Efficacy of biorationals in managing diamondback moth, Plutella xylostella (Linnaeus, 1758) in cauliflower

The diamondback moth (DBM) is one of the major pests of cauliflower and other crucifer crops. We evaluated the efficacy and economy of selected biorationals for DBM management under open-field conditions. A field experiment was conducted at Rampur, Chitwan, Nepal, from December 2019 to March 2020 in a randomized complete block design that comprised six treatments and three replications. The treatments included Bacillus thuringiensis, spinosad, emamectin benzoate, neem oil, botanical extract fermented with cow urine (BEFCU), and an untreated control. Three sprays were applied, the first after 44 days of transplanting and the two others followed by 10-day intervals. Spinosad resulted in the lowest DBM larvae, with 0.04, 0.09, and 0.04 larvae plant-1 after the first, second, and third sprays, respectively, followed by emamectin benzoate with 0.21, 0.25, and 0.17 larvae plant-1. In contrast, B. thuringiensis and BEFCU provided inconsistent control, with BEFCU occasionally recording larvae number comparable to or higher than the untreated control. Spinosad produced the highest curd yield (24.89 t ha-1), followed by emamectin benzoate (24.08 t ha-1), whereas emamectin benzoate recorded the highest benefit-cost ratio (2.29), followed by neem oil (2.20) and spinosad (2.16). Overall, spinosad provided the most effective DBM control and highest curd yield, whereas emamectin benzoate provided the highest economic return. Bacillus thuringiensis and BEFCU were less effective under the tested conditions.