For what purpose?

Yep, the old days of "Spray it with poison, just in case it will need it." are over--thank heavens!

Bayer make insecticides and fungicides for fruit trees. See their site for information as and when to spray, perhaps not when the flowers are open. I would avoid these sprays and go for the more organic contact sprays even then only when needed. I have to say that I believe that the fruit producers still spray their trees with many chemicals as a safeguard as they can't afford for their crops to be anything but perfect.

I hope there will be (lol) enough bees around to find and give some good compatable pollen for your apple tree so you can get as many apples as you had flowers. All the insecticides and fungicides in the world won't make any difference without the bee. Leave your apple tree... bee....for now:)

That's why modern Master Gardeners and Agricultural agents no longer recommend preventative spraying, except in certain, strictly limited cases.