Spray, spray and spray. However, if your trees are young and not very big or established just left them do there thing, see how the disease pressures are in your yard. If you spray small trees they will use up all their energy to push out just a couple mangos that you may or may not get to eat and then struggle to put out vegetative growth. If you let them be and let them grow they will be that much closer to being ready to hold a worth while amount of fruit. I continue my nutritional regiment on my not ready to hold fruit trees and cut off the fruit after the last of the cold weather is done and then tip/shape them every second flush until they look like an actual tree. If your trees are trees and you think they should be putting out a bunch of fruit but don't , you probably need to have plan to spray them and make sure they are getting the MICRO,s they need. I use plain old wetable powdered sulfur in my sprayer for Powdery mildew, first a little diluted to sanitize the trees when the panicles first start to push (maybe an inch or so or before, Hard to time it perfectly with every tree in the yard.) Again when they are to about the 3/4 to full but not open and lastly when they have set fruit but not if they blooms are open and no fruit has set yet. if i see PM growing spray as needed. The sulfur helps to acidify the soil as it washes off and helps the trees take up nutrients as long as your soil PH isn't already too low. ( Dont use sulfur on lemon zest! it burns the leaves, Ironically LZ is very susceptible to PM. I use a product called CEASE and it seems to do a very good job and I believe it is ok for organic)
As far as for anthracnose, Spray copper if you want but I prefer to do it lightly and less often. Copper is a necessary micro but too much of it will hurt the roots of the tree and will stay in the soil for a very long time ( It is used to kill roots in septic drain fields and tanks) I think the CEASE/ Serenade also does a good job with anthracnose control and provides Beneficial's to the soil health as well, but it isn't cheep. There are a lot of fungicides out there and some of them have a lot of horse power but i reserve those for as needed to treat known issues when other more organic methods are not working as they are hard on the pollinators. ( The Bee's, man the Bee's. AKA, the most important creature on earth)
