Kill diseased trees by using chemicals
Find out how to kill trees on site using chemical treatments to prevent the spread of pests and diseases.
Why you should kill trees by using chemicals
Sometimes it’s impractical or uneconomic to remove diseased trees by felling and extracting the tree from the site. You may be able to treat the trees with chemicals that will kill them in place and they can then be left on site to decay naturally. Dead wood can be an important resource for wildlife.
You can also use chemicals to prevent stumps of disease-infected broadleaved trees or shrubs, like rhododendron, from regrowing.
You should use chemical treatments rather than chainsaw or hand cut ringbarking to kill standing trees. Ringbarking is not always effective and weakens the stem of the tree. In strong winds or heavy snow trees can snap where they were cut and be a safety hazard.
The main methods of chemically killing trees are:
- surface treatments where herbicide is applied to cuts made in the tree known as cut and spray
- stem injection using products such as Ecoplugs or similar
Ecoplugs are capsules of powdered glyphosate which are inserted into holes drilled into trees or stumps.
Stem injection has advantages over surface treatment because it:
- can be used in wet and windy weather
- removes the need to handle liquid pesticides
- reduces the risk of non-target spray drift and environmental contamination
You should use stem injection rather than cut and spray to treat Phytophthora ramorum in infected larch where felling is not possible. This is because it kills the trees more quickly. You should do the work before the end of October to reduce the risk of Phytophthora ramorum spores being released the following year.
When not to use chemical treatments
You must not use chemical treatments to kill:
- trees infected with sweet chestnut blight
- an entire stand of coniferous trees unless conifers will never be grown on that site again
Dead conifer trees can get infected with a wood rotting fungus called Heterobasidion annosum. It can cause serious damage to conifer crops. The fungus will remain on site for many years so new conifer crops will be infected and damaged.
Before you start chemical treatments
You or your contractor must have the appropriate training and certification before using any chemical or herbicide.
You must read and follow the instructions on:
- the label of the product you’re using
- the safety data sheet included with the product you’re using
- your Control of Substances Hazardous to Health (COSHH) assessment
You should also consider the:
- appropriate treatment method that’s best for the site and conditions
- environmental and conservation issues on the site
- best time to carry out the operations and the impact of the weather
- potential chemical runoff when using the cut and spray method
How to kill trees by using chemicals
You can use either cut and spray or stem injections to kill the trees chemically.
Cut and spray
You’ll need:
- liquid glyphosate at a concentration of 360 grams per litre (g/l)
- girthing tape or a set of callipers
- an axe or slasher
- a forestry spot gun (also known as Drench gun), which can be metered to give the required dose
- appropriate personal protective equipment (PPE) – the operator must be trained and certificated to PA6 D
To cut and spray:
- Use the girthing tape or callipers to measure the tree diameter.
- Using the axe make a cut in the tree that it is through the bark to the stem (primary cut).
- Make a second cut below the first to collect any runoff.
- Make additional cuts in the same way as steps 2 and 3 for each whole 10cm diameter of the tree. For example a tree with a diameter of 35cm will have 3 cuts to accept the chemical and 3 below to catch any runoff.
- Use the forestry spot gun to spray a dose of 2ml of neat 360g/l glyphosate into each primary cut.
Cut and spray is most effective if applied within 2 days of cutting when used on rhododendron stumps.
Stem injection (Ecoplugs)
You’ll need:
- Ecoplugs or similar
- handheld drill with a 13mm drill bit
- hammer
- goggles
- gloves
- callipers or girth tape
To inject stems:
- Measure the diameter of the tree at 1.3 metres from the ground (dbh) to determine how many plugs are required. The number of plugs to use per cm of dbh is specified on the product label for stumps and the same is recommended for standing trees. The number required will vary depending on the species being treated.
- Ecoplugs should be spaced apart around the stem or stump. As a general rule they need to be 6 to 8cm apart.
- Using a drill, make the required number of holes around or in the stump or stem to a depth of 3.5 to 4cm. A specially designed drill bit is available from the Ecoplug supplier that permits the desired depth to be achieved. If this is unavailable, marking the depth on a drill bit with coloured tape will act as a substitute.
- Insert the plugs into the drilled holes, with the orange or coloured cap inserted into the stem and the white wider cap protruding from the bark.
- Tap them in using the hammer. Make sure the plug is driven in to force the end cap (orange) back into the cylinder to crack the outer shell and release the herbicide.
- Make sure the end cap on the plug is pressed into the bark to prevent spillage or loss of chemical.
If used on rhododendron stumps Ecoplugs are most effective if applied within 2 days of cutting.
Maintain safety on site
You or your land manager should have an appropriate inspection plan to:
- monitor the deterioration of treated, dead and dying standing trees
- check if any trees or stumps need follow-up treatment
- ensure the safety of any people who may be on site for follow-up operations or for access and recreation purposes