With introduced trees came many new pests and diseases. From the 1920s the Forest Service was concerned that insect pests might come into the country on imported forest products, and lobbied for effective inspection and quarantine systems. It also initiated research on forest insects and diseases.
In the early 1900s it was discovered that a wood wasp, Sirex juvencus, laid its eggs inside the stems of pine trees. In 1929 researchers at the Cawthron Institute released the parasitic ichneumon wasp (Rhyssa persuasoria, which means ‘persuasive burglar’) to prey on the wood wasp. This was one of the first attempts at biological control in New Zealand, and it was successful. Biological control is now an important way of managing insect pests.
Forest entomologists identify insects from overseas that are likely to cause problems in New Zealand. These species are targeted by MAF Biosecurity New Zealand whenever they are found in the country. There were large, and controversial, eradication campaigns against insect pests in the 1990s and 2000s, including the painted apple moth in Auckland, and the Asian gypsy moth in Hamilton.
The 1996 discovery of the white-spotted tussock moth in Auckland prompted the first successful pest-eradication exercise ever undertaken in an urban area. The moth – which could have damaged ornamental and fruit trees, and native beech forest – was eradicated over large areas of residential Auckland through aerial and ground spraying.
The first major disease of radiata pine was dothistroma needle blight, caused by the fungus Dothistroma pini. When it arrived in the 1960s the Forest Research Institute (FRI) urgently recruited forest pathology staff. There was intensive research on all aspects of the disease and trials refined techniques for spraying with copper, making it a cost-effective means of control. This treatment is still used.
Other common fungal diseases that have been made manageable by research include cyclaneusma needle cast (in pines), septoria leaf blight (in eucalypts) and Swiss needle cast (in Douglas firs).
In 2004 New Zealand quarantine specialists discovered and destroyed pitch canker fungus – a serious threat to radiata pine – during a routine check of imported plant material. As a result, the importation of Douglas fir from the USA was restricted.
In 1956 the Forest Service became responsible for controlling animal pests in New Zealand forests, including possums, rats and goats. A research team at the FRI began studying the impact of pests on forestry, and methods of controlling them. This team later shifted to Landcare Research.
Before its disestablishment in 1987, the Forest Service was responsible for controlling fires in forests and rural areas, but this job has passed now to local authorities and individual forest owners. The study of fire behaviour in different kinds of forest is a small but important area of forestry research.