What is it?
Japanese honeysuckle (Lonicera japonica) is a climbing vine from Asia that has a lovely fragrance and pretty flowers - but which can pose a significant threat to our forests when it spreads into the wrong place.
It is a vigorous evergreen shrub that will typically be seen winding its way up host plants or forming dense clumps along the roadside or on forest margins. Japanese honeysuckle is easily recognised by its tubular and sweetly-scented flowers, ageing from cream to yellow-cream from September through to May. Glossy black berries, from 5-7mm long, are also noticeable from October to June.
Why is it a problem?
Japanese honeysuckle has the ability to climb over and smother most plants in its path, from ground level to mid-canopy forest species. It can even cause the collapse of the forest canopy if it is allowed to get away.
It is often spread when pieces of stem are dumped with garden rubbish. In addition, its seeds are easily spread by birds and, possibly, by possums and the vine is hard to kill using existing herbicides.
Methods of Control
Manual control: Small sites can be cleared at any time of the year by removing the stems and digging out the roots. Because Japanese honeysuckle is a light seeder, sites usually remain clear after treatment so long as all living material has been removed.
Chemical control: A variety of chemical controls can be used against Japanese honeysuckle, including Vigilant, Grazon, Escort, and glyphosate-based herbicides.
The best method of control is the cut stump method. Cut vines to ground level at any time of the year, and then apply herbicide to the cut stump at the rate recommended by the manufacturer. Under the Biosecurity Act 1993, it is illegal to sell, propagate or distribute Japanese honeysuckle. Care should be taken to cut the vine horizontally, so that the herbicide will stay on the cut area and be absorbed. Herbicide uptake will begin to decrease as soon as 30 seconds after cutting, so apply immediately to ensure this method is effective. There are several convenient ways the application can be made, with a paintbrush, eyedropper or a small squeeze bottle. The cut vines should be removed from surrounding vegetation and disposed of carefully.
Spraying is also possible, using either glyphosate-based herbicides, such as Roundup and Touchdown, or Grazon or Escort at the rates recommended by the manufacturers. However, this method requires the use of more herbicide and is liable to affect non-target species as well. Take care to spray only in still conditions to avoid wind drift to non-target plants, and don't spray when rain is expected.
During spraying, non-target plants can be shielded with cardboard, plastic sheets or a large plastic container. The use of a marker dye helps to avoid double spraying and wastage, and a foaming agent can be added to the spray to help prevent spray drift. As with all spraying, you should read the instructions on the manufacturer's label closely and always wear protective clothing.
Japanese honeysuckle is hard to kill so, whichever method is used, it will be necessary to revisit the site to ensure there is no resprouting from stumps or that remaining stems have not layered into the soil.
Disposal: Japanese honeysuckle needs careful disposal. Any vines that have been removed should be burnt, or placed in a sealed black plastic bag and left to rot in the sun.
Contact any Department of Conservation office for further information on the identification and control of invasive weed species.
A useful reference book is "Native Forest Restoration: A Practical Guide for Landowners" by Tim Porteous (Queen Elizabeth II National Trust, 1993).
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