In vitro fungicide testing for control of Avocado fruit rots

Abstract

Avocado fruit rots are most commonly caused by five fungi, Colletotrichum acutatum, C. gloeosporioides, Botryosphaeria parva, B. dothidea and Phomopsis sp. These rots are controlled by applying copper fungicides in the field on eight occasions during the season. Alternatives to standard copper fungicides were screened in the laboratory against these five pathogens for inhibition of spore germination and mycelial growth. In total seven fungicides were tested (boscalid, boscalid/pyraclostrobin, three formulations of copper hydroxide, copper hydroxosulphate and dithianon). The effective concentration at which 50% of spore germination or mycelial growth was inhibited (EC50) was calculated for each fungicide. The EC50 values for spore germination were lowest for boscalid/pyraclostrobin and dithianon, and were ≤ 18.5 μg/ml against all five test fungi. For boscalid/pyraclostrobin all EC 50 values were ≤7 μg/ml. Copper formulations effectively inhibited spore germination by 50% at concentrations ranging from 0.1 μg/ml to 141 μg/ml, but were less effective against mycelial growth.