Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2011
Publication Date: 8/17/2011
Citation: Forcella, F., Papiernik, S.K., Gesch, R.W. 2011. Cuphea tolerates clopyralid. Weed Technology. 25:511-513. Interpretive Summary: Cuphea is a new crop that can grow in the northern regions of the United States. It produces a special oil in its seeds that can substitute for coconut and palm kernels oils of which the US imports about one billion pounds each year to manufacture detergents and other products. To promote commercialization of this new crop, a sufficient number of herbicides must be available for growers to ensure adequate weed control. At present only four herbicides are known to be tolerated by cuphea; thus, more herbicides are needed for successful commercialization, especially postemergence herbicides. The herbicides that cuphea tolerates cannot be used to control Canada thistle and biennial wormwood in Minnesota and North Dakota. Clopyralid is the active ingredient in the commercial postemergence herbicide, Stinger (and similar products), and it effectively controls both Canada thistle and biennial wormwood. Stinger was tested at rates ranging from 0 to 32 oz/acre in greenhouse and field trials. Cuphea was not injured by 8 oz/acre, a typical rate used in other crops, or even at 16 oz/acre. Thus, clopyralid (in the form of Stinger herbicide) can be applied at the commonly used rate of 8 oz/acre without fear of injuring cuphea. These results can be used by companies and state departments of agriculture to issue special use permits for clopyralid-based herbicides on cuphea, which will assist growers in raising this specialty oilseed crop and facilitate its further commercialization.
Technical Abstract: Cuphea is a new crop of temperate regions that produces seed oil with medium-chain length fatty acids, which can substitute for imported coconut and palm kernels 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 (USA), where cuphea currently is grown, better control of Cirsium arvense and Artemisia biennis 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 ha-1 in greenhouse and field trials. Cuphea was not injured by 200 g ae ha-1, a common rate used in other crops, in terms of visual injury, height growth or seed yield. Moreover, none of these traits was reduced significantly in field-grown plants even when clopyralid was applied at about 400 g ae ha-1. Thus, clopyralid can be applied safely at 200 g ae ha-1 to cuphea. These results can be used by the agricultural industry and state departments of agriculture to issue special use permits for clopyralid-based herbicides on cuphea, which will assist growers in raising this specialty oilseed crop and facilitate its further commercialization.