Question
These tibouchina are growing in Central Africa, at approx 1,000m above sea level.
htey are sturdy and more than 2m high. However, the leaves develop small brown patches whichthen eat through the leaf leavng holes; other leaves curlup into a small ball.
Is this an insect (I dont see any) or a fungus? And what treatment (preferably organic!) should I apply.

Answer
Hi Sophie,  I think your problem is over watering or too much rain.  Brown or black on leaves is usually too much water, fertilizer burn while yellow leaves is not enough water.  If you are using mulch and watering maybe take the mulch away so it can dry out.  Tibochinas are tough and are very xeric.  kathy