Answer: If the tree is severely weakened and near death, then it could potentially fall over and cause damage or hurt someone. It will also serve as a source of infection for other susceptible plants. Often, even severely ailing trees will continue to push out new growth in an effort to nourish themselves.
Borers are potentially fatal to trees, so I would strongly suggest you consult with your county extension (345-3283) as to the prognosis of the tree and whether or not it is worth trying to save it at this point. They will also be able to advise you of the most up to date control recommendations in Pennsylvania.
I'm sorry about your plum tree.
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