Ethephon and Other Chemical Stresses Increase the Incidence of Tip Rot in Mississippi Sweetpotatoes, Poster Board #019

Sweetpotato is a high value crop with an estimated production value of over 478 million dollars in 2010 (USDA, National Agricultural Statistics Service).  Mississippi production of sweetpotato increased from 13,000 acres, in 2000 to 23,000 acres, in 2011.  With this increase in acreage comes a pressure to harvest these acres while maintaining size and quality of the roots.  Harvest is often delayed due to dry conditions that promote skinning (the mechanical removal of skin) or excessive rain events preventing mechanical harvest.  Preharvest application of ethephon has been reported to harden or set the skin and therefore, reduce skinning in sweetpotato.  However, it was reported to increase the incidence of a relatively new disease in sweetpotato roots, named tip rot.  At this time the causal pathogen of tip rot is not known, but it appears that stress and soil moisture influence its incidence.  In an effort to understand the relationship between stress and tip rot in sweetpotato, ethephon and two herbicides (Paraquat and Aim) were applied to the foliage 5 days before harvest at the Pontotoc Experiment Station in Mississippi.  Storage roots were harvested and stored to evaluate the incidence of tip rot after 2 months. In addition, on-farm trials with ethephon were conducted to determine the potential increase in the incidence of tip rot in commercial fields.  Three treatments were a water control, a 0.84 and 1.68 kg·ha^-1 a.i. all treatments included a 0.25% v/v crop oil concentrate.  Treatments were applied using a back pack CO₂ sprayer with a 3 m boom with 8003 flat fan tips calibrated to spray 191 L·ha^-1.  Three strips 47.5m by 3 rows wide were each treated with an assigned treatment 5 days before harvest.  Half of the sampled roots were taken to storage while the rest were taken to a curing room.  Tip rot was found in sweetpotatoes from each area regardless to the treatment.   In the first study, tip rot incidence was 0.6%, 4.6%, 6.7%, and 13% for the untreated, Aim, paraquat, and ethephon, respectively. Similarly, the incidence of tip rot increased across on-farm trials from 2% to 6% with ethephon rate (R²=0.96).  The use of active curing (29 °C and 90% RH for 4–7 days) immediately after harvest reduced the incidence of tip rot in both treated and non-treated roots to near 0.