The plant disease identification/management handbook by Balaji Aglave is excellent for popular plants. A lot of modern handbooks are fluffy with information (maybe that’s popular) but this one gets straight to the point — I was very lucky to come across this book a while back.
Another wandering soul whispering into the void. If you are looking for my blog you are in the wrong place. The profile and header pictures are brought to you by cdd20.