This could be caused by one of three things: (1) Your tree is growing more leaves than it can support, (2) pests and diseases infect the leaves, or (3) your tree might be getting too much or too little water.
Zoom in please, and also, its blury.
I feel it is a horrid thing and absolutely messed up. It should never ever have been used or addressed as something allowed to happen. Also it was very racist obviously. It shouldn't happen ever again.
