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.

Magpies are very territorial and aggressive to other birds. Magpie control methods include trapping, shooting and poisoning.

There are a number of control methods you can try, such as possum and rabbit repellents, trapping, poisoning and shooting. Contact us for more information about animal pest control, and read Environment Canterbury’s pests and weeds information online.

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. A better name for these fish, at least in New Zealand, is "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.

You should be aware that it is an offence to introduce any aquatic life (including any plants or 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 (see our wetland contacts page for their details).

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 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, with a grubber or with herbicide. Another option is to use weed mats (for example, non-rubberised carpet underlay) which eventually decomposes.

Once native plants have grown tall enough, they will begin to shade out grasses and aquatic weeds, and weed control will no longer be required.

The use of a glyphosate herbicide will greatly reduce the need for manual weeding. The use of long-lasting residual herbicides is not recommended, as they remain toxic to plants three-to-four months after application. The best time to spray is in late summer when water levels are low 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.

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.

You can get information on suitable herbicides and suggested application rates from Environment Canterbury’s plant pest officers.  Also, check out our pests and weeds pages for online information or pictures of common weeds and suggested methods for their control.

Pond weeds

Ponds that get plenty of sunlight and nutrient rich run-off 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 6 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 run-off from the surrounding catchment.
• When working with spades and machinery in weedy areas, wash them down before using them elsewhere.
• Fencing out stock will also reduce the spread of weeds.

Remember that applying herbicide onto aquatic weeds requires a resource consent from Environment Canterbury.

Wandering willows

A variety of willows were introduced into New Zealand for bank stability, shelter belts and fodder. However, their dense growth can block stream flow and shade out native plants. 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 an appropriate glyphosate or picloram 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 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.

You can get information on suitable herbicides and suggested application rates from Environment Canterbury's plant pest officers.  Also, check out our pests and weeds pages for online information.