pH-responsive guar gum-based hydrogels for controlled release and antifungal applications of carvacrol

Plant essential oil-based pesticides are increasingly valued in green agriculture for their efficacy, environmental compatibility, low toxicity, and minimal impact on non-target organisms. However, their practical use remains limited by short efficacy periods, poor photostability, and low solubility. To overcome these limitations, this study developed a pH-responsive hydrogel composed of carvacrol and the natural polysaccharides chitosan (CS) and guar gum (GG), which improved photostability by 126 %. The CS-GG hydrogel exhibited accelerated carvacrol release under acidic conditions, showing a relative increase of 20 % and following a Weibull diffusion model, thereby enabling targeted drug delivery at infection sites. Encapsulation markedly enhanced antifungal performance against anthracnose, achieving superior mycelial inhibition on tomato surfaces in both preventive and curative treatments compared with unencapsulated carvacrol. Moreover, hydrogel encapsulation reduced acute toxicity by minimizing direct exposure, as reflected by zebrafish LC 50 values that increased by approximately 71 % at 48 h and 46 % at 96 h, thereby significantly improving ecological safety. These findings demonstrate that the pH-responsive CS-GG hydrogel offers a promising platform for controlled delivery of botanical pesticides. This approach not only provides an effective, environmentally friendly solution for anthracnose control but also establishes a versatile framework for advancing the application of other plant-derived pesticides in sustainable crop protection.