This is all anecdotal, obviously, but I would assume it would be related to nitrogen feeding at the wrong time. Comparing flowering here before and after installation of an irrigation system, I didn't note any differences. The factors that seem to influence production here are:
- Lack of nutrition (eg, zinc, iron, k, etc) -- very typical here in south florida
- Lack of cold. Cold seems to be the #1 trigger for reproductive growth here.
- Production from the previous year (in conjunction with nutrition levels), ie, high production the prev year without replacing nutrients usually means lower production in the current year.
- Nitrogen applied during the dormancy period.
- Shade.
- Over-pruning or pruning at the wrong time of year, which encourages vegetative growth.
With supplemental irrigation, I've got thousands of mangoes on 35 or so mango trees, after having a banner year last year.
Don't get me wrong I'm not complaining but on the subject of this being a bad year as far as fruit production this 2020 season for me is aptly called my nightmare season. I live in Kendall in a nice residential area with 230+ mango trees of about 30+ varieties. I counted every fruit on all the trees and my estimate for 230 trees of which 95 have been in the ground from 3-20 years was 235 fruit. Now what the heck has caused this catastrophe? I only have 2 variables I can blame. Over watering and untimely fertilization. Since I live in a residential area I must keep my lawn looking nice and since we've been in a drought for many months I've had to use the sprinklers a lot. Also I have about 10 potted trees from the nursery as backups in case a tree falters and I can't heal it that have to be watered regularly and I put them in a place where the sprinklers can hit them. So since my sprinklers also hit the mango trees and their roots my trees have been way over watered. Between the over watering and untimely fertilization/fertigation the trees are all spectacularly beautiful and healthy ""BUT"" no fruit to speak of.
As far as what trees did produce as of April 3, 2920 etc.
Pickering great crop
Rosigold great
Dwarf Hawaiian good with a smaller 2nd crop.
After this a spot here and there. Most spots are on 1 to a few Sweet Tarts and Cotton Candies and a Duncan and a Maha. That means as an example that out of 50 Sweet Tart trees maybe 6 have 1-20 fruit and the others have a big zero. But all total about only 235 fruit.
Next year/season I am not going to turn the sprinklers on or fertilize and I am going to hand water the grass by hand if conditions require """""BUT""""" that too may not work because the roots of my trees are still under the grass!!!!!!!! Jokes on me.
Even my 20 year old trees have zero fruit and that includes 2 Haden, 4 Keitt, 1 Van Dyke, 2 Glenn, 1 Valencia Pride, 2 Hatcher. Crazy Crazy Crazy but my own fault. Live and learn.