Dichotomous table for gallers on Juglans regia
by Hans Roskam
1a On leaflets of leaves => 4
1b On axial parts of shoots => 2
2a The causers of malformations are on the outside => 3
2b Axial parts of shoots, especially on young plants, with rotund proliferations, up to fist-size, with fissured surface. Agrobacterium tumefaciens
3a Bark of twigs with minor, rimmed depressions; containing causer. Epidiaspis leperii
3b Branches with spindle- to club-shaped swellings, bearing: Viscum album
4a Leaf roll and distortion caused by aphids => 6
4b Leaf blade and sometimes young fruits with pocks or felt-like upward archings on underside, caused by gall mites => 5
4c Leaves browned; at high densities vagrant mites may cause russeting Aculops unguiculatus
4d Yellowish spots or blotches apparent on both sides of leaflet, with whitish patches on underside. Microstroma juglandis
5a Pocks, up to 2 mm long, on both sides or only visible on upperside, rotund, if mature, black-brown with irregular cavity. Often many. Also on skins of fruits. Aceria tristriata
5b Crook-backed usually upward arching, reticulately striate by thickened venation and often angularly restricted. In depression on underside are whitish erinea consisting of long, cylindrical acuminate hairs. Aceria erinea
6a Loose roll of young leaflets, ± sickle-like distortion of midrib. Aphids on upper side of midrib. Panaphis juglandis
6b Similar roll of leaflets; aphids on leaf underside. Chromaphis juglandicola