Weed Technology 2011 25:511–513

Cuphea Tolerates Clopyralid

F. Forcella, S. K. Papiernik, and R. W. Gesch*

Cuphea is a new crop of temperate regions that produces seed oil that can substitute for imported coconut and palm kernel oils. Only four herbicides are known to be tolerated by cuphea to date. More herbicides, especially POST products, are needed for continued commercialization. In Minnesota and North Dakota, where cuphea currently is grown, greater control of Canada thistle and biennial wormwood is needed in cuphea. Because clopyralid is effective on both of these species, it was tested at rates ranging from about 25 to 850 g ae ha21 in greenhouse and field trials. Visual assessment of injury, height, growth, and seed yield of cuphea were not reduced significantly in field-grown plants when clopyralid was applied at rates up to 400 g ae ha21. Thus, at the rate commonly used in other crops, 200 g ae ha21, clopyralid can be applied safely to cuphea. Nomenclature: Clopyralid; biennial wormwood, Artemisia biennis Willd.; Canada thistle, Cirsium arvense (L.) Scop.; cuphea, Cuphea viscosissima Jacq. 3 C. lanceolata W.T. Aiton. Key words: Dose response, herbicide, injury, oilseed, postemergence, PSR-23, tolerance.

La cufea (Cuphea viscosissima Jacq. 3 C. lanceolata W.T. Aiton), es un nuevo cultivo de regiones templadas que produce semillas oleaginosas que puede sustituir a los aceites importados de coco y de semillas de palma. Que se conozca, a la fecha solamente existen cuatro herbicidas que la cufea tolera. Se necesitan ma´s herbicidas, especialmente productos POST para una continua comercializacio´n del cultivo. En Minnesota y North Dakota (USA), donde actualmente se cultiva la cufea, se necesita un mejor control de las especies Cirsium arvense y Artemisia biennis. Debido a que clopiralid es efectivo en estas dos especies de maleza, el herbicida se evaluo´ en estudios de invernadero y de campo, en dosis que variaron de 25 a 850 g ea ha21. En condiciones de campo, plantas de cufea no fueron significativamente disminuidas ya sea por dan˜o, altura de crecimiento y rendimiento de semilla, cuando clopiralid se aplico´ en dosis de hasta 400 g ea ha21. Por lo tanto, clopiralid en dosis 200 g ea ha21, que es la cantidad comu´nmente utilizada en otros cultivos, puede aplicarse de manera segura a cufea.

Approximately 1 billion kg of oils from coconut (Cocos with weeds in spring. Consequently, early-season weed control nucifera L.) and palm kernel (Elaeis guineensis Jacq.) are is important to reduce weed interference. imported by North America and Europe annually. These oils Cuphea currently is known to tolerate soil-applied contain medium-chain-length fatty acids, such as capric, herbicides such as ethalfluralin, isoxaflutole, and trifluralin, lauric, and myristic acids. They are used to manufacture but only one POST herbicide, mesotrione (Forcella et al. products such as detergents, personal care items, and 2005a). Combinations of these products control many species lubricants. These fatty acids can be synthesized from of weeds common in north-temperate regions. However, petroleum, but renewable sources are preferred. Very few biennial wormwood and Canada thistle have become temperate-growing plants produce these fatty acids and, to problems in commercial cuphea. Although isoxaflutole is date, of these only cuphea is thought to have agronomic effective on biennial wormwood (Kegode et al. 2007), it is not potential (Thompson 1984). labeled for use in Minnesota because of water-quality concerns Cuphea grows better in north-temperate states, such as (Papiernik et al. 2007), and none of the aforementioned Minnesota and North Dakota, than in more southerly states, products controls Canada thistle (Zollinger et al. 2010). such as Illinois and Iowa (Forcella et al. 2005b; Kim et al. Accordingly, additional herbicides are needed to assist grower 2011). However, low spring temperatures in these northern acceptance and continued commercialization of cuphea. areas restrict rapid seedling growth of cuphea (Gesch and POST products would be especially welcomed by growers. Forcella 2007). Rapid growth in cuphea is delayed until mid- Clopyralid is a POST herbicide that controls both biennial to late summer when most of its vegetative and reproductive wormwood and Canada thistle (Kegode et al. 2007; Zollinger development occurs and, therefore, it does not compete well et al. 2010). In north-temperate croplands, it typically is used DOI: 10.1614/WT-D-10-00173.1 to control Canada thistle and other broadleaf weeds in small * Research Agronomist, Research Soil Scientist, and Research Plant Physiol- grains and fallowed fields. Application rates usually do not 21 ogist, North Central Soil Conservation Research Laboratory, U.S. Department of exceed 200 g ae ha (Zollinger et al. 2010). Because Agriculture–Agricultural Research Service, 803 Iowa Avenue, Morris, MN 56267. clopyralid also can be used in broadleaf crops like canola Current address of second author: North Central Agricultural Research Laboratory, U.S. Department of Agriculture–Agricultural Research Service, (Brassica napus L.), sugarbeet (Beta vulgaris L.), and mint 2923 Medary Avenue, Brookings, SD 57006. Corresponding author’s E-mail: (Mentha spp.), we examined the potential for cuphea to [email protected] tolerate this herbicide.

Forcella et al.: Cuphea and clopyralid N 511 Materials and Methods Seeds of ‘PSR-23’ cuphea were sown in 10-cm-diam pots and allowed to develop in a greenhouse in Morris, MN (45u359N, 95u539W). Pots contained Barnes loam soil (Udic Haploboroll, fine loamy mixed; 5% organic matter, pH 6.5). Experiments were conducted from March 10 to April 8, 2005 (experiment 1) and April 5 to May 3, 2005 (experiment 2). Greenhouse conditions included natural radiation (about 2 2 400 mmol m 2 s 1 clear-day maximum), natural photoperi- ods of 12.1 6 0.09 and 13.5 6 0.08 h, but regulated day/ night temperatures of 25/15 C. Pots were watered daily and fertilized weekly with a complete nutrient solution. When seedlings reached the one- to two-leaf stage of growth in Figure 1. Assessment of tolerance (solid squares) and height (open squares) of experiment 1 or the two- to four-leaf stage of growth in greenhouse-reared cuphea seedlings 30 d after exposure to clopyralid applied experiment 2, they were thinned to one plant per pot and POST. Vertical bars represent standard errors of mean values. Smooth lines treated with clopyralid in a cabinet sprayer with a single flat- represent best-fit log-logistic functions of combined data; Y indicates visual 5 2 5 5 5 fan nozzle pressurized at 141 kPa and delivering 187 L ha21. tolerance (where C 1.66, D 10.0, I50 250.1, and b 3.91) or seedling height (where C 5 265465, D 5 209.7, I50 5 390,768, and b 5 2.82). Application rates were equivalent to 0, 26, 53, 105, and 210 g ae ha21 in experiment 1 and 0, 105, 210, 421, and 21 for 1 wk, cleaned of chaff and other debris, and yields per unit 841 g ae ha in experiment 2. From 22 to 25 plants were area calculated on the basis of 10% seed moisture. selected randomly and exposed to each treatment. At 30 d Dose–response data were analyzed with Statistix 9.0 after treatment, plants were evaluated visually for stunted software (Anonymous 2008). The ‘‘user-specified model’’ growth on a scale of 0 to 10 (10 represented full growth of the option for nonlinear regression allowed fitting of log-logistic control plants) in both experiments and height was measured functions (Seefeldt et al. 1995; Streibig et al. 1993) to in experiment 2. Chlorosis, necrosis, and morphological clopyralid–cuphea relationships. Starting values for parame- abnormalities never were apparent. ters were chosen on the basis of visual inspection of graphs Dose–response experiments were performed during 2010 in (Figures 1 and 2) and a 500-iteration limit chosen for final two commercial plantings of ‘PSR-23’ cuphea. The first was in solutions to equations. Parameters were not constrained, Swan Lake Township (45u449N, 95u499W), Stevens County, which minimized variances but created negative (and MN. Soil at this site was a Barnes loam (as above). The previous unrealistic) minimum asymptotes at high clopyralid doses. crop was soybean. The field was plowed, fertilized with N–P–K However, because the log-logistic equations were used at 78–22–22 kg ha21, and harrowed before sowing cuphea 21 primarily to calculate likely responses of cuphea to the seeds 1 to 2 cm deep at 9 kg ha in rows spaced 40 cm apart commonly used clopyralid rate of 200 g ae ha21, negative on May 18. The second site was in McCauleyville Township minima at high doses did not influence interpretation of (46u269N, 96u419W), Wilkin County, MN, on a Doran clay results. ANOVA was used to help explain differences among loam (Aquic Argiboroll, fine mixed; 6% organic matter, some treatments. For visual assessment of tolerance, transfor- pH 7.5). The previous crop was soybean. The field was mation of data (arc-sine, square-root) did not alter results. fertilized with N–P–K at 50–15–20 kg ha21 before seeds were sown as above on June 3. Ethalfluralin (Swan Lake) and trifluralin (McCauleyville) were applied PPI at 1 kg ai ha21 onto the finely prepared seedbeds. Weeds that escaped control and overtopped the crop were removed by hand. Experimental plots were 3.1 by 6.2 m long. Herbicide treatments were arranged in randomized complete block designs with three replications. Clopyralid was applied at 0, 105, 210, 421, and 841 g ae ha21 at both sites. Applications were made with a CO2-powered backpack sprayer that delivered 187 L ha21 at 207 kPa on July 9 at Swan Lake and July 28 at McCauleyville when plants were about 25 cm tall and branching profusely. Mid- to late July represents the time when biennial wormwood would be starting to bolt (Kegode et al. 2007) and Canada thistle would be in full anthesis (Donald 1994). Crop tolerances were estimated visually as indicated above and plant heights were measured on July 20 at Swan Lake and August 12 at McCauleyville. Figure 2. Relative seed yield (RSY) of cuphea in relation to rate of clopyralid applied POST at Swan Lake (solid squares) and McCauleyville (open squares), Seeds were harvested in a 1.6- by 6.2-m section in the center MN. Vertical bars represent standard errors of mean values. The curved line and of each plot with a plot combine on October 6 at Swan Lake equation represent a best-fit log-logistic function of the combined data, where and October 13 at McCauleyville. Samples were dried at 40 C C 5 20.562, D 5 0.942, I50 5 740.6, b 5 4.4575.

512 N Weed Technology 25, July–September 2011 Results and Discussion vulgaris L.) and strawberry (Fragaria 3 ananassa Duch.) (Figueroa and Doohan 2006). Nevertheless, lower rates had Nonlinear relationships between assessment of tolerance no apparent effects on cuphea seed yield. and clopyralid rate in greenhouse studies did not differ In summary, cuphea appears to tolerate clopyralid at rates between experiments (P . 0.10 for all parameters) and, of at least 400 g ae ha21, which is twice the amount therefore, data were combined. Both tolerance assessments commonly used in other crops. Accordingly, this herbicide and seedling heights 30 d after treatment decreased as can be used safely on cuphea at 200 g ae ha21, which would clopyralid rate increased, but only slightly (Figure 1). A log- facilitate the growing of this new oilseed crop in fields subject logistic function fit both data sets well and had the following to Canada thistle and biennial wormwood infestations. general form (Seefeldt et al. 1995): Tolerance assessment or height Acknowledgments ~ z { z { C ðÞD C=½1 expfgbðÞlog½ Rate log½I50 ½1 The following individuals expertly assisted with the For assessment of tolerance (0 to 10), coefficients and statistics experiments: Gary Amundson (cabinet sprayer), James Eklund and Dean Peterson (field studies), Myron Tschakert are C 5 21.66, D 5 10.0, I50 5 250.1, b 5 3.91, pseudo r2 5 0.99, SD 5 0.22, and Rate is in units of g ae ha21. For and Eric Odens (McCauleyville management), and Chuck Hennen and Scott Larson (Swan Lake management). The seedling height (mm), C 5 265465, D 5 209.7, I50 5 390,768, b 5 2.82, pseudo r2 5 0.99, SD 5 5.03. These commercial crops were grown for Aveda Corporation and formulae allowed estimates of tolerance and height of cuphea Technology Crops International. seedlings if the commonly used field rate of clopyralid 21 (200 g ae ha ) was applied. Under such conditions, Literature Cited assessment of tolerance was reduced 6% and seedling height 3% from their corresponding maxima. Anonymous. 2008. Statistix 9.0. Users Manual. Analytical Software, Inc., Tallahassee, FL. http://www.statistix.com. Accessed: March 31, 2011. No injury symptoms were apparent in the field experiments Donald, W. W. 1994. The biology of Canada thistle (Cirsium arvense L.). Rev. at either site, and there were no trends of decreased tolerance Weed Sci. 6:77–101. with increased rate of clopyralid. Additionally, no height Figueroa, R. A. and D. J. Doohan. 2006. Selectivity and efficacy of clopyralid on differences among treatments could be attributed to any strawberry (Fragaria 3 ananassa). Weed Technol. 20:101–103. herbicide rate (ANOVA, P 5 0.41 for Swan Lake and P 5 Forcella, F., G. B. Amundson, R. W. Gesch, S. K. Papiernik, V. M. Davis, and W. B. Phippen. 2005. Herbicides tolerated by cuphea (Cuphea viscosissima 3 0.12 for McCauleyville), and heights and rates were not lanceolata). Weed Technol. 19:861–865. correlated at either site (P 5 0.21 for Swan Lake and P 5 Forcella, F., R. W. Gesch, and T. A. Isbell. 2005. Seed yield, oil, and fatty acids 0.79 for McCauleyville). Average plant heights (6 SE) over all of cuphea in the northwestern Corn Belt. Crop Sci. 45:2195–2202. treatments were 71 6 1.4 cm at Swan Lake and 71 6 3.1 cm Gesch, R. W. and F. Forcella. 2007. Differential sensitivity to temperature of at McCauleyville. cuphea vegetative and reproductive growth. Ind. Crops Prod. 25:305–309. Gesch, R. W., F. Forcella, N. Barbour, B. Phillips, and W. B. Voorheees. 2002. Seed yields differed between the two sites. Maximum yield 21 Yield and growth response of cuphea to sowing date. Crop Sci. 42:1959–1965. at Swan Lake (424 6 49.6 kg ha ) was twice that at Kegode, G., R. Zollinger, and M. Ciernia. 2007. Biology and management of McCauleyville (221 6 15.9 kg ha21), probably because of the biennial wormwood. The Glyphosate, Weeds, and Crops Series. W-1322. late planting date at the latter site (Gesch et al. 2002). Despite NDSU Extension Service, Fargo, ND. 11 p. http://www.ag.ndsu.edu/pubs/ plantsci/weeds/w1322.pdf. Accessed: December 8, 2010. yield differences between sites, trends in seed yields in relation Kim, K.-I., R. W. Gesch, S. C. Cermak, W. B. Phippen, M. T. Berti, B. L. to clopyralid rate were similar, and for this reason the data Johnson, and L. Marek. 2011. Cuphea growth, yield, and oil characteristics as were normalized relative to maximum values at each site and influenced by climate and soil environments across the upper Midwest USA. combined (Figure 2). A log-logistic function fit these data Ind. Crops Prod. 33:99–107. Papiernik, S. K., S. R. Yates, W. C. Koskinen, and B. Barber. 2007. Processes well (C 5 20.562, D 5 0.942, I50 5 740.6, b 5 4.4575, 2 affecting the dissipation of the herbicide isoxaflutole and its diketonitrile pseudo r 5 0.99, SD 5 0.14) and was used to estimate seed metabolite in agricultural soils under field conditions. J. Agric. Food Chem. yield reduction at a commonly used rate of clopyralid. The 55:8630–8639. equation suggests that if clopyralid were to be applied at Seefeldt, S. S., J. E. Jensen, and E. P. Fuerst. 1995. Log-logistic analysis of 200 g ae ha21, then cuphea seed yield would decrease 4% herbicide dose–response relationships. Weed Technol. 9:218–227. Streibig, J. C., M. Rudemo, and J. E. Jensen. 1993. Dose–response curves and from its maximum (Figure 2). When the same data were statistical models. Pages 29–56. in J. C. Streibig and P. Kudsk, eds. Herbicide analyzed by ANOVA, only the highest clopyralid rate 21 Bioassays. Boca Raton, FL: CRC. (841 g ae ha ) reduced seed yield (by 37%,P5 0.05). Thompson, A. E. 1984. Cuphea—a potential new crop. HortSci. 19:352–354. Interestingly, neither assessment of tolerances nor plant Zollinger, R., M. Christoffers, and G. Endres, et al. (2010). North Dakota Weed heights was affected by the highest clopyralid rate 2 wk after Control Guide. W-253. NDSU Extension Service, Fargo, ND. http://www. ag.ndsu.edu/weeds/weed-control-guides/nd-weed-control-guide-1. Accessed: treatment, suggesting that very high rates of this auxin-type December 8, 2010. herbicide interfered with reproductive processes in cuphea, as it apparently also does in both common groundsel (Senecio Received December 28, 2010, and approved March 15, 2011.

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