New Tip Blight Recognized on Eastern Hemlocks
By William Ostrofsky, Forest Pathologist, Maine Forest Service
Adapted from an article printed in the February 2010 Maine Woodland Owners (formerly SWOAM) newsletter
Infection has been observed only on current-season shoot tips, so primary infection is believed to occur early in spring, probably within days after new shoot growth is initiated. Symptoms are most easily observed in the spring, but the infected dead tip will stay attached to the shoot for several months. Spore-producing structures of the fungus may be seen on individual needles with a hand lens, but are sometimes difficult to see and are often not present.
The disease is especially apparent on understory advance regeneration of hemlocks in natural stands, and has been recorded in Androscoggin, Cumberland, Kennebec, Knox, Lincoln, Oxford, Sagadahoc and York Counties.
Since 2006, a tip blight on eastern hemlocks has been observed across a wide area in central and southern Maine. The tip blight apparently affects only the tips of branches, seldom killing more than 0.5-inch of shoot tip growth. Often, however, tens or hundreds of shoot tips are affected on a single tree.
The causal pathogen of the tip blight has now been identified from fruiting structures collected in the fall of 2009, and confirmed by USDA APHIS as being Sirococcus tsugae. This determination is based on morphological characteristics and on genetic typing of the specimens.
This is believed to be the first report of Sirococcus tsugae occurring on eastern hemlock in the United States. A more formal survey of pathogen distribution in Maine will be conducted in the near future.
Fortunately, S. tsugae on eastern hemlock appears to be less aggressive than it is on western hemlock. The etiology and epidemiology of this disease on eastern hemlock is not yet known, but tree and stand damage so far appears to be light. It may be only because of the unusually wet weather we’ve had for the past four or five years that we’re seeing this cause any damage.
Foresters, landowners, and the members of the public who have seen the tip blight, are encouraged to report the location to the Maine Forest Service Forest Insect and Disease Laboratory (287-3008 or on-line). Sample submissions are also welcome, but not required at this time. Samples may be sent to: Forest Insect and Disease Laboratory, Maine Forest Service, 168 State House Station, Augusta, Maine 04333-0168.
MAINE DEPARTMENT OF AGRICULTURE, CONSERVATION AND FORESTRY
Maine Forest Service - Forest Health and Monitoring Division