I know you well enough to realize that you have a high level of practical intelligence- I doubt you need much from me to work out your own experiments.
One thing I believe to be understood- early water deprivation does not really affect brix, only size of fruit. This is why I think the same may be true of thinning, but I’m not suggesting that by thinning late instead of early you wind up with higher brix, only that it’s well worth thinning 2-3 weeks before harvest if trees are overloaded then, and that is what I want to experiment on myself, and it will be easy to do. Just don’t thin two similarly well lit branches on a tree at the normal early time and instead thin one of them 2-3 weeks before harvest while leaving the other be and compare brix levels of fruit from one branch to the other.
Arctic Jay and Zephyr I commonly had 20+ brix from. Both were in the two sunniest spots in my yard. Emeraude, H13-23 (the donut in the photo I posted above) and Ambre too, but were from a commercial orchard in PA.
An experiment well suited for your espalier set up would be to figure out how many leaves it takes to bring highest sugar to individual fruit because you are summer pruning serially, I assume. When I manage espaliers I always leave decent amount of leaves to serve each fruit by managing the shoot serving the fruit that way.
I’m thinking leave 6, 12, 18, and 24 leaves for different fruit on the same tree and see how brix compares.
Figuring out exactly how far away leaves can be to serve the fruit is a tougher assignment. Let’s think about that one. One problem is that the further away the leaves are the more shade they tend to caste on closer leaves to fruit so the question becomes pretty complicated. If you stripped off leaves closer to fruit it would change the dynamic compared to a more natural situation. For example, if you had a piece of fruit at the base of a long shoot and you stripped off the first 2’ of leaves I’m not sure what you learn about real life situations in regards to shuttling carbos. If the leaves had been left on the shoot, the carbos may have stopped with them instead of traveling to fruit.
This year my Satsuma plums responded to early rain and warmth by becoming quite large. If I’d known ahead of time I would have thinned them more, but by the time I realized it I thought it was too late. Now I’m harvesting a huge crop of sub-optimal plums- sweet but not sweet enough for me. If I’d thinned them again the moment I realized how big they were going to be I bet they would have gotten that extra point or two that is the difference between being good and being delicious.
This really is the biggest lesson of the season, if it keeps panning out next year.
Incidentally, to my taste a J. plum or nectarine only need to reach 16 brix to be sweet enough for me to be perfect, if texture and appearance is good. Sweeter is different but not really better to my palate. E. plums, however, need to be at least 20 to be great.
Satsuma on nursery trees with ample leaf to fruit ratio are just as bland- go figure.
I’ve come to believe that warm nights may increase respiration at night, generating higher vegetative growth at the expense of brix. At least the humidity does help the stomates function in high heat days.
I certainly am getting a late burst of growth in my peach and nectarine trees. Good in my nursery, bad in my orchard. The energy used for growth probably comes at the expense of sugar.
Actually, at least some of the Satsumas are quite good at 15 brix. Just sweet enough to be delicious for me. I also just picked a top of the tree Fantasia that reached 16 which is also sweet enough to be delicious by my standards. Fantasia is the most perfumed nect I grow.
I think the same about humidity. I think humidity a lot. What I think is yes how hot it is but since the humidity, the trees aren’t being cooked.
Evidently leaf surfaces can tolerate heat better than people when quick burning occurs on a living surface. Last week I happened to look at my hands and they were bubbling like pizza leaving an oven. No fluid inside what I would think are blisters, but that didn’t match a single Google image of ‘heat blisters’.
In the mid-west, the nursery stock grown is much beefier in terms of squatness vs. a tall tree with whispier growth from the Pacific Northwest. It’s so evident and I’ve worked at a few places in the mid-west where I was the guy balling & burlapping, so, I’ve seen a lot of trees being grown. Same for the PNW as I worked at nurseries for 3+years and saw a lot of plant material. I apologize for going off topic.
Back to topic, do you think foliar applications are worth a darn? I’ve never been inclined to fertilize leaves. I always fert. the roots.
Maybe, just maybe and I’m in-between the lines I think, maybe sugars could be increased with some kind of fertilizer but whether proven thru science, I doubt it. FoxFarm claims their ‘Bembe’ fertilizer increases flavors. My best friend likes Molasses as a root drench and Molasses happens to be in Bembe. Bembe however is a soil drench fertilizer. FoxFarm does carry another product, ‘Flowers Kiss’ that is their organic foliar application, fert. It says nothing of flavor increases, however. Anyways, sort of drifting still.
They are often recommended in university guidelines, but I need to search up some studies that compare spring foliar N apps to soil apps in late summer to early fall. The idea is to get abundant N in spur leaves but not into the later forming vegetative shoots.
Foliar calcium is extremely important in controlling rots on varieties like Honeycrisp, Jonagold and Fortune. That is accepted commercial knowledge that seems to hold true for me and wouldn’t be endorsed if it didn’t hold true for commercial growers.
One commercial consultant wrote an article I read claiming that foliar manganese was sometimes more affective than calcium at preventing apple corking and black and white rots. I tried that without calcium and it might have helped a lot, but I also got some weird distortions in the flesh of too many of the apples near the calyx.
These things probably require more precise reading of nutrient availability through leaf analysis than I’m currently willing to do. The straight calcium seems to work well enough- merely adding it to the soil does not.
Sometimes, I still feel like a bull in a china shop in still getting the results I get.
I need to design an experiment that will take into account the fact that I don’t get to the orchard but once a week. But I think I can solve the “thinning” question and your “leaf per fruit” question with the same experiment, as follows:
I will try to find two scaffold arms on the same tree preferably at the same level.
I will thin one one side as I normally do and the other TWICE as agressively.
I will not prune vegetative growth on these scaffold arms and with the different level of thinning, the “leaves per fruit” will automatically be higher on one side over the other.
As a side observation, I will prune the rest of the espalier as normal and will look to see if there is a difference in the fruits on the left & right which are under the scaffolds that I played with. I don’t know what value this "side observation will have, but, what the heck.
I ate a Red Gold nect I picked yesterday and let get soft for a day. At first it was a bit tart and I measured the brix at 14, but then on the other half of the nect it turned sweet and the contrast made the fruit delicious. The difference- just a little more than a single point.