Efficacy of fosthiazate (Nemathorin 10 % GR) in managing Meloidogyne enterolobii in chili crop in Thailand

Root-knot nematodes (Meloidogyne spp.) are among the most destructive pathogens affecting chili crops worldwide, causing significant economic losses. Fosthiazate, a nematicide with proven efficacy against plant-parasitic nematodes, has been understudied in Thailand for its impact on root-knot nematodes. This study aimed to evaluate the potential of fosthiazate (Nemathorin 10 % GR) against Meloidogyne spp., the causal agent of root-knot disease in chili, under both greenhouse and field conditions. In greenhouse experiments, fosthiazate was applied as preventive and curative treatments at rates of 7.9–31.6 mg/pot (1–4 kg a.i./ha). Both approaches demonstrated significant nematicidal activity against M. enterolobii, but preventive treatments consistently yielded higher efficacy. Preventive applications reduced gall formation, egg mass production, and egg counts by 55.3–98.7 %, 75.7–99.6 %, and 64.4–100.0 %, respectively, as compared to without fosthiazate application. Field trials conducted in Khon Kaen and Ubon Ratchathani provinces on “Super Hot” variety (Trial 1) and “Amphawa Hot Pepper” variety (Trial 2), naturally infected with root-knot nematodes further validated these findings. The best results were obtained with two applications of fosthiazate at rates of 2 and 3 kg a.i./ha, leading to reductions in the root-galling index by 22.6 %–59.6 % and egg counts by 49.4 %–80.1 %. Importantly, no phytotoxicity was observed at any application rate or number of application times. These findings suggest that fosthiazate could be a promising option for managing Meloidogyne spp. infestations in chili fields. This study provides the first comprehensive evaluation of fosthiazate's effectiveness against root-knot nematodes in chili crops in Thailand and highlights its utility in nematode management strategies.