Increased persistence of Beauveria bassiana spore viability under high ultraviolet-blocking greenhouse plastic

A field study was conducted to assess the effect of various commercially av ailable polyethylene plastic greenhouse coverings on the persistence of via ble spores of the microbial insecticide Beauveria bassiana. Selected coveri ngs blocked the transmission of UV light with wavelengths of 360 nm and bel ow or 380 rim and below. Two coverings also contained an infrared blocking component. A commercial formulation of B. bassiana was applied for 3 consec utive weeks to plants growing in the plastic covered hoop houses. The perce ntage of viable spores was calculated up to 13 days after the final applica tion. The persistence of viable B. bassiana spores was significantly longer under the plastic that blocked a greater portion of the UV spectrum (< 380 nm) than the plastics that only blocked UV wavelengths below 360 rim. One week after application, percentage of spore germination was at least twice as high under the <380 nm blocking plastic compared to <less than>360 nm bl ocking plastics.