Abstract
Beauveria bassiana (Bb) strain GHA is a major component of an integrated pest management (IPM) program for coffee berry borer (CBB) in Hawai‘i. Efforts to measure effectiveness of GHA spray applications have been complicated by activity of naturally-occurring Bb. Studies were thus designed to provide more accurate efficacy assessments by accounting for this natural activity. BotaniGard® ES + Widespread Max® (WSM) surfactant (2.3 + 0.6 L/ha) were applied in commercial coffee fields. Live CBB were collected at various times post spray and monitored for infection. GHA killed 12–15% of founder females collected 1–3 days post spray and 9–10% collected after 10 days (infections attributed to secondary transmission); each spray thus resulted in 20–25% mortality. Results were comparable at high- and low-elevation sites in summer-wet climate zones. Sprays applied May–August produced similar rates of infection. Peak counts of CBB recently killed by GHA were recorded 4–5 and 12–16 days post spray (reflecting infection by sprayed conidia vs. conidia produced in the field). Cumulative mortality assessed by counts of GHA-killed CBB plateaued at 50–60%, even after numerous sprays, and was attributed to factors unrelated to efficacy. Half rates of BotaniGard/WSM were nearly as effective as full rates. Sprays on intermediate-elevation fields in a summer-dry climate zone were less effective, but efficacy varied with crop-architecture. GHA spray residues infected 30–40% of host-seeking CBB trapped one day post spray, but activity of the spray residues decreased substantially after two days, producing <11% infection. Recommendations for use of Bb for CBB IPM are presented.
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