Lack of pollinators is an issue.
I helped the bees a bit with some hand pollination this year.
Kentucky has had a fine growing season so far, except some spots are a bit dry, but I did notice light fruit set, despite heavy blooms.
Again, I think limited number of pollinators.
Both apples, pears as well as honeybees are NOT native to Americas.
Because apples were light last year, I’m seeing mostly heavy set of them this year, although, in my own orchard, there are a few trees that are very lightly set.
Plums are extremely variable, but none have required much thinning. Early Magic, Elephant Heart, Satsuma and Ruby Queen J. plums have almost no crop. Elephant Heart was the star of my entire orchard last year, but the other plums mentioned performed poorly last year as well. Reema set the perfect amount of fruit.
Nectarines set light but peaches did require a lot of thinning with Silver Gem requiring some. Carene is the only nectarine that required a lot of thinning, which is nice because it is very early and tends to get up high sugar. It is the first year that Honey Royale, the low acid, very high brix nectarine you sampled here has a pretty good crop potential. I’ve never eaten one since the year you tasted it here because a light crop is impossible for me to protect from animals that love the low acid fruit and the sweeter the better.
I’ve seen very little apricot set this year as well, except for my Alfred growing against my house.
That would suggest to me that the problem was less about pollination and more about inadequate sun to provide the energy for the trees to develop their fruit. My house’s white walls would increase the solar power reaching the leaves of the cots. On the other hand, Carpenter bees are nesting in the trim of my house, so I can prove nothing.
All my trees got at least 2 or 3 days of attention from a lot of bees.
The conditions in my own orchard are pretty universal in my area in general, but there is quite a bit of variability in plum set- at some sites, E. plum set is normally heavy, but J. plums at the heaviest set locations don’t look to need thinning.
My fruit trees are new, so I accept that low fruit set. However, it was a very slow wet early spring in Vancouver/Portland, so other things are off. My Iris are late, strawberries early, and birds were thirsty so ate my cherries.
I have a few plums that are solidly set and growing rapidly now we got sun for 2 weeks. While not many, I am excited to taste a few.