Greetings Edward:
According to Dow AgroSciences, you are not too late -- you can use Remedy Ultra herbicide to control leafed-out Osage-orange (be mindful of off-target drift/damage). Listed below is a link to Dow AgroScience's webpage on Remedy Ultra herbicide:
http://www.dowagro.com/range/products/remedy_ultra.htm
Please remember that "the label is the law." Using a pesticide in a manner that is inconsistent with the use directions on the label is a violation of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA).