Aphidicidal activity of a novel botanical insecticide made by alkalization of bamboo tar

•Bamboo tar is a waste from charcoal processing and threatens industry sustainability.•Bamboo tar can be converted to sodium salt through alkalization.•The tar salt is aphidicidal in laboratory bioassays and field trials.

Bamboo tar is a water-insoluble semi-solid waste generated from bamboo charcoal processing, and its increasing accumulation threatens environment and sustainability of the charcoal industry that enhances the economic value of bamboo forestry in southern China. Here we converted bamboo tar to a completely water-soluble sodium salt through full alkalization with NaOH and evaluated its insecticidal activity against the cotton aphid Aphis gossypii, the soybean aphid Aphis glycines and the green peach aphid Myzus persicae in laboratory bioassays and field trials. The tar salt LC50s against the three global aphid pests decreased to 35–93 μg/ml on day 7 from 246 to 486 μg/ml on day 3. In three field trials, the tar salt at the application rates of 338–675 g/ha controlled the aphid pests as efficaciously as but more persistently than pymetrozine (a synthetic aphidicide) at the recommended rate. Our results highlight an easy approach to converting bamboo tar to a promising botanical aphidicide but extensive further work to determine its toxicity and environmental and crop safety is needed.