Diplodia tip blight, previously known as Sphaeropsis tip blight, is a common fungal disease of stressed conifers, especially pines with needles in bunches of 2’s and 3’s. Austrian pine (Pinus nigra) is the most susceptible host, although the following pines are also susceptible: Scots pine (Pinus sylvestris), red pine (Pinus resinosa), Mugo pine (Pinus mugo), Ponderosa pine and (Pinus ponderosa). Pines with needles in bunches of 5 are highly resistant.
The disease sometimes attacks other conifers such as Douglas-fir (Pseudotsuga menziesii), Norway spruce (Picea abies), Colorado blue spruce (Picea pungens), American larch (Larix laricina), noble fir (Abies procera), silver fir (Abies alba), some true cedars (Cedrus spp.), cypress (Cupressus spp.), arborvitae (Thuja spp.), and junipers (Juniperus spp.).
Except for young seedlings, the disease rarely attacks trees under 15 years of age and most severely damages trees that are older than 30 years. It is seldom seen in forests but prefers ornamental trees weakened by poor sites, drought, hail or snow damage, over shading, compacted soils, root restrictions, insect activity, or other mechanical wounding. The fungus kills current year shoots and sometimes branches, and can disfigure or even kill them under severe conditions.