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Posts tagged ‘pests’

Environmental change: awareness, actions, aspirations

September 1, 2015

Gabriel Hemery

Environmental change is impacting Britain’s trees and forests with increasing frequency and severity, caused by human influences and/or natural ecological processes.

Somerset owner William Theed replanted with different conifer species when Japanese larch in his woodland was the first in the UK attacked by Phytophthora ramorum. Photo Gabriel Hemery.

An important national survey about environmental change is seeking to explore awareness, actions and aspirations among all those who care for trees. It is open until 15th September and I encourage all those with a deep interest or professional connection with trees and forestry to take part.

If you can spare about 20 minutes you will be guided through a set of questions tailored to your role (namely woodland owner, professional forester or arboriculturist, tree nursery owner etc.). These cover the following broad themes:

  • What do you think about environmental change?
  • Have you been affected by environmental change?
  • What are you doing about making our trees and forests more resilient to environmental change?

Survey co-ordinators the Sylva Foundation report that over 1000 responses have been received to date (see Twitter), which is impressive, but more responses will mean more powerful science and better informed policies. This is an opportunity for many new voices to be heard on a very important subject.

Please take the survey

More about the British Woodlands Survey 2015

The national survey is aiming is to help understand progress in awareness and actions in adapting to environmental change among woodland owners and managers (including agents), tree nursery businesses, and forestry professionals.

The information gathered will be used by organisations, policy makers and researchers to help improve the resilience of the nation’s forests. The results will inform the government’s National Adaptation Programme.

The British Woodlands Survey 2015 on Resilience is supported by a very wide number of organisations, with funding provided by the Forestry Commission and the Woodland Trust. It is hosted and co-ordinated by the Sylva Foundation.

The survey is live from July 31st to September 15th 2015.

Take the survey:

Woodland biosecurity – a simple guide

November 11, 2012

Gabriel Hemery

Brushing boots to disinfect and sterilise

Biosecurity – preventing the introduction and spread of harmful organisms – is big news at long last! The arrival of Chalara fraxinea in Britain has brought this important issue to the fore. However, I found it difficult to find simple guidance on the steps we should take when visiting or working in woodlands, or with individual trees in our trees and cities. Many of the record number of readers of this blog over the last week have found it after using searches such as:

“what should I do if I find Chalara fraxinea?”
“how do I clean my boots?”

While we wait for more detailed specific advice to come from scientists and Government officials in relation to Chalara fraxinea it would be prudent to follow the protocols developed to minimise the spread of another pathogen; Phytophthora. So my first recommendation is to visit the Forestry Commission’s webpage on Biosecurity Measures, which includes the advice currently given to all Forestry Commission staff for their routine visits to woodlands in a handy pdf guide.

I have put together the following simple guide on woodland biosecurity.

Biosecurity behaviour

Brushing boots to disinfect and sterilise

Brushing boots to disinfect and sterilise

  • Clean your footwear after visiting a woodland. Wear Wellington boots, as these are easier to clean thoroughly. To do this effectively you must remove first all soil and leaf litter from your soles. You will need water and a stiff hand brush.
  • If you have been to a high risk site apply a detergent to sterilise them, although it is good practice after all visits.
  • Sterilise your tools. Be careful that the chemicals you use do not harm trees (or other wildlife). Read more about sterilising forestry and woodland tools.
  • If you drive into a woodland, even on a road, wash your tyres to remove soil and leaf litter.

Biosecurity personal kit

Spraying boots to sterilise with Propeller disinfectant

Spraying boots to sterilise with Propeller disinfectant, after they have been brushed to remove soil

The most common question I’m asked is what chemical should I use to sterilise or disinfect. The one recommended, or at least adopted, by the Forestry Commission currently is Propellar™. This is available only directly from one supplier (see below) and must be ordered wholesale in 12×1ltr containers as a minimum order. I was amazed when I searched the websites of two of the major forestry and arboricultural supply companies that neither had any disinfection chemicals listed. This is really shocking! Try it yourself. Go to and enter a search string that allows you to search within a certain website (you will need to know the url of the forestry/arb supplier): try “ disinfectant sterilise” [replace the url with the supplier’s]. I’d be happy to be proven wrong but I’ve not found one yet that came up with any goods.

  • Propellar spray to sterilise forestry equipment

    Propellar spray to sterilise forestry equipment

    Propellar™ – chemical to sterilise footwear and equipment (always read the Health & Safety label). The supplier for the disinfectant Propellar™ is:

    Evans Chemical Supplies,
    18B Barncoose Industrial Estate
    TR15 3RX.
    Tel. 01209 213643
    Email: Evans Chemicals

  • handbrush – to remove soil from boots
  • disposable gloves – protection from chemicals used
  • safety goggles – protection from chemicals used
  • water container (e.g. 5L for personal/15L for groups) – to carry water in vehicle for cleaning after visit
  • airtight storage container – to hold brush and chemicals
  • soap and towels – to wash hands
  • bags – to dispose of material
  • storage box – to hold all biosecurity items together

If you have advice born from experience or other comments then I would be pleased to hear from you. Use the Comment box then you can share your experiences with other readers.

Finally, this advice can be followed by woodland owners, arboriculturists, foresters and anyone who accesses woodland regularly. Whether it is practicable or feasible for the average member of the public to adopt these measures is doubtful. Nonetheless, we can lead by example and on high risk sites or those with special high value (e.g. ancient trees or important habitats) particularly, it may be possible to erect signage or equipment to encourage visitors to undertake simple biosecurity measures.

Gabriel Hemery

Further Information

Horse chestnut leaf miner moth on film

April 25, 2012

Gabriel Hemery

Today I watched a horse chestnut leaf miner moth, Cameraria ohridella, laying her eggs on the fresh young leaves of a horse chestnut tree. Here’s a short film that I captured.

The tiny larvae will hatch in about three weeks and start to feed on the tree’s resources.  First the sap by tapping the veins, then by eating the leaf tissue. This is when the brown spots appear as the larvae ‘mine’ the leaves. By mid summer, trees infected by heavy populations of the leaf miner larvae may appear Autumnal; their leaves brown, blotched and tatty.

The Sylva Foundation is looking for volunteers again this year to help spot the presence or absence of leaf miner damage on horse chestnut trees across Europe.  Why not get involved? See

Gabriel Hemery

Horse chestnut leaf miner spotting

August 27, 2011

Gabriel Hemery

Horse chestnut trees infected by the leaf miner

An avenue of horse chestnut trees infected by the leaf miner. They appear autumnal in colour while other trees around them are a healthy green.

Horse chestnut trees across much of Europe are looking worse for wear. Infestation by the horse chestnut leaf miner has by this time of year reduced their canopies to a ragged and pot-marked mass of dying leaves. From a distance horse chestnut trees are now easy to spot as they look autumnal in colour; their leaves are brown and orange while all around them other trees remain a healthy green.

The horse chestnut leaf miner Cameraria ohridella was first discovered  in Macedonia in 1984 and named as a new species in 1986. It has since spread rapidly across Europe and is found in most countries, although it is less common in hotter and drier climates.  It was first observed in the UK in July 2002, on Wimbledon Common. It has since been spreading about 40-60 km (24-37 miles) a year.


Tree and forestry charity the Sylva Foundation is looking for volunteers to help spot and record the spread of the horse chestnut leaf miner in their TreeWatch project. Volunteers can ‘adopt’ a tree and record the presence or absence of the pest.  According to the latest results displayed on the TreeWatch website, the mostly northerly record of the pest in England is near Leeds, with no records in Wales.  More records are required across most of Europe. I wonder if any of my readers can find newer records?

If you have an interest in trees, of any species, and want to help with other tree surveys why not sign up to TreeWatch: you could play an important and active role in an early warning system for tree diseases and pests!

Gabriel Hemery

Oak processionary moth – management implications

August 19, 2011

Gabriel Hemery

I wrote previously about a looming threat to man and trees from the oak processionary moth (OPM) that first appeared in the UK in 2006. It is a widespread pest in The Netherlands, Germany and Belgium.

Oak Processionary Moth caterpillars - visit Forest Research webpage

Oak Processionary Moth caterpillars. Photo Forest Research

I am grateful to Ron Melville, Director of Forestry Commission London, for sharing the following (below) Management Implications with me. Ron recently returned from a visit with Forest Research colleagues to Germany where the pest is a serious issue; perhaps a herald of things to come in the UK. Forest workers that had been involved in managing stands with OPM had all suffered from ‘rash’ problems, and difficulties of working in infected woods remained six years after an outbreak has passed. For example, one forester required hospital treatment after handling a log cut during clearance work six years previously.

Some important management implications for forest workers

  1. OPM has the potential to be not only a problem relating to open-grown mature oak trees, but also in younger plantation crops.
  2. Although oak is the preferred host tree species, OPM has been recorded in plantations of beech and hornbeam, and in orchard apples.
  3. OPM is a serious defoliator and with no control there is no doubt that tree’s leaves will be drastically removed. This will weaken the tree and if it doesn’t kill it directly, it will increase its susceptibility to attack from wood borers and possibly root pathogens, which will damage and kill the tree. In one German P1960 stand of Red Oak visited by Melville and colleagues, 75% of trees had been infected and removed.
  4. New nests are very obvious but previous year’s or older nests are less visible as they fade in colour. Close inspection is always needed to ensure absence of danger.
  5. It is difficult to imagine how spraying control pesticides in UK plantations could be achieved without the use of helicopters. Could this be justified financially (costs are in order of €230 per hectare)?
  6. Assuming helicopter spraying is not feasible in the UK, then control options within closed woodland are extremely limited. Vacuuming is an option for individual trees in urban areas, parks and gardens (costs €60-2000). However, the cost and difficulties of using the equipment in plantations are likely to prove insurmountable.
  7. Re-invasion in areas if left untreated appears to be considerable. Unless there is full and complete removal of nests or control of caterpillars, the treatment may ultimately be ineffective.
  8. The longevity of the hairs in the environment and related health problems could be a serious issue, not just for forest workers, but also for any indirect handling of logs or other cut material (e.g. lop and top for biomass or chipping).
  9. OPM caterpillar populations can reach significant levels in mature oak stands. In the UK, these are likely to be the areas with highest public usage. This is potentially a very serious problem for human health and for forest management.

Gabriel Hemery

Read more about Oak Processionary Moth

A looming threat to tree and man

May 4, 2011

Gabriel Hemery

The Oak Processionary Moth is a serious pest, not only for oak trees but also for human health.

The oak processionary moth

The oak processionary moth (OPM) Thaumetopoea processionea gets its common name from its habit of moving along oak (it’s food plant) in processionary columns.  It is a species native to southern Europe, which spread northwards during the late 20th Century, being recorded first in the Netherlands in 1991, and then Belgium, France and Germany soon afterwards.

Colonies of the OPM in the UK were first discovered in 2006, in a housing estate in the London Borough of Richmond. It was identified after a large number of local people reported skin rashes. It is apparent that the OPM had arrived on imported Cypress oak (Quercus robur f. fastigiata) trees.  Colonies were sighted later at Brent, Ealing, Hounslow and Richmond Upon Thames, including Royal Botanic Gardens Kew.  The OPM colonises urban areas readily, preferring warm, sunny and sheltered sites for breeding.  In 2010 a new infestation was spotted west of London, at Pangbourne in Berkshire (source).  It is likely that milder winters and fewer Spring frosts may be contributing to population expansion (read more about trees pests, climate change and global trade).

Significant resources have been expended in attempts to control OPM.  In 2011, Richmond Park alone will be spending £50,000 in attempting to control it (source).  Initial confidence that the first colonies across London could be contained has given way to real fear that OPM may now be out of control:

“The area affected by OPM is growing steadily. It seems possible that attempts to eradicate the pest may fail  …  despite the hard work and effort put in by many organisations and individuals, we may be on the brink of failure.”
London Tree Officers Association website (accessed 3rd May 2011)

Effects of OPM on oak trees

Oak processionary moth nest

Nest of oak processionary moths (Thaumetopoea processionea) on an oak stem. Photo Falko Seyffarth (Wikipedia)

Oak trees colonised by OPM can be seriously defoliated and there are reports of tree death in some instances.  However, the trees will normally recover and leaf the following year. On the European continent OPM has also been reported on beech, silver birch, hazel, hornbeam, and sweet chestnut but normally only when neighbouring infested oak trees.  Oak trees under 2m in height are not normally colonised.

Human health

The caterpillars of the third to sixth instars have poisonous hairs or setae that carry a toxin that can cause serious irritation to the skin, eyes, nose and throat of humans and other animals.  If inhaled they can cause respiratory distress, asthma and even anaphylactic shock.  Read more.

Not only should the caterpillars never be touched but even being in proximity to them can be dangerous as their hairs can be carried in the wind.


oak processionary moth health warningYou should never attempt to handle the caterpillars or disturb their nests.

If you suspect an incidence of oak processionary moth, sightings can be reported to Forest Research by telephoning 01420 22255 or by e-mail to

Gabriel Hemery

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