There is a guy wandering about in our woods right now spraying our hemlocks for adelgid and scale.  We use a lot of hemlocks here, mainly as screening from the road, but several are major specimen trees.  Wooly adelgid and scale have both turned into chronic issues in Connecticut, capable of knocking out even very large trees.  In areas along the coast the adelgid has killed almost all hemlocks. 

Now I have never pretended to be a devotee of the organic way, though it has its points; I like to use what works, if it is organic wonderful, if it isn’t also wonderful.  The little Pyrethin molecule (quite capable of killing just about anything) doesn’t know after all if it was distilled from a marigold or made in a lab.   The insecticide being used is somewhat close to black magic.  Highly water soluble, the stuff is sprayed on the trunk and is absorbed into the tree; if it rains and washes into the ground it is absorbed through the roots.  From there the only critters affected will be insects chewing on the needles. Upsides: reduces the potential drift problems (hence reducing the number of other insects that are unintentionally killed), works on our eighty foot monsters, reduces the amount needed; downsides: not cheap, and for God’s sake don’t dump it into any watercourse.   There is a place for correctly used, nasty tools.