Field studies were conducted to determine the influence of herbicides on the development of internal necrosis (IN) in sweetpotato storage roots. In a slip propagation study, herbicide treatments included PRE application (immediately after covering seed roots with soil) of clomazone (0.42, 0.84 kg ai ha-1), flumioxazin (0.11, 0.21 kg ai ha-1), fomesafen (0.28, 0.56 kg ai ha-1), linuron (0.56, 1.12 kg ai ha-1), S-metolachlor (0.8, 1.6 kg ai ha-1), flumioxazin plus S-metolachlor (0.11 0.8 or 1.6 kg ha-1), and napropamide (1.12, 2.24 kg ai ha-1), and POST application (2 to 4 wk prior to cutting slips) of ethephon (0.84, 1.26 kg ai ha-1) and paraquat (0.14, 0.28 kg ai ha-1). In a field production study, flumioxazin, fomesafen, linuron, and paraquat were applied PREPLANT (one d prior to sweetpotato transplanting), clomazone, S-metolachlor, and napropamide were applied PRE [4 d after transplanting (DAP)], flumioxazin PREPLANT followed by (fb) S-metolachlor PRE, and ethephon applied POST (2 wk prior to harvest). Herbicide rates were similar to those used in the slip propagation study. Yield of sweetpotato in both studies was not affected by herbicide treatment. In both studies, IN incidence and severity increased with time and was greatest at 60 d after curing. No difference was observed between herbicide treatments for IN incidence and severity in the slip production study which indicates herbicide application at time of slip propagation does not impact the development of IN. In the field production study, the only treatment that increased IN incidence compared to the nontreated was ethephon with 53% and 2.3 incidence and severity, respectively. The presence of IN affected roots in nontreated plots indicates that some other pre- or post-curing factors other than herbicides are responsible for the development of IN. However, the ethephon application prior to sweetpotato root harvest escalates the development of IN.
Nomenclature: Clomazone; ethephon; flumioxazin; fomesafen; linuron; napropamide; paraquat; S-metolachlor; sweetpotato, Ipomoea batatas (L.) Lam.