Dothistroma Needle Blight
Dothistroma needle blight causes premature dropping of pine needles the year after infection takes place. It is common on Austrian, ponderosa and mugo pines. Because Austrian and ponderosa pines normally keep their needles for 3 to 4 years, premature needle drop will reduce the amount of photosynthetic area, which, in turn, will result in a loss of tree vigor. If a tree is severely defoliated over several years, it may die.
The first symptoms of Dothistroma needle blight can be seen in late summer or early fall. Diseased needles show dark green bands or scattered yellow to tan spots, which often enlarge and develop into red bands that encircle the needle. The tip of the needle above the red band eventually turns brown, but the needle base remains green. Infection is usually seen on one-, two, or three-year old needles, but current season needles may show symptoms by mid-summer. Later, in the winter or early spring, the green base of the affected needles turns brown and the dead needles fall prematurely throughout the spring and summer. Symptoms of Dothistroma needle blight may resemble needle scorching or injury caused by chemical sprays, so remember that Dothistroma needle blight usually appears on the older inner needles and is most severe on the lower branches of the tree. For a firm diagnosis, take a branch sample showing the symptoms in progress to the Cooperative Extension Office. The Extension Office can also provide you with up-to-date information on the copper-based fungicides that can be used for control of Dothistroma needle blight. Two fungicide applications are preferred for good control, the first in mid-May, the second in mid- to late June. Make sure all needles are covered thoroughly. In most cases, yearly spraying will not be necessary once the disease is brought under control. Collect and remove all diseased needles that fall to the ground around the trees. In areas where Dothistroma needle blight is severe, consider planting another type of tree, and not necessarily another pine; even though Scots pine is considered resistant to this disease, it has its own vulnerabilities. Call the Extension Office for a list of recommended trees.