A disease to watch out for

BostonZest discusses efforts by state and city arborists and local volunteers to protect elm trees on the Commonwealth Avenue mall and along the Esplanade and Charlesgate from the dreaded Dutch Elm Disease:

... When we have a few days of hot weather, the elm bark beetle will come out of hiding and begin spreading the disease. That's when volunteers look to the treetops for signs of distress. "We call it flagging, which is the yellowing of the leaves on a certain section," said Greg Mosman, Boston's city arborist. ...