Technical
Case study - Coille Alba
COILLE ALBA, a not for profit organisation which manages native woodlands in the Highlands, recently carried out a review of Rhododendron control in Scotland for the Forestry Commission. The report assessed the pros and cons of a wide range of methods on different sites, and concluded that stem injection should play a more important role in control programmes.
Rhododendrons on North Hants Golf Club - invasive, but the members like them!
spray volume, can improve control and allows the recommended dose rate to be reduced to 8.0 l/ha. Roundup ProBiactive450 requires 8l/ha (6.4l/ha with Mixture B at 2%).
Stem injection has been used with great success by Coille Alba in Scotland
Image ©John Parrott, Coille Alba
“For big mature bushes, stem injection is far more cost-effective than other methods,” comments Coille Alba Chief Executive John Parrott. “Compared to conventional methods, stem treatment also causes minimal environmental impact.” Mr Parrott explains that large rhododendron bushes are usually cut and burned. “This is labour-intensive and carbon dioxide emissions from burning rhododendron are around 160 tonnes per hectare. Regrowth must also be sprayed. Stem treatment minimises damage to non-target plants as chemical is injected into a reservoir created with a drill.”
Coille Alba has found that 99% of injected rhododendron is killed in a single treatment, so follow-up visits are minimised.
No specialist equipment is required for stem injection - just a cordless drill and a plant sprayer. But, as with any technique, it is important that contractors are thorough and follow the right method. They also need to be patient, as it can take many months before bushes die, Mr Parrott points out.
“We worked on a site last winter and spent almost six months crawling through rhododendron stands. It wasn’t until May that we saw any sign of leaves falling off the bushes.”
Stem injection appears successful in all seasons and all weathers, even in near-freezing conditions. Monitoring of treatments last year showed no difference in control on rainy days or when the mercury hovered near zero.
132 PC OCTOBER/NOVEMBER 2013
All parts of the foliage should be sprayed since the plant exhibits transcendental translocation, which means spray droplets falling on one side of a bush will be translocated down to roots on the same side but will not be distributed across to the opposite side.
A small, missed area, can result in regrowth and rapid re-colonisation.
Dose rate Method
Rhododendron (overall spray) Ensure effective coverage of all foliage, but avoid run off
Rhododendron (cut stump)
Roundup Pro Biactive or Roundup ProBio
10 l/ha, or 8 l/ha + Mixture B @ 2% spray volume
20% solution in clean water. Apply using knapsack sprayer, spot gun or paintbrush
Roundup Pro Biactive 450
8 l/ha, or 6.4 l/ha + Mixture B @ 2% spray volume
8 l/ha, or 6.4 l/ha + Mixture B @ 2% spray volume
Drill and fill according to label instructions. Stump diameter: 3-6cm - 2 plugs 6-10cm - 4 plugs 10-14cm - 6 plugs 14-18cm - 8 plugs >20cm - 3-4cm between plugs
Rhododendron (chemical thinning) Two hatchet cuts per 10cm trunk diameter, one below the other to catch drips. Or
2ml per 10cm diameter of trunk
1.6ml per 10cm diameter of trunk
Ecoplug Max Cut stump
Cut stump treatments are best made from November through to March or April, and not during the period of active sap flow.
Application of Roundup must be made to a fresh cut so that uptake into the phloem (the living tissue that carries organic nutrients to all parts of the plant) is maximised. A two-man operation is often the most practical for a quick, post-felling treatment. If more than a few minutes of time have elapsed, recutting the stump will restore the effectiveness of the application. Uptake
Drill one hole with 8mm drill approx 40mm long downwards radially towards centre, per 10cm trunk diameter
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
Spot treatment via knapsack (Standard 200 l/ha nozzles) Area sprayed
Volume of
50 square metres 500 square metres 1000 square metres
50ml 500ml 1000ml 40ml
400ml 800ml
Roundup Pro
Roundup Pro Biactive Biactive 450 or Roundup ProBio
1 litre 10 litres 20 litres
Volume of water
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