Wild ginger: kahili and yellow

Why they are pest plants

Identifying features – kahili

Flower

• Large scented flower head (25-45cm long).
• Lemon-yellow flowers with red stamens.
• Flowers from January to March.

Fruit/seed

• Up to 100 red seeds produced per flower head.

Leaf

• Large waxy leaves, arranged alternately on stem.

Identifying features – yellow

Flower

• Smaller cone-like flower head.
• Smaller creamy yellow-white flowers.
• Flowers from May to June.

Fruit/seed

• Leaves are narrower and more upright.

Leaf

• Taller than kahili ginger – stems up to 3m high.

Wild ginger forms dense clumps in native forests, smothering young plants and preventing native seedlings from growing. This makes it a serious threat to native ecosystems. If left unchecked, wild ginger could permanently replace rare plants. Dense clumps of wild ginger in areas where kiwi are present will prevent them from foraging on the forest floor.

There are two types of wild ginger in New Zealand – kahili ginger (a native of India and Nepal) and yellow ginger (a native of India and Madagascar). In New Zealand only kahili ginger will set seed. The seeds are spread by birds. However, both spread vigorously from large, fleshy underground stems called ‘rhizomes’. Many new infestations come from garden waste dumped in the countryside.

Wild ginger is now scattered throughout the Waikato region and is classed as a ‘progressive containment pest’, requiring the removal of all plants (total control). The largest infestations within the Waikato occur on the Coromandel Peninsula and on the west coast between Raglan and Mokau.

Responsibility for control

All landowners/occupiers in the Waikato are responsible for controlling wild ginger on their properties. Wild ginger is also banned from being sold, propagated, distributed or included in commercial displays.

How to control wild ginger

Physical control

• Small seedlings can be hand pulled and disposed of carefully.
• Small clumps can be dug out, as long as all of the root system is removed and disposed of safely. Rhizomes can be placed in a black plastic bag and rotted, or placed in a weak herbicide mix, crushed, dried then burned. Larger clumps should be sprayed.
• When removing kahili ginger, remove flower heads as a stopgap before spraying or removing the whole plant. This won’t kill the plant but will stop it from seeding that year. Burn the seed heads.

Herbicide control

Cut stump treatment

• To treat larger plants, slash stems horizontally near the roots. Immediately apply the herbicide to the stems and roots with a paintbrush or small squeeze bottle. Leave the plants in the ground until the roots have dried off.
• If using the herbicide picloram gel and the plant has more than four rhizomes per shoot, also drill a 10mm hole into every fourth rhizome (from a shoot to 80 per cent the depth of the rhizome). Fill the hole with picloram gel.

Spray application

• Totally cover the foliage and roots until they are wet but not dripping. Be careful not to spray desirable plants. Do not remove the leaves or stems until they have gone brown and dried out (three or four months). Best results are achieved from spring to late autumn.
• Alternatively, cut and remove all stems and leaves and rake away ground litter to expose the rhizomes, spray them, and then cover with leaves. The plant may take 12 to 15 months to fully die and rot. This method is particularly suitable for densely covered steep banks where removal of the ginger could cause problems.

Safety when using herbicides

• Follow the instructions on the manufacturer’s label.
• Always wear protective clothing.
• Always minimise the risk to your other plants.
• Contact the supplier for further advice.

Summary of herbicides and application methods for control

Management

After initial control, it’s important to:

• clean out the site again at least annually to control regrowth
• stop weeds invading by replanting with non-pest plants (preferably native plants) once regrowth is no longer a problem.

More information

Advice

• For advice and additional information on control methods, call our pest plant staff on freephone 0800 BIOSEC (0800 246 732).
• Chemical company representatives, farm supply stores and garden centres can also be good sources for advice.

Publications

View, download or order the following publications or call our freephone 0800 800 401.

• National Pest Plant Accord (Manual of plants banned from sale, propagation and distribution) ($10.00 plus GST)
• Plant Me Instead! (Plants to use in place of common pest plants) (free)
• Waikato Regional Pest Management Plan (RPMP) (free) (Section 5.3, page 46)
• Waikato Regional Council pest guide (free)

Web

• www.weedbusters.org.nz
  
• www.waikatoregion.govt.nz/regional-pest-management-plan/

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