Bob,
On our website (under Plant Advice) we have a plant information leaflet on Preventing or Reducing Fruit on Ornamental Trees & Shrub. Unfortunately, the window of opportunity for applying hormone-type sprays is during flowering before fruit set. Spraying before or after flowers results in wasted time and money. Because the tree is large, you may want to consult with a certified arborist for additional cost and information. Please read the leaflet thoroughly; you may find the wife is always right.
dt, Plant Clinic