A detached fruit study on the post-inoculation activity of lime sulfur against brown rot of peach (Monilinia fructicola)

Abstract

Fungicides with curative activity are important tools for disease management in stone fruits. Lime sulfur (LS) is the only fungicide registered for organic fruit production with demonstrated curative activity against apple scab, but such activity against Monilinia fructicola is unknown. In this study, the 6, 12, and 24 h post-infection activity of 1.5% lime sulfur (LS) against M. fructicola was investigated on two peach fruit cultivars (early- and mid-season cultivars, Coronet and Contender, respectively) at two maturity stages (commercially mature and immature fruit) in a wound-inoculation detached fruit study. Brown rot incidence, sporulating area, and production of conidia per fruit were higher on commercially mature fruit in all treatments as compared with immature fruit, and LS treatments showed consistent results for both cultivars tested. All three disease measurements were significantly lower (P=0.05) for the 6 and 12 h post-inoculation applications of LS compared with either the untreated or 24 h post-inoculation applications of LS, irrespective of fruit maturity stages or cultivar. Disease incidence was reduced from 98.5–100% in the control treatment to 9–12% in the 6 h post-inoculation application. Both the 6 and 12 h post-inoculation applications reduced sporulating area from 64–72% in the control treatment to 0.0–1.3%. Disease incidence was not significantly (P=0.05) different between the water-treated control and the 24 h post-inoculation treatment with LS, while percent sporulating area and number of conidia per fruit were significantly different (P=0.05). Our results show up to 12 h post-inoculation activity of LS on M. fructicola in controlled environment studies and indicate that LS has potential for post-infection brown rot control in organic stone fruit production. Additional keywords: disease management, organic fruit production, stone fruits.