The potential of a new fungicide fludioxonil for stem-end rot and green mold control on Florida citrus fruit

Fludioxonil is a newly registered and classified as reduced-risk fungicide by the US EPA for citrus fruit postharvest treatments. The efficacy of fludioxonil for the control of diplodia stem-end rot caused by Lasiodiplodia theobromae and green mold (Penicillium digitatum) on Florida citrus fruit was evaluated. The ED50 values of fludioxonil against L. theobromae and P. digitatum in potato dextrose agar were 0.012 and 0.020 mg/L, respectively. Application of fludioxonil at 250–1200 mg/L on oranges using a simulated commercial drench system before fruit ethylene degreening reduced diploda stem-end rot incidence by 75.7–88.6%, and fludioxonil at 500–1200 mg/L performed similarly to the commercial postharvest fungicide imazalil or thiabendazole (TBZ) at 1000 mg/L. Fludioxonil was compatible with chlorine in drench suspension as measured by the efficacy of fludioxonil for diplodia stem-end rot control. Fludioxonil also effectively reduced both diplodia stem-end rot and green mold when applied through a simulated commercial packingline system. Fludioxonil was more effective for diplodia stem-end rot control on non-ethylene-treated oranges than on ethylene-treated fruit. Fludioxonil was also effective for the control of TBZ-resistant P. digitatum isolates on oranges. An active suppression of P. digitatum sporulation by fludioxonil on citrus fruit was observed. However, fludioxonil showed a much less activity for P. digitatum sporulation control compared to postharvest fungicide imazalil. The registration of fludioxonil has provided a new alternative, reduced-risk compound for citrus postharvest disease control and fungicide resistance management in Florida.