The fungus Exobasidium japonicum causes galls on the leaves of azaleas (Rhododendron cultivars of gardens).  The galls cause the leaves to become large and fleshy, pale green at first then chalky white.  

Large red, pink or peach coloured apple-galls caused by Exobasidium rhododendroni may be found on the leaves of some species and hybrids of Rhododendron

host

Provide photos showing gall and host plant; ensure you have identified and noted the host species

Azaleas

Rare.