My otherwise very healthy Hoya 'Chiang Mai' suddenly started to develop red spots/blotches, firstly in definite long lines (2 - 4 mm wide) around the outer sides of a couple of leaves. Some of these lines then started turning in irregular circular fashion, as though a caterpillar with a paint can was crawling around on the leaf, but there has been no sign of any living creature on the leaves. Then the spots/blotches more generally spread across leaves, without any sign of elongation or circular patterns. Now some of the elongated marks are starting to 'peel' - just the top thin silvery layer .
A nursery I showed one of the leaves to suggested it was sunburn, but this doesn't make sense as red spots have also started to develop under the leaves, and the plant was quite sun hardened to morning sun.
There is no sign of powdery pock marks underneath, like Red Spot Disease, but I'm wondering if I should treat this condition with a fungicide like copper oxychloride. I'm also wondering if all my other hoyas in the surrounding area will become infected if I leave this one where it is.
Please help.
Help - sick hoya
