Tutsan (Hypericum androsaemum) was described as a serious pasture weed in New Zealand back in 1955 and has become a significant invasive plant in the Taumarunui area. In recent times tutsan appears to have begun to spread even more rapidly into valuable pastureland, production forestry, and conservation areas, and has formed monocultures in some areas. The plant is estimated to have a greater than 60% cover over 1500 ha in Taumarunui alone, and threatens a much greater area than that. Tutsan is also found, and is of concern, in seven other regions throughout New Zealand. Like its close relative St John’s wort (Hypericum peforatum), tutsan is also harmful to livestock because it contains hypericin, which induces photosensitisation and dermatitis in sheep and cattle.
Conventional methods for tackling tutsan are inadequate, uneconomic and unsustainable. Spraying is diffi cult because there are no chemicals registered for tutsan control in New Zealand, and the results of off -label herbicides are not always satisfactory. The plant also often grows in places where spraying and mechanical control are difficult or impossible owing to the topography.
Biological control of tutsan was explored in a cursory manner in New Zealand about 60 years ago. While its primary host is St John’s wort, the lesser St John’s wort beetle (Chrysolina hyperici) was also released on tutsan in some areas in 1948 and 1950, and there are anecdotal reports that they achieved good results on several farms in the Taumarunui area. However, the beetle did not persist and is believed to no longer be found on tutsan infestations, possibly because the plant is a suboptimal host on which the beetle can only survive for a short time.
A rust (Melampsora hypericorum) was found to be attacking tutsan in the Wellington Region about the same time, and spread rapidly throughout New Zealand from Raglan to Stewart Island. Rust symptoms appear in late spring or early summer causing characteristic yellow to red blotches on the upper surface of the leaves with corresponding golden rust pustules underneath. The leaves may turn brown and shrivel up, and if the infection is severe the whole plant may be defoliated and even killed. Unfortunately severe infections do not seem to commonly occur in New Zealand and therefore the rust is not able to provide adequate control.
Recently a group of concerned people – including farmers, regional council and Department of Conservation staff – in the Taumarunui area formed to tackle the tutsan problem head on. They have called themselves the Tutsan Action Group and have successfully applied for funds from the MAF Sustainable Farming Fund and Meat and Wool New Zealand. This year Landcare Research, on their behalf, will look at the feasibility of developing an effective biological control programme against tutsan in New Zealand. The Tutsan Action Group will also obtain information about the economic impacts of tutsan and better document its current distribution. Lesser St John’s wort beetles will be sourced and released this spring so the group can study what happens when they are released on tutsan. If the feasibility study suggests that promising biocontrol agents might be available then the group hopes in future to apply for funding to pursue them further.