Gorse

Scientific name: Ulex europaeus

Gorse flowers

Gorse plant

Gorse infestation
  • Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • Large, very prickly woody perennial shrub growing up to 2 – 4 m high that invades pasture easily, especially in lower-producing grassland
  • Bright yellow, pea-like flowers in autumn, winter and early spring (May – November)
  • True leaves are present on seedlings, changing to sharp rigid spines on mature plants
  • Roots are deep, branched and woody
  • Seed heads are 25 mm long black pods which split explosively to disperse seeds
  • Grows on hill and extensively farmed country, in river-beds, forest clearings and edges, waste-land, pasture and scrubland.

Origin

  • Originated in Europe and introduced to New Zealand for making stock-resistant ‘living fences’ for paddock boundaries on farms
  • In the 1800s government officials encouraged planting gorse hedgerows for the improvement of the country as these provided cheap fencing as well as valuable shelter in areas prone to snow and cold winds. Seeds were available from many stockists.

Lifecycle

  • Seedlings have broad, soft leaves but later form narrow, deeply furrowed, rigid spines 15 – 30 mm long. These main spines can also have short lateral spines
  • Gorse grows from spring through to summer and then growth slows down. Earliest shoots are soft and can be readily grazed, especially by goats but also by other livestock. Shoots produced in the growing season turn brown during the following season, leaving a large quantity of brown, dry and inflammable material in the centre of the bush
  • Stems are branched and furrowed, with many stiff spines. Branches can be erect or spreading
  • Gorse plants flower in their second to third year, with most flowering occurring during spring  However, flowers can appear in autumn, winter and early spring
  • Flowers are pea-like and bright yellow, 15 – 20 mm long and are pollinated by insects
  • Seed set occurs about two months after flowering. Gorse produces black seed pods up to 25 mm long, covered with soft grey hairs. The pods explode and disperse the smooth, round shiny seeds which are 2 – 3 mm in diameter. Many of the seeds are ‘hard’ and there is a low germination rate
  • Gorse can produce between 500 to 36,000 seeds per m2 per year which may remain viable in the soil for more than 30 years. Seeds can be spread to some extent by wind or water, and some are spread in the fleeces of sheep.

Benefits

  • Can act as a nurse crop for the regeneration of native bush
  • Livestock (especially goats) will eat gorse when it is young
  • Gorse fixes nitrogen, which can change the nutrient status of the soil for better (for improved grasses and clovers) or worse (many native species prefer low nitrogen levels in the soil).

Occurrence

  • Gorse has been estimated to occupy over 500,000 hectares of agricultural land in New Zealand
  • In 1984 gorse was estimated to cause production losses of approximately $22 million each year
  • The control cost was then estimated to be $27 million a year to the forestry and farming industries (Monsanto, 1984)

Impact on pasture and forestry

  • Forms dense stands that exclude stock and replace pasture
  • Gorse can compete with young trees in plantation forests and reduce their growth significantly
  • In older plantations, gorse competes with trees for water, light and nutrients, reducing the yield of harvestable timber. Gorse also makes it difficult to access the trees for pruning and thinning
  • Gorse plants and surrounding areas are avoided by stock so pasture available for grazing is reduced
  • Gorse is a fire risk, as much of the older foliage is dry, burning very easily and fiercely.

Grazing management
  • Intense rotational grazing with sheep and goats can help reduce gorse seedling survival and establishment
  • A combination of pasture competition, trampling and grazing will reduce seedling numbers.

Pasture species/cultivars and fertiliser application

  • A dense, vigorous pasture will help to prevent re-infestation
  • Spreading fertiliser over locally appropriate grasses and clovers, can help a pasture outcompete gorse seedlings establishing after burning.

Chemical control

  • Chemical control of gorse became possible in the 1950s, with 2,4,5-T based products that have now been replaced by less controversial products
  • Chemical control can be applied in combination with cutting.

ALWAYS READ PRODUCT LABELS BEFORE APPLYING

Active ingredient When to apply Residual effect Grass damage Clover damage
triclopyr 600 EC Summer and Autumn Yes No Severe
metsulfuron-methyl All year – best when actively growing Yes Moderate Severe
triclopyr/ picloram During active growth – Spring and Summer Yes No Very severe
glyphosate* All year No Severe Severe but temporary

*        Must be used in conjunction with an appropriate spreader/sticker. See the label for               details.

Consult your farm consultant, industry rep or the New Zealand Agrichemical Manual for more information about chemical control.

Cutting

  • Gorse can be slashed and dragged out with chains by bulldozers or tractors. This can be done in combination with herbicides
  • Cutting is sometimes very difficult as gorse can grow on inaccessible hillsides and valleys.

Biological control

  • Many biological control agents for gorse are present in New Zealand
  • While they are all damage gorse and suppress its growth, elimination of the weed on a large scale has not yet been achieved.
Gorse spider mite (Tetranychus lintearius)
  • Has established well in some locations, but predatory insects can reduce its impact
Gorse seed weevil (Apion ulicis)
  • Has become established in most parts of New Zealand, and reduces seed production, but not so much as to affect gorse populations.
Gorse colonial hard shoot moth (Pempelia genistella)
  • Caterpillars feed on the spines, leaves, buds, shoots and flowers causing death to the leaves and stems of affected areas.
Gorse pod moth (Cydia ulicetana)
  • Well established throughout New Zealand
  • Caterpillars destroy seeds, with each one eating the contents of 3 – 5 pods.
Gorse soft shoot moth (Agonopterix ulicetella)
  • Has established at a few sites in both islands
  • Caterpillars damage the new buds and soft branch tips during spring. Each caterpillar can destroy up to five shoots.
Gorse thrips (Sericothrips staphylinus)
  • Established in New Zealand in several sites and are slowly spreading
  • Gorse thrips feed on new growth, as well as older, woody stems during winter
  • They can reduce the growth and flowering of gorse and may kill gorse seedlings.
Gorse stem miner (Anisoplaca ptyoptera), lemon tree borer (Oemona hirta)
  • The gorse stem miner is present throughout the South Island while the lemon tree borer is more prevalent in the northern regions of both South and North Islands
  • The larvae of both species can sometimes ring bark stems and cause dieback of the stem due to water stress in dry periods. This may damage several shoots or even the whole plant if the ring barking occurs close to the ground.

Burning

  • Burning a stand of gorse usually results in a rapid and prolific establishment of gorse seedlings, because heat stimulates the germination of many of the seeds lying dormant in the soil
  • Although burning kills seeds near the soil surface, more deeply buried ones are not affected
  • Slashing gorse in spring, then burning in autumn was advocated from the early 20th century onwards
  • A good hot fire helps kill more seeds but it is important to sow good quality pasture seed into the ash once it has cooled and make sure appropriate lime and fertilisers are applied
  • Follow up with hard intermittent grazing once the new grass is well established, and be prepared to use herbicides to kill any gorse seedlings that survive.