I am guessing Magnesium deficiency from the UF site.
The overal health of the tree is very good. The yellow leaves make up about 10-20% of the tree.
when was the last time you fertilized? what brand do you use? does it have micro nutrients?
I was out of my citrus fertilizer so I used 10-10-10 and it does have micros. That was three weeks ago.
Here is a picture of the tree.
Mg & possibly a slight N deficiency too. Not surprising with the fruit load you have. I notice Mg deficiency on my trees with large fruit load too. You probably will not be able to reverse it, but you can stop it from progressing.
The first thing I would do if I was growing my trees in the ground is make sure the pH is correct.
Anything you add to the soil will not provide ALL the needed nutrients unless the pH is on target.
Also, I would do a nice read of an article that helps you understand how nutrients work with plant tissue of just about every plant.
"Tissue analysis of plants will nearly always show NPK %s to be very close to an average ratio of approximately 10:1.5:7. If we assign N the constant of 100, P and K will range from 13-19 and 45-70 respectively. (I'll try to remember to make a chart showing the relative ratios of all the other essential nutrients plants normally take from the soil at the end of what I write.) All we need to do is supply nutrients in approximately the same ratio as plants use them, and at concentrations sufficient to keep them in the adequate to luxury range at all times."
"I use a liquid fertilizer with a full compliment of nutrients and micronutrients in a 3:1:2 ratio. Note that 'RATIO' is different than NPK %s. Also note how closely the 3:1:2 ratio fits the average ratio of NPK content in plant tissues, noted above (10:1.5:7). If the P looks a little high at 4, consider that in container soils, P begins to be more tightly held as pH goes from 6.5 to below 6.0, which is on the high side of most container soil's pH, so the manufacturer probably gave this some careful consideration. Also, P and K percentages shown on fertilizer packages are not the actual amount of P or K in the blend. The percentage of P on the package is the percentage of P2O5 (phosphorous pentoxide) and you need to multiply the percentage shown by .43 to get the actual amount of P in the fertilizer. Similarly, the K level percentage shown is actually the level of K2O ( potassium oxide) and must be multiplied by .83 to arrive at the actual amount of K supplied."
To get more info like this, just clink of the link below before you target one nutrient at a time. Good luck.
Here is a link that might be useful: Fertilizing plants info
Your newer growth looks good; so I wouldn't stress.
I would guess the yellow leaves look more like a combination of Phosphorous deficiency, sunburn, and a big load of fruit.
That "brassy" tone to the leaf usually means Phosphorous; at any rate, you cannot "re-color" those leaves; it is the new growth you have to watch.
I am just wodering......
Why is it that many say it is only the new growth you have to worry about?
If it were my tree, I would worry about the old as well a the new. I would worry about the well being of the whole tree. I am thinking that a happy growing tree whould have healthy looking leaves as a rule all over, from top to bottom, new and old?
I have also heard that a tree may be too weak to support its old growth and only support the new, causing the old growth to shed. I would guess that something is arry in this case? I could be mistaken? Could someone clear this up for me and the OP too?
Thanks a milion.
You are right that a healthy growing tree should look healthy and green all over. Based on my experience with Meyers, I can tell you that is pretty hard to achieve in a normal garden setting with competing grass, other plants, insects and fungus deriving from nearby host, etc.
So, in the "real" world there will be times when the tree is "over-tasked"; i.e., growing, blooming, developing fruit, fighting molds and insects, not getting enough food or water... or too much. At these times, the tree will take back nutrients from older leaves to use in promoting new leaves, flowers, fruits; these leaves that are "sucked dry" will eventually wither and fall off; they cannot in most cases be rejuvenated (Iron and Zinc deficiencies being some exceptions). So, if the new growth is of good color and normal size leaves, the tree, at this moment is not stressed. The odd colored, odd shaped, partially eaten, etc. leaves only indicate that some time in the past the tree suffered a little.
That is about all I understand from my limited experience and far too limited education (Sadly a B.S. in agriculture from UCDavis, does not go far in teaching one to grow citrus; I have a minor in chemistry; but still what I know comes far more from experience than from schooling).
Thanks everybody for the replies. The soil pH is low. I have been slowly trying to bring it back up. Best I can tell you are all right. It is not a single problem but several small ones. For the first time ever, I got sunburn on some of the lemons.
The tree has always been such a producer, I need to take good care of it.
Careful not to raise the pH too much; I don't know what "low" means to you; but citrus generally do best at 5.5 to 6.5.
John...Thank you for explaining that. Have a great night and I hope all is well.
All goes well; we have 15,000 Meyers now, on track for our 5 year plan of 50,000 producing 15 million fruits (2,000 tons).
Here's a photo of our newest project at 1 month from planting.