Submitted to: Society for Invertebrate Pathology Annual Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: May 15, 1999
Publication Date: N/A
Field tests were conducted to assess the L. decemlineata-control potential of Beauveria bassiana applied alone and in combination with Bacillus thuringiensis. Applications were made in small plots using a backpack sprayer fitted with two hollow-cone nozzles. The nozzles were mounted on drop tubes and were directed upward to target the leaf undersides. The sprayer delivered 280 l/ha at 50 psi. Three rates (1.25, 2.5, and 5 x 1013 conidia/ha) of an emulsifiable oil-based formulation of B. bassiana were applied. Applications were delayed by rain, and most larvae were third instars when initially sprayed. Three sprays of the low, medium, and high rates applied at 3-4 d intervals reduced larval numbers by 48, 58, and 90%, respectively. Sprays at 7-d intervals were significantly less effective. Control achieved with a wettable powder formulation was equivalent to the emulsifiable oil formulations. Tests with the oil formulation also compared applications from a sprayer configured as described above to thos from a sprayer configured with nozzles directed to spray downward from above the canopy. The sprayer with drop tubes deposited an average of 668 and 558 spores/ mm2 onto the upper and lower surfaces of the leaves, respectively, while the alternative sprayer deposited 858 and 9 spores/mm2 onto the respective leaf surfaces. Nevertheless, the applications from above and below canopy provided equal levels of control. A low (2.3 l/ha) and high (7.0 l/ha) rate of Bt tank-mixed with the intermediate rate of Bb acted synergistically in reducing larval numbers by 80 and 87%, respectively, within 10 days. However, no synergism was observed when the two biocontrol agents were mixed at the low rates.