I have a quince that has white speckles on the leaves that my neighbor says
is a virus.

What is your neighbor's background and training? Unless this person is really
familiar with viruses in the Rosaceae, the only way you will know for sure is
by having it tested by a competent laboratory. If it really is virused, the
only treatment is to discard the tree, soil, & label in the garbage (not
outdoors), and sterilize the pot, preferably in the self-cleaning oven.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)