Plant Parasites of Europe

leafminers, galls and fungi

gallers on genus Hydrangea

Dichotomous table for gallers on Hydrangea macrophylla

by Hans Roskam

1a On parts above ground => 3

1b On root collar or on roots => 2

2a Roots with slender- to broad spindle-shaped galls, a few mm long.
Meloidogyne hapla

2b Root collar or also basal axial parts with conspicuous proliferations, irregularly fissured at surface, almost walnut-size. Agrobacterium tumefaciens

3a Malformations mainly on leaf blades => 4

3b Stem shortened, spongy, thickened and ± distorted; the stalks and basal vein parts at infestation site clustered, leaves bloated, the leaf blades variously curved. Flowers, if present close to infestation, disfigured and ± greened, stalks ± strongly thickened. Ditylenchus dipsaci

4a Curling, arching and upwards development of leaf blade caused by aphids; or malformations of flowers => 5

4b Leaf blade with pustule-shaped galls which are soon surrounded by an expanded area of dead tissue. Cause unknown – ? gall midge

5a Malformations on plants cultivated in greenhouse. Aulacorthum solani and/or Macrosiphum euphorbiae

5b Flowers on variously stunted stems more densely arranged, greened; corolla leaves usually stunted in development. Stamens and ovaries sometimes leafy. Virus disease

Last modified 18.xi.2023