How to sweep away broom
It’s no secret that plant pests are fast-growing and very persistent, and broom is one of the worst. Give these tips a go to combat this pesky plant.
Words: Nadene Hall
Broom (Cytisus scoparius) is one of the worst plant pests in New Zealand, rating right up there with gorse and thistles, and it’s likely to become the number one weed in years to come. While gorse can act as a nursery crop to other trees and be eventually shaded out, nothing grows through broom.
Until recently, the best bet for beating broom was herbicides but it’s expensive and must be repeated every 18 months. It is also possible to manually remove it by grubbing or pulling it out in small infestations, or to use a tractor-mounted slashed to chop it down, allowing for pasture to sown over the top.
But over the past few years some natural invaders have taken big bites out of the broom problem. The broom gall mite – which only feeds on broom – was released in some areas 10 years ago and while it has taken time to become established, biosecurity experts are now seeing its obvious effects, particularly in broom-infested areas of North Canterbury, Kaikoura and Marlborough.
Talk to your regional council about biological control options for broom, or other weeds.
HOW TO CONTROL SMALL AREAS OF BROOM
Professor Nick Ledgard of forestry research company Ensis is an expert in the spread and natural regeneration of wilding woody plants like broom and gorse.
“Broom is very competitive. The seed bank in the soil can last for a long time. Controlling it depends on what you want to replace it with. You can develop it into pasture, but then you’ll need to put on fertiliser, pasture seed and follow that up with grazing. Make it attractive to animals.”
With a pasture base above it, young broom plants will find it harder to get through the sward and when it does, it can easily be picked off by cattle, sheep or goats as compared to old plants that are not as palatable. If they dominate an area, animals are unlikely to want to graze it.
“If she does that it should work, but if she reworks that soil in 20 years time, it (broom) will still come back, even then.”
You could help the process by hand-pulling or hand-grubbing young plants that do emerge through the grass (spring to early summer is the best time to do this).
Professor Ledgard says the only real way to replace a vigorous species like broom is to out-compete it but it’s very hard to do without creating a major soil disturbance.
“You could also replace it with an over-storey such as radiata pine. That certainly works if the radiata can get away, and can shade it out. Even douglas fir is not fast enough.”
If you do choose to plant radiata pine, Professor Ledgard says you will still need to beat the broom back from over-whelming the trees until they are about 2m tall.