Thousands of hectares of new biodiverse broadleaved woodland are being planted each year with generous government grants, but there is only one species of tree that does not qualify for this grant aid - the ash tree, Fraxinus excelsior. Government has a simple reason for this, “it would not be good use of public money to plant ash when research has shown that 90% will die due to Chalara disease”.

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The research mentioned above involved new plantations of 100% ash trees planted at close spacing. In these circumstances it is not surprising that Chalara swept through the plantations killing all but the most tolerant individuals. This is similar to what happens in patches of natural regeneration. The 10% survival rate is enough to ensure the successful regeneration of ash with Chalara tolerant genes that they will pass on to the next generation.

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When planting new woodlands, we cannot afford to lose 90% of our carefully planted and cared for ash trees, but 5 simple management techniques would reduce the death rate from 90% to 10% or lower, and make planting ash trees viable again.

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Research has shown that Chalara spores are released in Summer from dead ash leaves on the ground. They then infect the living ash leaves. Young ash saplings can have a shoot growth of a metre or more. They are still growing in July and August when Chalara spores are being released. It is easy for Chalara spores to infect these young leaves because they have not yet developed a waxy cuticle.

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A large spore load is required to start an infection, so any action that reduces the number of spores reaching a leaf will reduce infections.

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1)     Do not plant 100% ash as in the government trials. I would plant a maximum of 20%. Selective thinning can later increase or reduce the proportion of ash.

2)     Plant the ash trees as an intimate mixture with other trees. No single species blocks or lines.

3)     When the ash trees have developed a strong leading shoot, prune all side branches. This reduces the risk of spores landing on a leaf.

4)     Continue pruning side branches to leave 2 metres of clean, straight stem.

5)     If an ash tree has a Chalara infection in the leading shoot, prune it and promote a side shoot to take the place of the leading shoot. The resulting kink in the main stem will disappear after a few years.

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I planted and managed Nursery Wood following these 5 points. Only one ash tree died from Chalara. This tree was not pruned at all. Every year new shoots near the ground were infected by Chalara spores released from the previous year’s dead leaves. In 2023 the poor tree finally died as it became overshadowed by neighbouring trees.

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As an ash tree grows taller its leaves will be less likely to be infected by Chalara spores from the ground which drift away horizontally.

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As the crown develops any infections will be restricted to the crown – they are unlikely to reach the main stem. Small branches may show dieback, but the overall health of the tree is not affected by Chalara.

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In a mature ash tree, the annual shoot extension is very short (5-10cm) and stops in June. By July, when Chalara spores are released, the leaves have a thick cuticle which inhibits infection. Sometimes Chalara infections on old ash trees can be seen as a dark smudge on the fallen leaves.

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Ash trees will never be planted in new broadleaved woodlands until the government allows grant to be paid for planting. Meanwhile new woods are being planted with a key component missing, to the detriment of biodiversity and good firewood.

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The situation could be changed immediately if government allowed the same grant for planting ash as any other broadleaved tree and publicised the 5 points for managing ash as described above.

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