Needle tip blight on white pine
An unknown condition affecting white pines has been observed during the summer for the last four years, primarily in the Bemidji area. The tips of the current year needles are brown or tan but the base of the needles are green and healthy. This year many white pine trees have a brownish cast to them especially in the lower and mid-crowns. See map. The distal portions of current needles wilt and die-back either partially or completely. The new needles look chlorotic and are continually being shed and is especially noticeable during mid- to late- summer. Stomates are a normal white color and no fruiting bodies or other evidence of pathogenic fungi were detected.
The July 15th, 1998 issue of Maine's Forest & Shade Tree-Insect & Disease Conditions Newsletter reports a similar condition that they call "semi-mature tissue needle blight of white pine". The cause of this condition is uncertain but they feel it is probably weather related. They believe it is a physiogenic disease that occurs in the spring when partially hardened but still emerging young needles are damaged by rapidly changing weather conditions. As young needles emerge in the spring, the tissue at the needle tip is the oldest while that at the base in the needle sheath is the youngest. In between is a zone of semi-mature tissue. This semi-mature tissue collapses, due to some rapid weather change and tissue death then extends towards the needle tip causing the tip burn symptom.
According to the article, this condition has been reported in the northeastern US and Canada in past years and was common over large areas in southern and central Maine this year. The symptoms are most common in the lower and mid-crowns and less common in the upper crown. They report it on about one out of ten trees with affected trees growing right next to unaffected trees.
It is not considered a serious problem and no treatments are recommended. Because it is caused by weather conditions it will only occur next year if the weather conditions occur again when the needles are in a susceptible stage of development.