Silver Leaf Disease – Signs, Symptoms and Prevention

Foliage affected by Silver Leaf Disease
RHS (2011). Silver Leaf [On-line]. Accessed: 24/05/2012. Available from: http://apps.rhs.org.uk/advicesearch/profile.aspx?pid=245

Now is the time of year to be carrying out pruning work on Prunus spp. including cherries and plums. With a lot of orchard pruning taking place over winter while the trees are dormant, Prunus spp. often get lumped in with other orchard trees, but it is often better to wait until spring and early summer to minimise the risk of silver leaf disease.

Silver leaf (Chondrostereum purpureum) is a fungal disease which attacks a wide range of deciduous trees and shrubs, however Prunus species are particularly susceptible to it. The fruiting bodies of the fungus produce spores which are carried by wind and infect trees and shrubs through wounds, mainly caused by pruning.

The fungus produces most of its infectious spores in autumn and winter where drizzly, rainy, foggy or humid days with no wind or sun provide the perfect conditions for spore release and infection. By pruning susceptible species at this time, you will open up wounds which will be slower to heal as the tree is in its dormant stage and will provide an entry point for infection.

Once infected, the characteristic symptom of silver leaf disease is a silvery sheen on the foliage. This is caused by the fungal toxins in the sap stream being transported to the leaves and causing the leaf tissue to separate, giving the leaf a silvery appearance. Symptoms can develop throughout the whole tree or on just a few branches depending on the point of infection, however, once branches die, fruiting bodies grow on the dead wood and the cycle starts again. When branches are cut across, an irregular, dark stain may also be observed in the centre.

As with many infections, prevention is better than cure. Good orchard hygiene can reduce the amount of spores on the orchard, minimising the risk of infection. Poplars and Willows can act as hosts for silver leaf so careful management of the surrounding trees is just as important as managing those trees within the orchard boundary. Potential host species surrounding the Orchard should be pruned during the growing season to enable wounds to heal rapidly, with trimmings being burnt or mulched. Removal and burning of major deadwood can also help minimise the amount of spores by reducing the available growing medium for the fungus. Dead or dying trees should be removed by autumn and burned before fruiting bodies can develop and release spores over Autumn and Winter. If you are removing trees completely, try to grind out the stumps or cover them over with soil to smother the fungal fruiting bodies.

It is also important to utilise good pruning practices which can be found in detail in BS3998:2010 Tree Work Recommendations. If you are using a Tree Surgeon/Arborist, check that they have a copy of this British Standard and that they are working to it. If you are undertaking small scale pruning yourself, speak to your Arborist for advice on pruning. A good Arborist will care about the health of trees and will be happy to provide a reasonable amount of advice for free to help you manage your trees effectively. It is most important that all pruning cuts result in a minimal exposure of unprotected wood and cuts are cleanly made with a sharp pruning saw/secateurs so that they can heal quickly and cleanly.

Which brings us back to where we started! If you are thinking of carrying out work on Prunus spp. now is the time to be undertaking this work to the above guidelines. In spring and summer, there are not only less Chondrostereum purpureum spores about to infect open wounds, but the trees are actively growing rather than dormant which means they can heal more quickly, covering over and compartmentalising the wound to prevent infection.

Notes:

Similar silvering of foliage can be caused by cold, drought or other forms of stress. This is known as false silver leaf and can be identified by the absence of stain in the wood.

Binding, wrapping or painting pruning cuts is no longer recommended. The best thing to do is allow the tree to heal itself naturally while giving it the best chance of success by following correct pruning techniques and observing the best time of year for work to be undertaken.

Identifying Tree Hazards

Graham Beer of Treecreeper Arborists carrying out an aerial inspection of a Horse Chestnut tree

Trees provide a wide range of benefits to the landscape, to wildlife and to ourselves, but how can you tell when your tree becomes unhealthy? Degeneration over time is natural and in the right environment deadwood provides vital habitat for a huge range of wildlife. In the wrong environment however, unhealthy trees can also be liabilities. Weak, diseased or stressed trees can cause damage to property and personal injury but in many cases preventative measures can significantly reduce risks and prolong the tree’s life.

One of the first measures you can take is spending a bit of time finding a reputable local arborist. Anyone can call themselves a tree surgeon and offer a service but this does not guarantee quality of work or that it will be carried out safely. Take a look at our blog entry: How to Avoid Rogue Trader Tree Surgeons for more information on selecting an arborist. A reputable arborist will be more than happy to visit and offer advice on your trees and they will provide a free, no obligation quotation for any work that needs doing. Arborists are highly trained and experienced and will be invaluable to you as a source of personal advice.

If you have trees on your property, you have a responsibility to keep them healthy and safe. Regular tree care can help to identify hazards and preventative measures can be taken to reduce the likelihood of damage to people or property.

What are the Signs?

The International Society of Arboriculture (ISA) suggests the following considerations which can help to identify tree hazards:

  • Are there dead branches in the tree?
  • Are there detached branches hanging in the tree?
  • Does the tree have cavities or rotten wood along the trunk or in major branches?
  • Are fungi present at the base of the tree?
  • Are there cracks or splits in the trunk or where branches are attached?
  • Have any branches fallen from the tree?
  • Have adjacent trees fallen over or died?
  • Has the trunk developed a strong lean?
  • Do many of the major branches arise from one point on the trunk?
  • Have the roots been broken off, injured, or damaged by lowering the soil level, installing/repairing pavements, or digging trenches?
  • Has the site recently been changed by construction, raising the soil level, or installing lawns?
  • Have the leaves prematurely developed an unusual color or size?
  • Have trees in adjacent wooded areas been removed?
  • Has the tree been topped or otherwise heavily pruned?
Take the time to check your trees over using this list of considerations. If you answer yes to any of the above questions, contact a professional arborist and ask them to conduct a safety assessment on your trees

Regular routine care should work out cheaper and is much better for your trees than sporadic hard pruning to get trees back under control. An experience arborist will be able to put together an ongoing management plan for your trees, saving you the need to remember what needs doing when.

If you live in Gloucestershire or the surrounding counties, visit our website at http://www.tree-creeper.com to contact us to arrange a free visit and health check for your trees (aerial inspections will be quoted for). If you live outside of our area, please feel free to contact us for advice over the telephone or by email.

Remember: Prevention is better than cure