DPA Has No Effect on Postharvest Control of Blue Mold of Apple with Fludioxonil

Blue mold of apple, caused by Penicillum expansum, can cause severe losses in stored apples under favourable conditions. In recent years some of the isolates of P. expansum have developed resistance to MERTECT (thiabendazole, TBZ). A time course experiment was conducted to test the efficacy of different concentrations of a reduced-risk fungicide, SCHOLAR (fludioxonil) and diphenylamine (DPA, an antiscalding agent) for control of blue mold caused by TBZ-resistant P. expansum. Wounded and P. expansum inoculated ‘Empire’ apples were treated with fludioxonil and DPA, and stored for 4.5 months at 4E C in a common storage.

Apples were evaluated every 30 days after the treatment and disease incidence was recorded. The efficacy of the fludioxonil decreased with time. At higher concentrations (600 μg/ml), fludioxonil gave 100% control of blue mold for 3 months and an increase in the disease incidence was observed after 4 months. This reflects the effectiveness of the fludioxonil as a postharvest treatment. DPA neither negatively nor positively interacted with the postharvest fungicide, fludioxonil. While TBZ was affective against blue mold caused by TBZ-sensitive isolates of P. expansum, TBZ was not effective against blue mold caused by TBZ-resistant isolates. In these experiments SCHOLAR was used experimentally, and is not registered for postharvest treatment on apples in Canada and cannot be used commercially.