I have never seen and heard of a rhodoendron suffering from mold.It sounds like you have a older plant that has been happy in its spot for a while but that is no longer the case.they are very fussy about p.h. and favor it around 4.5- 5.5 .To high a p.h will cause a yellowing and less then vigor apperance, even curling of the leafs.I agree with the other post,its very hard to say without seeing the plant .Iron sulfur will lower p.h. Us mulch to keep the plant roots evenly moist.Since they are so shallow rooted they really need fertilized in spring or early summer.I use ammonium sulfate.They are beautiful plants .I have the P.J.M. in bloom right now .
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