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Fruiting bodies on cone scales
Symptoms include the browning of needles on new shoots as the needles grow from the fascicle sheath. The shoots die. One of the first indications that a shoot is infected is the oozing of small drops of resin from the shoot buds as growth begins in early spring. Infected buds stop growing and do not reach normal size. New buds will grow to replace the dead bud but these too become infected. As the disease continues, whole branches may be killed but the needles remain attached. Small black structures erupt through the surface of the infected needles, especially below the sheath at the base of the needles. Similar small black structures also develop on the scales of second-year cones. These structures are the spore-forming fruiting bodies of the fungus from which thousands of spores ooze during wet weather and are splashed throughout the tree. Lower branches on the tree are usually first to be infected.
Diplodia persists in the black fruiting structures in dead shoot tips and infected cones that remain on the tree. The holding of dead needles and the resin flow from shoots and branches are typical of tip blight. Although trees of all ages are susceptible, disease severity increases as they reach 20-30 years of age. Trees weakened by drought, insects, or mechanical injury (hail, frost) are prone to attack. It has also been shown that high nitrogen fertilization predisposed trees to attack.
Diplodia symptoms on tree and twig.
Prepared by Gary W. Moorman, Professor of Plant Pathology
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