Chlorosis is a descriptive rather than a diagnostic term. Causes are many: wrong soil pH, compacted soil, too wet, too dry, lack of an essential nutrient, excessive amount of one or more nutrients, etc., etc. A soil test is the only sure way to know the cause in a specfic case like this one.

planted last fall ...

how bad was winter.. where are you ... i had some rather severe.. unexpected damage on plain old RB ...

second... i have had repeated droughts of a few weeks in between good rains... many trees are showing yellow leaves due to the stress ...

a pic of the whole plant might help ...

when you start the post.. with a premise.. on some level.. you start the conversation.. by ruling out too many things ... e.g. i am suggesting a water management issue ... but you started at soil deficiency ... or disease ...

is anything else chlorotic in your yard??? .. if not.. the i would question how there would be a soil deficiency ... and i would fall back to transplant stress .. aka water management ...

ken