Diplodia tip blight (Sphaeropsis sapinea)
Damage, symptoms and biology
Normally appearing as a shoot or tip blight, Diplodia kills the tips of individual branches. Damage is usually scattered about the tree giving the crown a peppered appearance of dead tips. As the disease develops, the killed tips increase in number and size until 30-40 % of the crown is affected. By this time the tree has been so seriously weakened that pine bark beetles drop by for the kill. Bark beetles are much like Diplodia in the way they act. They will normally only invade weakened tissue that is incapable of fighting off attack. Severe infections in the Toronto and Ottawa areas (Ontario) resulted in the death of the whole tree in a matter of 2-3 years after initial infection.
There has been a dramatic increase in the incidence of a common blight and canker disease of conifers throughout much of the world in recent years. Recently, scientific journals have regularly been printing articles about Diplodia tip blight, Sphaeropsis sapinea and its new importance in natural and urban forests. Until 10 years ago, this disease seldom caused much damage in Ontario. It is now common to see whole stands of pines killed by Diplodia in southern Ontario. Until very recently, it was unusual to see it causing damage in northeastern Ontario. We have seen damage to a few Austrian pines and some large stands of Scots pine in this region.
Under normal circumstances, Diplodia lives in forest and urban ecosystems, surviving as a weak parasite on pine cones and unhealthy branches. Weak parasites are seldom a problem on healthy, "happy" trees, but add stress to the equation and you can have a problem. Trees in an urban environment are always living under stress. The level of this stress increased dramatically in the late 1980s, early 1990s and more recently in the late 1990s and early 2000s because of drought conditions throughout Ontario. We know that drought-stressed trees are especially susceptible to infection by Diplodia tip blight.
In areas where the disease is a chronic problem, planting resistant species should be considered; avoid species such as Austrian or Scots pine.
If you think your tree is infected with Diplodia tip blight, consult an expert for confirmation. To accurately diagnose the problem they will need to examine a tip that has been dead for at least 1 year or a 2 year-old cone; these are the areas where the disease forms the characteristic fruiting bodies that allow it to spread.
Diplodia tip blight has been the subject of several research projects at the Great Lakes Forestry Centre (CFS) over the past few years. We have isolated the fungus on artificial media from a number of hosts and locations throughout Ontario. In collaboration with researchers in Manitoba and the USA, we compared our isolates with others from all over the world to see how or if they differed. These comparisons can be as simple as making visual observations of differences in cultural growth to as complex as looking at their DNA.
Canadian Forest Service Publications
Information on host(s)
Diplodia commonly infects the hard pines in North America. In Ontario these include jack, red, Scots and Austrian pines; Austrian is the most susceptible with Scots being a close second. It is also found in high-value ornamental conifers or Christmas tree plantations.
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