Clay-based azoxystrobin formulation enhances cotton protection against charcoal rot disease

Abstract Background Cotton charcoal rot disease, caused by Macrophomina phaseolina , is a major threat to cotton production in Israel and globally, leading to severe yield loss due to post-flowering plant collapse. Current management relies heavily on chemical fungicides. However, rising environmental concerns and fungicide resistance underscore the need for sustainable alternatives. This study evaluated novel clay-based formulations for the controlled release of azoxystrobin (AS). The approach aims to protect cotton during the sensitive early growth stages when pathogen penetration and colonization occur. Two types of clay carriers—bentonite (montmorillonite) and sepiolite—were tested for their ability to deliver AS effectively. Results While seedlings grown in the greenhouse showed minimal visible symptoms at the disease latent stage, quantitative real-time PCR analysis indicated that both formulations effectively suppressed root infection, reducing M. phaseolina DNA levels by 81%. In a full-season open-enclosure trial, bentonite-AS treatment exhibited reduced efficacy, possibly due to phytotoxicity at the tested concentration. In contrast, the sepiolite-AS treatment increased flower bud number by 87% and reduced pathogen infection by up to 92% at 68 days post-sowing, although these effects were not statistically significant due to high variability. At harvest, sepiolite-AS and bentonite alone increased shoot dry weight per plant by 129% and 128%, respectively, and reduced pathogen DNA levels by 63% and 69%, respectively. Conclusion Overall, although environmental variability led to statistical insignificance, the findings support the clay–AS approach, especially sepiolite, as an effective means to prevent early infection and reduce late-season disease outbreaks. This formulation holds promise for seed coating or sowing strip applications, offering a practical, eco-friendly approach that can be integrated with biological control to reduce chemical inputs across diverse cultivation systems.