Sorbus Help

Hi all,
I have a Sorbus that i havnt planted yet. Its been in the pot in my place for about 2 months now. Ive noticed that on the leaf's there are some black spots, mainly on the lower leaf's. Some are turning red and dropping off although the plant looks healthy.

Any clues guys ?

G

 

I think when the leaves start turning red when they're not meant to, its usually a sign of starvation.

 

Been in the pot/bag too long ?

 

I was thinking the same Clueless. If you can't get it in the ground yet Mr. Grinch, you'd best start feeding it.

 

Its been planted with plenty of BF&B.

G