Potato Witches Broom is caused by

Potato Witches Broom is caused by MLOs.
Potato witch broom is a plant disease that occurs as an abnormal brushlike cluster of dwarfed weak shoots arising at or near the same point.
Witches broom are caused by a phytoplasma transmitted by several species of leafhopper and within the potato plant seed pieces.
Leaves started rolling up and have yellow margins. Plants are dwarfed in the field.