My Question, what time of year would be best to fertilize apple trees?

Fertilizing your apple trees....

homeguides.sfgate.com › Garden › Gardening

Don't fertilize them now, unless you live in the southern hemisphere and your seasons are backwards from Europe and North America. Fertilizing in the late summer or fall is likely to prompt your tree to put forth new growth that would be vulnerable to frost. Instead, fertilize your tree no earlier than a month before the spring growing period in your zone. The ideal time is just before bud break, though you can fertilize shortly after if you miss your chance. Give the tree a fertilizer rich in nitrogen, but don't over-fertilize or it will put most of its energy into developing new shoots instead of fruit.

perhaps spray in spring to prevent bad apples ,,, instead of fertilizig the tree

http://everythingaboutgarden.blogspot.com/2017/04/different-tips-about-how-to-grow-apples.html

http://www.ehow.com/info_8044514_fertilize-apple-trees.html?p=d

Best is right as the flowers appear in the spring

thanks