In Britain, Dothistroma Needle Blight (DNB), also known as Red Band Needle Blight, is caused by the fungus Dothistroma septosporum. It has been found on a range of conifer species, but pine (Pinus) are by far the most common hosts, with Corsican pine, lodgepole pine and Scots pine all now affected. Defoliation can continue year on year and gradually weaken the tree, significantly reducing timber yields. It can also eventually lead to mortality. Experience in New Zealand and on Corsican pine in England suggests that the percentage of crown infection equates to the percentage yield reduction.
Trees of all ages can become infected. Symptoms are first seen at the base of the crown on older needles. Infected needles typically develop yellow and tan spots and bands, which soon turn red. As the disease progresses, the ends of the needles then turn reddish-brown whilst the needle base remains green. It is within the red bands that the small black spore containing fruit bodies tend to be found, with symptoms being most apparent in June and July. Spores are released from the fruit bodies during this period, leading to infection of the current year's needles. After this point, the symptomatic needles are shed, and branches can have a typical 'lion's tail' appearance, with only a tuft of the recently infected current year's needles remaining at the branch ends. This defoliation can continue year on year and gradually weaken the tree, significantly reducing timber yields and causing mortality.
The disease has been found in all of the Forestry Commission's districts in England and Scotland, and three out of four forest districts in Wales. In 2006, 70 per cent of the Corsican stands inspected in Britain had the disease, and it is estimated that 44 per cent of these infected stands had crown infection levels greater than 30 per cent. Lodgepole pine is now also being severely affected in north and east Scotland. Although Scots pine has generally been considered to be of low susceptibility, an increase in the distribution and severity of the disease on this species is now being seen, particularly in Scotland. It is not yet known whether this will lead to mortality or extend significantly into the Caledonian pinewoods. The other main conifers used in British forestry continue to appear to have low susceptibility.
In 2010, the disease was found infecting pine plants in three forestry nurseries in Scotland.
In 2011 the extent of nursery findings increased, when for the first time both of the Forestry Commission's Delamere and Newton nurseries were found to be infected in the same year.
Moisture is required for natural dispersal of the fungus, and long-distance dispersal is thought to occur in moist winds and mists. Movement of infected plant material, including infected needles on footwear, clothing, machinery and timber, could also potentially spread the disease.
Management of Dothistroma Needle Blight is overseen by a Programme Board, (Terms of Reference) set up in 2009. The Forestry Commission’s research programme includes: disease surveillance; monitoring of the disease’s extent, severity and impact; increasing our understanding of the fungal biology and disease epidemiology; and investigations into potential management strategies.
The Programme Board has produced a GB strategy for addressing the issues posed by DNB. The strategy sets out the current status of the disease, the risks it poses, and actions required to achieve the three key objectives of of the strategy. These are to:
- maintain pine as a silvicultural option to protect the social, economic and environmental functions of pinewoods, and avoiding impacts of DNB on other conifer species;
- conserve Great Britain’s iconic Caledonian pinewoods; and
- reduce collateral damage from other pests and diseases (e.g. bark beetles).
Forestry Commission Scotland has established a forest tree nursery transition scheme, which provides support for infected forest tree nurseries in Scotland, conditional on their setting out and implementing a Dothistroma needle blight resilience action plan for their nursery.
Within the European Union the movement of pine plants intended for planting is regulated though plant passport arrangements. Our plant health authorities inspect growers of pine each year, and only grant authorisation to issue passports if a place of production and its immediate vicinity is free from DNB. In the event that DNB is found on plants, they must be destroyed and authorisation to issue passports will not be granted for that place of production. In exceptional cases authorisation may be granted to move asymptomatic pine to specified regions within Britain where DNB is already present. Growers of pine plants for planting are obliged to inform the relevant Plant Health Authority if they suspect that DNB is present.
There are no movement controls on logs, sawn wood, cut trees (e.g. Christmas trees), branches, foliage or seeds, because these products are not considered a significant pathway for spreading the disease in the natural environment. However, visitors to nurseries should adopt appropriate biosecurity measures to prevent unintentional movement of infected material from the natural environment.
If you find the disease in a nursery or garden centre, you must report it to a local Defra Plant Health & Seeds Inspector in England and Wales (or their central helpline 08459 335577) or, in Scotland, to Scottish Government Rural Payments & Inspections Directorate's Horticultural Marketing Unit (tel: 0131 244 6303). There is no statutory requirement for notification if it is found in woodland or other mature trees. Although there is no requirement to report the disease on mature and woodland trees, it would be helpful for monitoring disease spread if newly discovered outbreaks in Wales and Scotland could be reported to the Anna Brown, Forest Research.
Irrespective of the above statutory position, it is strongly recommended that woodland owners and their agents need to be aware of the distribution and severity of DNB on and adjacent to their land so that appropriate management strategies can be put in place as part of their overall risk management.