Diplodia (Tip Blight)
Diplodia (Tip Blight) dead, brown needles at the tips of pine branches may signal the presence of Diplodia tip blight. Surveys indicate that no species of pine (Pinus) is immune to this disease, although some species are more severely affected than others. Austrian pine (Pinus nigra) is one of the most severely damaged species. Tip blight infection year after year can weaken and even kill large Austrian pine trees. Douglas-fir, white, Norway, and blue spruce may also be infected, but infection of these species usually develops only on trees that are injured or stressed and when infected pine are nearby to provide a source of inoculums (spores). The fungus which causes tip blight of pine trees is Sphaeropsis sapinea (also known as Diplodia pinea). This fungus is present throughout the year in dead needles, leaf sheaths, twigs, and cones located either on an infected tree or on the ground. Small black fruiting bodies mature during late spring or early summer in this material. The brown oval spores ooze out of the fruiting structure during wet conditions and are scattered by wind, splashing rain, animals, or pruning equipment. Some spores land on young needles of the current season’s growth. After the spore germinates, the fungus enters the needle through a stomata (or pore) and grows toward the base of the needle. A few hours later, a brown area develops near the point where the fungus entered the needle. By this time, the fungus has grown into the twig. The progressive invasion of the twig by the fungus results in browning of the attached needles and canker production in the twig. The damage caused by this disease is most severe on old or weakened trees. Old trees or trees exposed to unsuitable growing conditions, mechanical injury, or damage by insects may eventually be killed. Thorough weekly watering during extended dry periods of the growing season and spring broadcast fertilization will result in a tree that is more vigorous and more resistant to tip blight. When only a few branches of a tree show symptoms of tip blight, a program of pruning, sanitation and fertilization should help minimize disease. Prune off blighted twigs and destroy or discard them. Since fungal spores can be transported to healthy twigs during the pruning operation, prune when the tree is dry. Where disease is severe on smaller landscape trees, applying some fungicides will help to minimize new infections.