Uncontrolled weeds a disaster

Press, 31 December 1982, Page 18

Uncontrolled weeds a disaster

By

OLIVER RIDDELL

Aquatic weeds may look fine in an aquarium or fish pond, but in New Zealand's lakes and rivers they "ould mean no swimming, no fishing, no boating, and higher electricity costs. The spread of free-floating plants is being restricted at present by continuous and costly control programmes; should the controls ever be relaxed the result would be a disaster.

The Electricity Division of the Ministry of Energy has mounted a publicity" programme to warn aquarium owners not to put their plants into a natural environment. A number of species are classified as “dangerous" and their potential threat is viewed with deadly seriousness.

How serious is the prob-

lem? What, is being done to check the spread of noxious weeds in lakes and waterways? Aquatic plants are .an essential component of waterways, but certain introduced species have become so well established that they are affecting adversely the many uses of the waterways, and are also threatening native flora, says Mr J. M. Hercus. the representative of the Ministrj’ of Agriculture and Fisheries on the Noxious Plants Council.

The problem species have not yet reached the limits of their distribution. The problems and cost to the country

if their spread is not checked would be great. Twenty per cent of our large lakes have exotic plant populations which cause weed problems in recreational areas, and hamper the generation of electric power, and navigation.

Mr Hercus says a preventive weeds strategy aims to prevent further weed problems by keeping plants out of new areas. One important way of doing this is to prevent their sale and distribution around the country, and into areas where they could cause new infestations. The Noxious Plants Council is using the Noxious

Plants Act, 1978, to prohibit the sale and distribution of six plants, all listed as Class B noxious plants, when they are sold, distributed or actively propagated:—

• Lagarosiphon major (oxygen weed). • Egeria densa (oxygen weed).

• Hydrilla verticulata (hydrilia or oxygen weed). • Ceratophyllum demersum (hornwort).

• Valjisneria gigantea (eel grass). • Salvinia molesta.

The other two free-floating plants — water hyacinth (Richhornia crassipes) and water lettuce — are classifed as Class A noxious plants and it is illegal to hold, plant or sell them.

Before the Noxious Plants Council was set up, the aquatic environment had been largely neglected, says Mr Hercus. Efforts were mainly directed towards controlled land weeds. The aquatic environment presented more complex management problems. To resolve this, the council suggested that management be vested in three groups:— 1. Natural lakes — Department of Lands and Survey, or the private owners.

2. Man-made lakes or natural lakes modified to generate hydro-electric power — Electricity Division of the Ministry of Energy.

3. Rivers, streams, drainage ditches and canals — regional water boards.