Question
I have a China Doll in my work office that no one looked really looked after nor watered consistently. It stood approx 1 metre (3 stems) tall and was in a north-westerly window and was healthy, everyone commenting that it was tall and large. All of a sudden it formed black blisters, black leaves and sap started falling from the foliage making the pot and bench around it very sticky. It then lost all of its leaves and was cut back so that its 3 stems are all that was left. It has now started growing again to my amazement but not that the foliage is getting bigger its is developing the black blisters and leaves are becoming black and flaking away! It's in a plastic pot 20cm in diameter and deep. I really dont want to throw it away, and i am scared that if we got another one it would eventually do the same thing.

Answer
Ash,

I suspect it is very root bound in that small pot and because of that itcontracted a fungal infection called Corynespora leaf spot. The only description of this problem I could find follows: Symptoms of Corynespora leaf spot vary depending upon the host. Lesions start on lower leaves, especially those in contact with the potting medium or those which are wounded. Lesions expand rapidly and are black and may encompass the entire leaflet and cause abscission when conditions are favorable. There is rarely any halo surrounding lesions on China Doll.
Control -
Keep plants as free of excess water as possible and avoid crowding to promote rapid drying of foliage. Mixed results in controlling this disease have been seen with the fungicides available.

This means you should be very careful to keep water off the stems and any foliage and empty the drain tray 1/2 hour after watering. I suggest that you repot the plant into a pot that is 30 cm in diameter and replace as much soil as possible without disturbing the roots too much.  After that make sure you water the plant lightly and let the top half of the soil in the pot get dry before watering again. You can get a bamboo skewer to insert in the soil and don't water it until it comes out with the top half dry. I would also try spraying the plant twice a week with Lysol spray  making sure that you get the fronts and backs of all leaves and the surface of the soil. It contains a fungicide that I have found frequently works well on plants without causing problems in that home or office as long as it is used regularly until the problem has disappeared and been gone for at least a month. Then you should be able to safely stop without the problem coming back. Good luck!

Darlene