scoparia L. Schrad.) to alternative herbicides

Transcription

1 SHORT COMMUNICATION Response of glyphosate-resistant kochia (Kochia scoparia L. Schrad.) to alternative herbicides Nikki Burton 1, Scott W. Shirriff 2, and Hugh J. Beckie 2 1 Department of Plant Sciences, College of Agriculture and Bioresources, University of Saskatchewan, 51 Campus Drive, Saskatoon, Saskatchewan, Canada S7N 5A8; and 2 Agriculture and Agri-Food Canada, Saskatoon Research Centre, 107 Science Place, Saskatoon, Saskatchewan, Canada S7N 0X2 ( hugh.beckie@agr.gc.ca). Received 9 May 2014, accepted 24 June Published on the web 26 June Burton, N., Shirriff, S. W. and Beckie, H. J Response of glyphosate-resistant kochia (Kochia scoparia L. Schrad.) to alternative herbicides. Can. J. Plant Sci. 94: A greenhouse study was conducted to examine the response of glyphosate-resistant (GR) plus acetolactate synthase (ALS) inhibitor-resistant kochia to five post-emergence herbicide treatments commonly used to control the weed species in chemical fallow, cereals, or oilseed crops in western Canada. The treatments, which were applied to two GR kochia biotypes and one non-gr (susceptible) biotype, included the labeled rate of dicamba, dicamba/fluroxypyr, dicamba/diflufenzopyr, MCPA/bromoxynil, and glufosinate. Both GR and non-gr biotypes responded similarly to each of the herbicide treatments. Although both GR biotypes were sensitive to the herbicides, MCPA/bromoxynil was the most effective treatment in reducing shoot biomass 3 wk after application (99%), followed by glufosinate (91%) then the dicamba mixtures (82%). Dicamba alone only suppressed kochia biomass (76% reduction). Key words: Glyphosate resistance, herbicide resistance, Kochia scoparia L. Schrad., weed control Burton, N., Shirriff, S. W. et Beckie, H. J Réaction de la kochie (Kochia scoparia L. Schrad.) re sistante au glyphosate à d autres herbicides. Can. J. Plant Sci. 94: Les auteurs ont procéde a` une e tude en serre pour voir comment la kochie résistante au glyphosate (RG) et à l inhibiteur de l ace tolactate synthase (ALS) réagirait à cinq herbicides post-leve e couramment employe s pour combattre les adventices dans les jache` res chimiques et les cultures de ce re ales ou d oléagineux, dans l Ouest canadien. Au nombre des traitements appliqués à deux biotypes de kochie RG et à un biotype non-rg (sensible) figuraient le dicamba, le dicamba/fluroxypyr, le dicamba/diflufenzopyr, le MCPA/bromoxynil et le glufosinate (taux recommande sur l e tiquette). Les deux ge notypes RG et le génotype non-rg ont re agi de la meˆme façon a` chaque herbicide. Bien que les deux biotypes RG soient sensibles aux herbicides, le MCPA/bromoxynil est celui qui a le plus re duit la biomasse des pousses trois semaines apre` s l application (99 %). Venaient ensuite le glufosinate (91 %) et les me langes à base de dicamba (82 %). Employe seul, le dicamba ne réduit que la biomasse de kochie (baisse de 76 %). Mots clés: Re sistance au glyphosate, résistance aux herbicides, Kochia scoparia L. Schrad., lutte contre les mauvaises herbes In western Canada, glyphosate is a key herbicide for weed control in chemical fallow, preseeding in direct-seeding systems, pre- and post-harvest control, and in glyphosateresistant (GR) canola (Brassica napus L.), corn (Zea mays L.), soybean (Glycine max L. Merr.), and sugar beet (Beta vulgaris L.). Glyphosate was first introduced in 1974, and is the most widely used herbicide in the world. In western Canada, glyphosate usage surpasses that of the next top 12 herbicides combined (Agdata, courtesy N. Harker, personal communication). Frequent glyphosate use has selected for GR weeds currently 28 weed species in several countries, including eastern Canada (Vink et al. 2012; Heap 2014). Until 2011, GR weeds had not been identified in western Canada. Kochia is the 10th most abundant weed across the prairies (Leeson et al. 2005). It is a competitive tumbleweed with early emergence (Schwinghamer and Van Acker 2008), abundant seed production, and stress tolerance (Friesen et al. 2009). Kochia occurs in agricultural areas, waste lands, and rangelands. Kochia resistant to acetolactate synthase (ALS) inhibitors was first reported in the Canadian prairies in Beckie et al. (2011, 2013b) found that 20 yr later, about 90% of prairie populations tested were ALS inhibitor-resistant. Resistant genes may be transmitted through pollen movement (Stallings et al. 1995); however, long-distance transport of resistant genes occurs via seed dispersal from mature plants tumbling across the landscape. Glyphosate-resistant kochia was first identified in Kansas in 2007 (Waite 2008; Waite et al. 2013), and is now present in seven states (Heap 2014). In 2011, kochia with multiple resistance to glyphosate and ALS inhibitors was discovered in southern Alberta (Beckie et al. 2013a). Initially, three populations were identified in Abbreviations: ALS, acetolactate synthase; ANOVA, analysis of variance; EPSPS, 5-enolypyruvyl-shikimate-3-phosphate synthase; GR, glyphosate resistant Can. J. Plant Sci. (2014) 94: doi: /cjps

2 1408 CANADIAN JOURNAL OF PLANT SCIENCE chemical-fallow fields, with an additional seven populations confirmed later in the year from a survey conducted within a 20-km radius of the initial sites. Glyphosate resistance level was considered low to moderate, with a resistance factor (ratio of the rates required for 50% control of the resistant and susceptible populations) of 4 to 7. In 2012, kochia resistant to glyphosate was identified at 13 of 309 sites surveyed (4% of fields) in southern Alberta (Hall et al. 2014). Seven sites were located in Warner county, where GR kochia was previously confirmed in 2011 (Beckie et al. 2013a). Besides those 13 sites, 9 sites were also confirmed in Alberta that year from samples submitted by growers (Hall et al. 2014). Moreover, 10 kochia samples submitted by growers in westcentral and southwestern Saskatchewan in 2012 were confirmed as GR (Hall et al. 2014). Most populations originated in chemical-fallow fields where glyphosate was typically applied alone and at multiple times during the season to control vegetation. However, in the 2012 Alberta survey, two of the locations where GR kochia was found were non-agricultural areas (ditch and railway rights-of-way) adjacent to agricultural areas. In fall, 2013, a survey of 283 sites across southern Manitoba confirmed two GR kochia populations in the Red River Valley (Beckie, unpublished data). In contrast to GR kochia in Alberta and Saskatchewan that originated mainly in chemical-fallow fields, these two populations were found in fields cropped to GR corn and soybean. The economic and agronomic impacts of this GR weed biotype are compounded because of consistent multiple resistance to ALS-inhibiting herbicides. Resistance to both modes of action is endowed by target-site alteration: 5-enolypyruvyl-shikimate-3-phosphate synthase (EPSPS) gene amplification (P. Westra, personal communication) and ALS mutation. Dicamba (auxinic herbicide, group 4) is commonly used to control resistant or susceptible kochia pre- or post-emergence in most cereal crops such as spring wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). However, dicamba only suppresses kochia in chemical fallow (Beckie et al. 2013a). Dicamba-resistant kochia has not been identified previously on the prairies, but has been reported in the midwestern USA (Cranston et al. 2001; Preston et al. 2009; Heap 2014). A recently registered herbicide in chemical fallow is dicamba/diflufenzopyr mixture (group 4/19) (Saskatchewan Ministry of Agriculture 2014). Diflufenzopyr is an inhibitor of indoleacetic acid transport. In field trials in Alberta and Saskatchewan, this mixture was generally more efficacious on ALS inhibitor-resistant kochia than dicamba alone (R. Low, personal communication). Another dicamba mixture, dicamba/fluroxypyr, is commonly used in wheat and barley. These two active ingredients are the top two herbicides used to control kochia in cereals. MCPA/bromoxynil mixture (group 4/ photosystem-ii inhibitor, group 6) is a common herbicide treatment in cereals and flax (Linum usitatissimum L.) to control kochia and other broadleaf weeds. Another increasingly important herbicide to control GR kochia and other GR weed species worldwide is glufosinate (group 10) used in glufosinate-resistant crops, such as canola. Because resistance to glyphosate and ALS-inhibiting herbicides is target-site based, we do not expect this biotype to be resistant to herbicides of other modes of action. To confirm this null hypothesis, a greenhouse study was conducted to examine the response of GR plus ALS inhibitor-resistant kochia to five post-emergence herbicide treatments commonly used to control the weed species in chemical fallow, cereals, or oilseed crops in western Canada. These herbicide treatments were chosen among those recommended or commonly used to manage GR plus ALS inhibitor-resistant kochia (Beckie et al. 2014). MATERIALS AND METHODS Kochia Biotypes Three previously characterized kochia biotypes, two GR and one non-gr (susceptible), were used in the greenhouse experiment. The two GR kochia biotypes, 139W and SK-F3, were collected in 2012 from Vulcan county, Alberta and near Eston, Saskatchewan, respectively. When screened with glyphosate in early 2013 [as described in Hall et al. (2014)], the frequency of GR individuals of both biotypes exceeded 90%. The confirmed susceptible biotype, HS, was also collected in 2012 and originated near Lethbridge, Alberta. Germination of the three kochia seed lots was high (]98%). Experimental Procedures The greenhouse experiment was conducted at Saskatoon, Saskatchewan in the fall of 2013 and repeated. The factorial (biotype, herbicide treatment) experiment was arranged in a completely randomized design with four replicates (pots) per treatment. Five seeds were planted 1 cm deep in 10-cm square pots containing a potting mixture composed of soil, peat, vermiculite, and sand (3:2:2:2 by volume). The pots were watered daily and kept in the greenhouse under 230 mmol m 2 s 1 lighting with a 16-h photoperiod and a 20/168C day/night temperature regime. The herbicide treatments were applied in a spray volume of 200 L ha 1 at 275 kpa using a moving-nozzle cabinet sprayer with a TeeJet 8002VS flat-fan nozzle tip when the seedlings were 7 to 8 cm tall. The treatments included the following (Table 1): (1) dicamba (140 g a.i. ha 1 ), (2) dicamba/fluroxypyr mixture (122 g a.i. ha 1 ), (3) dicamba/diflufenzopyr mixture (100 g a.i. ha 1 ), (4) MCPA/bromoxynil mixture (550 g a.i. ha 1 ), and (5) glufosinate (400 g a.i. ha 1 ). Herbicides were applied at rates labeled for crops or chemical fallow indicated above (Saskatchewan Ministry of Agriculture 2014). Nontreated controls of each biotype were also included. At 21 d after treatment, plants were visually assessed as susceptible: dead (0) or nearly dead (1), or resistant: some injury but new growth (2) or no injury (3) (Beckie et al.

3 BURTON ET AL. * GLYPHOSATE-RESISTANT KOCHIA 1409 Table 1. Herbicide treatments used in the greenhouse experiment Active ingredients(s) Product Formulation z Rate (g a.i. ha 1 ) Manufacturer Dicamba Banvel II 480 g L 1 S 140 BASF Canada Dicamba/fluroxypyr Pulsar 87/113 g L 1 EC 122 Syngenta Canada Dicamba/diflufenzopyr Distinct 50/20% WDG 100 BASF Canada MCPA/bromoxynil Buctril M 280/280 g L 1 EC 550 Bayer CropScience Glufosinate Liberty 150SN 150 g L 1 S 400 Bayer CropScience z EC, emulsifiable concentrate; S, solution; WDG, water dispersable granule. Distinct applied with Merge adjuvant at 0.5 L ha b). The above-ground shoot biomass was harvested, oven-dried for 3 d at 608C, then dry weight was determined. Statistical Analyses Data (shoot biomass) were converted to a percentage of the nontreated control for each biotype and herbicide treatment. Results were combined across experiment runs upon confirmation of homogeneity of variances (Steel and Torrie 1980). Data were arcsine-transformed prior to analysis of variance (ANOVA). Data were subjected to ANOVA using the Proc Mixed procedure in SAS software (SAS Institute, Inc. 1999). Replicate was considered a random effect; kochia biotype and herbicide treatment were considered fixed effects. Treatment means were compared using the least significant difference (LSD) test (P B0.05) using appropriate error terms. Results were back-transformed for presentation. RESULTS AND DISCUSSION The ANOVA indicated no significant difference (P] 0.05) among the three biotypes (GR: 139W and SK-F3; glyphosate-susceptible: HS) in shoot biomass response to the five herbicide treatments (Table 2 and Fig. 1). Averaged over herbicide treatment, the shoot biomass of the three kochia biotypes was 14% of the nontreated controls. In addition, there was no significant interaction between kochia biotype and herbicide treatment (Table 2). Therefore, the three biotypes responded similarly to the five herbicide treatments. This similar response among resistant and susceptible biotypes to herbicides with alternative modes of action confirmed our null hypothesis. For the main factor of herbicide treatment, ANOVA indicated a highly significant difference at P B0.01 among herbicide treatments (Table 2 and Fig. 2). When averaged over the three kochia biotypes, dicamba applied Table 2. Analysis of variance: shoot biomass response of three kochia biotypes to five herbicide treatments Factor PF Significance (PB0.05) Biotype NS Herbicide B ** Biotypeherbicide NS **Highly significant (PB0.01); NS, not significant. alone reduced shoot biomass by 76% (i.e., 24% of nontreated controls). These plants were uniformly rated 1, i.e., nearly dead, not 0, i.e., dead (data not shown). Because weed control is defined by the Pest Management Regulatory Agency (PMRA) as ]80% efficacy (PMRA 2003), this herbicide treatment only suppressed the biomass of the three kochia biotypes. However, the plants were clearly not resistant to the herbicide. Dicamba is rated by weed extension personnel as controlling the weed at preseeding and in-crop, but not in chemical fallow (suppression only) because of lack of crop competition (Beckie et al. 2013a). In a field trial at Lethbridge in 2012, dicamba suppressed growth of GR plus ALS inhibitor-resistant kochia by 75% when applied at the recommended rate (140 g a.i. ha 1 ); however, when the rate was increased to 210 and 280 g a.i. ha 1, control increased to 90 and 98%, respectively (R. Blackshaw, personal communication). The other four herbicide treatments reduced kochia shoot biomass greater than that of dicamba (Fig. 2). When either fluroxypyr or diflufenzopyr was added to dicamba, biomass reduction was significantly (P B0.05) greater compared with that of dicamba alone. Kochia biomass was 18% of nontreated controls for both herbicide treatments, i.e., 82% control. Plants were visually scored as either 1 or 0. Fluroxypyr, an auxinic herbicide, has good activity on kochia (Saskatchewan Ministry of Agriculture 2014). A previous field study found dicamba/diflufenzopyr to be more effective on ALSinhibitor resistant kochia than dicamba alone (R. Low, personal communication), and dicamba/diflufenzopyr is registered for kochia control in chemical fallow. Therefore, in situations of advanced growth stage or less than optimum environmental conditions near time of spraying, either of these dicamba mixtures would be expected to be more effective on kochia than dicamba alone. Of the five herbicide treatments, those containing a contact herbicide (glufosinate or bromoxynil) were more effective at reducing kochia biomass than systemic herbicides (Fig. 2). Movement of glufosinate and bromoxynil in the xylem or phloem is limited. Plants treated with glufosinate or MCPA/bromoxynil were uniformly rated 0, i.e., dead. Glufosinate provided greater biomass reduction than the two dicamba mixtures. Kochia biomass in response to glufosinate was 9% of nontreated control, i.e., 91% control. However, the best herbicide treatment was MCPA/bromoxynil. Kochia shoot biomass at 3 wk

4 1410 CANADIAN JOURNAL OF PLANT SCIENCE Fig. 1. Response of shoot biomass (% of nontreated control) of two glyphosate-resistant (139W, SK-F3) and one glyphosate-susceptible (HS) kochia biotype to five herbicide treatments under greenhouse conditions. There was no significant difference (PB0.05) among biotypes in response to each of the five herbicide treatments (bars denote standard errors). after this treatment was reduced by 99% relative to nontreated controls. Bromoxynil has activity on kochia, although MCPA has limited activity (E. Johnson, personal communication). Fig. 2. Response of shoot biomass (% of nontreated control) of two glyphosate-resistant and one glyphosate-susceptible kochia biotype (combined because of no significant interaction) to five herbicide treatments under greenhouse conditions. Similar letters above columns indicate no significant difference at PB0.05. This controlled-environment study showed that MCPA/bromoxynil, glufosinate, dicamba/fluroxypyr, and dicamba/diflufenzopyr are all effective herbicides for controlling GR plus ALS inhibitor-resistant kochia, but dicamba alone at the labeled rate (140 g a.i. ha 1 ) only provides suppression of the weed (i.e., B80% control; PMRA 2003). Field efficacy trials are required to determine the influence of spray parameters and variable environmental conditions on level of control of this weed biotype. For example, glufosinate efficacy is highly dependent upon environmental conditions near time of application. In addition, contact herbicides require good coverage of the target weed to be effective, particularly a hard-to-wet weed like kochia (hairy surface). The application parameters of the laboratory cabinet sprayer (200 Lha 1 carrier volume, fine spray quality) are conducive to retention and uptake of the two contact herbicides. The spray parameters of commercial field sprayers (e.g., lower water volumes) may result in reduced efficacy of bromoxynil or glufosinate on kochia relative to that observed in this controlled-environment experiment. Regardless of differing efficacy among the five herbicide treatments, GR kochia is equally sensitive as non- GR kochia. Because of the strong association of GR

5 BURTON ET AL. * GLYPHOSATE-RESISTANT KOCHIA 1411 kochia with chemical fallow in western Canada, tankmixing and rotating herbicide modes of action are important practices in this phase of the crop rotation to lessen the risk of selection of more complex multipleresistant biotypes. The utility of an alternative modeof-action herbicide for kochia control in chemical fallow can be quickly lost, similarly to that of glyphosate or ALS inhibitors, if it is repeatedly used as the sole weed control tool. ACKNOWLEDGEMENTS This research project was an undergraduate thesis submitted in partial fulfillment for the course requirements of PLSC in the Department of Plant Sciences, University of Saskatchewan. Beckie, H. J., Blackshaw, R. E., Low, R., Hall, L. M., Sauder, C. A., Martin, S., Brandt, R. N. and Shirriff, S. W. 2013a. Glyphosate- and acetolactate synthase inhibitor-resistant kochia (Kochia scoparia) in western Canada. Weed Sci. 61: Beckie, H. J., Lozinski, C., Shirriff, S. and Brenzil, C. A. 2013b. Herbicide-resistant weeds in the Canadian Prairies: 2007 to Weed Technol. 27: Beckie, H. J., Sikkema, P. H., Soltani, N., Blackshaw, R. E. and Johnson, E. N Environmental impact of glyphosateresistant weeds in Canada. Weed Sci. 62: Beckie, H. J., Warwick, S. I., Sauder, C. A., Lozinski, C. and Shirriff, S Occurrence and molecular characterization of acetolactate synthase (ALS) inhibitorresistant kochia (Kochia scoparia) in western Canada. Weed Technol. 25: Cranston, H. J., Kern, A. J., Hackett, J. L., Miller, E. K., Maxwell, B. D. and Dyer, W. E Dicamba resistance in kochia. Weed Sci. 49: Friesen, L. F., Beckie, H. J., Warwick, S. I. and Van Acker, R. C The biology of Canadian weeds Kochia scoparia (L.) Schrad. Can. J. Plant. Sci. 89: Hall, L. M., Beckie, H. J., Low, R., Shirriff, S. W., Blackshaw, R. E., Kimmel, N. and Neeser, C Survey of glyphosateresistant kochia (Kochia scoparia L. Schrad.) in Alberta. Can. J. Plant Sci. 94: Heap, I. M International survey of herbicide resistant weeds. [Online] Available: [2014 May 01]. Leeson, J. Y., Thomas, A. G., Hall, L. M., Brenzil, C. A., Andrews, T., Brown, K. R. and Van Acker, R. C Prairie weed surveys of cereal, oilseed and pulse crops from the 1970s to the 2000s. Weed Survey Series Publ Agriculture and Agri-Food Canada, Saskatoon, SK. 395 pp. Pest Management Regulatory Agency Regulatory directive: Efficacy guidelines for plant protection products. [Online] Available: dir /index-eng.php [2014 Jun. 25]. Preston, C., Belles, D. S., Westra, P. H., Nissen, S. J. and Ward, S. M Inheritance of resistance to the auxinic herbicide dicamba in kochia (Kochia scoparia). Weed Sci. 57: SAS Institute, Inc SAS online Doc. Version 8. SAS Institute, Inc., Cary, NC. [Online] Available: com/sashtml [2014 Jan. 15]. Saskatchewan Ministry of Agriculture Guide to crop protection: weeds, plant diseases, insects. Saskatchewan Ministry of Agriculture, Regina, SK. 546 pp. Schwinghamer, T. D. and Van Acker, R. C Emergence timing and persistence of kochia (Kochia scoparia). Weed Sci. 56: Stallings, G. P., Thill, D. C., Mallory-Smith, C. A. and Shafii, B Pollen-mediated gene flow of sulfonylurea-resistant kochia (Kochia scoparia). Weed Sci. 43: Steel, G. D. and Torrie, J. H Principles and procedures of statistics: a biometrical approach. 2nd ed. McGraw-Hill, New York. NY. pp Vink, J. P., Soltani, N., Robinson, D. E., Tardif, F. J., Lawton, M. B. and Sikkema, P. H Glyphosate-resistant giant ragweed (Ambrosia trifida) control in dicamba-tolerant soybean. Weed Technol. 26: Waite, J. C Glyphosate resistance in kochia. MS dissertation. Kansas State University, Manhattan, KS. 31 pp. Waite, J., Thompson, C. R., Peterson, D. E., Currie, R. S., Olson, B. L., Stahlman, P. W. and Al-Khatib, K Differential kochia (Kochia scoparia) populations response to glyphosate. Weed Sci. 61: