Diplodia tip blight is caused by the fungus, Sphaeropsis sapinea (formerly classified as Diplodia pinea ). It is one of the most destructive fungus disease of pines trees. Most Conifers are susceptible to infection, especially the exotic species such as the Austrian pine. Afghan pine, Scots Pine and Mugo pine with the exception of white pines. Diplodia usually attacks mature trees, stressed by drought, poor site, mechanical wounds and insects. If not controlled, over a period of years it will cause mortality. Early in the spring Diplodia also appears on Live Oaks and Texas Red Oaks as flags ( a grouping of several leaves at the tip of the limb) throughout the tree canopy. However is not usually life threatening to oaks.
Symptoms and Diagnosis
Tip Blight usually attacks older trees that bear mature pine cones, but also can affect younger trees if conditions are right. The obvious symptoms is the browing and stunting of needles of the new growth. The needles are retained on the tree and excess resin flow builds up on the dead twigs and needle bases. Small black pimples (pycnidia), the size of fly specks as very noticeable on the bases of the browned needles, on the dead twigs and cones.
These are the fruiting bodies of the fungus. Diplodia tip blight may be confused with pine tip moth damage but in the case if the later the fungal fruiting bodies will not be present, and moth larvae and tunneling in the shoots will be evident.
Diplodia overwinters as mycelium or fruiting bodies (pycnidia) in the shoots, bark, cones and needle litter. Spores (condia) are released during in early spring and fall in moist, humid conditions. Peak spore production and infection usually conifer with host bud break and shoot and needle elongation. The fungus invades and kills succulent shoot tissue, and forms pycnidia of dead tissue. Infected cones are a major source of inoculum and are often observed on plants that show no sign of infection.
Prevention is the best way to control Diplodia infections. Avoid planting highly susceptible exotic conifers where Diplodia has been a problem. Dead branches, cones and litter are a source of inoculum. During dry weather remove dead branches, cones and rake up and dispose of the litter. Sterilize pruning equipment with Lysol, kitchen disinfectant, which contains ammonium chloride, known as Consan 20, or a chlorine bleach to one part water solution.
Fungicidal sprays, such as fixed copper, Bordeaux or Benlate can reduce infection significantly with timed applications. Apply early spring at bud break and repeat in one or two weeks according to label instructions.
Weakened and stressed trees are more susceptible to disease. Watering during drought periods and fertilize if trees lack vigor. Spores of Sphaeropsis sapinea are ever present and can be found on branches of most pine trees. The spores only infect weakened and stressed trees.