48th TWC, Tob. Work. Conf., 2018, abstr. 21

Dark tobacco response to 2,4-D and Saflufenacil applied at various pre-transplant intervals

University of Kentucky, Princeton KY USA

Marestail (Conyza canadensis L.) has become a major weed problem in dark tobacco production in western Kentucky due to its tolerance to glyphosate herbicide that is typically used in burndown applications prior to transplanting in minimum-tillage production. 2,4-D and saflufenacil herbicides are effective burndown options for marestail control prior to planting other crops such as corn and soybean, but are not viable alternatives prior to tobacco transplanting due to long rotational intervals given on product labels. In discussion with chemical manufacturers of these herbicides, the primary reason for the long rotational intervals is lack of field research data showing tolerances in a crop such as tobacco that occupies relatively minor acreages in the U.S. Field experiments were conducted in 2015 and 2016 to evaluation tobacco response to 2,4-D and saflufenacil applications made at various intervals prior to transplanting dark tobacco in a strip-tillage system. Treatments in the 2,4-D experiment included 2 rates of 2,4-D (1 or 2 pt/A of 2,4-D amine product (Shredder®)) applied at five timings prior transplanting. Timings were 50, 40, 30, 20, and 10 days prior to transplanting. An untreated check was included that received no 2,4-D. No injury was seen from either rate at any timing. There were no significant differences in yield of treatments. In a separate experiment, saflufenacil was applied at 2 oz/A of product (Sharpen®) at the same timings as in the 2,4-D experiment. In the saflufenacil experiment, substantial injury and stand reduction was seen at 10 and 20 days prior to transplanting, but no injury was seen at 30 or more days prior to transplanting. (Reprinted with permission)