Kumquat fruit drop: Always the same result, no matter what

Question

I got different responses, often conflicting ones: It could have been from excess water as well as lack of water. While June drop may be associated with heat, even fruits which formed later in the fall dropped down in large numbers. Here are all the suggestions I was given, none has worked:

1- Lack of water

2- Excess water: I have tried a wide range of water supply.

3- Excess fruits - natural culling, so-to-speak. It should never end with five or six fruits remaining on the tree till maturity.

4- Hot weather: Even late fruits have fallen in large numbers.

5- Lack of nutrients - I have added humus & compost and supplemented with fruit trees fertilizer. I used slow-release pellets to avoid over-fertilizing.

6- Fruit fly: No maggots were observed inside the fruit.

The drop process is quite fast. The fruits are still green and may suddenly turn soft and partly yellow and drop overnight. I followed-up the process by keeping only the green fruits and watched how the ground is covered with fruit the next morning.

My climate is Mediterranen. It is zone 11, so I have no frost. Summers are hot. Main heat waves occur between July and August.

Answer 1

Right so I hate to sound like an echo but the reasons you listed are the only reasons I can think of for why your tree is dropping it's fruit. The best I can do is prioritize them by likelihood:

1. Lack of water
2. Lack of nutrients
3. Bugs
4. Natural (tree has too much fruit)

The others are either under the umbrella of those first four or are not relevant. So, next season, I would plan on doing some testing. It sounds to me like you have multiple tree's. So I would plan on setting one of them up with a regulated (automated) supply of water and fertilizer. Prune it before next spring (fairly heavily) and give it some special tlc. Try your best to keep bugs off, since it's only one tree, this just means tending to it daily the old fashion way: manually. If this tree still ends up dropping fruit just like the others then I would be shocked tbh... and can't help you. Good luck!

Answer 2

It's time to get your soil tested. You tested most of what that is to be tested. The the biggest reason for fruit drop is some sort of nutrient deficiency. I had suggest you use a Citrus or Palm Tree fertiliser because they have higher amount of certain micro-nutrient, but now I think you might as well test your soils before you go adding more fertiliser to a soil that already has some fertiliser in it. You will not know exactly what the problem is until you get the soil tested. Everything gets back to the soil. Soil is life.

You can start with some of the DIY testing kits, but they do not test micro-nutrients and a list of other things a laboratory soil test will give you.