Witches' Brooms are masses of densely branched small twigs amongst the branches of trees. Taphrina betulina affects Birch trees.  A layer of yellow asci is produced on the underside of the swollen leaves within the broom; these stunted leaves are often produced and fall before the normal leaves open.   The broom growths may last for several years.

Some Witches' Brooms on Birch may be caused by a phytoplasma; checking for the presence of a layer of yellow asci on the leaf undersides will rule this out.

host

Provide photos of the gall on the host plant.  If possible, a close-up of gall showing evidence of fungal infection

Found on birch, particularly Downy Birch and Silver Birch

Witches' Brooms on birch are fairly common in Leicestershire & Rutland, but rarely if ever checked for presence of the fungal spores on the leaves.  All records should therefore be regarded as unconfirmed.