Question
I have been growing mandavilla vines on my deck every summer for the last several years and have beautiful growth every year, however this year the leaves at the bottom of the plant are turning yellow with brown spots.  The rest of the plant looks healthy but this has been going on for several weeks now.  Any ideas?

Answer
Dear Beth,

Since you have been successfully growing your plants for several years and are, presumably, treating them just the same as always, I would imagine that your plants have either been attacked by insects or are suffering from a disease.  Investigate the soil to see if you can see any insects.  

I would suggest you take a couple of leaves to your garden centre and see if they can identify the problem after which they will be able to recommend an insecticide or fungicide.   

Do you perhaps have a cat or visiting cats which could have been using it instead of their litter tray?

Alternatively could this just be old leaves dying off?

I do hope you manage to solve the mystery.

Diana