Impact of Sirococcus shoot blight (Sirococcus tsugae) and other damaging agents on eastern hemlock (Tsuga canadensis) regeneration in Northeastern USA

In 2009, Sirococcus tsugae was first reported in Maine on eastern hemlock. Our goal was to quantify the impact of the shoot blight disease caused by this fungal pathogen of unknown origin on eastern hemlock regeneration. From 2013 to 2014, 59 long-term monitoring plots established by the US Forest Service (USFS) Forest Inventory and Analysis (FIA) program in New England and New York were surveyed to determine the impact of S. tsugae. Damage by hemlock woolly adelgid (Adelges tsugae), elongate hemlock scale (Fiorinia externa), white-tailed deer (Odocoileus virginianus), or other causes was also recorded. Disease incidence and severity (percentage of shoots blighted and percentage of crown defoliated) were assessed for 20 seedlings per plot. Sirococcus shoot blight symptoms were present in most plots (90%) and on most seedlings (72%). For the majority of seedlings, blight affected less than 10% of shoots, but the percentage of shoots blighted did range up to 75%. Similarly, needle loss was limited to less than 25% of the crown for most seedlings. Disease severity was positively correlated with overstory hemlock density. Using species-specific polymerase chain reaction (PCR) primers, Sirococcus tsugae was identified from samples collected in the majority of sites (68%) in New England and New York. In permanent plots at the Massabesic Experimental Forest in Maine, disease symptom severity increased from 16% blighted shoots in 2011 to 47% blighted shoots in 2013. Results confirm that Sirococcus shoot blight of eastern hemlock is more widespread in natural forests of northeastern USA than previously known and that symptoms can be severe (>75% blighted shoots) in some locations.