Diplodia shoot blight, Diplodia sapinea, is a fungal disease that kills the tips of the branches of pines, and less frequently spruce and firs. In the blight stage, it can cause severe dieback and the fungus can grow into the stems and main trunk where it becomes a canker disease. It is considered a secondary infection in that weakened trees are more readily infected. Healthy trees are more resistant to infection.
During moist weather in spring, spores ooze from last year’s fungus that is growing on dead tissue. Wind and rain carry the spores to young needles and buds, infecting current season needles and developing shoots from late April to midJune. Within a year, the fungus produces more spores. Wet conditions during this period are needed for the disease to continue its infection progression.
Diplodia shoot blight most frequently affects Austrian pines but can also damage Scots pine, ponderosa pine, and Mugo pine. Spruce and fir can also be affected. The disease occurs most often in well established plantings; trees 25 to 30 years old can be especially vulnerable.
The most common symptoms are stunting and browning of current-year shoots in the lower branches. Dieback of the current season’s growth year-after-year, eventually results in dead limbs and stunted tree growth. The disease is initially confined to the lower branches. With time however, it progresses upward until only the very upper branches are green, while the middle and lower portion of the tree are brown with brittle, dead branches. Stunted, straw-colored-to gray needles are most likely to host fungal spores, but cones can also be infected. Small black dots, the spores, are visible at the base of needles and on cones.
If you think your pine trees may be infected with Diplodia shoot blight, contact Cutting Edge Tree Care Specialist. With over 20 years as a licensed arborist, we have solutions that can help save your pines!