Host of the month - Pine

‘Host of the month’ is a series of Blogs and PDF’s that highlight a tree host and their associated priority pests and diseases that are best seen and recorded in that month. For August we’re looking at pines and Dothistroma needle blight.

Pines (Pinus) are the largest Genus of conifers with around 115 species and are part of the Pinaceae family along which also includes spruce (Picea), fir (Abies), cedar (Cedrus), larch (Larix), hemlock (Tsuga) and Douglas firs (Pseudotsuga). In the UK we have one native species, Scots pine (Pinus sylvestris) which has the second widest range of any conifer, stretching from the west of Scotland to Kamchatka, and from central Spain to the Arctic circle - a range exceeded only by common juniper (Juniperus communis). Scots pine is ubiquitous across the UK but is considered truly native only to a few areas of the Scottish Highlands where it is the dominant tree species of the once extensive Caledonian pine forest.

Pines are popular forestry species in the UK where three species have dominated: Scots pine, Corsican pine (P. nigra subsp. laricio), and Lodgepole pine (Pinus contorta subsp. latifolia). That changed dramatically with the impact of Dothistroma needle blight, one of the Observatree Priority diseases.

Dothistroma needle blight (DNB)

DNB is a disease of conifers caused by the fungus Dothistroma septosporum with pines being particularly susceptible. Until the late 1990’s the disease was rarely seen in the UK and was primarily a problem on radiata pine in southern hemisphere countries like New Zealand. By 2006 it was found in 70% of the Corsican pine stands that were inspected in England, Scotland, and Wales but lodgepole pine (P. contorta) is also adversely affected and neither species is now planted to the same extent. Other affected species include Scots pine, Ponderosa pine (P. ponderosa) and Bishop pine (P. muricata) though the latter two are rare in the UK. Larches (Larix), firs (Abies), hemlocks (Tsuga), spruces (Picea) and Douglas fir (Pseudotsuga) seem to have low susceptibility. The disease causes premature loss of needles older than one year and although trees can tolerate this, repeated and severe infections gradually weaken the tree and can eventually lead to death.

Identification

The first symptoms of infection with DNB are to be found on older needles towards the base of the crown. Soon after infection they develop a yellow-tan banding which gradually turns rusty red-orange, hence one of the former names for DNB, red-band needle blight. As the infection builds the ends of the infected needles turn brown while the bases remain green. This becomes increasingly apparent as summer progresses and eventually black fruit bodies appear on affected needles and release spores which are spread via moist, misty air or rain-splash. Finally infected needles are shed prematurely, giving rise to a characteristic ‘Lions tail’ appearance.

Lookalikes

There are many pathogens which can affect pine needles, many of which can be mistaken for DNB and include Lophodermium species, Cyclaneusma, Lophodermella which affect individual needles, and Ramichloridium pinii and Brunchorstia pinii which affect whole shoots. Identification is often only possible via the fruiting bodies (x10 hand lens essential) and sometimes only with microscopic examination of the spores. For more information on the symptoms of DNB and lookalikes see the Observatree DNB resources page or Host  of the month page. You can also test your knowledge with the Pines host of the month quiz.