any of the foramsulfuron rates tested. Reduced yields at Harrow and Woodstock may have resulted from higher initial common lambsquarters populations prior to herbicide application in the foramsulfuron-treated plots.

Tank-Mixing Foramsulfuron with a Broadleaved Herbi- cide Improved Weed Control and Corn Yield. At 28 DAT, percentage weed control with foramsulfuron did not differ from weed control observed in the nicosulfuron + rimsulfuron (standard) treatment (Table 4). Nicosulfuron + rimsulfuron have good activity on annual grasses but must be tank-mixed with a broadleaved herbicide to provide a broad spectrum of control. Therefore, we compared treatments of foramsulfuron and nicosulfuron + rimsulfuron that were tank-mixed with the broadleaf herbicides prosulfuron + dicamba. There were no significant differences between the two tank-mix treatments for weed control and the addition of prosulfuron + dicamba




Table 4. Mean percentage weed control at 28 d after treatment and mean corn yield with application of foramsulfuron, nicosulfuron + rimsulfuron (standard), and foramsulfuron + prosulfuron + dicamba pooled across location and years.a

Visual weed control

Treatmentb Rate ABUTH AMARE AMBEL CHEAL SETVI Corn yield

g ai/ha % t/ha

Foramsulfuron 35 90 91 85 76 95 5.9 Nicosulfuron + rimsulfuron 12.5 + 12.5 90 86 75 72 99 5.8 Foramsulfuron + prosulfuron + dicamba 35 + 10 + 140 96 100 99 98 96 8.0 Nicosulfuron + rimsulfuron + prosulfuron + dicamba 12.5 + 12.5 + 10 + 140 96 99 98 97 97 7.9 LSD (0.05) 3 4 4 4 4 2 Contrastsc Foramsulfuron vs. nicosulfuron + rimsulfuron NS NS NS NS NS NS Foramsulfuron + prosulfuron + dicamba vs. nicosulfuron

+ rimsulfuron + prosulfuron + dicamba NS NS NS NS NS NS Foramsulfuron vs. foramsulfuron + prosulfuron + dicamba NS NS * * NS * Nicosulfuron + rimsulfuron vs. nicosulfuron + rimsulfuron

+ prosulfuron + dicamba NS * * * NS *

a Interactions of location and year with treatment were nonsignificant. bHerbicides were applied at the four- to six-leaf stage of corn.

COrthogonal contrasts denoted by an asterisk (*) are significant at the 5% level.

improved the control of common ragweed and common lambsquarters (Table 4). A direct comparison of foramsulfuron applied alone vs. a tank mixture with prosulfuron + dicamba revealed that the improved early-season control of common ragweed and common lambsquarters resulted in a 27% increase in final corn yield. Therefore, tank-mixing foramsulfuron with a broadleaved herbicide may provide better wide-spectrum biologically effective weed control and protect final corn yield.

These data show that the weed control response to foramsulfuron was variable by weed species. The dose- response curves show that the most susceptible weed species in this study was green foxtail, followed by common lambsquarters and common ragweed. The registered rate (35 g/ha) of foramsulfuron also provided excellent full-season control of redroot pigweed and velvetleaf. Furthermore, these data show that only green foxtail has the potential for control above a 90% level at reduced foramsulfuron rates. Therefore, to control a wide range of weed species and maintain corn yield, foramsulfuron must be applied at a rate of at least 35 g/ha. In fields with a combination of both grass and broadleaf weeds, an off-registered foramsulfuron rate of 70 g/ha or higher would be required, which is higher than allowed by the herbicide registration. However, to prevent overreliance on a singular mode-of-action a more sustainable solution would be to tank-mix foramsulfuron with a broadleaf herbicide.

Sources of Materials 1 Statistical Analysis Systems (SAS) Software, Version 8. SAS

Institute, Inc., Box 8000, SAS Circle, Cary, NC 27512.

Acknowledgments The authors thank Todd Cowan, Christy Shropshire, Peter

Smith, and Mac Whaley for technical assistance. This work

was supported in part by Bayer CropScience and the Ontario Ministry of Agriculture, Food and Rural Affairs through enhanced partnership with the University of Guelph.

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Received April 5, 2006, and approved November 30, 2006.




Weed Control and Yield Response to Foramsulfuron in Corn

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