i am trying to stop my massive walnut tree from producing. does anyone know
how to do this? i think it's a black walnut. it's pretty old, it shades
about 1/3 of an acre.

See above comment about hormone spray to prevent fruit setting. See if there is
one for walnuts. However, with a tree that size, you may need to have it
sprayed by a professional arborist, at considerable cost. If you don't need the
tree, a professional logger will pay you big bucks for the privilege of cutting
down the tree and hauling it away. Black walnut is extremely valuable wood.
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)