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: