Citrus is an important economic plant in Thailand. The infection of citrus roots by Phytophthora nicotianae leads to root rot, reduced growth, and branch death. Although fosetyl aluminum and metalaxyl are commonly employed to address citrus root rot, they possess limitations in terms of their ability to diffuse to the root of citrus. Vernonia amygdalina leaf ethyl acetate extract (VLE) has been demonstrated to effectively inhibit Pythium deliense, a fungus closely related to Phytophthora nicotianae. This study aimed to investigate the anti-fungus activity of fractions obtained from the ethyl acetate extract of Vernonia amygdalina leaf against Phytophthora nicotianae, identify the most effective fraction, and formulate it into polymeric micro/nanoparticles using the electrospray process. The findings revealed that the VLE fraction eluted with ethanol:chloroform 1:1 had a high alkaloid content from metabolomic study and exhibited the potential to inhibit Phytophthora nicotianae at a concentration of 200 mu g/mL. Consequently, this fraction was selected for incorporation into polymer blends of Poly Vinyl Alcohol/cellulose acetate to generate electrosprayed particles with a diameter of 0.97 +/- 0.55 microns. These particles effectively suppressed in vitro Phytophthora nicotianae, thereby suggesting that VLE-containing electrosprayed particles have the potential to be applied and their in vivo performance in the treatment of citrus root rot evaluated in future experiments.