Typically, the disease is most severe in the lower portion of the tree crown. In late winter or early spring, small black fruiting structures of the disease-causing fungus rupture through dead portions of the needle. The green base of the needle turns brown, and dead needles are cast prematurely throughout the spring and summer. Loss of older needles and the production of new shoot growth in the spring give the branch a tufted appearance. Newly developed needles are resistant at first but become susceptible by mid-summer.
Older needles are susceptible throughout the growing season.
Symptoms of Dothistroma needle blight may resemble needle scorching or injury caused by chemical sprays. Heavy loss of older, inner needles plus the appearance of small black fruiting structures on needles in the spring are good diagnostic symptoms and signs of Dothistroma needle blight. A single fungicide application in early June normally will protect foliage from infection. Make sure that all needles are covered thoroughly with the fungicide. It is a good idea to spray adjacent susceptible pines.