Apple trees should be sprayed at least three times as a preventative for insects and/or diseases, but could actually require more throughout the season. The first spray should be in late winter/early spring while the tree is still dormant and just as you begin to see a little pink in the buds. The second spray is during the growing season just as the flower petals have all fallen. The third spray should be done ten days after all of the flower petals have fallen. There are several different fruit tree brands on the market today.

I have attached these three sources of information for you:  University of Delaware Cooperative Extension, University of Maryland Cooperative Extension and Virginia Cooperative Extension. Hopefully this information will help you decide which pesticide to use. Other information is also included on how best to take care of your apple tree.

If you have any other questions about your apple tree, please feel free to write to Ask Extension again or if you prefer to speak with someone in person, contact the Delaware Cooperative Extension in your county.  Your tree looks like it's off to a good start!

https://extension.umd.edu/resource/growing-apple-and-pear-trees-home-garden/

https://www.udel.edu/academics/colleges/canr/cooperative-extension/fact-sheets/home-orchard-production-apple-pear-and-stone-fruit-disease-management/