I haven't started spraying my jacks yet. This was the first year that I had fungal issues, and I attribute it to what will likely be one of the rainiest summers in recent south florida history.
Your best bet for getting a maintenance program figured out is to call Har out to your place for a consultation / recommendation. He really helped me zero in on mine. Right now I'm trying to get him on a quarterly schedule to come and give recommendations based on anything new that I've run across.
Now, with the TL;DR version out of the way, here is the magna carta for those of you who are still reading:
It's going to be really specific to your soil and micro-climate (you'd be surprised how much variance there is in South Florida, especially in the former). But here are some general guidelines that I've learned per Mr Har.
For most mango trees grown inland, it's imperative to establish a monthly or bi-weekly fungicide spraying routine starting from flower and lasting til the end of growing season. A powdery mildew fungicide should be used during the cool season (eg, sulfur) and switched for copper or another warm weather / anthracnose fungicide once temps start to rise. You can skip the fungicide once harvest is finished for most trees. However, some trees will continue to need applications until growth stops, depending on how much rain we're getting.
Nordox has been my favorite warm weather fungicide to date, but it is high in copper, so you may want to get a soil test done first. (If you're using enough mulch, you may actually have a Cu deficiency and can use Cu fungicides without worry.) One nice thing about Nordox is that it is extremely rainfast, so application frequency can be dropped to once per month. It's a good idea to rotate something else in to stave off formation of resistance. Abound is probably the best rotator I can think of, unless you're staunch on going 100% organic, in which case you can use something like double nickel 55.
You will want to be pruning most of your trees either yearly or biennially to keep them at around 14 feet. This is a major pain in the neck (both literally and figuratively) if you have more than a couple of trees. It also seems to be a catalyst for mango infection on many cultivars -- as all the new growth can rapidly become infested with anthracnose -- requiring you to continue your fungicide regimen until end of growing season.
As far as fertilizer goes, the mulch will not be enough. It will provide an excellent base for your trees to grow in, but the organic material has a tendency to lock up micronutrients. So, you will want to use something like the
Hartilizer which has a complete micro package with a high amount of slow release potassium and zero nitrogen. Your normal 8-3-9 or any home depot fertilizer will be comprised of purely water soluble ingredients, which will be gone in 2 good downpours. The K in Hartilzer, on the other hand will last for weeks or months.
Based on your own unique situation, you may need to add specialty fertilizers to your routine. For example, I also use gypsum to provide Ca due to the fact that most of my trees are growing in a foot of compost. Suflur may also be used to drop the pH in areas where it's both a problem and the soil has a composition that is amenable to pH adjustment.
If you have annonas (eg, sugar apple, atemoya), you will very likely need to spray insecticide to keep the leaf hoppers at bay, which will decimate their host trees if left uncontrolled. And if you have carambola, lobate lac scale will be a persistent problem requiring treatment. There are various biologicals which are effective against both. I have had success with a neenix and botanigard combo. Just be warned that both products need to be stored in a cool environment if you wish to keep them for more than a few months, as they degrade quickly in high temps. A weekly or bi-weekly spray regimen is most effective.
