Botanical name:
Gorse - Ulex europaeus
Broom - Cytisus scoparius, C. multiflorus, Teline monspessulana

Background

Gorse and broom first arrived in New Zealand in the early 1800s. Seed was brought in by English settlers to grow plants for hedging. A lack of natural control agents in New Zealand in combination with high seed production, unpalatability to stock, and invasive, colonising growth habitats have allowed gorse and broom to become the widespread problems they are today.

Plant pest status

Gorse and broom are containment control plants in Canterbury’s Regional Pest Management Strategy. The objective for gorse and broom, over the duration of the strategy, is to prevent infestation of land that is presently free of gorse and broom.

To achieve this, land occupiers need to:

• Protect neighbouring land. A 10-metre boundary clearance is required if neighbouring land is clear of or being cleared of gorse and broom, in order to stop seed spread.
• Keep “clear” land free of gorse and broom. Isolated plants have to be eradicated quickly as plants left to seed will develop into large infestations.
• Contain large infestations. Any isolated and scattered plants on the perimeters of large infestations should be controlled to prevent further spread. There is no requirement to eradicate infestations greater than 50 square metres unless they are on a boundary.

Control

Firstly establish the plant(s) are not a New Zealand native broom species.

Chemical control

Foliar spray: An all year round method depending on chemical used and weather conditions.  The optimum spray time is from spring to summer when plants are in leaf and actively growing.  Foliar spraying is a useful technique for large infestations and scattered plants. NOTE: Plants need to be covered on all sides with spray for an effective kill.

Cutting and stump treating: An all year round method. Useful technique in ecologically sensitive sites (e.g., rocky outcrops). Cut the stump as close to the ground as possible and apply chemical to the fresh wound with an appropriate herbicide.  This method is effective and  reduces harm to desirable species.

Herbicide active ingredients registered to control  broom & gorse
 Picloram & Trichlopur  mix– A selective herbicide, it doesn’t kill grass but will kill broadleaf weeds.  Picloram has a residual control effect on legumes.  During periods of slow growth or when growth is dormant (e.g., winter spraying) or stressed, hot, dry, dusty, frosty or salty conditions or when plants have been slashed or grased, the addition of penetrant to spray mix is recommeded.
 Trichlopyr – A broad spectrum systemic herbicide. Does not damage grass.  Also controls broadleaf weeds in turf.  Best results are acheived when applied during periods of active growth. No residual control effect.
 Metsulfuron -  A non-hormone herbicide.  It can be used in winter but it takes longer for plants to turn off.  Has a residual control effect.  Can cause damage to some trees.
Glyphosate – A non-selective herbicide i.e., it will kill most plants that it comes in contact with. To work effectively broom & gorse plants need to be actively growing and not under drought stress with clean foliage (not dusty!) at time of spraying.  NOTE: For gorse - do not treat plants stressed by drought, grasing or previous herbicide treatment.  A surfactant MUST be added or poor results will occur! Rates are only recommended for handgun application in the Agrichemical manual. Glyphosate is inactivated on contact with the soil thus no residual weed control effect. 

• For choosing the best chemical for your location and situation contact your local chemical supplier or contractor.  Always follow the manufactures instructions when using chemicals and prevent spray from entering water ways and contacting the soil.  If spraying near waterways contact your local Regional Council to check if what you intend to do is permitted or will require a permit.

Mechanical control

Slashing/trimming: A useful method to prevent plants seeding along roadsides.  This method requires control at least once annually as the plants do not die but will re-sprout (all year round method).
Pulling/digging: Useful in ecologically sensitive sites with scattered small plants (all year round method). Ensure minimum soil disturbance as disturbance encourages seed germination. Leave plants on site to rot down. 
Cultivation/Grazing: Cultivation encourages seed germination and must be followed by either blanket spraying or intensive grazing. Over sowing with grass seed and applying fertilisers to improve grass growing conditions can also help to reduce broom seedling re-growth.

Biological control
• A good option for large block infestations that are not likely to be sprayed (over 50sqm in area) to reduce plant vigour.  Note biological controls assist in reducing plant vigour and rate of spread rather than killing and controlling a broom infestation.  Contact your Regional Council (Environment Canterbury) or Landcare Research for more information on broom biocontrol agents for your area.
 

Maintain a dense pasture sward to reduce competition from weeds like gorse and broom. Eradicate gorse and broom before seed is produced. Spot spraying, or cutting and immediate stump treatment is useful for isolated plants. Cut stumps must be treated (with herbicide) while the cut is still wet to allow the absorption of herbicide.

Larger infestations can be slashed. Burning encourages seed germination and must be followed by blanket spraying or heavy grazing. Sheep will only graze gorse at the soft seedling stage (about 6-8 weeks). Spraying of large infestations is successful but 100% coverage of each plant is essential.

Biological control for gorse and broom may be an option to assist in containing large infestations. Insects are available at specific times of year and agents work together to reduce plant vigour and seed production. (However biological control is unlikely to kill plants and so does not achieve compliance with the requirements of the Regional Pest Management Strategy.)

Follow-up control work will be necessary with all options.