Organic green route synthesis of multifunctional colloidal sulfur formulation for pesticidal application

Crop protection through multifunctional low dimensional sulfur particles has numerous benefits over conventional chemical pesticides and formulations based on colloidal sulfur are emerging recently. A simple wet chemical route with acetic acid-thiosulphate-SDS system was reported to produce an aqueous colloidal sulfur formulation (CSF) of size ∼190 ​nm. This formulation was also stabilized with plant protective additives (neem oil, chitosan, tannic acid) and Taguchi methodology was applied to optimize the process and improve the stability of the formulation. Microscopic studies revealed that sulfur particles in the formulation are free from agglomerates and the developed formulation was investigated for antimicrobial and insecticidal activities. CSF was found to be effective on the tested phytopathogens (Aspergillus terreus, Fusarium solani and Venturia inequalis) with the supportive zone of inhibition and radial growth assays. Furthermore, CSF spraying onto the Pseudococcus mealybugs resulted in >80% mortality in 24 ​h and electron microscopy analysis displayed ultrastructural variations in the bodies of the insects with distorted morphology. CSF (with 18 ​mM sulfur) being non-toxic to earthworms and with its multifunctional properties could protect a wide range of crops. Its application as a foliar spray has the potential to replace commercial toxic pesticides.