I have 6 holly bushes I’ve shaped into trees that over 15 years old. They have always been healthy up until last year when one of them started turning yellow (leaves). Right now the other 5 are dark green with few berries and this one oddball has yellow leaves and full, I mean FULL, of berries. Do you have any idea what is wrong and how I can bring it back to health? The picture I’m uploading was this summer and the leaves are yellow, but no berries. Now it’s full of berries and less leaves, but the other 5 trees look the same.
This is vary well a deficiency in iron, called iron chlorosis.
Here is a link with more information.