Really? So do you know what kind of texture is the soil? if we know which soil he used we can know nearly the soil Ph. Also he just said that he irrigate yesterday he didn't say how often he is doing.
Probably he just notice this problem but is bad since before just now he can appreciate it.
Also the problems with pests and diseases depend mostly of the soil, watered and enviroment.
Anyway I'm trying to help him, What are you doing?