Thanks for the question.

As you may know, a single walnut tree contains both male and female flowers. For this reason, there is no such thing as a “male tree” or a “female tree”.  Confusion arises when it is often asserted that one needs two walnut trees for successful pollination.  This is a true statement, because generally on a single tree the male flowers and the female flowers do not mature at the same time.  The male flowers on a tree mature before the female flowers on that same tree do.  The female flowers then have to be pollinated from another tree whose male flowers are still producing pollen. To the best of my knowledge, there is really only one way to prevent female flowers from being pollinated. This is to put bags around all female flowers. Obviously if the tree is large, as I suspect is true in your case, this bagging is neither feasible nor realistic. So the short answer to your question and presumably in your situation, there is no way by which to prevent walnut production and dropping. These events come with the territory of having a walnut tree. 

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