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

Abstract

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 3000μgmL−1 in carnauba wax coating at rates of 0.6, 1.2 and 1.8Ltonne−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 1.75μgg−1) with increasing coating load. However, the resistant isolate could not be controlled (>74% infection). Dip only treatment (IMZ sulphate at 500μgmL−1 for 45s and 90s) gave good curative control (≈77%) of the sensitive isolate at residue loading of 0.12–0.73μgg−1. Wax coating only treatment (IMZ at 3000μgmL−1 at 1.8L wax tonne−1) gave good protective control and improved sporulation inhibition (≈80%) at residue loading of 1.32–7.09μgg−1. The MRL of 5μgg−1 was exceeded at higher wax loads on navels and clementines. Double application with dip (45s in IMZ sulphate at 500μgmL−1) followed by 2000μgmL−1 IMZ in wax coating at 0.6, 1.2 and 1.8L wax tonne−1 resulted in residue loading of 1.42 to 2.83μgg−1, increased protective control (≈69%) as well as curative control (≈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.