Wild ginger: kahili and yellow

Both species of wild ginger (kahili and yellow ginger) present in New Zealand can grow to over 2 metres tall and produce deep beds of branching fleshing underground stems (called rhizomes). They form dense stands on the edges and through the understorey of forests, along the margins of water ways, on roadsides and in fernlands and shrublands. They can smother and replace all understorey species and seedlings. The rhizomes though dense are shallow rooted, so can be displaced on steep slopes after heavy rain, causing erosion.

In New Zealand only kahili ginger can set seeds. Kahili ginger seeds are spread by birds, with both species of ginger able to be spread and establish from pieces of their rhizomes. Many new infestations come from garden waste dumped in the countryside.

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

Herbicides rule will apply. You may need to notify neighbours if spraying. The Waikato Regional Plan explains the agrichemical (herbicides) use rule in section 6.2.

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.