Forestry pest and disease management
Managing potential pests and diseases is an important part of caring for a forest. Find out what sorts of pests and diseases could affect your forest and what to do if you find any.
There are many pests in New Zealand that can affect our forests – from plants and flowers to insects and animals.
The New Zealand Farm Forestry Association (NZFFA) has a database of forest-specific pests known to be in New Zealand.
Some pests are more common in New Zealand than others.
Conifers are trees which spread seeds from cones – such as pine trees. A 'wilding conifer' is an unwanted conifer that has spread naturally (instead of being planted by foresters). Wilding conifers have become a threat to New Zealand's native landscape, high-country farming and biodiversity.
MPI encourages forest owners to manage and control their conifer stands to minimise the spread of wilding trees.
Gorse is a scrub weed, originally introduced as a form of farm hedging. It is easily distinguished from other pest plants by its thorny leaves and bright yellow flowers.
Gorse can spread quickly over large distances. The seeds disperse explosively, spreading across many metres. They can also be picked up by the wind and by the fur or fleece of passing animals.
Gorse grows quickly and densely and can outcompete pasture and forestry for nutrients, water, light and space. It can regrow quickly from any remains left after burning or cutting, making it hard to control and even harder to eliminate. Biological methods (animals and insects) seem to be the most effective control methods.
Gorse plants dry out over summer, increasing the risk of fires.
Landcare Research has a list of weeds that have been or may be targeted for control in New Zealand. Many of these can pose a risk to forest stands and should be monitored and managed.
Borer and termites are insects that burrow into timber to build their homes. They damage wood and can affect how much harvested timber can be sold for production or export.
Find out more about termites [PDF, 4.1 MB]
Caterpillars are the larval stage of moths – winged insects resembling butterflies. Caterpillars feed on the green growth of plants, including both hard- and softwood trees.
Looper caterpillars are native to New Zealand and particularly common in forests and gardens. At normal population levels, they're unlikely to cause significant damage. In certain weather conditions, populations can explode and cause large-scale forest damage.
Other types of caterpillars
Leafroller and light brown apple moth caterpillars can cause more damage than loopers in plantation forests. These caterpillars bind pine needles together in webs and feed on new growth. The damage they cause, particularly to buds on young trees, can cause malformation and stunted growth.
Weevils are small beetles whose larvae tunnel holes into dead logs or trees, planks of wood and treated timber buildings.
Weevils tend to be a problem only in harvested timber.
A population of Eucalyptus variegated beetles was discovered in Hawkes Bay in March 2016. MPI is investigating and encouraging the public to call us with any suspected sightings outside the Hawkes Bay area.
Aphids are small insects that feed on the sap of new plant growth. They can reproduce asexually (without a male and female coupling) and can occur in large numbers.
Most species of aphid are considered of little economic importance in New Zealand forests.
There are 3 types of wasp in New Zealand:
- social wasps
- parasitic wasps
- sawflies and wood wasps.
Wasps don't normally cause problems for foresters. But large populations may cause stunting and damage to small, closely packed stands of trees.
Social wasps include German wasps, common wasps and paper wasps. They have a varied diet, feeding on small insects, fruit, nectar, honey, or fish and animal carcases. They create nests out of wood fragments and mud. Their nests are often found attached to houses and other buildings. These wasps are the most likely to sting humans.
Parasitic wasps lay their eggs in other insects. There are many known species of parasitic wasps in New Zealand.
Sawflies and wood wasps bore into trees to lay their eggs. Fungus then gets into the trees through the holes, rotting the timber. When the larvae hatch, they burrow out through the rotted wood, leaving more holes in the trees.
Possums can be very damaging to young stands of trees, particularly in winter and spring when nutrition sources are harder to find. Possum damage may be minimal over a single season but can become economically significant if it continues to occur over several years.
All trees are prone to some level of disease threat. Some diseases only affect certain species of tree or certain regions of forestry.
Kauri dieback is threatening New Zealand's kauri trees with extinction. MPI is working with central and local government, tangata whenua and the wider community to stop the spread of the disease.
Pine needle diseases
Pine needle diseases can cause large-scale damage to plantation forests and have significant economic impact.
Regional pest management plans
Many regional and district councils require landowners to manage and control certain pests and diseases – as per the National policy direction for pest management. Check with your council to find out what responsibilities you may have.
Just as some organisms can be bad for your forest, others can be good. Beneficial organisms are creatures and plants that help control pests and diseases in your forest and boost the forest's overall health.
Insects can be used to control weeds
Some insects can be used to control invasive weeds. Landcare Research has a good guide to collecting and distributing insects as control agents for a range of weeds, including:
- Japanese honeysuckle
- mist flower
- old man's beard
MPI is also working with Scion to investigate the use of insects to control other insects. Import of a Tasmanian parasitic wasp, Eadya paropsidis, has been approved so Scion can research how effective it would be in controlling Eucalyptus tortoise beetles.
A list of Scion's current biocontrol projects can be found on its website.
In New Zealand, symbiotic fungi from the genus (a level of grouping plants or animals that's broader than species) Trichoderma are used to protect against pathogens (organisms that cause disease). A symbiotic fungus is a type of organism that produces spores and relies on its relationship with other organisms in its environment to survive.
When the fungus is applied to soil at the same time as seed, it colonises the outer shell of the seed and provides a protective layer that shields the seed from diseases in the soil.
The forestry industry has invested heavily in research into these fungi. If successfully managed and applied, they have the potential to protect against current threats and help trees protect themselves from unfamiliar diseases.
Monitoring pests and diseases
MPI keeps a register of pests and diseases known to affect primary industries.
Tell us if you see anything unusual
New Zealanders are expected to report unusual organisms to MPI. An unusual organism may be:
- an animal pest
- a plant pest
- signs of plant or animal disease.
If you spot anything out of the ordinary in your forest, call 0800 80 99 66 and let us know.
Who to contact
If you have questions about the information on this page, email email@example.com.