Survey of fungicide resistance of Colletotrichum gloeosporioides from different avocado production areas

Registered treatments for the control of avocado anthracnose caused by Colletotrichum goeosporioides are post-harvest applications of prochloraz and thiabendazole. Pre-harvest treatments to reduce inoculum levels in the field are also an important factor for successful anthracnose disease control. Pre-harvest application of benomyl was previously registered for this purpose, although at this stage it is only registered for Cercospora control. However, it is still generally recommended that the copper spray programme be preceded by a benomyl treatment. Isolates of C. gloeosporioides collected during a three-year market survey were used to determine the incidence of resistance to benomyl, thiabendazole and prochloraz using an in vitro assay. A total of 17.7% of all isolates tested were resistant to benomyl, of which 8.5% were highly resistant and 9.2% moderately resistant. No isolates were resistant to thiabendazole or prochloraz.