The spring plan for blackberry and gorse, and why the order matters

Early October, and the rough corners of a block are doing what they do every spring. The blackberry down the gully is throwing new green cane over last year's dead wood, the gorse along the boundary is thickening up, and the patch behind the shed that looked manageable in July is quietly closing over again.

Here is the timing that catches people out. The best window for actually killing blackberry is summer, roughly January to March, when it is in full leaf and growing hard. But what you do about it now, in spring, decides whether that summer window is worth anything at all. Get the order wrong and you spend money in January on a job that was never going to work.

Why you cannot just spray a thicket

Woody weeds are not boom sprayed like a paddock of capeweed. They are spot sprayed with a handgun off a hose reel, and the method is to wet the bush thoroughly, right through to the point of run-off. That works beautifully on a bush you can walk around: you get chemical onto every leaf, the plant takes it down into the crown, and that is the end of it.

It does not work on a thicket. Once blackberry has been left for a few seasons it is chest high and metres deep, a tangle of live cane over dead cane with the crowns buried somewhere in the middle. You can wet the outside of that. You cannot reach the centre. The outer canes brown off, the owner thinks the job is done, and by the following spring it has come back from the crowns that never saw a drop. You also cannot see what you are walking into: old wire, rabbit burrows, fallen timber and whatever else the thicket has grown over.

Mulching does not kill blackberry. What it does is make the blackberry sprayable.

Knock it down, then follow it up

The sequence that works on a real infestation has two parts, and both of them are the job.

First the knock-down. A forestry mulcher head on a skid steer, positrack or excavator shreds the canes and woody stems in one pass and grinds the crowns at or just below ground level, with very little soil disturbance. What you are left with is ground you can see and walk on, covered in a thin layer of chipped woody mulch.

Then the follow-up. The plant is not dead, and it will shoot again from the crowns and the roots. After roughly six to eight weeks that regrowth is about 40 centimetres high: soft, leafy, actively growing and completely accessible. That is the spray target, treated with a registered herbicide at label rates. Anyone quoting a mulch pass on its own is quoting you half a job, and the half that does not hold.

The spring arithmetic

Now put those two parts on the calendar and the reason for a spring plan becomes obvious.

• Mulch the thicket in October or November, and the regrowth comes up ready to spray around December into January, landing squarely inside the summer window while the plant is still growing hard and pulling chemical down into its roots.
• Leave the mulch pass until February, and the regrowth turns up as the season slows and the plant shuts down. You have paid for the knock-down and missed the kill, and you get to do the spraying part again next year.

That is the whole argument for looking at your rough corners this month rather than in the heat. The work is sequenced backwards from the summer spray window, so the first move happens well before it.

Scattered bushes are a different job

Not every blackberry problem needs a machine. Where it is a dozen isolated bushes along a fence line, or gorse coming up near the shed, the answer is cut and paint. The stem is cut low with a chainsaw or brushcutter and the cut stump is painted with herbicide straight away, with a brush, a dabber or a spray bottle. Straight away is the part that matters, because the cut surface seals over quickly and the chemical has to go on while the plant is still drawing.

It is slower per bush and far cheaper per block when the numbers are small. Being honest about which situation you actually have is worth doing before you ring anyone. More on how we approach the chemical side sits on the weed spraying page.

Know what is a weed and what is not

Blackberry and gorse are declared weeds in Victoria, not native vegetation, and they can be removed. Remnant natives are another matter. Removing native vegetation generally needs a planning permit, with some well-known exemptions such as the 10/30 rule around a dwelling built before 2009 and the combined four metre width allowed along pre-2009 boundary fence lines.

In practice this is less complicated than it sounds, because a good operator works around the natives rather than through them. The finished job should read as understorey and weeds removed, trees kept, with the bushland edge behind it intact. Still, it is worth walking the area and knowing which is which before a machine turns up.

Walk it now, while you can see it

Spring is the easiest time of year to find this stuff. The new growth is bright green against a duller background, and the infestations stand out before summer grass grows up and hides the edges of them. Walk your fence lines, the gully country, the dam surrounds and the shaded ground under the trees, and note four things for each patch:

1. Scale. Is it a handful of separate bushes, or a continuous run you cannot walk into.
2. Access. Can a tracked machine get there, and is the ground firm enough, and are the gateways wide enough.
3. What is nearby. Remnant trees, a waterway, a neighbour's garden, the house.
4. Whether it sits on a line that matters. Blackberry hard against a boundary fence is also a length of firebreak you will not be able to cut, and a fence you cannot get to for repairs.

That short list is the plan. It tells you what gets mulched, what gets cut and painted, what can wait another year, and roughly when each piece has to happen so the follow-up lands in the window. If you would like a straight read on which of your corners is worth the machine and which is a morning with a brushcutter, that is part of what we do around Whittlesea and the ranges.

Oak Ridge Agriculture

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