Comparative Efficacy of Chemical and Biological Management of Root-Knot Nematodes (Meloidogyne spp.) on Tomato in Plateau State, North Central Nigeria

Root-knot nematodes (Meloidogyne spp.) are major soilborne pests of tomato in Plateau State, causing characteristic gall formation, nutrient disruption, and significant yield losses in both open-field and greenhouse production. The comparative efficacy of chemical nematicides, biological agents, and cultural practices for nematode management under highland conditions in Plateau State has not been empirically established. This study evaluated eight management treatments, including carbofuran, fosthiazate, Purpureocillium lilacinum, Bacillus firmus, Trichoderma asperellum, marigold intercropping, soil solarisation, and untreated control, in a randomised complete block design at two field sites over two growing seasons. Soil nematode densities, root gall indices, plant growth parameters, and marketable tomato yield were measured at transplanting, mid-season, and harvest. Fosthiazate achieved the greatest nematode population reduction, lowering final-season soil juvenile counts by 83 percent. Purpureocillium lilacinum and B. firmus biological treatments reduced gall index scores by 56 and 48 percent respectively, performing comparably to carbofuran at one of two sites. Marigold intercropping reduced second-season nematode densities by 41 percent, consistent with allelochemical suppression mechanisms. Combined P. lilacinum and marigold intercropping produced the greatest yield advantage among non-chemical treatments at 17.4 tonnes per hectare, compared to 9.8 tonnes in the untreated control. Biological options showed improved performance in the second season, suggesting that cumulative soil population effects enhanced efficacy over time. The study recommends a staged adoption pathway from chemical to biological management in Plateau State tomato systems. Keywords: root-knot nematodes, Meloidogyne, biological control, tomato, Plateau State.