Pest Plants

There is a wide range of woody, creeping and climbing weeds that can invade our forests and bush. Some of the more common climbing weeds that fit into this category include elaeagnus, Japanese honeysuckle, climbing asparagus, smilax, moth plant, blue morning glory, ivy and mignonette vine. These plants smother trees from ground level up, eventually causing the host trees to collapse. They can spread into forests from the margins or grow from seed or plant material dispersed into the forest from nearby sources.

Old mans beard is a fast growing vine that has become a major pest in the cooler central and southern north island and parts of the south island. Cathedral bells is another fast growing dense vine, which is not currently widespread and has only been found in a few sites around the country. Cathedral bells is possibly second only to old mans beard in terms of speed of growth and it’s ability to smother, damage or kill trees because of its blanket affect.

Weeds like Queensland poplar, tree privet and monkey apple compete with vegetation, reducing their growth, and have become major problems in both exotic and native forests in parts of the north island. Woolly nightshade is common in forest margins and disturbed sites also in parts of the north island. It can grow up to three metres a year and form pure colonies, crowding out and suppressing some plants.

There are many different ways of controlling pest plants, and the one used will depend on the type of plant, the size of the infestation and the type of habitat it is growing in. Small-scattered plants can be dug out, making sure that any plants that produce tubers such as climbing asparagus, smilax and mignonette vine also have tubers collected and removed along with the plant. Plant material and tubers need to be disposed of safely as they can regrow into new plants.

For larger scattered plants, the trunk or stems can be cut and painted with a herbicide mixed with water or a herbicidal gel applied. This allows the pest plant to be selectively killed without damaging any neighbouring species, both native or exotic.

Larger infestations can be controlled by spraying the plants. If pest plants are growing over trees, the vines or vegetation covering the desirable trees should be carefully cut back with the remainder sprayed with a suitable herbicide.

Greg Hoskins

Find out more.....