Evaluation of curative and protective control of Penicillium digitatum following imazalil application in wax coating

Imazalil (IMZ) is widely used in citrus packhouses to manage green mould, caused by Penicillium digitatum. The aim of this study was to investigate green mould control efficacy of IMZ applied in a wax coating, and the combination of aqueous dip and coating IMZ applications. Single application of IMZ at 3000 mu g mL(-1) in carnauba wax coating at rates of 0.6, 1.2 and 1.8 Ltonne(-1) of fruit gave better protective (mean 13% infection) than curative (mean 70% infection) control of the sensitive isolate. Imazalil residue levels increased (0.85 to 1.75 mu g g(-1)) with increasing coating load. However, the resistant isolate could not be controlled (>74% infection). Dip only treatment (IMZ sulphate at 500 mu g mL(-1) for 45s and 90s) gave good curative control (approximate to 77%) of the sensitive isolate at residue loading of 0.12-0.73 p,g g-1. Wax coating only treatment (IMZ at 3000 mu g mL(-1) at 1.8 L wax tonne(-1)) gave good protective control and improved sporulation inhibition (approximate to 80%) at residue loading of 1.32-7.09 mu g g(-1). The MRL of 5 mu g g(-1) was exceeded at higher wax loads on navels and clementines. Double application with dip (45 s in IMZ sulphate at 500 mu g mL(-1)) followed by 2000 mu g mL(-1) IMZ in wax coating at 0.6, 1.2 and 1.8 L wax tonne(-1) resulted in residue loading of 1.42 to 2.83 mu g g(-1), increased protective control (approximate to 69%) as well as curative control (approximate to 83%). In all treatments, poor curative and protective control of the resistant isolate was observed (<46% and <55%, respectively). Double application demonstrated superior green mould control by giving good curative and protective control and sporulation inhibition. (C) 2012 Elsevier B.V. All rights reserved.