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27 March 2019 Evaluating risks of plant growth regulator–resistant soybean technologies to horseradish production
Kayla N. Wiedau, Ronald F. Krausz, S. Alan Walters, Joseph L. Matthews, Karla L. Gage
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Off-target movement of dicamba and 2,4-D may injure and reduce the yield of many fruit and vegetable crops, impacting specialty crop producers and herbicide applicators alike. Two field experiments were established, using plant growth regulator–resistant soybean herbicide technologies, to evaluate drift and carryover risks to horseradish production. The drift experiment was conducted in 2015 and 2016 to evaluate impact of dicamba and 2,4-D simulated drift on horseradish production with a mid-POST application in soybean. Simulated drift rates were 1/10,000X, 1/1,000X, and 1/100X, with 1/2X, 1X, and 2X of standard application rates. Injury and yield loss was greater following application of 2,4-D than with dicamba. Yield reductions were observed beginning at the 1/1,000X rate of 2,4-D, with complete crop loss occurring when rates exceed 1/2X. In comparison, dicamba only reduced yields when applied at the 1X and 2X rates. Only horseradish roots from plants treated with dicamba at the 2X rate had greater dicamba residue than the nontreated control, and the amount detected, 0.32 parts per billion (ppb), was lower than the EPA tolerance of 100 ppb in root crops. There was little to no harvestable tissue for 2,4-D residue analysis for plants treated with 2,4-D at rates above 1/2X. The carryover experiment was a 2-yr rotational evaluation conducted in 2014, 2015, and 2016 to assess dicamba carryover to horseradish following application to dicamba-resistant soybean the previous season. Observations taken at 4, 6, and 8 wk after planting indicated no significant horseradish injury, nor was height, stand, or root weight reduced. These results suggest that horseradish growers should have few concerns about injury from dicamba drift or carryover. While 2,4-D applicators may need to be cautious when making applications near horseradish fields, 2,4-D may be an effective tool for controlling volunteer horseradish in 2,4-D–resistant soybean.

Nomenclature: 2,4-D; dicamba; horseradish, Armoracia rusticana G. Gaertn., B. Mey. & Scherb ARWLA; soybean, Glycine max (L.) Merr.

© Weed Science Society of America, 2019. This is an Open Access article, distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives licence (, which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is unaltered and is properly cited. The written permission of Cambridge University Press must be obtained for commercial re-use or in order to create a derivative work.
Kayla N. Wiedau, Ronald F. Krausz, S. Alan Walters, Joseph L. Matthews, and Karla L. Gage "Evaluating risks of plant growth regulator–resistant soybean technologies to horseradish production," Weed Technology 33(1), 75-86, (27 March 2019).
Received: 26 July 2018; Accepted: 30 November 2018; Published: 27 March 2019

Auxinic herbicides
crop rotation
herbicide drift
herbicide residues
residue levels
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