Evaluation of Alternative Decay Control Products for Control of Postharvest Rhizopus Soft Rot of Sweetpotatoes

Abstract

Postharvest Rhizopus soft rot of sweetpotato, caused by Rhizopus stolonifer, is managed by minimizing injuries incurred during harvesting and packing, curing roots immediately after harvest, and applying fungicide during packing. The United States sweetpotato industry relies heavily on a single fungicide (dicloran) to control Rhizopus soft rot, however, many markets (export, infant food, and organic) no longer allow dicloran residues. Dicloran is currently the only fungicide labeled for control of Rhizopus soft rot. Thirty-three products were tested in nine individual experiments over a 5-year period to identify alternative control products. The reduced-risk fungicides boscalid plus pyraclostrobin (Pristine) and fludioxonil (Scholar) significantly reduced Rhizopus soft rot and performed similarly to dicloran. The biological products Bio-Save 10LP and 11LP suppressed Rhizopus soft rot although results were variable among tests. Generally recognized as safe (GRAS) treatments were ineffective in controlling soft rot by our methods. Accepted for publication 1 December 2008. Published 6 February 2009.