Hi, I have a pink grapefruit plant that I grew from a seed around 12 years ago. This spring I have noticed a yellowing and brown mottling occurring in the leaves but, try as I might, I am not able to properly diagnose it. I'm not particularly green-fingered and this plant is my pride and joy. I was hoping somebody on here could help me diagnose the issue. I am hoping it isn't citrus canker, and was thinking it may be citrus blackspot?