- Email: [email protected]
diflufenzopyr drift followed by postemergence herbicides
Crop Protection 28 (2009) 539–542
Contents lists available at ScienceDirect
Crop Protection journal homepage: www.elsevier.com/locate/cropro
Soybean response to simulated dicamba/diflufenzopyr drift followed by postemergence herbicides Lynette R. Brown a, *, Darren E. Robinson a, Robert E. Nurse b, Clarence J. Swanton c, Peter H. Sikkema a a
Department of Plant Agriculture, University of Guelph, Ridgetown Campus, 120 Main Street East, Ridgetown, Ontario N0P 2C0, Canada Agriculture and Agri-Food Canada, Greenhouse and Processing Crops Centre, 2585 County Road 20, Harrow, Ontario N0R 1G0, Canada c Department of Plant Agriculture, University of Guelph, Guelph, Ontario N1G 2W1, Canada b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 January 2008 Received in revised form 9 February 2009 Accepted 18 February 2009
Five field experiments were conducted in 2007 to determine the effect of simulated dicamba/diflufenzopyr drift followed by postemergence applications of chlorimuron-ethyl, imazethapyr or bentazon on soybean (Glycine max Merr.) crop injury, dry weight, height and yield. In the absence of a postemergence herbicide, as the dose of simulated dicamba/diflufenzopyr increased there was an increase in soybean injury and a decrease in dry weight, height and yield. The application of registered postemergence herbicides following simulated dicamba/diflufenzopyr drift resulted in a synergistic increase in crop injury in some environments. There was no synergistic response in respect to dry weight and height when simulated drift was followed by postemergence herbicides. A synergistic yield response was observed with yield being decreased 4–7% more than expected due to simulated dicamba/diflufenzopyr drift followed by the application of chlorimuron-ethyl. No synergistic yield response was observed for dicamba/diflufenzopyr drift followed by either imazethapyr or bentazon. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Bentazon Chlorimuron-ethyl Dicamba/diflufenzopyr Imazethapyr Synergism
1. Introduction Maize (Zea mays) and soybean (Glycine max Merr.) are frequently planted in fields that are adjacent to one another. When these two crops are grown in close proximity, there is the potential for soybean injury due to herbicide drift from an adjacent maize field. Previous research conducted by Maybank et al. (1978) and Wolf et al. (1992) has determined that herbicide drift from unshielded sprayers can range from 1 to 16% depending on nozzle type, spray additives, boom height and wind velocity. Possible synergistic responses in respect to crop injury and yield from herbicide drift followed by the application of a registered postemergence herbicide have been postulated. The interaction of herbicides when applied either simultaneously or sequentially, may result in responses that are not predictable based on their response when applied alone. The interaction of herbicides in combination is synergistic if the actual effect is greater than the sum of the effects from the two herbicides applied individually (Gressel, 1990; Lich et al., 1997). These herbicide combinations can cause a synergistic response that increases crop damage. An example of this was documented by Simpson and * Corresponding author. Tel.: þ1 519 674 1645; fax: þ1 519 674 1600. E-mail address: [email protected] (L.R. Brown). 0261-2194/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2009.02.004
Stoller (1996) who reported that individual applications of thifensulfuron (4.4 g a.i. ha1) and imazethapyr (70 g a.i. ha1) caused 0 and 28% injury, respectively in soybean, but the combination of both herbicides caused 50% injury. Dicamba/diflufenzopyr is a postemergence herbicide registered for broadleaf weed control in maize in Canada. Diflufenzopyr is an auxin transport inhibitor and dicamba causes irregular accumulation of indoleacetic acid (Vencill, 2002) and stimulates ethylene production. Soybean injury symptoms due to dicamba/diflufenzopyr drift appear as cupping and puckering of the leaves, twisted stems, shortened internodes, and a triangular shaped canopy. Chlorimuron-ethyl and imazethapyr are registered for postemergence broadleaf weed control in soybean. They are acetolactate synthase (ALS) inhibitors (Vencill, 2002) and are widely used due to their low mammalian toxicity, broad-spectrum weed control, and flexibility of use on a wide variety of crops. Both chlorimuron-ethyl and imazethapyr have the potential to cause some initial soybean injuries. Bentazon is a photosystem II inhibitor (Vencill, 2002) that provides annual broadleaf weed control in soybean. The objective of this research was to determine if simulated dicamba/diflufenzopyr drift followed by postemergence applications of chlorimuron-ethyl, imazethapyr or bentazon has a synergistic effect on soybean crop injury, dry weight, height and yield.
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L.R. Brown et al. / Crop Protection 28 (2009) 539–542
2. Materials and methods Five field experiments were established in 2007 at the University of Guelph, Elora, Ontario, at the Agriculture and Agri-Food Canada Research Centre, Harrow, Ontario and at the University of Guelph Ridgetown Campus, Ridgetown, Ontario. At Elora and Ridgetown, trial areas were moldboard plowed in the fall and worked twice with a cultivator with rolling basket harrows in the spring to prepare the seedbed. At Harrow the seedbed was prepared by cultivation in the spring. At each location, the experiments were established as a randomized complete block design with four replications. Glyphosate-resistant soybean were planted in 60–76 cm rows at a seeding rate of 400,000–480,000 seeds ha1 at Elora (DK27-02) on May 24, 2007, Harrow (DK31-52) on June 11, 2007, and Ridgetown (DK30-07) on May 23 and May 24, 2007, into plots that were 2 by 7 m, 1.8 by 8 m, and 2 by 8 m, respectively. The soil at Elora was a silt loam with 31% sand, 50% silt, 19% clay, 4.2% organic matter, and a pH of 7.4. The soil at Harrow was sandy loam with 83% sand, 5% silt, 12% clay, 2.6% organic matter, and a pH of 6.0. The soil at two of the Ridgetown locations was a sandy clay loam with 52% sand, 26% silt, 21% clay, 5.3% organic matter, and a pH of 6.8. The soil at the third Ridgetown location was a sandy loam with 54% sand, 27% silt, 19% clay, 5.6% organic matter, and a pH of 6.4. The two herbicide treatments (simulated drift followed by the registered postemergence herbicide) at the Ridgetown sites were applied on June 15 and 18, June 22 and 25 and June 25 and 28. At Elora, the treatments were made on June 23 and 25 and at Harrow, the treatments were applied on July 3 and 7. Plots were maintained weed-free with s-metolachlor/benoxacor plus glyphosate applied preemergence, glyphosate applied postemergence and hand hoeing as required. The sodium salt of dicamba in combination with diflufenzopyr (5:2 ratio) was applied to soybean at the two to three trifoliate stages at 0, 2, 10, 20 and 40 g a.i. ha1, representing 0, 1, 5, 10, and 20% of the recommended labeled dose, respectively, to simulate herbicide drift. Chlorimuron-ethyl (9 g a.i. ha1), ammonium salt of imazethapyr (100 g a.i. ha1) or sodium salt of bentazon (1080 g a.i. ha1) was applied 2–4 days after the simulated dicamba/ diflufenzopyr drift application. Chlorimuron-ethyl, imazethapyr and bentazon treatments included urea ammonium nitrate (UAN) at 2.0% v/v. A nonionic surfactant was added at 0.10% v/v to the chlorimuron-ethyl treatments and at 0.25% v/v to the imazethapyr treatments. Herbicides were applied with a CO2 pressurized backpack sprayer equipped with 120-02 ultra low drift nozzles calibrated to deliver 200 L ha1 at 207 kPa at the Elora and Ridgetown locations, and using flat-fan 11004XR (Teejet Spraying Systems Co. Wheaton, IL) nozzles at Harrow. Crop injury was rated 7, 14, 28, and 56 days after application (DAA) with 0% indicating no crop injury and a rating of 100% indicating complete plant death. Average soybean height was determined by measuring the height of 10 plants from the soil surface to the top trifoliate leaf 28 DAA. Soybean dry weight was determined at 42 DAA by destructively harvesting 10 plants per plot at ground level and placing them into a paper bag. The plants were then dried at 60 C to a constant moisture, and the weight was recorded. Soybean grain yield was determined by harvesting the middle two rows of each plot with a small-plot combine. Yields were adjusted to 13.0% moisture. All data were subjected to analysis of variance, and analyzed using the PROC MIXED procedure of SAS (Ver. 9.1, SAS Inst., Cary NC). To meet the assumptions of variance analyses, means of injury ratings 7 DAA (Ridgetown and Harrow) were transformed using log and square root transformations. Injury ratings 14 DAA (Ridgetown) and 56 DAA were transformed using an arcsine square root transformation. Dry weight was transformed using a square root
transformation. Means were back-transformed to the original scale for presentation of results. Injury at 28 DAA, height and yield data met the assumptions of normality, therefore no transformations were necessary. The random effect of location and its interaction with herbicide treatments was significant for several of the variables analyzed. As a result, data for some parameters were reported by location. Means were separated using Fisher’s protected LSD at P < 0.05. Colby (1967) Equation (1) was used to determine the expected combination means by using the observed means for dicamba/diflufenzopyr (A) alone and the postemergence herbicide (B) alone.
expected ¼ A þ B A B=100
(1)
Yield, dry weight and height were calculated as a percent of the untreated check and Colby’s modified Equation (2) for percent of control values was used to determine the expected combination means.
expected ¼ A B=100
(2)
Following the calculation of the expected means, observed versus expected means were compared at the 0.05 level of significance using a paired t-test in order to determine synergistic or antagonistic responses. 3. Results and discussion 3.1. Crop injury Generally, as dicamba/diflufenzopyr dose increased, soybean foliar injury increased at 7 (data not shown), 14, 28, and 56 DAA (Tables 1–3). Dicamba/diflufenzopyr injury included cupping and crinkling of newly emerged leaves and twisting of the fully expanded leaves. Similar dicamba injury symptoms have been reported by Andersen et al. (2004), Kelley et al. (2005) and Weidenhamer et al. (1989). Chlorimuron-ethyl, imazethapyr and bentazon applied postemergence caused little injury to soybean. Combinations of the simulated dicamba/diflufenzopyr drift followed by the postemergence herbicides resulted in synergistic responses in some environments. When dicamba/diflufenzopyr drift was simulated without the postemergence herbicide, there was an increase in soybean injury with increasing dose at all three locations 7 DAA (data not shown). Generally, there was no synergistic response from simulated dicamba/diflufenzopyr drift followed by the postemergence herbicides (chlorimuron-ethyl, imazethapyr or bentazon) at the Harrow and Elora locations. In contrast, synergistic responses were observed at Ridgetown with all three postemergence herbicides. The application of dicamba/diflufenzopyr at 2, 10, 20 and 40 g a.i. ha1 followed by chlorimuron-ethyl or imazethapyr resulted in a synergistic response. In addition, the simulated drift of dicamba/ diflufenzopyr at 10 and 20 g a.i. ha1 followed by bentazon application showed a synergistic response. For example, the observed crop injury from the dicamba/diflufenzopyr drift at 2, 10, 20 and 40 g a.i. ha1 followed by chlorimuron-ethyl was 6, 31, 27 and 11% greater than the expected values indicating a synergistic response. Similar increases in crop injury were observed with the application of imazethapyr and bentazon. At 14 DAA, there was an increase in crop injury in soybean with increasing doses of dicamba/diflufenzopyr (Table 1). Kelley et al. (2005) also reported observing more injury with increasing doses of dicamba/diflufenzopyr. When dicamba/diflufenzopyr was applied at 0.2 g a.i. ha1 plus 0.08 g a.i. ha1 and 2.0 g a.i. ha1 plus 0.8 g a.i. ha1, soybean injury two weeks after application was 22 and 42%, respectively (Kelley et al., 2005). Generally, there was no
L.R. Brown et al. / Crop Protection 28 (2009) 539–542
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Table 1 Percent soybean injury 14 DAA with simulated dicamba/diflufenzopyr drift alone or followed by the application of a postemergence herbicide at Elora, Harrow and the three sites at Ridgetown in 2007.a
Table 3 Percent soybean injury 56 DAA with simulated dicamba/diflufenzopyr drift alone or followed by the application of a postemergence herbicide at Elora, Harrow and Ridgetown in 2007.a
Dicamba/diflufenzopyr Injury (14 DAA)b (%) drift (dose) Dicamba/ Drift fb Drift fb Drift fb (g a.i. ha1) diflufenzopyr chlorimuron-ethyl imazethapyr bentazon
Dicamba/diflufenzopyr Injury (56 DAA)b (%) drift (dose) Dicamba/ Drift fb Drift fb Drift fb (g a.i. ha1) diflufenzopyr chlorimuron-ethyl imazethapyr bentazon
Elora Untreated check 0 2 10 20 40 SE Harrow Untreated check 0 2 10 20 40 SE Ridgetown Untreated check 0 2 10 20 40 SE
Untreated check 0 2 10 20 40 SE
0a 0a 11 b 11 b 18 c 28 d 2.1
0a 5 a (5)c 16 b (15) 21 bc (15)þ 24 c (22) 36 d (31) 2.6
0a 10 b (10) 13 b (19) 24 c (20) 26 c (26) 28 c (35) 2.3
0a 0 a (0) 13 b (11) 13 b (11) 21 c (18) 27 d (28) 2.1
0a 0 a (0)c 13 b (11) 25 c (23) 34 d (28)þ 47 e (42)þ 2.2
0a 0 a (0) 17 b (11)þ 27 c (23)þ 33 c (28)þ 45 d (42) 2.0
0a 0 a (0) 16 b (11)þ 27 c (23)þ 32 c (28)þ 47 d (42)þ 2.1
a
Abbreviations: DAA, days after application; fb, followed by. Means have been back-transformed to original scale. Means followed by the same letter in each column are not significantly different according to Fisher’s protected LSD test (P < 0.05). c Expected responses, based on Colby’s equation (E ¼ A þ B A B/100), for combinations are shown in parentheses following each observed response. Significant differences based on a paired t-test between observed and expected values are shown by a ‘‘þ’’ sign to indicate synergism. b
0a 0a 16 b 30 c 34 c 55 d 4.4
0a 0 a (0) 16 b (16) 20 b (30) 39 c (34) 58 d (55) 4.4
0a 0 a (0) 16 b (16) 29 c (30) 34 c (34) 46 d (55) 3.8
0a 6 b (6) 16 c (22) 25 d (35) 28 d (38) 53 e (58) 3.6
0a 0a 16 b 36 c 51 d 70 e 3.3
0a 0 a (0) 33 b (16)þ 55 c (36)þ 66 d (51)þ 76 e (70)þ 3.6
0a 0 a (0) 38 b (16)þ 54 c (36)þ 63 d (51)þ 72 e (70) 3.4
0a 0 a (0) 27 b (16)þ 45 c (36)þ 61 d (51)þ 71 d (70) 3.3
a
Abbreviations: DAA, days after application; fb, followed by. Ridgetown means have been back-transformed to original scale. Means followed by the same letter in each column are not significantly different according to Fisher’s protected LSD test (P < 0.05). c Expected responses, based on Colby’s equation (E ¼ A þ B A B/100), for combinations are shown in parentheses following each observed response. Significant differences based on a paired t-test between observed and expected values are shown by a ‘‘þ’’ sign to indicate synergism and a ‘‘’’ sign to indicate antagonism. b
synergistic response from simulated dicamba/diflufenzopyr drift followed by the three postemergence herbicides at the Harrow and Elora locations. At Harrow, there was an antagonistic response with the simulated drift (2 g a.i. ha1) followed by bentazon. However, this was an isolated response that was not observed in any of the other data. At Ridgetown, there were synergistic responses with all three postemergence herbicides. The application of dicamba/ diflufenzopyr at 2, 10, 20 and 40 g a.i. ha1 followed by
Table 2 Percent soybean injury 28 DAA with simulated dicamba/diflufenzopyr drift alone or followed by the application of a postemergence herbicide at Elora, Harrow and Ridgetown in 2007.a Dicamba/diflufenzopyr Injury (28 DAA)b (%) drift (dose) Dicamba/ Drift fb Drift fb Drift fb (g a.i. ha1) diflufenzopyr chlorimuron-ethyl imazethapyr bentazon Untreated check 0 2 10 20 40 SE
0a 0a 11 b 23 c 28 c 42 d 2.1
0a 0a 18 b 31 c 43 d 60 e 2.6
0a 0 a (0)c 21 b (18) 42 c (31)þ 49 c (43)þ 64 d (60) 2.8
0a 0 a (0) 28 b (18)þ 42 c (31)þ 50 c (43)þ 63 d (60) 2.7
0a 1 a (1) 24 b (18) 36 c (32) 48 d (43) 62 e (61) 2.6
chlorimuron-ethyl had 17, 20, 15 and 6% more injury, respectively than what was expected indicating a synergistic response. Similarly, synergistic responses were also observed with dicamba/ diflufenzopyr at 2, 10 and 20 g a.i. ha1 followed by imazethapyr and bentazon. Soybean injury at 28 DAA increased with increasing doses of dicamba/diflufenzopyr (Table 2). The application of dicamba/ diflufenzopyr at 10 and 20 g a.i. ha1 followed by chlorimuron-ethyl and imazethapyr resulted in 6–11% more injury than expected indicating a synergistic response. Similarly, the application of dicamba/diflufenzopyr at 2, 10 and 20 g a.i. ha1 followed by imazethapyr resulted in a synergistic response. There was no synergistic response from simulated dicamba/diflufenzopyr drift followed by bentazon. At 56 DAA, there was an increase in crop injury in soybean with increasing doses of dicamba/diflufenzopyr (Table 3). The application of dicamba/diflufenzopyr at 2 and 10 g a.i. ha1 followed by either imazethapyr or bentazon resulted in a synergistic response. In addition, the simulated drift of dicamba/diflufenzopyr at 20 g a.i. ha1 followed by either chlorimuron-ethyl, imazethapyr or bentazon, resulted in injury that was 6, 5 and 4% greater than the expected values, respectively. Similarly, synergistic responses were also observed with the application of dicamba/diflufenzopyr at 40 g a.i. ha1 followed by either chlorimuron-ethyl or bentazon. 3.2. Crop height Height decreased with increasing doses of dicamba/diflufenzopyr (data not shown). Height decreased by 13, 29, 37 and 47% when dicamba/diflufenzopyr was applied at 2, 10, 20 and 40 g a.i. ha1, respectively. Similarly, Kelley et al. (2005) also reported a 12–24% height reduction, despite the development of lateral branches on the more severely injured plants. There were no synergistic responses from simulated dicamba/diflufenzopyr drift followed by any postemergence herbicides. 3.3. Crop dry weight
a
Abbreviations: DAA, days after application; fb, followed by. b Means followed by the same letter in each column are not significantly different according to Fisher’s protected LSD test (P < 0.05). c Expected responses, based on Colby’s equation (E ¼ A þ B A B/100), for combinations are shown in parentheses following each observed response. Significant differences based on a paired t-test between observed and expected values are shown by a ‘‘þ’’ sign to indicate synergism.
Percent dry weight reflected the amount of injury observed. Dry weight decreased by 19, 26, 36 and 50%, respectively, with increasing doses of dicamba/diflufenzopyr (data not shown). There were no synergistic responses from simulated dicamba/diflufenzopyr drift followed by the postemergence herbicides.
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Table 4 Percent soybean yield in comparison to an untreated check when dicamba/diflufenzopyr drift was simulated alone or followed by the application of a postemergence herbicide at all three locations in 2007.a Dicamba/diflufenzopyr Yieldb (%) drift (dose) Dicamba/ Drift fb Drift fb Drift fb (g a.i. ha1) diflufenzopyr chlorimuron-ethyl imazethapyr bentazon Untreated check 0 2 10 20 40 SE
100 a 100 a 94 ab 94 ab 87 b 69 c 1.7
100 a 102 a (102)c 98 a (96) 90 ab (97) 81 b (89)þ 62 c (70)þ 1.8
100 a 95 ab (95) 94 abc (90) 86 bc (90) 82 c (83) 63 d (65) 1.6
100 a 98 a (98) 96 a (92) 90 ab (92) 83 b (85) 64 c (67) 1.6
a
Abbreviations: DAA, days after application; fb, followed by. Means followed by the same letter in each column are not significantly different according to Fisher’s protected LSD test (P < 0.05). c Expected responses, based on Colby’s equation (E ¼ A B/100), for combinations are shown in parentheses following each observed response. Significant differences based on a paired t-test between observed and expected values are shown by a ‘‘þ’’ sign to indicate synergism. b
3.4. Crop yield Soybean yield decreased with increasing doses of dicamba/ diflufenzopyr (Table 4). Synergistic responses were observed with the simulated drift of dicamba/diflufenzopyr at 10, 20 and 40 g a.i. ha1 followed by the chlorimuron-ethyl application which resulted in a 7–8% greater yield reduction than expected. The application of dicamba/diflufenzopyr at 2, 10, 20 and 40 g a.i. ha1 followed by imazethapyr or bentazon did not result in a synergistic yield response. Similarly, dicamba/diflufenzopyr (2 g a.i. ha1) followed by chlorimuron-ethyl also did not result in a synergistic response in yield. This study confirms that injury in soybean is accentuated when dicamba/diflufenzopyr drift is followed by some registered postemergence herbicides. A synergistic response for crop injury 7, 14,
28 and 56 DAA and soybean yield was documented when soybean was stressed due to herbicide drift followed by the postemergence herbicide. Weed management practitioners and crop consultants must be aware that herbicides with an acceptable margin of crop safety can cause injury if the crop was stressed due to a previous herbicide drift event.
Acknowledgements The authors would like to acknowledge the University of Guelph and Harrow Research Station weeds labs for their expertise and technical assistance in these studies. Funding for this project was provided in part by the Ontario Soybean Growers and the CanadaOntario Research and Development Program.
References Andersen, S.M., Clay, S.A., Wrage, L.J., Matthees, D., 2004. Soybean foliage residues of dicamba and 2,4-D and correlation to application rates and yield. Agron. J. 96, 750–760. Colby, S.R., 1967. Calculating synergistic and antagonistic responses of herbicide combinations. Weeds 15, 20–22. Gressel, J., 1990. Synergizing herbicides. Rev. Weed Sci. 5, 49–82. Kelley, K.B., Wax, L.M., Hager, A.G., Riechers, D.E., 2005. Soybean response to plant growth regulator herbicides is affected by other postemergence herbicides. Weed Sci. 53, 101–112. Lich, J.M., Renner, K.A., Penner, D., 1997. Interaction of glyphosate with postemergence soybean (Glycine max) herbicides. Weed Sci. 45, 12–21. Maybank, J., Yoshida, K., Grover, R., 1978. Spray drift from agricultural pesticide applications. J. Air Pollut. Control Assoc. 28, 1009–1014. Simpson, D.M., Stoller, E.W., 1996. Physiological mechanisms in the synergism between thifensulfuron and imazethapyr in sulfonylurea-tolerant soybean (Glycine max). Weed Sci. 44, 209–214. Vencill, W.K., 2002. Herbicide Handbook, eighth ed. Weed Science Society of America, 493 pp. Weidenhamer, J.D., Triplett Jr., G.B., Sobotka, F.E., 1989. Dicamba injury to soybean. Agron. J. 81, 637–643. Wolf, T.M., Grover, R., Wallace, K., Shewchuk, S.R., Maybank, J., 1992. Effect of protective shields on drift and deposition characteristics of field sprayers. Can. J. Plant Sci. 73, 1261–1273.
Contents lists available at ScienceDirect
Crop Protection journal homepage: www.elsevier.com/locate/cropro
Soybean response to simulated dicamba/diflufenzopyr drift followed by postemergence herbicides Lynette R. Brown a, *, Darren E. Robinson a, Robert E. Nurse b, Clarence J. Swanton c, Peter H. Sikkema a a
Department of Plant Agriculture, University of Guelph, Ridgetown Campus, 120 Main Street East, Ridgetown, Ontario N0P 2C0, Canada Agriculture and Agri-Food Canada, Greenhouse and Processing Crops Centre, 2585 County Road 20, Harrow, Ontario N0R 1G0, Canada c Department of Plant Agriculture, University of Guelph, Guelph, Ontario N1G 2W1, Canada b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 January 2008 Received in revised form 9 February 2009 Accepted 18 February 2009
Five field experiments were conducted in 2007 to determine the effect of simulated dicamba/diflufenzopyr drift followed by postemergence applications of chlorimuron-ethyl, imazethapyr or bentazon on soybean (Glycine max Merr.) crop injury, dry weight, height and yield. In the absence of a postemergence herbicide, as the dose of simulated dicamba/diflufenzopyr increased there was an increase in soybean injury and a decrease in dry weight, height and yield. The application of registered postemergence herbicides following simulated dicamba/diflufenzopyr drift resulted in a synergistic increase in crop injury in some environments. There was no synergistic response in respect to dry weight and height when simulated drift was followed by postemergence herbicides. A synergistic yield response was observed with yield being decreased 4–7% more than expected due to simulated dicamba/diflufenzopyr drift followed by the application of chlorimuron-ethyl. No synergistic yield response was observed for dicamba/diflufenzopyr drift followed by either imazethapyr or bentazon. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Bentazon Chlorimuron-ethyl Dicamba/diflufenzopyr Imazethapyr Synergism
1. Introduction Maize (Zea mays) and soybean (Glycine max Merr.) are frequently planted in fields that are adjacent to one another. When these two crops are grown in close proximity, there is the potential for soybean injury due to herbicide drift from an adjacent maize field. Previous research conducted by Maybank et al. (1978) and Wolf et al. (1992) has determined that herbicide drift from unshielded sprayers can range from 1 to 16% depending on nozzle type, spray additives, boom height and wind velocity. Possible synergistic responses in respect to crop injury and yield from herbicide drift followed by the application of a registered postemergence herbicide have been postulated. The interaction of herbicides when applied either simultaneously or sequentially, may result in responses that are not predictable based on their response when applied alone. The interaction of herbicides in combination is synergistic if the actual effect is greater than the sum of the effects from the two herbicides applied individually (Gressel, 1990; Lich et al., 1997). These herbicide combinations can cause a synergistic response that increases crop damage. An example of this was documented by Simpson and * Corresponding author. Tel.: þ1 519 674 1645; fax: þ1 519 674 1600. E-mail address: [email protected] (L.R. Brown). 0261-2194/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.cropro.2009.02.004
Stoller (1996) who reported that individual applications of thifensulfuron (4.4 g a.i. ha1) and imazethapyr (70 g a.i. ha1) caused 0 and 28% injury, respectively in soybean, but the combination of both herbicides caused 50% injury. Dicamba/diflufenzopyr is a postemergence herbicide registered for broadleaf weed control in maize in Canada. Diflufenzopyr is an auxin transport inhibitor and dicamba causes irregular accumulation of indoleacetic acid (Vencill, 2002) and stimulates ethylene production. Soybean injury symptoms due to dicamba/diflufenzopyr drift appear as cupping and puckering of the leaves, twisted stems, shortened internodes, and a triangular shaped canopy. Chlorimuron-ethyl and imazethapyr are registered for postemergence broadleaf weed control in soybean. They are acetolactate synthase (ALS) inhibitors (Vencill, 2002) and are widely used due to their low mammalian toxicity, broad-spectrum weed control, and flexibility of use on a wide variety of crops. Both chlorimuron-ethyl and imazethapyr have the potential to cause some initial soybean injuries. Bentazon is a photosystem II inhibitor (Vencill, 2002) that provides annual broadleaf weed control in soybean. The objective of this research was to determine if simulated dicamba/diflufenzopyr drift followed by postemergence applications of chlorimuron-ethyl, imazethapyr or bentazon has a synergistic effect on soybean crop injury, dry weight, height and yield.
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2. Materials and methods Five field experiments were established in 2007 at the University of Guelph, Elora, Ontario, at the Agriculture and Agri-Food Canada Research Centre, Harrow, Ontario and at the University of Guelph Ridgetown Campus, Ridgetown, Ontario. At Elora and Ridgetown, trial areas were moldboard plowed in the fall and worked twice with a cultivator with rolling basket harrows in the spring to prepare the seedbed. At Harrow the seedbed was prepared by cultivation in the spring. At each location, the experiments were established as a randomized complete block design with four replications. Glyphosate-resistant soybean were planted in 60–76 cm rows at a seeding rate of 400,000–480,000 seeds ha1 at Elora (DK27-02) on May 24, 2007, Harrow (DK31-52) on June 11, 2007, and Ridgetown (DK30-07) on May 23 and May 24, 2007, into plots that were 2 by 7 m, 1.8 by 8 m, and 2 by 8 m, respectively. The soil at Elora was a silt loam with 31% sand, 50% silt, 19% clay, 4.2% organic matter, and a pH of 7.4. The soil at Harrow was sandy loam with 83% sand, 5% silt, 12% clay, 2.6% organic matter, and a pH of 6.0. The soil at two of the Ridgetown locations was a sandy clay loam with 52% sand, 26% silt, 21% clay, 5.3% organic matter, and a pH of 6.8. The soil at the third Ridgetown location was a sandy loam with 54% sand, 27% silt, 19% clay, 5.6% organic matter, and a pH of 6.4. The two herbicide treatments (simulated drift followed by the registered postemergence herbicide) at the Ridgetown sites were applied on June 15 and 18, June 22 and 25 and June 25 and 28. At Elora, the treatments were made on June 23 and 25 and at Harrow, the treatments were applied on July 3 and 7. Plots were maintained weed-free with s-metolachlor/benoxacor plus glyphosate applied preemergence, glyphosate applied postemergence and hand hoeing as required. The sodium salt of dicamba in combination with diflufenzopyr (5:2 ratio) was applied to soybean at the two to three trifoliate stages at 0, 2, 10, 20 and 40 g a.i. ha1, representing 0, 1, 5, 10, and 20% of the recommended labeled dose, respectively, to simulate herbicide drift. Chlorimuron-ethyl (9 g a.i. ha1), ammonium salt of imazethapyr (100 g a.i. ha1) or sodium salt of bentazon (1080 g a.i. ha1) was applied 2–4 days after the simulated dicamba/ diflufenzopyr drift application. Chlorimuron-ethyl, imazethapyr and bentazon treatments included urea ammonium nitrate (UAN) at 2.0% v/v. A nonionic surfactant was added at 0.10% v/v to the chlorimuron-ethyl treatments and at 0.25% v/v to the imazethapyr treatments. Herbicides were applied with a CO2 pressurized backpack sprayer equipped with 120-02 ultra low drift nozzles calibrated to deliver 200 L ha1 at 207 kPa at the Elora and Ridgetown locations, and using flat-fan 11004XR (Teejet Spraying Systems Co. Wheaton, IL) nozzles at Harrow. Crop injury was rated 7, 14, 28, and 56 days after application (DAA) with 0% indicating no crop injury and a rating of 100% indicating complete plant death. Average soybean height was determined by measuring the height of 10 plants from the soil surface to the top trifoliate leaf 28 DAA. Soybean dry weight was determined at 42 DAA by destructively harvesting 10 plants per plot at ground level and placing them into a paper bag. The plants were then dried at 60 C to a constant moisture, and the weight was recorded. Soybean grain yield was determined by harvesting the middle two rows of each plot with a small-plot combine. Yields were adjusted to 13.0% moisture. All data were subjected to analysis of variance, and analyzed using the PROC MIXED procedure of SAS (Ver. 9.1, SAS Inst., Cary NC). To meet the assumptions of variance analyses, means of injury ratings 7 DAA (Ridgetown and Harrow) were transformed using log and square root transformations. Injury ratings 14 DAA (Ridgetown) and 56 DAA were transformed using an arcsine square root transformation. Dry weight was transformed using a square root
transformation. Means were back-transformed to the original scale for presentation of results. Injury at 28 DAA, height and yield data met the assumptions of normality, therefore no transformations were necessary. The random effect of location and its interaction with herbicide treatments was significant for several of the variables analyzed. As a result, data for some parameters were reported by location. Means were separated using Fisher’s protected LSD at P < 0.05. Colby (1967) Equation (1) was used to determine the expected combination means by using the observed means for dicamba/diflufenzopyr (A) alone and the postemergence herbicide (B) alone.
expected ¼ A þ B A B=100
(1)
Yield, dry weight and height were calculated as a percent of the untreated check and Colby’s modified Equation (2) for percent of control values was used to determine the expected combination means.
expected ¼ A B=100
(2)
Following the calculation of the expected means, observed versus expected means were compared at the 0.05 level of significance using a paired t-test in order to determine synergistic or antagonistic responses. 3. Results and discussion 3.1. Crop injury Generally, as dicamba/diflufenzopyr dose increased, soybean foliar injury increased at 7 (data not shown), 14, 28, and 56 DAA (Tables 1–3). Dicamba/diflufenzopyr injury included cupping and crinkling of newly emerged leaves and twisting of the fully expanded leaves. Similar dicamba injury symptoms have been reported by Andersen et al. (2004), Kelley et al. (2005) and Weidenhamer et al. (1989). Chlorimuron-ethyl, imazethapyr and bentazon applied postemergence caused little injury to soybean. Combinations of the simulated dicamba/diflufenzopyr drift followed by the postemergence herbicides resulted in synergistic responses in some environments. When dicamba/diflufenzopyr drift was simulated without the postemergence herbicide, there was an increase in soybean injury with increasing dose at all three locations 7 DAA (data not shown). Generally, there was no synergistic response from simulated dicamba/diflufenzopyr drift followed by the postemergence herbicides (chlorimuron-ethyl, imazethapyr or bentazon) at the Harrow and Elora locations. In contrast, synergistic responses were observed at Ridgetown with all three postemergence herbicides. The application of dicamba/diflufenzopyr at 2, 10, 20 and 40 g a.i. ha1 followed by chlorimuron-ethyl or imazethapyr resulted in a synergistic response. In addition, the simulated drift of dicamba/ diflufenzopyr at 10 and 20 g a.i. ha1 followed by bentazon application showed a synergistic response. For example, the observed crop injury from the dicamba/diflufenzopyr drift at 2, 10, 20 and 40 g a.i. ha1 followed by chlorimuron-ethyl was 6, 31, 27 and 11% greater than the expected values indicating a synergistic response. Similar increases in crop injury were observed with the application of imazethapyr and bentazon. At 14 DAA, there was an increase in crop injury in soybean with increasing doses of dicamba/diflufenzopyr (Table 1). Kelley et al. (2005) also reported observing more injury with increasing doses of dicamba/diflufenzopyr. When dicamba/diflufenzopyr was applied at 0.2 g a.i. ha1 plus 0.08 g a.i. ha1 and 2.0 g a.i. ha1 plus 0.8 g a.i. ha1, soybean injury two weeks after application was 22 and 42%, respectively (Kelley et al., 2005). Generally, there was no
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Table 1 Percent soybean injury 14 DAA with simulated dicamba/diflufenzopyr drift alone or followed by the application of a postemergence herbicide at Elora, Harrow and the three sites at Ridgetown in 2007.a
Table 3 Percent soybean injury 56 DAA with simulated dicamba/diflufenzopyr drift alone or followed by the application of a postemergence herbicide at Elora, Harrow and Ridgetown in 2007.a
Dicamba/diflufenzopyr Injury (14 DAA)b (%) drift (dose) Dicamba/ Drift fb Drift fb Drift fb (g a.i. ha1) diflufenzopyr chlorimuron-ethyl imazethapyr bentazon
Dicamba/diflufenzopyr Injury (56 DAA)b (%) drift (dose) Dicamba/ Drift fb Drift fb Drift fb (g a.i. ha1) diflufenzopyr chlorimuron-ethyl imazethapyr bentazon
Elora Untreated check 0 2 10 20 40 SE Harrow Untreated check 0 2 10 20 40 SE Ridgetown Untreated check 0 2 10 20 40 SE
Untreated check 0 2 10 20 40 SE
0a 0a 11 b 11 b 18 c 28 d 2.1
0a 5 a (5)c 16 b (15) 21 bc (15)þ 24 c (22) 36 d (31) 2.6
0a 10 b (10) 13 b (19) 24 c (20) 26 c (26) 28 c (35) 2.3
0a 0 a (0) 13 b (11) 13 b (11) 21 c (18) 27 d (28) 2.1
0a 0 a (0)c 13 b (11) 25 c (23) 34 d (28)þ 47 e (42)þ 2.2
0a 0 a (0) 17 b (11)þ 27 c (23)þ 33 c (28)þ 45 d (42) 2.0
0a 0 a (0) 16 b (11)þ 27 c (23)þ 32 c (28)þ 47 d (42)þ 2.1
a
Abbreviations: DAA, days after application; fb, followed by. Means have been back-transformed to original scale. Means followed by the same letter in each column are not significantly different according to Fisher’s protected LSD test (P < 0.05). c Expected responses, based on Colby’s equation (E ¼ A þ B A B/100), for combinations are shown in parentheses following each observed response. Significant differences based on a paired t-test between observed and expected values are shown by a ‘‘þ’’ sign to indicate synergism. b
0a 0a 16 b 30 c 34 c 55 d 4.4
0a 0 a (0) 16 b (16) 20 b (30) 39 c (34) 58 d (55) 4.4
0a 0 a (0) 16 b (16) 29 c (30) 34 c (34) 46 d (55) 3.8
0a 6 b (6) 16 c (22) 25 d (35) 28 d (38) 53 e (58) 3.6
0a 0a 16 b 36 c 51 d 70 e 3.3
0a 0 a (0) 33 b (16)þ 55 c (36)þ 66 d (51)þ 76 e (70)þ 3.6
0a 0 a (0) 38 b (16)þ 54 c (36)þ 63 d (51)þ 72 e (70) 3.4
0a 0 a (0) 27 b (16)þ 45 c (36)þ 61 d (51)þ 71 d (70) 3.3
a
Abbreviations: DAA, days after application; fb, followed by. Ridgetown means have been back-transformed to original scale. Means followed by the same letter in each column are not significantly different according to Fisher’s protected LSD test (P < 0.05). c Expected responses, based on Colby’s equation (E ¼ A þ B A B/100), for combinations are shown in parentheses following each observed response. Significant differences based on a paired t-test between observed and expected values are shown by a ‘‘þ’’ sign to indicate synergism and a ‘‘’’ sign to indicate antagonism. b
synergistic response from simulated dicamba/diflufenzopyr drift followed by the three postemergence herbicides at the Harrow and Elora locations. At Harrow, there was an antagonistic response with the simulated drift (2 g a.i. ha1) followed by bentazon. However, this was an isolated response that was not observed in any of the other data. At Ridgetown, there were synergistic responses with all three postemergence herbicides. The application of dicamba/ diflufenzopyr at 2, 10, 20 and 40 g a.i. ha1 followed by
Table 2 Percent soybean injury 28 DAA with simulated dicamba/diflufenzopyr drift alone or followed by the application of a postemergence herbicide at Elora, Harrow and Ridgetown in 2007.a Dicamba/diflufenzopyr Injury (28 DAA)b (%) drift (dose) Dicamba/ Drift fb Drift fb Drift fb (g a.i. ha1) diflufenzopyr chlorimuron-ethyl imazethapyr bentazon Untreated check 0 2 10 20 40 SE
0a 0a 11 b 23 c 28 c 42 d 2.1
0a 0a 18 b 31 c 43 d 60 e 2.6
0a 0 a (0)c 21 b (18) 42 c (31)þ 49 c (43)þ 64 d (60) 2.8
0a 0 a (0) 28 b (18)þ 42 c (31)þ 50 c (43)þ 63 d (60) 2.7
0a 1 a (1) 24 b (18) 36 c (32) 48 d (43) 62 e (61) 2.6
chlorimuron-ethyl had 17, 20, 15 and 6% more injury, respectively than what was expected indicating a synergistic response. Similarly, synergistic responses were also observed with dicamba/ diflufenzopyr at 2, 10 and 20 g a.i. ha1 followed by imazethapyr and bentazon. Soybean injury at 28 DAA increased with increasing doses of dicamba/diflufenzopyr (Table 2). The application of dicamba/ diflufenzopyr at 10 and 20 g a.i. ha1 followed by chlorimuron-ethyl and imazethapyr resulted in 6–11% more injury than expected indicating a synergistic response. Similarly, the application of dicamba/diflufenzopyr at 2, 10 and 20 g a.i. ha1 followed by imazethapyr resulted in a synergistic response. There was no synergistic response from simulated dicamba/diflufenzopyr drift followed by bentazon. At 56 DAA, there was an increase in crop injury in soybean with increasing doses of dicamba/diflufenzopyr (Table 3). The application of dicamba/diflufenzopyr at 2 and 10 g a.i. ha1 followed by either imazethapyr or bentazon resulted in a synergistic response. In addition, the simulated drift of dicamba/diflufenzopyr at 20 g a.i. ha1 followed by either chlorimuron-ethyl, imazethapyr or bentazon, resulted in injury that was 6, 5 and 4% greater than the expected values, respectively. Similarly, synergistic responses were also observed with the application of dicamba/diflufenzopyr at 40 g a.i. ha1 followed by either chlorimuron-ethyl or bentazon. 3.2. Crop height Height decreased with increasing doses of dicamba/diflufenzopyr (data not shown). Height decreased by 13, 29, 37 and 47% when dicamba/diflufenzopyr was applied at 2, 10, 20 and 40 g a.i. ha1, respectively. Similarly, Kelley et al. (2005) also reported a 12–24% height reduction, despite the development of lateral branches on the more severely injured plants. There were no synergistic responses from simulated dicamba/diflufenzopyr drift followed by any postemergence herbicides. 3.3. Crop dry weight
a
Abbreviations: DAA, days after application; fb, followed by. b Means followed by the same letter in each column are not significantly different according to Fisher’s protected LSD test (P < 0.05). c Expected responses, based on Colby’s equation (E ¼ A þ B A B/100), for combinations are shown in parentheses following each observed response. Significant differences based on a paired t-test between observed and expected values are shown by a ‘‘þ’’ sign to indicate synergism.
Percent dry weight reflected the amount of injury observed. Dry weight decreased by 19, 26, 36 and 50%, respectively, with increasing doses of dicamba/diflufenzopyr (data not shown). There were no synergistic responses from simulated dicamba/diflufenzopyr drift followed by the postemergence herbicides.
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Table 4 Percent soybean yield in comparison to an untreated check when dicamba/diflufenzopyr drift was simulated alone or followed by the application of a postemergence herbicide at all three locations in 2007.a Dicamba/diflufenzopyr Yieldb (%) drift (dose) Dicamba/ Drift fb Drift fb Drift fb (g a.i. ha1) diflufenzopyr chlorimuron-ethyl imazethapyr bentazon Untreated check 0 2 10 20 40 SE
100 a 100 a 94 ab 94 ab 87 b 69 c 1.7
100 a 102 a (102)c 98 a (96) 90 ab (97) 81 b (89)þ 62 c (70)þ 1.8
100 a 95 ab (95) 94 abc (90) 86 bc (90) 82 c (83) 63 d (65) 1.6
100 a 98 a (98) 96 a (92) 90 ab (92) 83 b (85) 64 c (67) 1.6
a
Abbreviations: DAA, days after application; fb, followed by. Means followed by the same letter in each column are not significantly different according to Fisher’s protected LSD test (P < 0.05). c Expected responses, based on Colby’s equation (E ¼ A B/100), for combinations are shown in parentheses following each observed response. Significant differences based on a paired t-test between observed and expected values are shown by a ‘‘þ’’ sign to indicate synergism. b
3.4. Crop yield Soybean yield decreased with increasing doses of dicamba/ diflufenzopyr (Table 4). Synergistic responses were observed with the simulated drift of dicamba/diflufenzopyr at 10, 20 and 40 g a.i. ha1 followed by the chlorimuron-ethyl application which resulted in a 7–8% greater yield reduction than expected. The application of dicamba/diflufenzopyr at 2, 10, 20 and 40 g a.i. ha1 followed by imazethapyr or bentazon did not result in a synergistic yield response. Similarly, dicamba/diflufenzopyr (2 g a.i. ha1) followed by chlorimuron-ethyl also did not result in a synergistic response in yield. This study confirms that injury in soybean is accentuated when dicamba/diflufenzopyr drift is followed by some registered postemergence herbicides. A synergistic response for crop injury 7, 14,
28 and 56 DAA and soybean yield was documented when soybean was stressed due to herbicide drift followed by the postemergence herbicide. Weed management practitioners and crop consultants must be aware that herbicides with an acceptable margin of crop safety can cause injury if the crop was stressed due to a previous herbicide drift event.
Acknowledgements The authors would like to acknowledge the University of Guelph and Harrow Research Station weeds labs for their expertise and technical assistance in these studies. Funding for this project was provided in part by the Ontario Soybean Growers and the CanadaOntario Research and Development Program.
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