Scrub, Brushwood and Trees

The Control of Scrub, Brushwood and Trees With Roundup ProBiactive

This category includes weeds such as Brambles, Briars, Ivy, Buddleja, Gorse, Broom, Rhododendron, Nettles, Rosebay Willow herb, self-set tree saplings as well as mature trees and stumps.

Brush and scrub weed species are all perennials with a reputation for invasion of non-cropped areas and being difficult to kill. They are commonly found in situations such as overgrown waste ground and roadsides, neglected industrial or urban sites, railway embankments and disused areas.

Many of these weeds have been traditionally treated with specialist 480g/l formulations of triclopyr but the current approvals for products such as Timbrel and Garlon 4 will be phased out during 2011, pending environmental and operator issues being addressed and users are seeking environmentally friendly and efficient alternatives.

Roundup Pro Biactive can be very successfully used to control most of these weeds, but the techniques and timings are not always the same as the triclopyr products. This technical note looks at the optimum use of Roundup Pro Biactive in controlling scrub and woody weeds.

Roundup Pro Biactive can be used as a foliar treatment in the spring and summer at or just after flowering or as a cut stump treatment in the dormant season and has the following advantages over triclopyr:

  • Does not have the six week planting interval restriction
  • No CHIP classification of Xn or N, environmentally and operator friendly
  • Roundup ProBiactive 450 can be used through CDA applicators.
  • Remember always to take a planned and programmed approach to weed control in such areas – one well timed application may kill off all those weeds present but if no follow-up activity is carried out weeds will simply re-infest the area and within a few years it will revert to its original state.

Control With ProBiactive

Roundup Pro Biactive has an unrivalled operator and environmental safety profile and is ideal for areas with public access or of environmental sensitivity, including near water.

Foliar treatment

Woody weeds and scrub can be sprayed overall with Roundup Pro Biactive at 5.0 l/ha in 80-200l/ha of water. Timing will depend upon species mix but trees will be controlled by an application after the shoots have sufficient leaf growth. For flowering perennials like Nettles, Rosebay Willowherb Brambles and Briars the optimum time is once they reach the flowering stage but before they die-back. Poor control may result from treatment of small perennial plants early in the spring since not only is there insufficient leaf area but also the sap flow from perennial root systems is strongly upwards and translocation of glyphosate to the roots is inefficient-resulting in an initial kill followed by re-growth from ground level.

The combination of Roundup Pro Biactive plus the adjuvant Mixture B NF, at 2% of total spray volume, will help improve the reliability of control of very waxy-leaved weeds like Rhododendron, Ivy, Broom, Gorse and Laurel by increasing coverage and penetration of the leaves.

Stump Treatment and Chemical Thinning

These methods work well on all woody species including scrub like Gorse or Buddleja and even Ivy so long as there is a discernable lignified stem or trunk large enough to treat.

Unlike triclopyr, stump treatment is not advised in the summer months, there is no recommendation for winter shoot sprays and Roundup Pro Biactive should never be mixed with diesel or paraffin.

Stump treatment

Timing: Trees must be dormant; this usually occurs between November and February, although in some seasons and in the most Northern parts of the country this could extend until the end of March. (Watch species like Hawthorn and Willow which start spring growth very early).

Rate: 10% solution of product in clean water for deciduous species.

20% solution in clean water for evergreens, including Rhododendron

Method: Apply Roundup Pro Biactive to a fresh cut using a paintbrush or clearing saw with built-in applicator. When using a paintbrush saturate the rim of stumps, concentrating on the live wood just inside the bark. Stumps with a diameter of less than10 cm diameter should be completely covered; larger stumps will be effectively controlled using a 5-10 cm band width around the perimeter. A two-man operation is often the most practical to achieve a quick post-felling treatment, because it is essential to treat the cut stump within a few minutes of cutting. If this is not possible re-cutting the stump will restore the effectiveness of the herbicide application. Application to a cut that has partially sealed means absorption is slow and rain within 6 hours will wash some of the product off. Rapid uptake through a fresh cut ensures the treatment is rain fast within 10 minutes. A suitable spray marker dye may be added to show up treated stumps.

Chemical Thinning

Timing: Autumn/winter. This method works from slightly earlier in the season, (i.e. October), which may be useful to use before stump painting could commence in November.

Rate: 2 mls of neat productper hatchet cut per 10 cm diameter of trunk

Method: Neat Roundup Pro Biactive is introduced straight into the phloem through a hatchet cut into the bark of the tree or stump. This has the benefit of not requiring the stump to be freshly cut; it can be used where trees have already been cut back, or where the tree is to remain in place. It is also easy to see which areas have been treated. A Spot Gun with a solid stream nozzle is recommended, but a large disposable syringe can also be used.

It is advisable to make a second cut under the first to catch any surplus herbicide. Work out how many hatchet cuts are needed according to the diameter of the trunk and space them round the girth. E.g. trunk of 30 cm diameter requires 3 x 2 mls cuts.

Alternatively the concentrate can be introduced through an 8 mm drill hole, about 40mm long, aimed slightly downwards and radially towards the centre of the stem.


It is possible for collateral damage to occur to nearby trees where the product is overdosed and the trees are the same species and are intimately connected by mycorrhyzal fungi or root grafts.

Stem Filling/injection tool for Japanese Knotweed and Giant Hogweed.

In certain situations such as when the Japanese Knotweed is growing on sites with a ground flora considered of particular value, near water or where the J.Knotweed is growing close to other plants, a stem filling technique may prove more suitable than foliar treatment. Although requiring a far higher labour input, the herbicide can be more accurately directed. This technique involves cutting the stem and introducing 10 ml of a 20% solution directly through the top. It has been developed by the National Trust, in conjunction with the Cornwall Japanese Knotweed Forum. Full details of the method are available on request.

The JK Injection tool uses a needle to inject directly into the stem rather than cutting the stem down. More at


ProblemDose RateApplication tips
Tough perennial weeds (foliar spray)

5 l/ha, in waste ground & amenity situations. Add Mixture B at 2% of spray volume for waxy leaved species

Spray at least 50cm of new leaf growth of trees and saplings.

For flowering perennials like Brambles, Briars, Nettles etc the optimum timing is from flowering, until before die-back.

Woody weeds, (cut stump)

10% solution

(deciduous species)

20% solution (Evergreens and coniferous species)

Apply to freshly cut stumps with a knapsack sprayer, spot gun or paint brush during the dormant season,(November to End February)

Woody weeds (chemical thinning)

2 ml per 10 cm diameter of trunk

Two hatchet cuts per 10cm trunk diameter, one below the other to catch drips.
Drill one hole with 8mm drill approx 40mm long downwards radially towards centre, per 10cm trunk diameter.

Hollow-stemmed invasive species (chemical thinning)
E.g. Japanese Knotweed Giant Hogweed, Horsetail

2 ml per stem

Stem fill with spot gun, syringe or injection with specialist injection equipment e.g. JK Injection gun

Spot treatment by knapsack

Most knapsack sprayers are supplied with a set of 4 deflector nozzles giving different swath widths but all delivering 200l/ha of water at 1 bar pressure and a walking speed of 1 metre per second.

(Using standard 200l/ha nozzles)

Area sprayed

Volume of Roundup Pro Biactive

Volume of water

50 square metres

25 ml

1 litres

500 square metres

250 ml

10 litres

1000 square metres

500 ml

20 litres