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Wild-Ginger

WILD GINGER

Hedychium gardnerianum -  Kahili ginger
Hedychium flavescens – Yellow ginger
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Wild-Ginger

DESCRIPTION

There are two types of wild ginger in New Zealand: Kahili ginger and Yellow ginger  Both are very serious invaders of native vegetation sites, and both are subject to strict plant pest controls by many NZ authorities, including total control orders.

The two types are similar, both being originally introduced as fragrant and very attractive garden plants. However, as is so often the case, an initially appealing guest turned into an unwelcome invader.

The Kahili ginger plant is the more serious of the two, due to its production of about 100 viable seeds from every flower head, and these are widely distributed by birds. In contrast, the Yellow ginger does not produce viable seeds in New Zealand and thus is less aggressively and readily invasive.

KAHILI GINGER

The Kahili ginger plant is about 2 metres tall when mature, and carries large waxy leaves arranged alternately along its erect stems. The leaves are long and slim (to 40cm in length), with pointed tips. In Jan-Mar it produces large and spectacular yellow flowers with very conspicuous reddish stamens and a strong pleasant fragrance. The seed capsule is orange and contains numerous bright scarlet seeds.

YELLOW GINGER

A taller plant, reaching 3 metres, the yellow ginger has even narrower leaves than the Kahili, and they grow more upright. The flowers appear later, normally May-Jun, and are smaller and creamy-yellow, on a cone-like flower head.  The yellow ginger plant produces no seeds. 

Both types have large and tuberous rhizome-type root systems, from which the plants of both varieties will multiply. This ready growth from the extensive rhizome system will quickly produce a very dense mass of vegetation that will block the light and effectively smother native species. The thick underground mats formed by the rhizome systems themselves are very deep (up to a metre into the soil) and make it very hard for any other plants to penetrate and grow successfully.

HABITAT

Wild ginger tends to appear in roadside areas and damp locations, often in the vicinity of the gardens from which it originally escaped. It will then move into adjacent areas of native vegetation, especially the Kahili ginger variety due to the bird-borne transport of its seeds. Both types are most common in the northern half of the North Island, and are a very substantial problem in parts of Northland.

MANUAL CONTROL

Seedling plants can be removed by hand, and isolated larger plants can be grubbed out, but in that case, the entire rhizome system must be carefully removed and taken off the site. Removed plants mustn't be dumped carelessly, because they will readily grow where they have been dumped. Removed material must be bagged and transported to a proper waste disposal site or transfer station. Alternately it can be bagged and sprayed with a herbicide, then retained in the bag until totally dead and dessicated.

HERBICIDES TO CONTROL KAHILI GINGER AND YELLOW WILD GINGER

There are two chemical control methods; spraying and stump swabbing.

Spray Herbicides to Kill Wild Ginger (Kahili Ginger and Yellow Ginger

Wild ginger plants are best sprayed in the spring before the flowers have set, but the plant is susceptible right through until late autumn. Spray coverage should be as thorough as possible, with all foliage sprayed to just short of the point of runoff.  In many sites where native plants are adjacent, this may mean that a protective shroud will have to be fashioned and used to avoid overspray damage.

Cut Stump Herbicide Treatment to Kill Wild Ginger

This method is suitable for larger plants, especially in locations where spraying is impractical or too risky for adjacent valuable plants.

  • MSF600 – 3-5g/L water brushed, swabbed or squeezed/droppered onto the freshly cut stump of the plant. Cut as close to the ground as practicable and horizontal, to try to retain as much of the herbicide solution on the cut area as possible.  The remains of the plant should then not be removed from the soil until it has totally died (a minimum of several months after treatment).
  • Cut'n'Paste MetGel applied as a paste on the freshly cut stems is a simple and effective control

The metsulfuron methyl herbicide-based weedkillers like MSF600 and Cut'n'Paste MetGel have a reasonably long kill time.