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Distribution and impact in Northeastern USA of the emerging disease: Sirococcus shoot blight of eastern hemlock (Tsuga canadensis)

Isabel Munck: USDA Forest Service

<div>In 2009, eastern hemlock was confirmed as a new host of the fungal pathogen <em>Sirococcus tsugae</em>. Because of the potential that hemlock regeneration could be impacted, the objectives of this project were to: 1) delineate the geographic range of Sirococcus shoot blight in the Northeastern USA, 2) verify the association of the pathogenic fungus <em>S. tsugae</em> with both shoot blight and needle loss, 3) quantify impact of the disease on eastern hemlock regeneration, and 4) monitor changes in severity during 3 consecutive years. From 2013-2014, 59 long-term monitoring plots throughout the northeastern USA were surveyed. Disease incidence and severity (percent shoot blight and crown defoliation) were assessed for 20 seedlings per plot. Sirococcus shoot blight symptoms were present in most plots (95%) and on most seedlings (71%). For the majority of seedlings, blight affected less than 10% of shoots, but 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 seedling and overstory hemlock density. Using species-specific PCR primers, <em>Sirococcus tsugae</em> was identified from samples collected in New England and New York. In permanent plots, symptom severity increased from 2011 to 2013. Results confirm that Sirococcus shoot blight of eastern hemlock is more widespread in natural forests of northeastern USA than previously known and that impacts can be severe in some locations.</div>