From classical to inundative control: Mycosphaerella polygoni-cuspidati as a potential mycoherbicide for Japanese knotweed.
This paper presents the use of Mycosphaerella polygoni-cuspidati to control Japanese knotweed (Fallopia japonica). Studies showed that inoculations with mycelial concentrations of the pathogen at 107 fragments/ml led to leaf-drop in inoculated plants while concentrations of 105 to 106 fragments/ml reliably caused disease symptoms in the form of necrotic leaf-spots. However, disease severity was variable and strongly dependent on the age of the leaf-spot culture used for mass production, as well as the post-inoculation ambient relative humidity; fungal cultures older than 3 months and lower relative humidity impacted negatively on disease expression. Inoculation with M. polygoni-cuspidati stimulated the production of new shoots linked with an increased length of and number of leaves on these shoots in treated Japanese knotweed plants. This observation can currently only be documented as a trend due to high variability, but it suggests that the pathogen interferes with shoot apical dominance and thereby activates the growth of rhizome buds, a phenomenon also seen in Japanese knotweed plants as a result of cutting or poisoning of aerial shoots. It is hoped that an approval of the pest risk assessment (PRA) for the Mycosphaerella leaf-spot and permission for its release from quarantine will allow experimental field trials to take place in order to assess the efficacy of the pathogen under field conditions. If mycelial applications of M. polygoni-cuspidati prove to give good control, and the concept of a mycoherbicide for Japanese knotweed based on a single mating type of the pathogen is to be taken forward, a partnership with the private sector will be crucial and talks with industry regarding this are already in progress.