CORESTA Congress, Berlin, 2016, Agronomy/Phytopathology Groups, AP 34

Evaluation of non-tobacco labeled herbicides for late season application

North Carolina State University, Dept. of Crop Science, Raleigh, NC, U.S.A.

Recently, viable seed from various weed species has been found in tobacco exports from the United States, initiating great concern in foreign markets and a zero tolerance policy. University specialists believe the majority of weed seed contamination is a reuslt of mechanicanized harvest. At present, farmers have a variety of management options, such as cultivation, herbicide application, and hand weeding, to reduce weed pressure and lower seed bank populations for future years. However, the spectrum of herbicide options for tobacco is extremely limited, specifically for post-transplanting application. An evaluation of non-tobacco labeled herbicides for late season application is greatly needed to give farmers alternative strategies in weed management. Research was conducted in 2014 and 2015 in North Carolina to evalute various herbicide programs applied late in each growing season. Treatments were arranged in a randomized complete block design and replicated four times. Eight different herbicides were evaluated, each at two different application timings: before topping and after first harvest. The eight herbicides were as follows: S-metolachlor, sulfentrazone, trifloxysulfuron, fomesafen, glufosinate, mesotrione, linuron, and carfentrazone-ethyl. A ninth herbicide, sethoxydim, was applied after first harvest only and a control plot of sulfentrazone + clomazone (PRE-T only) was included as well. Applications were made with a backpack sprayer containing a twenty inch boom and two Teejet VisiFlo flat spray tip nozzles. Application occurred at a spray volume of 187 L/ha. Spray applications covered the row middles as well as a portion of the tobacco bed. Product rates were based upon Extension recommendations. Following application weed control efficacy, crop injury, leaf yield, quality, value, and chemistry were quantified. In both years, herbicide injury was greatest in before topping applications of glufosinate (2.75-3.75%), mesotrione (3.50-25.00%), and carfentrazone-ethyl (2.00-2.50%); however, leaf yield was not affected. Palmer amaranth suppression ranged from 80-100% following application for all treatments.