Have you looked very closely for damaging insects? Mites & aphids? They both leave all my edulis alone, but I've seen the curlies caused by spider mites.

I wrote about the red ones here and here's a few pics of the white "two spot" ones:

The web:
{{gwi:1133883}}

The critters:
{{gwi:1133885}}

As you can see they are very small- The two spot ones are easily missed on a leaf. They hang out on the underside, and only a few can screw up a leaf pretty bad if they begin feeding when it is still young.

Bayer Advanced kills them.. After a while. It will not repair the 'curlies' though.