Red Band Needle Blight in the UK

RBNB affects conifer species, particularly pines and especially black pines, overall around 70% of pine species are susceptible to varying degrees.  It has been known as an economically important disease affecting trees, largely in the southern hemisphere, since the 1960s.

The disease has increased exponentially in Britain since the late 1990s, and Corsican pine has proved highly susceptible, infection of lodgepole pine in northern England and Scotland also can be damaging, but Scots pine appears to have a lower susceptibility.  European larch, Norway spruce, Sitka spruce and Douglas fir all appear to be slightly susceptible.     

In Britain and to date it is caused by the fungus Dothistroma septosporum.  The fungus produces yellow and tan band spots and small, dark fruiting bodies visible upon the host needles, these produce asexual spores.  It is believed that water is essential for the spread of these spores and locally ‘splash dispersal’ allows dissemination.  As water droplets fall from needles the spores spread the fungus within the tree and to its neighbours.  Medium to long range dispersal of the pathogen may be caused by mists and cloud; long range dispersal is likely to be caused by the movement of planting stock.

The spread of the pathogen appears to have been facilitated by the increase in warmer, wetter weather conditions in Britain, optimising conditions for spore dispersal.  The monoculture nature of many British forest stands has further allowed rapid spread of the infection.

Spring and early summer is the period when infection is most likely and by autumn affected older needles will have been shed.  First and second year needles remain on the tree and are the main source of the spores in the following year.

As could be expected with a loss of needles, and therefore a loss of capacity to photosynthesise, the effect of RBNB is the reduction of yield.  It usually takes a few years before yield is reduced, if infection rates are low then there is a linear relationship between crown infection and expected increment in volume, e.g. 10% crown infection = 10% loss of volume, however loss of increment increases once there is <40% crown infection and at 80% infection there is virtually no growth.

Corsican pine (CP) is the main area of interest in Britain because it is the second most planted crop tree (60,000 ha) and though stands of over 30 years of age are less susceptible than crops at pole stage all ages of CP can be affected.  In the southern hemisphere aerially-applied copper-based fungicides are routinely used for species that demonstrate a natural resistance upon achieving a certain age, but this would have a limited effect upon CP because of its continued susceptibility.   Trials of stand manipulation upon the FC estate are underway, e.g brashing and heavy thinning, but even if such treatments are effective they will be expensive and a less attractive option for private owners compared to a crop which does not require such interventions.

The FC currently has a five-year moratorium on the planting of CP upon its estate.  It would appear unlikely that for applications to the English Woodland Grant Scheme which include CP for replanting or restocking will be looked upon favourably.  In reality, unless there are dramatic developments in the next five years this may be the end of CP as a commercial species in the UK.