Abstract

Winter cover cropping has the potential to suppress root-knot nematodes while also improving yield and quality in tobacco production systems. This three-year study aimed to determine whether the incorporation of winter cover crops enhances nematode suppression and tobacco productivity, as measured by yield and leaf quality, under continuous tobacco production systems. The experiment was established in a 2 × 2 × 5 split–split plot design, replicated three times, with three factors: tobacco variety (K RK76, K RK26), nematicide application (with and without nematicide), and cover crop type (sunhemp, chia, velvet bean, silverleaf Desmodium, and a fallow control). Soil samples for nematode bioassays were collected at three intervals: 5, 10, and 15 weeks after planting. Tobacco yield and the grade index of cured leaves were measured post-harvest. Year and assessment date were included as factors in the data analysis. Results showed no significant interaction among year × assessment date × variety × nematicide × cover crop on the root-knot nematode index (P > 0.05). However, a significant three-way interaction was observed among year, assessment date, and nematicide (P < 0.05). Across all three years, nematode galling significantly declined at 5, 10, and 15 weeks after planting in plots without nematicide (P < 0.05). Yield was significantly influenced by a year × variety interaction (P < 0.05), with yields increasing from 2022 to 2024, and the highest yields recorded in 2024. Cover crop type and nematicide treatment significantly affected the quality grade index. Although no significant differences in quality grade index were observed between nematicide-treated and untreated plots across all cover crops, a significant (P < 0.05) decline in quality occurred in the fallow plot when nematicide was not applied. Overall, tobacco velvet bean, tobacco–chia, and tobacco silverleaf Desmodium cover cropping systems performed comparably to the standard tobacco–sunhemp cover cropping. These cover crops effectively suppressed root-knot nematode galling while maintaining tobacco yield and leaf quality and can therefore be utilised in continuous tobacco production systems.

Key words: Nematode bioassays, grade index, parasitic nematodes, yield.