On Sun, 18 Sep 2016 20:34:56 -0400, wrote:

A chain saw. The grass will never thrive under the pine

Um, the lawn turf is not directly under the pine tree.

OP posted a drawing that shows a distance between the tree and the
turf.

Cite:

"...Here's a rough sketch of the area
http://i63.tinypic.com/2enuomq.gif "

IMHO the cherry tree roots "could" be sucking moisture from the lawn
turf -- root prune the cherry tree if that is in fact an issue.