Suppressive Effects of Biochar and Vermicompost on Yellow Wilt in Lamb’s Lettuce (Valeriana locusta): Insights from Two-Year Greenhouse Trials

Yellow wilt is a soil-borne disease affecting lamb’s lettuce ( Valerianella locusta ) production in Central Europe, with limited effective chemical control options. This two-year greenhouse study evaluated the suppressive effects of biochar, vermicompost, and compost extract—applied individually and in combination—on yellow wilt symptoms and plant performance. Eight treatments were tested under naturally infested soil, including single amendments and combinations. In the first year, disease incidence and severity were generally low and not significantly different across treatments. However, in the second year, disease pressure increased markedly, indicating significant treatment effects. Biochar in combination with vermicompost decreased the incidence of the disease compared to other treatments. Vermicompost alone on the other hand reduced disease severity more effectively than other treatments. The triple combination vermicompost, biochar and compost extract did not outperform the treatments with simpler combinations. Fresh biomass and dry matter content were also influenced by treatment and year. In 2021, vermicompost yielded the highest fresh matter (796 g m⁻²), while biochar resulted in the lowest significantly. Ground coverage measurements showed numerical trends aligned with biomass results, though not statistically significant. These findings suggest that vermicompost, particularly when combined with biochar, can offer a promising biological alternative to manage yellow wilt and improve productivity in lamb’s lettuce cultivation under organic or low-input systems.