Abstract
ABSTRACT Fungal propagule persistence on avocado bolts (small logs) under fruit tree canopies in Florida, USA was assessed for three entomopathogenic fungus-based biopesticides containing Cordyceps javanica, Metarhizium brunneum, or Beauveria bassiana. Bolts were sprayed with a biopesticide or water control to the point of runoff. After drying, four bolts, one from each treatment, were hung randomly under each of three fruit tree canopies in a randomized block design. Bark plug samples were removed from the bolts at 1, 7, 14, and 21 days after treatment (DAT) to determine the persistence of each fungus. Mean numbers of colony-forming units (CFUs) observed in vitro per product were compared. From 1 to 21 DAT, the mean number of CFUs per plate decreased from 100 to 7 for B. bassiana and from 25 to 6 for M. brunneum. However, CFUs of C. javanica increased slightly from 4 to 8. The total mean number of CFUs at 21 days from highest to lowest was B. bassiana > M. brunneum > C. javanica. At 21 DAT, CFUs of C. javanica were observed in plates for the B. bassiana and control treatments, suggesting that C. javanica blastospores may have germinated on the bark and then formed aerial conidia that dispersed to other bolts. Each fungus on the avocado bark was photographed by using scanning electron microscopy. This study demonstrated that EPF-based biopesticides persist for at least 2 weeks on avocado bark in tree canopy shade and are potential biological control agents against ambrosia beetles that attack avocado trees.
Published Version
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