Unfortunately, it is causing a slightly different problem for me, Citrus Split.
This is a picture of one of the Republic of Texas Oranges that split and fell off.
Splitting is what is known as an Abiotic Disorder. That is a disorder that can not be attributed to any living organism, such as an insect or pathogen, but happens because of an environmental or cultural condition.
Splitting may start as early as July, with most occurring in late August and early September. It can be caused by a combination of factors including extreme fluctuations in temperature, humidity, soil moisture and fertilizer levels. I am pretty sure mine is happening because of extremes in my moisture level. Since the beginning of August, I have registered a little over 5 inches of rain in my yard. I usually try to keep a steady level, but it had been so hot just prior to this rain and I had gotten busy at work, so I was a little lax in my watering duties.
No variety of Citrus is immune to this, however, Navel Oranges are the worst, followed by Tangelos and other Oranges along with Mandarins. Grapefruit rarely split.
Usually the thinner skinned Citrus are more prone to this. Also, Citrus that have been sunburned or the skin has been damaged by some other means are very prone. I am not sure if you can tell from the pictures, but these particular fruit have major bird damage. The skin is all pecked and pitted.
This is the gist of what happens. If you allow the moisture level to drop too much, the tree starts to steal water from the fruit to survive. Splits occur when the excess water and sugars are transported from the roots of the tree to the ripening fruit, and the rind is unable to expand quickly enough to accommodate the added volume. It then bursts open under the pressure. The split usually starts at the blossom end of the fruit, which is the weakest point in the rind.
The split can be a shallow one or a deep one, exposing the juice vesicles, as seen here.
Fruit on young trees are more prone to fruit splitting than fruit on older trees, probably because there is more tree to absorb the excess water.
This situation is very disheartening, not only does it waste the fruit, it creates a good breeding ground for fruit flies and attracts other insect pests. The split fruit should be removed as soon as it is found and discarded as it may also harbor fungi or other bacteria.
The split fruit is edible, however most of the time it is not ripe enough to be usable.
I hope that you can learn something from my mistake this year. Had I been able to keep my moisture level at a more moderate level, I might not be losing as much fruit as I am. I am not at liberty to use a drip irrigation, I have way too many trees, all of which are in containers, but this could be an option for you.
There is a plus side to getting all this rain, my Banana is doing fantastic!
Happy Growing!
Darren