Plant Parasites of Europe

leafminers, galls and fungi

gallers on Vaccinium

Dichotomous table for gallers on Vaccinium

by Hans Roskam

1a Galls on parts above ground => 2

1b Roots with sometimes almost star-shaped swellings, 2–3 mm long, white on outside- and inside. Inducer unknown

2a Galls on leaves, on tips, also terminally on shoots or witches’ broom-like malformations => 4

2b Galls on axial parts of shoot => 3

3a Young stem parts locally broadened, with small, rimmed depressions, which harbour the causer under a pear-shaped white scale. V. myrtillus, vitis-idaea: Chionaspis salicis

3b Stem, usually over several internodes, swollen on all sides, up to 2–3 times the normal volume. Diseased parts rigidly erect, abnormally elongated; galls sometimes interrupted by normal parts, at first white or pink to reddish, later on cork-brown. Epidermis cells contain fruiting bodies. Lower leaves on galled shoots disfigured, usually dropping prematurely. V. corymbosum, membranaceum, vitis-idaea: Pucciniastrum goeppertianum

4a Malformation of several leaves or organs on tips or terminally on sometimes witches’ broom-like disfigured shoots => 9

4b Leaves, exceptionally also flowers, with ± expanded, localised galls => 5

5a Leaf blade with rolled margins or weak protrusions => 6

5b Smaller or larger parts of leaf blade or flowers often strongly swollen; on leaf upperside crimson-red or yellow, usually ± depressed; the arching on underside at maturity densely covered with dusty, chalk-white, basidia with 4 (‒6) spores. V. vitis-idaea: Exobasidium vaccinii

6a Roll of leaf margin => 7

6b Small depressions on lower surface of leaves. The upper part of the gall is usually red coloured and surrounded by a yellow patch. V. uliginosum: Contarinia sp.

7a Leaf margin rolled; on V. oxycoccos, uliginosum => 8

7b Roll of margin on V. myrtillus, vitis-idaea. Roll narrow, 1–1.5 mm broad, compact, often downwards, sometimes upwards, cartilaginously thickened; at first not, later on yellowish discoloured, margin ± concave. Containing a single larva: Dasineura myrtilli

8a On V. oxycoccos. Roll downwards, compact, slightly thickened and reddened. Containing several yellow-red larvae. Unidentified gall midge

8b On V. uliginosum. Leather-like thickened, yellowish or reddened downward roll. Containing a single yellow or reddish larva: Hygrodiplosis vaccinii

9a Leaves on shortened shoot tips keel-shaped, slightly thickened, uneven, imbricate; developing into a gall, sometimes ± blood-red, up to 8 mm long and 5 mm broad, in which the exterior leaf mostly encloses the inner ones containing a single red larva. V. myrtillus: Jaapiella vacciniorum

9b Malformations of larger expansion => 10

10a Malformations by fungi; at maturity densely covered by white fruiting bodies => 12

1b Malformations caused by animal parasites => 11

11a Leaf blades of several leaves reduced, ± undulately folded or wrinkled; margin and tip curved ± upwards. V. myrtillus, uliginosum: Phyllocoptes vaccinii

11b Several leaves on shoot tips slightly twisted; glossy green-yellow aphids occur on underside. V. vitis-idaea: Wahlgreniella vaccinii

12a Malformations without conspicuous thickening of stem => 13

12b Terminal part of stem or axis of inflorescence conspicuously succulent to varied extent. Leaves inserted on the galled part or flowers also variously strongly thickened. V. vitis-idaea: Exobasidium vaccinii

13a Stem usually not hypertrophied, in often large expansion and bearing several often vividly red or more yellowish coloured leaves. Leaf blades often larger, sometimes smaller than normal ones, less glabrous and glossy, weakly thickened, arched in many cases. Mycelium on underside. Malformations almost witches’ broom-like. Flowers usually atrophy on such shoots; sometimes all parts are moderately enlarged, but hardly thickened. On V. myrtillus, uliginosum, vitis-idaea => 14

13b Similar malformations on V. oxycoccos. The diseased parts slightly hypertrophied, distinguished from healthy parts by their erect growth. Leaves thickened and enlarged: Exobasidium oxycocci

13c Slightly disfigured shoots; first-year leaves sometimes enlarged, pale green or rarely becoming red. V. uliginosum: Exobasidium expansum

14a Basidia usually 4-spored. Spores 10–13 x 3–4 µm: Exobasidium myrtilli

14b Basidia 2-spored. Spores 18–32 x 7–12 µm: Exobasidium vaccinii-uliginosi

14c Furthermore may occur the following closely related smuts:

a Red thickened spots on V. macrocarpon, microcarpum, oxycoccos: Exobasidium rostrupii

b Distorted twigs on V. macrocarpon, microcarpum, oxycoccos: Exobasidium oxycocci

c Red malformations of twigs and leaves. V. myrtillus: Exobasidium myrtilli and rarer: E. aequale

d Red spots on leaves of. V. uliginosum: Exobasidium pachysporum

e Red distortions of twigs and leaves on V. vitis-idaea: Exobasidium juelianum and/or E. splendidum

Last modified 25.iv.2020