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Ash Dieback Top Ten Tips

Tree Maintenance

Ash Dieback Top Ten Tips

Just before Christmas, ProArb – a leading industry magazine asked me as a regular contributor to provide an article for their February issue. The premise was to provide a Ash Dieback Top Ten Tips for the practitioners of Arboriculture. I tried to take a slightly different approach and provide a more holistic approach and not fill my article with facts and figures.

What I came up with…. the article in full.

The published article is edited and I think better for it It can be viewed on the ProArb website.

Ash Dieback top ten tips


We are starting to see a substantial amount of Fraxinus excelsior – common ash with signs of Ash Dieback (ADB) and I think year on year for the foreseeable future it is likely to be more common place with us dealing with the trees, the owners and the risks both real and perceived. Some knowledge on the subject is vital in order for us as professionals to be able to offer advice that is correct, honest and suitable. It’s a serious situation and the appearance of Hymenoscyphus fraxineus fungus (used to be called Chalara fraxinea) in Britain has left the future of this widespread woodland, hedgerow and urban tree unknown let’s not forget Ash is said to be the 4th most common tree in Britain with an estimated population of between 90-120 million.

Currently there is NO cure for Hymenoscyphus fraxineus  (Chalara)

As professional Arborists we should be able to identify, and put in place management strategies to ensure our customers are well informed and have options that they can choose from. Yes of course we could all take the approach to fell ALL ash trees that show the signs of ADB – after all they’re going to die anyway aren’t they?

I’m pretty sure this ISN’T the way forward, there’s a degree of management of these trees that we can adopt. I think we can manage the risk and take a more holistic approach

Let’s have a look at my Top Ten Tips on how to manage Ash Dieback. It’s by no means exhaustive and for the main part is my interpretation on how we as a company work and maybe it reflects the industry as a whole. There’s a few fact included which may help get a handle on the significance of the disease also:

  • Positive identification. This has to be where we start off after all if we cannot ID it what recommendations can we offer. Springtime is an ideal time to spot the signs of ADB – wilting growth and possibly even bark lesions. You may see scars on the main stems; they are darker in colour to the surrounding wood and are often centered around a small shoot that has also died. With the exception of canker, lesions are general quite rare in ash and so this is the tell-tale sign. These scars may also be present on the smaller branches. Is the top of the tree dead? If so, this is characteristic of ADB – This happens because the fungus enters through the leaves in the crown of the tree. If the leaves have fallen there will be a distinctive dis-coloration on them, take a look at surrounding ash trees and the difference will be apparent – browning on the leaf stalk and discoloration on the underside of the leaf (yellow to brown).
  • Ok, so we are confident that we have positively ID’d ADB, what next? Well, we need to make a judgment call on the extent of the infection and assess risk this posses. I think the best current advice is from the Forestry Commission, they state: “Public safety is likely to be one the biggest management issues for owners of ash trees in woodlands, parks, roadsides etc. as the disease kills or weakens trees over the coming years. Trees in areas with high levels of public access need to be monitored carefully for risks to public safety, and some felling or pruning of dead or dying trees is advisable if risk assessments show they are a hazard.”
  • Not all of us are involved in the forestry side of operations, but we can learn something from the investigations that have been carried out by Defra and FC. We know that younger trees are most susceptible to ADB and are killed rapidly. This is useful knowledge for us when assessing an entire site and maybe can dictate to us timescales for when sites i.e. gardens, roadside boundaries etc. should be re-monitored.
  • Can we cure ADB? In short it seems the answer is no, but we can put in to place measures to help reduce the risk of further spread. This focuses efforts on reducing the level of spores present. As we know fungi for the most part like damp conditions, therefore if we can help increase light levels and airflow into densely planted areas at risk this could be beneficial. Maybe consider the selective and responsible thinning out of densely planted stands of trees. But by far and away the most effective option in reducing the spread of the spores and therefore disease is to encourage the owners, (or if they’re willing to pay you) to remove all ash leaf litter from around the trees in the autumn and winter to reduce the local source of spores the following summer.
  • Arisings – what do we do with them? We’ve just felled an ash tree that we diagnosed as having an ADB infection, what measures should we have in place so we don’t spread the spores and infect other trees nearby? Current advice seems to contradict itself a little, but my interpretation is; with regards to the removal of arisings, unless a Statutory Plant Health notice has been served the wood/timber can be removed. The leaf matter should not be removed from site. Several options are available, they are; composting, burial and incineration. Composting is the least preferred option because we are still not 100% sure in the effectiveness of this, burial works well but please be aware, that if we as contractors bury our arisings we are effectively land-filling and as such should have a permit to do so (a private person needs no such permit). I’d go with a cheap incinerator (dustbin type) and burn them.
  • Infected urban and veteran trees. OK, so I’ve lifted this directly from the Forestry Commission’s website, but I think this is most pertinent to us as responsible and professional Arbs.“ There should not be a presumption to fell these trees. Veteran trees in particular can provide many important environmental and social benefits, even when dead. Any work on a tree should be undertaken after a risk assessment, which should consider age, condition, the number of other trees in the locality and their species, the potential risk of further infection, and the danger to the public. The cost of taking or not taking action is also likely to be a factor in any final decision.” This advice is very similar to that given for hedgerow trees and those in rural situations. I guess what I’m trying to say that a dead tree is still a tree, it’s still valuable, it still provides a wealth of habitat and is still a wondrous thing to look at. I think a lot of us Arbs are guilty of regarding a dead tree as useless and something that has to be dealt with, usually by their removal – felling. My view is the driving force behind our decisions must be SAFETY and we should view trees as equally as valuable in terms of habitat etc. when dead.
  • Large mature trees in open surroundings such as street and parks etc. can survive and sometimes escape infection for many years. Urban situations help these trees out because the dark damp woodland environment is clearly not an issue, leaf matter is usually removed by the LA and secondary damage by bark beetles and basel infections which further stress trees are less likely in the urban environment.
  • study based on the infections in Denmark show that there is a 1% resistance to ADB amongst ash trees; these trees show a less than 10% dieback in their Crowns. Using these figures for Britain this means there could be some 2 million disease resistant trees in the countryside – somewhere. That’s not many, so we really should refrain from becoming a little too chainsaw happy when around ash trees. A recent research paper dated from end of 2016 (Journal of Nature) states that after genome sequencing the British ash trees may be significantly more resistant than Danish trees, this is positive news, but lets all air on the side of caution for the time being.
  • How do we approach ADB? As a company we do not see this as a cash cow situation, I feel we need to move our industry on and strive to make the general population aware that we as Arborists are educated and trustworthy professional trades people. We will use our knowledge (which is by no means exhaustive) to obtain a suitable and safe outcome. This is our chance to build a relationship with clients, offer decent honest advice and realise they want someone they can trust. I’m not afraid to put my hands up to a client and say we need more qualified advice on this – to suggest a visit from a consultant would be a wise move.
  • Ultimately we are dealing with dead or dangerous trees – this is what we do, right? Climbing or working from a MEWP on a dead Ash tree from ADB carries the same risks as any other dead tree job. So as always take care and work safe.

Hope you waded through my Ash Dieback Top Ten Tips  OK. If you need help please take a look at https://www.abouttrees.co.uk/ash-dieback/