Gorse (Ulex europaeus) is a spine bearing, nitrogen fixing bush. Originally from southern Europe, gorse is now easily New Zealand’s most widespread and problematic weed.

One of the key factors in the  successful introduction of gorse is the plant’s ability to tolerate a wide range of climatic and soil conditions. In addition, an average gorse bush will produce 8000 seeds per year, many of which will survive for well over 30 years in the soil!

Controlling gorse requires a stringent management plan and will only be successful in the long term with a combination of several farm management practices. Herbicides are the preferred tool for the initial control of gorse. To reduce variability when using herbicides, it is important to understand the seasonal growth pattern of gorse in your area and which herbicide is the most appropriate for your conditions.

In most regions, gorse will flower continually for many months but peak flowering occurs in spring each year, with pod development and ‘soft’ growth occurring a few weeks later. Gorse is most easily and effectively controlled with herbicides when soft growth is present. Regional and climatic variations dictate how much ‘soft’ growth develops and how long this growth remains ‘soft’. Gorse usually starts to ‘harden off’ after February.

Herbicides like  Grazon and Tordon Brushkiller are generally the preferred herbicides in pastoral situations as they are not damaging to grasses, although clovers will be temporarily removed from the sward. Removal of grass during spraying only increases the opportunity for both gorse and broadleaf weed seedlings to establish, further reducing pasture quality.

There are not many options organically for Gorse control as burning seems to stimulate the seed into germinating. One option is to slash the Gorse down and, mulch heavily, replant with natives that will eventually choke out the Gorse.

Water rates are very important when using herbicides on gorse. Large gorse needs a higher volume of spray mix, as these bushes have large surface areas to treat. It is not recommended to burn treated gorse, as this damages pasture and encourages dormant gorse seeds to germinate.

Follow up treatments will almost certainly be required

after burning.

When trying to control gorse on your property, it is very important to budget for and to plan your strategy. Scattered bushes should be controlled as soon as possible, as smaller bushes require less spray and gorse spreads very quickly.

Some new seedling growth and some follow-up must be expected, and plans should include treatment of this 12-18 months after the first treatment. It is more effective to treat a smaller area, and ensure you can meet the follow up costs, than do larger areas and not follow-up.

It is just as important to increase soil fertility and maybe even reseed after spraying.  Large blocks should be fenced so grazing can be controlled. This will encourage a dense, competitive, higher quality pasture sward, which will in turn decrease establishment of noxious weeds. On steep or water logged country, grazing management should ensure that pugging is kept to a minimum. Pasture, which is “opened up” i.e. pugged, by stock during grazing is more likely to encourage establishment of weed seedlings.

Do you know of a successful organic method of fighting gorse? Why not drop us a line to viring@bmp.co.nz and we can share it with readers in the next issue.