white pests on my hackberry tree
 

There is a big hackberry tree in the yard, and the lower branches' leaves
are geting a blackish- mottled appearance. It is infested with some tiny
pest. They appear as a tiny white flyspeck, like a tiny cotton ball, all
white, covered with white hairs. Not long ago it had bark lice, which turned
out to be a good "pest", is this one good or bad?