Improving the efficacy of nuclear polyhedrosis virus and Bacillus thuringiensis against Helicoverpa spp. with ultra-violet light protected petroleum spray oils on cotton crops in Australia

Nuclear polyhedrosis virus (NPV) and Bacillus thuringiensis (Bt) are the most commonly used biopesticides for the control of Helicoverpa spp. larvae on cotton crops in Australia. The performance of NPV and Bt against Helicoverpa spp. larvae on cotton crops, is inconsistent and at times totally unsatisfactory against high densities of Helicoverpa spp. larvae. We determined the effect of mixing petroleum spray oils, containing ultra-violet light absorbing compounds, with NPV and Bt for efficacy against Helicoverpa spp. larvae, levels of cotton plant damage, and persistence of efficacy. The study showed that the efficacy and persistence of NPV and Bt were increased when mixed with petroleum spray oil (PSO – Canopy®) at the rate of 2% (v/v). In the field experiments, mixing NPV with 1 and 2% (v/v) PSO, increased Helicoverpa spp. mortality from 25.9 to 31.5 and 44.8%, respectively. Similarly, the mortality caused by Bt, when mixed with 1 and 2% (v/v) PSO, was increased from 31.5 to 36.0 and 48.2%, respectively...