Suppression Efficacy of Clubroot on Cruciferous Crops Through Application of the Humic Acid Material

Clubroot in cruciferous plants remains a significant threat to growers worldwide. We investigated whether humic acid material (HAM) could control clubroot in Chinese cabbage and broccoli as an alternative to fungicides. Six independent experiments were conducted, and the results were analyzed using a general liner mixed model (GLMM) and a network meta-analysis (NMA). Some HAM treatments significantly controlled clubroot incidence on Chinese cabbage in three experiments, but no significant effects were observed in the others. HAM treatment effects varied across experiments. The GLMM indicated that HAM treatment and the interaction between the HAM amount and planting timing were significantly associated with disease incidence. HAM effectiveness depended on application amount and planting timing after treatment. The NMA estimated a statistically significant risk ratio of 0.85 for planting four weeks after HAM treatment, suggesting low efficacy in suppressing clubroot. Two field trials aligned with the greenhouse results.