Suspension concentrate formulation of Bacillus thuringiensis var. kurstaki for effective management of Helicoverpa armigera on sunflower (Helianthus annuus)

A local strain DOR Bt-1 belonging to Bacillus thuringiensis var. kurstaki (Bt.k) was multiplied through solid state fermentation and the resulting technical powder was milled and sieved to obtain particles of various sizes. Efficacy of Bt.k. against larvae of Helicoverpa armigera was found to increase with the decrease in particle size. Boric acid was found to be synergistic to DOR Bt-1 technical powder. LC₅₀ of the Bt and boric acid mixture (75:25) was lower at 89.63 mg/100 mL in comparison to Bt alone at 116.75 mg/100 mL. A suspension concentrate formulation with DOR Bt-1 technical was developed using boric acid as an adjuvant. The formulation was found to be highly effective against H. armigera in laboratory bioassays with an LC₅₀ of 185 µL (containing 53.36 mg Bt). The formulation gave effective control of H. armigera on sunflower within 3 days after spray even at the lowest dose of 1.0 mL/L under field conditions.