Does rosemary even get sick?

Does rosemary even get sick?

I have a potted rosemary plant that's been having random leaves yellowing and dropping off all season. I thought it was lacking in nutrients, but several applications of fertilizer haven't affected it at all. Also, before falling, the leaves develop purple specks that leave the surface looking like a mosaic. I can identify most common garden diseases, but I never hear about rosemary coming down with problems the way roses or tomatoes do. Anyone have thoughts on what it might be? Should I cut the plant out and try another one next spring?
Quick mystery plant ID?

Quick mystery plant ID?

Plant Identification Needed

Plant Identification Needed

Muscari

Muscari

Green rose

Green rose

What are these 2 evil weeds? How do I make them dead?

What are these 2 evil weeds? How do I make them dead?

Mystery plant

Mystery plant