Gorse (Ulex europaeus) first arrived in New Zealand in the early 1800s. Seed was brought in by English settlers to grow plants for hedging. Gorse is a pioneer plant which provides an important ecosystem service. A member of the pea family, it fixes nitrogen and its prickly, bushy growth habit provides habitat for birds and animals whilst its dense root structure helps combat erosion. To maintain a healthy, effective Gorse hedge, which provides shelter for Stock and crops, managing gorse is a priority.  Regular Maintenance cutting / trimming promotes healthy growth and makes the hedge denser. Gorse Hedges provide good wind shelter for stock and crops.

Gorse is particularly good on poor soils (even sandy soils or rocks) as long as it’s well drained and it has nitrogen fixing capacity so it can improve the soil for the benefit of other plants.

Gorse is not a fast grower (15-30cm pa) but will grow to 2.5m and is particularly recommended for intruder-proof hedging because its spines are so vicious. It’s also very good for windy, exposed, coastal sites and historically was used as a windbreak which could be cut to provide animal feed. Its dense prickly nature provides good wildlife shelter. Whilst Gorse hedges will tolerate alkaline soils, it’s particularly good on acid soils.

The attempt to control gorse biologically in New Zealand was one of the earliest undertaken worldwide. The value of gorse as an inexpensive live fence and shelter plant was taken into account, and the initial search for control species in Europe was restricted to insects that damage gorse’s reproductive capacity. The gorse seed weevil was imported from England in 1928, and widely released between 1931 and 1947. Before long, studies showed that the proportion of spring seedpods infested with the weevil was more than 90% – similar to the levels observed in England – intimating that successful control could be expected. However, in response to the New Zealand climate, gorse has adapted to form seeds in both spring and autumn. The newly imported gorse weevil was only active in spring, leaving the autumn seeds untouched. Various studies have concluded that, as a result, the reduction of the annual seed crop by the weevil is only about 35%.

Following the Second World War New Zealand entered a period of enthusiastic land development, with the aim of increasing exports. The campaign against gorse intensified and heavier weaponry was employed, particularly in North Island hill country. During the previous two decades the area of land overrun by gorse, blackberry, wild briar and ragwort had been increasing at the rate of 40,000 acres annually. By 1947 weeds covered almost 20% of total occupied land.

Fire, grazing, and the use of phenoxy herbicides such as 2, 4, 5-T were considered the best solutions. While carefully managed burn-offs can result in near-total destruction of an infestation, more often than not a thick cover of gorse seedlings appears soon after burning, as fire helps to break the dormancy of the seeds and provides nutrients for growth. Often the cost of clearance was prohibitive, especially on marginal land or extreme terrain. Control activities also had to be carefully correlated to plant life-cycles.

The failure of ‘classical’ control methods led to a review in the 1960s of the role of biological agents in European gorse control. However, it was not until the early 1980s, with the termination of most farm subsidies (including those for land development and weed control) that the introduction of further biological control organisms was reconsidered. Insects were seen as a low-cost alternative to poison, lessening the economic impact on landowners.

Amid divergent public opinion, the program of introduction stalled in 1982. While the use of gorse hedges and recognition of the value of the plant in the broader agricultural community had been rapidly declining since the 1950s, gorse was not without its supporters. To beekeepers, gorse provides a valuable source of pollen, especially in early spring when few other natural pollen sources are available for feeding larval bees. The country’s burgeoning goat farming industry also saw gorse as a valuable forage plant.

A more complex endorsement came from advocates for native forests. While generally supportive of campaigns against aggressive invasive species, many conservationists feared that the indiscriminate nature of biological control would undercut the role gorse plays as a nurse-plant in the restoration of native vegetation on abandoned agricultural land.

The very nature of gorse as a pioneering, fast-growing, short-lived shrub means that it can only survive where the land is constantly open and disturbed. Undisturbed, gorse grows vigorously for the first few years, but then slows to a relative standstill. Because it needs full light to germinate, gorse cannot regenerate significantly under its own shade. More shade-tolerant native species such as mahoe (whiteywood), fuchsia, wineberry, lemonwood and five-finger, together with taller trees such as totara, matai, kahikatea or beech, grow up through the ageing gorse canopy, overtop it, shade, and kill it. The irony here, as Hugh Wilson has noted, is that a deliberate policy of disturbing gorse as little as possible will rapidly lead to its demise.

Importantly the greatest threats to this process are the classic gorse ‘management’ practices of burning and grazing. As Wilson concludes, natural succession provides another option for gorse management besides the knee-jerk reaction of spraying.

Perhaps ironically, the eradication of gorse has made the remaining stands more precious to some people. As geographer Larry W. Price noted in a 1993 field study, in Canterbury gorse hedges “give the area much of its distinctive character”. As a consequence of the wholesale removal of hedges on the Canterbury plains between 1962 and 1989, gorse hedges are now viewed as features of historical significance. Some landscape architects even recommend their retention. “The irony of the situation,” Price remarks, “is that those who want to keep their hedges now face an even greater maintenance burden since they must spray to protect against the introduced spider mite.

The variety of attitudes held towards gorse has affected the direction of research into its elimination. Approval to introduce biological controls was finally given in 1989. DSIR (now AgResearch Limited) imported the gorse pod moth, which is now established in the North and South islands. In Canterbury, observation suggests that the gorse pod moth and gorse weevil are jointly destroying between 90-100% of spring/summer seed crop, and the gorse pod moth is destroying about 15-20% of the autumn/winter crop.

In addition to this, between 1989 and 2001 five foliage feeding control agents were introduced; the gorse spider mite, gorse thrips, gorse soft and hard shoot moths, and the gorse colonial hard shoot moth. Foliage feeders suppress growth by damaging the gorse plant, lowering its ability to photosynthesise, flower and produce seeds.

Finally, the concept of biological control of gorse using fungi was raised in 1995, with several species identified as potential mycoherbicides. One of these – Fusarium tumidum, a naturally occurring gorse pathogen – was selected for development. There are currently no plans to introduce further biological control agents for gorse until the status and likely impact of the seven already established species is clarified. In reality, the success of biological control schemes is notoriously unpredictable – the most common outcome of such programmes is only partial control.