New Zealand is now home to many introduced pests that feed on or compete with native plants and animals. Ongoing pest control will enhance the native bird life in your wetland and protect young plantings.
On this page: Problem animals, mosquitoes, pukeko on the rampage, weed control around plantings, pond weeds, willows
Problem animals
Rabbits, hares and possums eat wetland plants.
Possums, hedgehogs, stoats, weasels, ferrets, feral cats and rats eat birds’ eggs and most will also eat chicks and adult birds. They will also kill other native animals such as bats, insects and lizards.
There are a number of control methods you can try such as possum and rabbit repellents, trapping, poisoning and shooting. Find out more about possums and check out our tips for control.
Magpies and mynas are very territorial and aggressive to other birds. Magpie control methods include trapping, shooting and poisoning, find out more on our magpie page.
Mosquitoes
Mosquitoes may become a problem near open water. The best solution is to allow water boatmen (native aquatic insects) and other natural predators to keep them in check.
Don’t be tempted to introduce mosquito fish (Gambusia). They are not native or effective in controlling mosquitoes. In New Zealand, they could be called ‘anything but mosquito’ fish, as they prefer to eat almost every other freshwater insect first. Mosquito fish attack other fish, including natives, and breed so rapidly that they will either drive out or kill other fish in the area.
It is also an offence to introduce any aquatic life including all plants and fish to a new area without a permit. Permits may be required from the Ministry of Fisheries, the Department of Conservation and the Fish and Game Council.
Pukeko on the rampage
Pukeko may undo a lot of your good work by nibbling and uprooting newly planted seedlings. To deter them use larger and heavier potted plants or try placing a hedge of short sticks around the young plants.
Although pukeko are game birds and not legally protected during hunting season, they are native to New Zealand, and are a natural part of a wetland ecosystem.
Weed control around plantings
In the first one to three years weeds can overwhelm new plantings. Smothering by tall grass is the most common cause of planting failure.
Weeds can be cleared by hand or with a grubber or herbicide. Another option is to use weed mats (for example, non-rubberised carpet underlay) that eventually decompose. Once native plants have grown tall enough they will begin to shade out grasses and aquatic weeds, and no longer require weed control.
Herbicides
The use of a glyphosate herbicide will greatly reduce the need for manual weeding. Grass-specific herbicides can be useful for selectively reducing weedy grasses. The use of long lasting residual herbicides is not recommended, as they remain toxic to plants three to four months after application. Herbicides should be used sparingly and only when necessary in wetland areas. Chemicals are transported rapidly through water, making wetlands more sensitive to pollution and herbicides.
The best time to spray is in late summer when water levels are lower and most nesting and flowering has taken place. Only spray on calm days to avoid spray drift affecting neighbouring plants. New herbicides available in gel form avoid spray drift problems.
Applying herbicide onto aquatic weeds or clearing more than 1 ha of willow may require consent from Waikato Regional Council, so check with us first. You can get information on suitable herbicides and suggested application rates from our Plant Pest Officers.
Find out more about how to identify and control weeds on the Weedbusters website.
Pond weeds
Ponds that get plenty of sunlight and nutrient rich runoff can become choked with algae and water plants. A good inflow of water is needed to continually flush the pond and extra depth will help keep it cool.
Here are a few helpful hints on how to reduce unwanted water plants:
- Bales of barley straw inhibit algal growth when placed in slow moving water. Two bales will keep around half a hectare of shallow, open water free of algae for six months. The straw can be spread out or anchored in one position. Eventually it will sink and decompose, boosting aquatic insect life.
- Overhanging trees and plantings will provide shade and trap runoff from the surrounding catchment.
- When working with spades and machinery in weedy areas, wash them down before using them elsewhere on the farm.
- Fencing out stock will also reduce the spread of weeds.
Remember that applying herbicide onto aquatic weeds requires a resource consent from Waikato Regional Council.
Wandering willows
A variety of willows were introduced into New Zealand for bank stability, shelterbelts and fodder. However, their dense growth can block stream flow and shade out native species. Crack willow and grey willow are particularly invasive. Broken branches take root easily in muddy soils, and grey willows have tiny wind blown seeds.
Options for control include:
- Cutting trees off close to the ground and stacking cuttings in a dry place for burning. All stumps should be coated immediately with a glyphosate herbicide.
- Drilling a hole in the base of each tree at a 45° angle before injecting 80 ml of a glyphosate herbicide. This method only works during summer.
- Willows can form an effective shelter for native plant seedlings but they need to gradually be removed, or injected with herbicide and left to decompose, as the understorey develops. It can help to cut through any willow roots around new plantings to reduce root competition. Clearing overhead willow branches will provide more light for the new plants.
- Aerial spraying can be used for large-scale willow control but may require a consent from Environment Waikato.
You can get information on suitable herbicides and suggested application rates from Waikato Regional Council's Plant Pest Officers.
Find out more about plant and animal pests in the Waikato region, and pest and weed control in native forest fragments.
Use this information to help you prepare your wetland plan.