This app was mentioned in 1 comment, with an average of 2.00 upvotes
Have no clue about citrus diseases but I know there's an app for that... if this helps?
Android https://play.google.com/store/apps/details?id=com.lucidcentral.mobile.citrus_diseases
iOS https://play.google.com/store/apps/details?id=com.lucidcentral.mobile.citrus_diseases