Diplodia tip blight is a fungal disease of Austrian, Scots, mugo, red, and other two needled pines. The disease does not usually kill the tree, but results in brown shoot tips that many people find unattractive. When large numbers of shoot tips are affected over several years, entire branches may die.
Shoot tips that have already been infected by the Diplodia fungus cannot be cured. New shoot tips that form each spring can be protected with fungicides. The fungicides must be applied prior to fungal attack.
Trees in stressful situations may be more seriously affected. Also, individual trees vary in their susceptibility to the disease.
The Diplodia fungus overwinters on infected needles, cone scales, or the bark of infected twigs. Spores are released from the overwintering lesions from spring through late autumn. Splashing rain or irrigation water are the primary means of moving the spores about. Spread of the disease is therefore more likely during rainy spring weather or where trees are watered through overhead irrigation.
New shoots are infected during the spring from the time of bud break to the point where the shoots have stopped growing for the season (usually a period of 6 to 8 weeks). The cones are infected during the spring of their second season of growth (2 years are required for pine cones to mature). Spores are continually released during the summer, but once the new shoots have completed their development, they are no longer susceptible to infection. Most of the spores are released from infected cones.
The first noticeable symptoms include yellowing and stunting on the tips of the lowermost branches of infected trees. These symptoms are most noticeable from midsummer into autumn. Because the pathogen usually builds up on the cones before spreading to infect the shoot tips, trees of non-cone bearing age are often relatively symptom free. Once a tree reaches cone bearing size (about 10-15 feet), symptoms of Diplodia are much more likely to appear. Because the disease tends to overwinter and spread from diseased cones, the lower branches are most likely to be affected. The lower branches are closer to the diseased old cones that have fallen to the ground and lay beneath the trees.
Read more about diplodia tip blight management.