Leaf-spotting is something that is a regular part of my job, but the Leaf Spot Fungus is not something I have encountered much.
There is a particular variant of this fungus – the (Mycosphaerella polygoni-cuspidati) which has been suggested as a method of natural control for Japanese knotweed. The fungus is one of a few natural predators for Japanese knotweed in its native Japan.
According to the Commonwealth Agricultural Bureaux International [CABI], initial testing of the leaf spot fungus progressed well, and the fungus remains “highly promising” as an option for combatting Japanese knotweed in the UK.
Junior Environment, Food and Rural Affairs minister, Lord Taylor of Holbeach told peers: “We are working towards sustainable natural control of Japanese knotweed.” and he is positive about the leaf spot fungus too.
Sustainable natural control is an admirable goal, however, the release of the Japanese Knotweed psyllid in the UK hasn’t been as successful as it might, and it could be a decade or longer before the psyllid is well-established in every 100km2 of the country – let alone every 10km2 like Japanese knotweed.
Furthermore, research in to the leaf spot fungus has run in to difficulties due to mapping the complex life-cycle of the fungus. It looks like it could be a long, tough process before we get viable cultures growing in the wild.
It is well and good to try to combat Japanese knotweed on all fronts – education, eradication and any forms of natural and artificial control, but we will undoubtedly run in to problems.
Wikipedia says that “With more than 10,000 species, [Mycosphaerella] is the largest genus of plant pathogen fungi.” Fortunately, fungi do not have the gene-swapping mutative powers of bacteria and viruses and this variety has never been recorded on any plant other than Japanese Knotweed.
I think I speak for many of the team at Japanese Knotweed Solutions when I say that we do support these efforts, but many of us also worry about the introduction of more and more non-native species in to our green and pleasant land.