A novel nematicide application method based on nematode life cycle for managing root-knot nematode, Meloidogyne...

Organic vegetable growers face significant challenges in managing plant-parasitic nematodes, particularly root-knot nematodes (RKN; Meloidogyne spp.), because of restrictions on the use of synthetic chemicals. This study evaluated the efficacy of seven commercially available Organic Materials Review Institute-certified bionematicides against Meloidogyne incognita under greenhouse and field conditions. A cucumber plasticulture field study was also conducted to compare the efficacy of four best-performing bionematicides, including azadirachtin, cold-pressed neem oil, thyme oil and saponins of Quillaja saponaria, identified in the greenhouse study and a chemical nematicde (oxamyl) using two application regimes: calendar-based (following the product label) and nematode life-cycle-based (following the M. incognita life cycle using degree-days assessment).

In the greenhouse study with tomato, azadirachtin and thyme oil significantly reduced M. incognita root galling and reproduction factor (final nematode population/initial nematode population) compared with a positive control. In the field trial with cucumber, the nematode life cycle was completed in 23 days during the spring season and 24 days during the fall season, accumulating 380 and 398 degree-days, respectively, above a base temperature of 10 °C. For calendar-based applications, only azadirachtin significantly reduced nematode density, whereas for life-cycle-based applications, all treatments except saponins of Q. saponaria were effective. Oxamyl was more effective when applied according to the nematode life cycle than on a calendar-based regime. Life-cycle-based applications generally outperformed calendar-based applications based on numerical values, even in cases in which the differences were not significant. For the galling index, calendar-based applications of azadirachtin and cold-pressed neem oil reduced the galling index more than life-cycle-based applications at mid-season. At the end of the season, only azadirachtin under the calendar-based application differed significantly from the control, while all other treatments (except saponins of Q. saponaria) had lower root galling indices than the calendar-based applications.

These findings indicate that both application regimes can be used to manage M. incognita in organic farming systems. Of particular significance is the novel life-cycle-based approach developed in this study, which may confer enhanced sustainability benefits by optimizing nematicide application timing and reducing treatment frequency, ultimately leading to a decline in soil nematode population densities. © 2025 Society of Chemical Industry.