Can rhododendrons get sunburned? All of a sudden the upper leaves are turning brown and black.

Question

We have had an excessively wet winter and early spring. Now we are excessively hot and dry.

Answer 1

Yes, rhododendrons can get leaf scorch. Some varieties take more sun than others but generally they like some shade and protection from wind.
Since you had a wet winter and early spring, the plant may have been overwatered, and now drought. Those kinds of stress factors can lead to leaf scorch (marginal leaf necrosis). Gray blight, a fungal disease, can set in after sun scald. Check out the extension sheet below and see if the photos for marginal leaf necrosis or gray blight resemble your leaves. In both cases, non-chemical management is suggested first. Prune out the affected branches. If the rhododendron is getting too much sun, it can be moved to a shadier location or other plants added that would shield it. Water when rain is not sufficient.

Here is more information:
http://hortsense.cahnrs.wsu.edu/Search/MainMenuWithFactSheet.aspx?CategoryId=1&SubCatId=4&PlantDefId=32&ProblemId=525

https://www.gardeningknowhow.com/ornamental/shrubs/rhododendron/rhododendron-care.htm