Florida orange tree, fruit is failing to mature?

My mom has had an orange tree and a ruby grapefruit tree in St. Augustine (North Florida) for about 4 years now with no troubles of fruit development. However, last year and this year, the fruit on both trees, which are on opposite ends of the acre-sized garden, has failed to mature. It's definitely being pollinated by bees (as the fruit grows somewhat, showing that bees are pollinating it) and my mom is an avid gardener, taking much care of her plants - not over or under-watering, fertilizing correctly, etc. I'm wondering if anyone else has experienced a similar situation with their citrus in Florida this year? She has been in touch with the local agricultural department, but they say it's a pollination problem, which is not the case since the fruit is developing somewhat and not just falling off like un-pollinated fruit does. Any help would be greatly appreciated! Thanks!

Florida orange tree, fruit is failing to mature?
Citrus can be tricky things. Since you point out that that the fruit has been developing correctly for the last four years and it is a sudden problem only occuring last year and this year I think you are right, it is unlikely to be a fertilisation problem, though it could be if something has occured to affect pollinators over these last seasons.





I looked up the literature on the pollination needs of oranges though. You don't mention which variety your mother has but the two main varieties in Florida are Valencia and Washington Navel. Neither aparently need pollination to set fruit as they are both self compatable. Citrus trees have both male and female parts in the same flower so are capable of self pollination without pollinators like bees. All citrus have a little fruit drop, there is some evidence to suggest that Navel oranges have a little less fruit drop if they are pollinated. However even with no pollinisation whatsoever it would be unlikely that all fruit would drop.





The most likely causes of fruit drop are:


Lack of water


Mineral imbalance in the soil





Check the leaves, if they seem discoloured eg if the tips of older leaves are yellowed suggests a magnesium deficiency. Iron deficiency is also common. You could try checking the acidity of the soil if it is too acid can lock up some trace minerals which may produce fruit drop.





There is also a disease in Florida, first appearing in 1983, called postbloom fruit drop disease. It is not uncommon in Florida and outbreaks become more severe after rain. Did the fruit drop occur after rain? Check the blossoms if they have peach to reddish brown necrotic spots on open petals then it may be this condition.





See the pictures on this web site:





http://edis.ifas.ufl.edu/CH094





Hot dry or windy weather can also cause fruit drop so if you have had these conditions, then that could be the cause. Alternatively, cold wet weather can cause oranges to drop (this is why I said citrus can be tricky)





Different types of oranges also go through a series of five flushes of growth per year, each flush is accompanied by a differing amount of fruit drop, so it could be that. Chances are if the tree is healthy and there is no evidence of mineral deficiency then there is every reason to expect that next season the fruit will be fine. (Just watch the watering!)
Reply:Sometimes it's just now a good growing year.

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