Gorse

ADVICE: Describing gorse to a Kiwi farmer is like describing a jockstrap to an All Black; hardly necessary. It's an uncomfortable fact of life and you already know what it looks like. But for the sake of form, gorse is a woody, deep-rooted perennial brushweed that can grow to four metres high in dense, impenetrable stands. Its small green leaves are hard spines, and in autumn and spring it produces the masses of bright yellow flowers so beloved of tourists. And of course to the Scots, who in a moment of brain fade brought the things into New Zealand in the first place. Alas, gorse also produces about 8000 seeds per bush per year. And these seeds can survive in the soil for at least 30 years.

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So it's hardly surprising that controlling and ultimately eradicating gorse is a long-term proposition, involving a combination of several management practices.

MANUAL AND MECHANICAL REMOVAL

If stands of gorse are not too dense and mature, ploughing or rotary slashing can be an effective approach. Any of you that have hacked away at gorse will understand what a soulless task this can be.

After ploughing, seedlings and regrowth will require follow-up spraying with herbicide (see below). Slashing will need to be repeated, probably several times, interspersed with hard grazing by sheep, as well as some follow-up spraying as necessary. Cutting smaller gorse with a scrub cutter or chainsaw and treating the stumps with herbicide, although labour intensive, is very cost-effective for isolated plants or small stands. Large individual gorse bushes can be successfully cut off just above ground level, and the stumps swabbed with herbicide. BURNING

Gorse burns well and if conditions (and regulations) allow, burning can be a cost-effective option. But seeds are not killed by the fire, and even the burnt stumps will regrow, so follow-up spraying with herbicide is inevitable. Most authorities advise spraying with herbicide some months before burning, because the dying bushes will burn better.

GOATS

Goats can contain or even eliminate gorse given time, but the property needs to be suitably fenced and carefully managed over several years. Up to 20 goats per hectare are required to make good progress. We recommend giving the poor beggars a break from a gorse-only diet periodically.

BIOLOGICAL AGENTS

There is a widely-occurring gorse seed weevil that has some impact during the summer months, but is ineffective against seeds produced outside that season. Other biological agents are being developed and tested and may prove beneficial in the future. Of course, they said that about the rabbit. And the possum. And the cane toad.

HERBICIDE CONTROL

Stump treatment

· Glyphosate at 200ml/L water. Effective year-round, grass-friendly.

· Picloram + Triclopyr (eg GrassMate, Tordon Brushkiller, Conquest, Synergy Brushkiller, Eliminate Brushkiller).

· Triclopyr (eg Triclo, Grazon, Brushoff, Eliminate, Scrubcutter) at 50ml/L water. Warmer months only, grass-friendly.

· Metsulfuron-methyl 600g/kg (eg MSF600, Escort, Eradicate, Mustang, Synergy MET600, Apache, Associate) at 5g/L water. Effective year-round, most cost-effective.

In all cases, add organosilicone wetting agent at 10ml/L water to aid penetration. Plants should be cut as low to the ground as possible and treated soon after cutting. Use a paintbrush on large stumps to totally cover the top and sides of the stump down to ground level. A spray bottle or knapsack sprayer can also be used.

Spraying

The best option for dense and inaccessible stands. While gorse can be successfully sprayed year-round, the best time is during the flush of "soft" growth that occurs a few weeks after flowering. The time when this occurs varies in different parts of the country, and even then varies a bit from year to year. It generally coincides with late spring, summer and early autumn.

· Metsulfuron-methyl 600g/kg (eg MSF600, Escort, Eradicate, Mustang, Synergy MET600, Apache, Associate) at 500g/ha by air, in 400L water plus 2L organosilicone wetting agent.

· Metsulfuron-methyl 600g/kg at 30g/100L by handgun (knapsack 5g/10L).

· Picloram + Triclopyr (eg GrassMate, Tordon Brushkiller, Conquest, Synergy Brushkiller, Eliminate Brushkiller) at 6ml/L water for hand spraying, or 10L/ha by air.

· Triclopyr (eg Triclo, Grazon, Brushoff, Eliminate, Scrubcutter)at 6ml/L water for hand spraying, or 10L/ha by air. Warmer months only.

· Glyphosate at 1L/100L plus organosilicone at 100ml/100L water.

· Note: All the above require organosilicone wetting agent at the rate of 100ml/100l water if no specific rate is mentioned.

Notes:

1. Picloram + Triclopyr is grass-friendly. Triclopyr is both grass and clover-friendly. MSF600 and Glyphosate are not grass-friendly.

2. MSF600 is the slowest acting (takes several months) but the lowest cost. It's also the most popular.

Brand names mentioned in this article are trademarks of various well-known New Zealand companies, and are given here for reference only. Before these products are used check suitability with the manufacturer and read the label.

- Paul Martin recently retired after more than 25 years in the farm service sector, involving directorships in dairy hygiene, milk quality and weed control businesses. Now he mutters into his daily glass of cabernet sauvignon and writes this column in order to avoid having to attempt the crossword.

- Shayne McNamara has been involved in the farm service sector for the last five years and has been involved in the chemical and agchemical importing industry for more than 20 years.