Looks like fungus. Are all the leaves like that or just the oldest? I get something similar on older leaves during the wet season on my H. australis. Seems all the excess water stops the leaf from drying out normally when it senesces. In the dry season the leaves dry out normally. Otherwise, the plants are unaffected. So if it's only the old leaves, most likely a lot of or too much water with fungus getting on the dying leaf.
I'm not real sure. That particular H.Kerri variegated seems to be more prone to this issue. Since I brought it inside for winter, it has gotten worse. As far as my green Kerri..
It gets a leaf like that once in a while by soil line. I hope its nothing. I love the variegated one. Thanks for your input. :) Melanie
It looks like a fungal infection to me too. I've had this happen to Hoya as well as other plants, especially if we get a lot of rain after I've already watered. I found a couple of leaves like that recently ... I watered everything really well, then we had tons of rain for two days, and then we had another cold snap with some very cold nights ... triple whammy to my poor plants!
Scroll down this page in the "sticky" thread at the top of the hoya forum regarding pests and diseases of Hoya's. There are photo's of leaves with sun damage and one a bit farther down showing fungal infection: http://davesgarden.com/community/forums/t/471984/
I have a Hoya, which originated from cuttings my father brought home from a farm his parents used to own in Tennison, Vic. I have been growing it ever since and given heaps of cuttings away. I have since moved to Qld and then back to Victoria, and it has managed to stay alive in both climates. I don't know the name, but salmon pink flower. However, I have had the same thing happen to leaves and it doesn't seem to worry the plant. I cut them off and throw them away, in case they carry spores. I think it only happens to old leaves too! Sometimes also sun damage! If the leaf is wet and then hit by hot sun. Sorry I can't believe I haven't got a flower photo. My father has been dead since mid 1980's - I will have to take photo's this year for sure!