Double-Encapsulated Controlled Release System for the Staged Delivery of a Growth Stimulant and Herbicide

Weed control remains a critical challenge in agriculture, especially with parasitic weeds such as Orobanche spp., Striga spp., and Cuscuta spp., which significantly reduce crop yield. Although herbicides are effective against common weeds, they are less effective against parasitic weeds due to their unique germination mechanisms and close association with host plants. Growth regulators can stimulate the germination of parasitic weeds (suicidal germination) in the absence of host plants, providing a potential opportunity for controlling parasitic weeds, especially Striga sps. We report here a double-encapsulated staged delivery system, wherein herbicide (atrazine) is encapsulated in the inner polyurea shell and a growth stimulant (Gibberellic acid, GA3) in the outer alginate matrix. In vitro release study conducted in an aqueous medium showed that the time required for 50% release of atrazine from this double-encapsulated system is 96 h against 3 h for GA3. The quick release of GA3, followed by a slow and sustained release of atrazine, is expected to first induce the germination of parasitic weed seeds using GA3 and subsequently exterminate them upon exposure to atrazine. Interpretation of release data using the Weibull model led to the conclusion that the release of atrazine and GA3 is primarily governed by Fickian diffusion. Soil breakthrough profile shows that double encapsulation of atrazine helps to control the overleaching of atrazine into the soil.