Occurrence of Japanese Yam (Dioscorea japonica) as Vine Weed in Tea Gardens

Dioscorea japonica (Japanese yam) is the most troublesome weed species of tea gardens in Japan. In recent years, effective integrated weed control methods in tea gardens that do not rely on hand weeding or herbicides have been sought, but the ecological properties of Japanese yam in tea gardens, and the basis for technological development, remain unclear. This study aimed to elucidate the actual occurrence, type of emergence, and characteristics of flowering of Japanese yam in tea gardens. The study observed emergence of many plants from propagules, whereas no plants from seeds were found. Additionally, many vines produced propagules, and only a few produced flowers, which were all female plants. This suggests that propagation of the Japanese yam in tea gardens is likely through clonal propagation by propagule, not by seed. Conversely, it was observed that half of the plants from propagule were in simple form, in which only the petiole and leaf blade are present without extending the above-ground stem, similar to forest floor plants. It is of concern that this type would be problematic as they are "reservoirs" for outbreaks in subsequent years.