Sick Series: Why do the needles on my pine look like they’re dying?

19th April 2019

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The colourful symptoms of Dothistroma Needle Blight (DNB) have led to it also being known as Red Band Needle Blight. If you’ve never seen it before, it can be hard to imagine a pine tree with red needles, but the consequences aren’t pretty – the end result of this disease, after the kaleidoscope of colours the pine needles go through, is bald patches where needles once were and, potentially, the death of your tree.

Conifers are most affected by the disease, especially pine trees, with 86 pine species worldwide believed to be susceptible. Until the 1990s, it was mostly found in the southern hemisphere, but it has since breached our shores and spread rapidly throughout Britain, particularly in East Anglia. DNB is now found in many of our forests, particularly in Corsican, Lodgepole and Scots pines.

A survey was undertaken in 2006 on the Forestry Commission Estates of all strands of Corsican pine under the age of 30 that found the disease in a number of previously unreported locations across the UK, with a shocking 70% of Corsican pines affected.

Stages and signs of symptoms
DNB is caused by the Dothistroma septosporum fungus, which we know needs temperatures of between 12 and 18 degrees and a moist environment to germinate. Spores are released from small black fruit bodies on infected needles, landing on new trees and they too germinate on the needle’s surface.

Visible symptoms are seen most clearly in the mid-summer months with yellow bands and tan spots appearing on needles which will then die from the tip, turning a reddish brown. This dieback can be so extreme that all that’s left are a few green branches of needles at the top of the tree after others have fallen off, leaving a ‘lion’s tale’ appearance.

In most countries where the disease has had a significant economic impact, treatment has focused on fungicides. It’s been found that the best protection of uninfected needles is the application of copper-based compounds. A trial of copper fungicides has been used in New Zealand’s pine plantations and the results have been promising. In Britain the focus seems to be on felling infected trees and planting more resistant species of pine. This disease spreads so quickly that it’s critical to keep up regular assessments on your trees.

Prevention of spread
There are some things you can do to avoid spreading the fungal spores and, therefore, the disease from tree to tree:

  • Tend to trees you know to be healthy first.
  • Do not prune infected trees during wet weather as this can cause spores to be carried from tree to tree on your tools and clothes.
  • Dip tools in denatured alcohol for three minutes to sterilise them after pruning affected trees.

The more vigilant you are in your assessment and treatment of your trees, the more likely they are to stay healthy.

If you would like an expert to come to look at your pines to assess whether there is an issue (remember DNB can look like other pine dieback diseases so it’s always good to get an expert’s opinion), or to talk through the health options of your conifer trees, please give us a call on 020 8292 8992.

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