Yes, this is sun scald. It is made worse by fertilizing, especially fertilizing after flowering. Sun scald is especially common if shade trees have been pruned. Most rhododendrons adapt to their location. However, if the sun exposure is changed, this happens. In your case, it is very easy to see the cause. In each case where there is severe sun scald, there is a stump where the stem was cut, maybe to cut off a flower. In any case, the pruning caused leaves to be exposed to the sun that were previously shaded by other leaves and they burned. There is no biological reason to prune off the damage. If you don't like the looks of it, you can remove the damaged leaves, however this will cause the leaves underneath to get sun scald, just as these leaves got sun scald because the leaves above them were cut off. This is one reason why it is very important, if you are going to prune, to prune immediately after blooming and even then expect some sun scald.

nomen_nudum: and when scientists did exactly that, they found that yes, indeed, waterdrops on plant leaf surfaces CAN cause sunburn to varying degrees. Oddly, the above research paper has been widely referenced in articles claiming that water on plant leaves = burnt foliage has been entirely debunked. When that is exactly NOT what the researchers said, LOL! Here in the hot arid desert, if I water and get water drops on the leaves, it does - sometimes - damage the leaves. But not always, or even as often as I sometimes fear. And the damage is generally slight when it does occur. And no, it is not leafminers or some other pest. Fortunately (and I never thought I would use the word "fortunately" in this context) since it IS a desert, it rarely rains. I can see where even small amounts of damage could accumulate to lots of damage in an area where it rains nearly every day, followed by hours of fierce sunshine. Sadly I have no solution - except maybe to run out after it rains and try to knock some of the excess water off the leaves. The use of shade cloth might be worth trying however. When I lived in Puerto Rico, I never had a problem with sunscald. I grew peas and lettuce under shade cloth. Peppers, eggplant, tomatoes, all grew like mad things. We would get torrential downpours several times a week, but they didn't generally last long. I don't know why this would be a problem in FL but not in PR - maybe something about the different varieties being grown? I have NO IDEA any more what exact varieties I was growing there, but I really regret not being there long enough to establish a good plot of pineapple! I did have a couple of orange trees in the yard that grew the most hideous, scabrous, scary-looking, juicy, delicious oranges I have ever tasted. This post was edited by zensojourner on Wed, Oct 8, 14 at 15:51

This is just MHO I contribute it to the UV rays are slowily intensifying. As I noticed back when I did landscaping. Each year it took less time to tan or sunburn. An noticed the older tree leaves scorched very easily. An am noticing now full sun plants can't handle that many hours of sun without shade clothes or breaks of shade. I agree something strange. As cool weather and clear sky days are scalding plants.

Jean: Sorry, I don't have any photos, this was 2 years ago. Last year I covered them and they did well. I guess I just wanted to avoid maneuvering around the stakes this summer. John: I see all the mature citrus around here without any sunburn, and I guess I expected too much from a dwarf mature and youngster tree. I got my water bill today and it doubled from last month - so early! I guess I'll have to find some stakes and erect their little cabanas.