Efficacy and dose response of soil-applied neem formulations in substrates with different amounts of organic matter, in the control of whiteflies, Aleyrodes proletella and Trialeurodes vaporariorum (Hemiptera: Aleyrodidae)

Neem products have been used frequently as an alternative to synthetic pesticides, because of their insecticidal, insect antifeedant, and growth-regulating effects. Moreover, new formulations are continually being developed and therefore, they have to be evaluated for their efficacy and persistence. In this regard, two soil-applied products—a liquid-based drenching solution NeemAzal-T and NeemAzal granules—were evaluated against two whitefly species, Aleyrodes proletella L. and Trialeurodes vaporariorum (West) on Brussels sprout and tomatoes, respectively. The plants were grown in two substrates: one was a commercial substrate (CS) composed of 15% humus, 35% clay, and 50% peat, and the other was a commercial substrate and sand mixture in 1:1 ratio. The main objective of the study was to evaluate the efficacy, persistence, and dose response of the two soil-applied NeemAzal formulations in substrates with different amount of organic matter. The results show that the efficacy of neem formulations was dose dependent, with the highest doses of NeemAzal granules (300 mg/kg = 21 mg azadirachtin [AZA]/kg of substrate) and NeemAzal T (2 ml/kg = 20 mg AZA/kg of substrate) achieving up to 100% mortality of immature stages of whiteflies. NeemAzal caused significantly higher mortality in immature stages of both whitefly species with CS + sand mixture than with pure CS. Persistence of the NeemAzal formulations was not influenced by the substrate type but rather by time span between treatment application and infestation, with significant decrease in efficacy when whiteflies were exposed 10 d after treatments