I use Nordox 75 about a tablespoon per gallon of water on my Keitt trees. It sticks better to leaves/limbs/etc. better than blue liquid copper products. It also costs more... There are many other brands that also stick pretty good and some may be less expensive so shop around & google it.
Keitt mango trees often get die back/anthracnose/etc. etc. Cooper sprays in my yard are needed for growing Keitt mango trees more than any other variety in my yard except my Rapoza needed it just as bad a few years ago and now it's ok.