Field efficacy of application of Beauveria bassiana formulation and low rate pyridaben for sustainable control of citrus red mite Panonychus citri (Acari: Tetranychidae) in orchards

An emulsifiable formulation of Beauveria bassiana conidia was applied alone or together with pyridaben 15% EC at approximately 5% of its labeled application rate for control of citrus red mite Panonychus citri in three citrus orchards (Trials 1-3) of Taizhou, Zhejiang, southeastern China during the mild, rainy season of autumn 2006. Aqueous dilutions (150 l/ha) of two fungal rates (1.5 and 3.0 x 10(13) conidia/ha in Trials 1 and 2; 1.2 x 10(12) and 1.2 x 10(13) in Trial 3) or the low chemical rate (562.5 mg AI/ha) were sprayed to plots in randomized blocks (40-m-long row of trees per plot, three plots per treatment) with mean density of 17.8, 15.0 and 12.0 mites per leaf in Trials 1-3, respectively. Based on percent density declines and relative efficacies estimated by sampling all plots at 3-5 day intervals, the two fungal rates in each trial gave significant control and the fungal/chemical combinations always resulted in better control. The pyridaben-inclusive sprays of > or = 1.5 x 10(13) conidia/ha applied twice at 15-day interval provided excellent mite control for 35 days, yielding overall mean efficacies of 83.2-92.3% and mite density declines of 73.8-91.2%. In contrast, the relative efficacy in a standard pyridaben treatment (11.25 g AI/ha) reached 83.8% on day 3 but decreased from 72.0% on day 5 to 4.1% on day 15. Field conditions, featured with the records of approximately 20 °C and >95% RH for 216 and 300 h in Trials 1 and 2 (35 days) and 52 h in Trial 3 (15 days), were favorable. The effects of local weather on the trials in topographically different hillside orchards are discussed. Conclusively, combined application of the fungal formulation with pyridaben at the low rate is a potential alternative for sustainable control of the mite pest in orchards of southern China.