Bunchy top in sugarcane is caused by

Bunchy top disease in sugarcane is caused by Top shoot borer.
Top shoot borer is a pest that damages the cane crop by making holes in emerging leaves, boreholes at the top of the shoot, and dead heart when formed is reddish brown, appears charred, and cannot be easily pulled out. Hence, in tillering phase of the crop, the attacked shoots die, and side shoots develop producing a bunchy top appearance.