Effect of Preharvest Application of Pyrimethanil and Calcium Chloride for the Control of Postharvest Blue Mold and Gray Mold of Apples

Preliminary experiments were conducted to evaluate the efficacy of preharvest application of pyrimethanil (800 g/ha) and calcium chloride (12 kg/ha) on the control of postharvest blue mold caused by Penicillium expansum Link and gray mold caused by Botrytis cinerea Pers.:Fr. in apples. Cultivars tested were, ‘McIntosh’ and ‘Empire’ in Ontario (ON) and ‘Gala’ and ‘Jonagold’ in British Columbia (BC). Apples were inoculated with 1x10⁴ conidia/ml of either thiabendazole (TBZ)-resistant or -sensitive isolates of P. expansum or B. cinerea immediately after harvest and stored at 0^oC or 1^oC for 20 weeks. Observations were recorded at 4-week intervals in ON and after 20 weeks in BC. In 2004-2005, pyrimethanil + calcium chloride, applied 2 weeks prior to harvest significantly decreased the incidence of both diseases compared to the application 4 weeks before harvest in all the 4 cultivars in both locations.

In 2005-2006, the treatment of pyrimethanil + calcium chloride, applied 2 weeks prior to harvest gave significant control of postharvest blue mold for up to 8 and 12 weeks in ‘McIntosh’ and ‘Empire’, respectively. The combination treatment significantly reduced blue mold in ‘Gala’ and ‘Jonagold’ in BC and gray mold in all four cultivars in both locations; however, the diseases increased with time in ‘McIntosh’ and ‘Empire’.