If you own pasture in New Zealand chances are that a grey-green shrub with painful spines and bright yellow flowers is eating into your bank account. It’s presence damages the returns from a given piece of land by reducing grazeable acreage, and getting rid of it burns up valuable time and labour.
Description and History
Gorse (Ulex europaeus) was originally imported into New Zealand from Europe as a hedge plant. Unfortunately, a favourable climate has led to widespread colonisation and the plant is now a major pest. Gorse is a woody perennial that grows up to 4 metres tall and, if left unchecked, will form thickets. New (or “soft”) growth on the plant hardens into spines, a characteristic which makes the plant both impenetrable and unpalatable to livestock. Between May and November Gorse displays its signature bright yellow flower. New growth and seed pod development occur in late spring. Hardening of new growth generally begins in early autumn.
Gorse thrives in a wide variety of conditions. An average plant will produce about 8,000 seeds each year and each of these seeds can lie dormant in the ground for up to 30 years.
A number of factors contribute to gorse infestation:
- Gorse readily takes hold where native vegetation has been cleared or other land disturbance has taken place.
- Fire encourages gorse seeds to germinate.
- Pugging (the churning up of ground by livestock, particularly in wetter or over-grazed areas) encourages gorse colonization.
Given its virulent nature and the fact that its seeds survive for such long periods of time, gorse is difficult to get rid of entirely. Effective eradication will usually involve a combination of manual removal, herbicide application and pasture management.
Manual removal of gorse is a labour-intensive process involving the physical uprooting or destruction of the plant. Hand-pulling works well for small stands of new plants. Large infestations, though, will require digging, cutting or mechanized removal. Larger plants can be stumped and then coated with a herbicide gel. Burning is not recommended as it damages surrounding pasture and encourages gorse seed germination.
The application of a herbicide spray is an effective method of gorse control that requires less labour than manual removal. Herbicide application should be carried out immediately after spring flowering. At this point new growth is at a maximum and the plant is most vulnerable to the action of the herbicide. When spraying, it is essential to penetrate to the inner, older areas of the plant. A wetting agent should be used in conjunction with the herbicide to facilitate this. The type of herbicide used should have as little impact on surrounding grasses as possible as the destruction of grasses will create an environment where new outbreaks of gorse can take hold.
Ensuring that grass and native plant cover are not excessively reduced will leave fewer opportunities for gorse to establish itself. Avoid over-grazing, pugging, bad drainage and low levels of soil fertility.
An Ongoing Battle
The favourable conditions in many parts of New Zealand and the hardy nature of the gorse plant mean that for many farmers getting rid of gorse is an ongoing battle. However, by using an appropriate herbicide, good pasture management techniques and a planned eradication strategy the problem can be managed effectively and the yearly appearance of those bright yellow flowers kept to a minimum.