To me the leaves look like the plant is not taking in enough water. If its hot and dry I water some smaller containers daily. There are some secondary insect or fungal issues which you also have seen but those may clear up once the plant is healthier.

To me it just looks like bad sun burn. How mature are your trees? How many hours of light is it getting? Is it in the sun durring the hottest hours of the day (3-6)? If it's in full sun all day you may want to move it to a place where it gets light from sunrise to about 2 or so. Or you can get a sun shade.

Definitely no sunburn shown in any of the pictures.

The necrotic spots in all the photos look like the result of a hand too heavy on the watering can, though the top 2 photos could be nutritionally related (a high TDS level [salts] in the soil solution, the result of using a high-P [bloom-booster] fertilizer, or possibly low fertility due to not fertilizing at all).

Al

Interesting Al. Thanks for the info.

Al - how do we tell the difference between a leaf that's been fried from the sun & a leaf that is fried from TDS?

thanks, always learn a lot from you.

Chlorophyll molecules rise to a state of high excitement when photo load (light level) is high enough. The energy that is released as
electrons during molecules' return to their normal energy state may be
sufficient to form O2 negative radicals. These are the same O2-
radicals found in H2O2 (hydrogen peroxide) and are extremely reactive
particles that readily destroy (oxidize/bleach) chlorophyll molecules. The entire
process and technical term is photo-oxidation, and it is made manifest when organic molecules are bleached/oxidized. Initially, photo-oxidation is expressed as irregular white/silver/gray blotches (never as chlorosis) on foliage or immature bark tissues due to the effects of the bleaching/oxidization. Later, depending on the nature of the tissue affected, tissues turn black (usually in plants with more succulent foliage) or brown.

Expression of symptoms in plants affected by a high level of salts in the soil solution vary by plant and the severity of the problem. Some plants first exhibit necrotic areas in the plant's most distal parts (leaf tips and margins); other plants might simply exhibit symptoms of the process of leaf abscission (shedding - symptoms like your first two pictures) as a drought response (since a high TDS level inhibits a plant's ability to take up water). It's difficult to pinpoint cause of chlorosis as seen in your first two pictures w/o a feel for soil type and watering/fertilizing habits because all three (over-fertilizing/high TDS, under-watering, and over-watering all cause the same drought response.

It's possible that high root/soil temps might have caused the chlorosis, but it wasn't sunburn.

Al

I appreciate your comments al, & love learning from those who know more than me!

So the whole sunburn issue sounds very similar to what happens in humans. I know that porforins in the blood absorb electrons from the sun to send to mitochondria to run through electron chain transport. When the sun is too intense oxidation occurs & skin problems develope.

it seems from what your saying is no chlorosis should happen from sun burn of foliage, just browning or blackening.

Now I am aware that dha can help absorb electrons to run through electron chain transport. If chloroplast is like the mitochondria, & chlorophyll is like the porphorins in our blood (almost same molecular structure but with mg in the center of the ring instead of iron), is their something that can be given to the plant to decrease oxidation? Silicon helps strenghthen cell walls, does this lower oxidation?

So if I get this right, the necrotic area in the distal parts of the leaf are a sign of drought stress, along with the shedding, which causes the chlorosis. From there, the cause must be determined from media, water, & fertility practices.

Now the chlorosis from shedding, in I believe the 2nd picture, was all over the tree, what if it was just a leaf or 2 at the bottom of the leaf canopy? Is this the same drought stress signs, just less severe, or is it just an old leaf?

this is COOL stuff AL!