Dichotomous table for gallers on Ribes

by Hans Roskam

1a On inflorescences, flowers or fruits => 28

1b On vegetative parts => 2

2a On parts above ground => 3

2b Roots with spindle-shaped to nodular swellings, usually bearing some side roots. R. rubrum: Meloidogyne hapla

3a On buds or leaves => 11

3b On shoot axis => 4

4a On higher parts => 6

4b On root collar => 5

5a Nodular to walnut-, sporadically chicken egg-sized proliferations on root collar, tuberculate on surface, at first white, succulent, later on browned and woody; galls sometimes also on larger roots close to surface and on higher situated stem parts. R. rubrum, uva-crispa: Agrobacterium tumefaciens

5b Excessive branching at stem base; shoots only a few cm long, strongly succulent, variously striate, with disfigured stump-like branchings. R. uva-crispa: Rhodococcus fascians

6a Causer not occurring on gall surface => 8

6b Younger axial parts usually with many rotund- to oblong-oval pock-shaped swellings, which contain a flat causer in a rimmed depression => 7

7a Scale ± rotund; 1.2–1.6 (1.8) mm wide, dirty to brownish-grey, flat arched, with dark yellow central area. Froth-covered nymph red, mainly harmful on R. nigrum: Epidiaspis leperii

7b Scale pear-shaped, white to grey-white, up to about 2.5 (3.0) mm wide. Female wine-red. Ribes spp.: Chionaspis salicis

7c Sporadically recorded on R. alpinum, R. rubrum, R. uva-crispa: Viscum album

8a Swellings on thin axial parts, elongate, ± spindle-shaped, often inconspicuous. Caused by insect larvae boring inwards => 10

8b Conspicuous, nodular or bulging or almost witches’ broom-like malformations => 9

9a Branches, more rarely stems, with warty-nodular, usually several burr tubers. R. uva-crispa, less frequently on R. alpinum, aureum, rubrum and other Ribes species: Inducer unidentified – ? bacterium, fungus; may partially be caused by: Agrobacterium tumefaciens

9b Cauliflower-like proliferations, occurring mainly on root collar. R. uva-crispa: Rhodococcus fascians

= Sporadically witches’ broom-like malformations have been associated with the rust fungus Cronartium ribicola; aecia develop on Pinus strobus, non-cecidogenic, Uredinia and telia developing mycelium in protruding cylinders clustered on leaf underside of several Ribes species

10a Inconspicuous oblong swellings of bark, mainly visible in autumn, on young axial parts. Older larvae boring in spirals in inner bark. Rare on R. nigrum: Agrilus cuprescens

10b Similar swellings on young woody shoots; older larvae feeding in pith; whitish with dark dorsal band and brown head. Ribes spp.: Synanthedon tipuliformis

10c Midge larvae live gregariously under bark. The bark is peeling off, sometimes accompanied by a dying back of the top shoots. R. nigrum: Resseliella ribis

11a On leaves => 12

11b Young side-, also apical buds distinctly swollen, producing ‘big buds’. Infestations especially conspicuous in spring, because diseased buds only partially open, and do not unfold. R. alpinum, nigrum, rubrum, rarely on R. uva-crispa: Cecidophyopsis ribis

11c Similar terminal or lateral big buds on R. rubrum: Cecidophyopsis selachodon

= The gall mite Colomerus riberini causes silvery white erineum on the underside of the leaf of R. nigrum, and the gall mite Cecidophyopsis grossulariae causes foliar injury, cavities at vein bases, enations on leaf disk, discoloration. R. nigrum, rubrum, uva-crispa

= Leaf buds of R. alpinum swollen to almost one cm in diameter, do not unfold; caused by the gall mite Cecidophyopsis alpina. Similar swollen leaf buds of R. aureum are caused by the gall mite Cecidophyopsis aurea

12a Curls, archings or bladder -shaped swellings caused by aphids => 19

12b Expanded folds, rolls, curls, or abnormal pubescence or localised warts and bulges caused by other parasites => 13

13a Localised swellings by rust fungi => 17

13b Malformations caused by animals => 14

14a Expanded malformations => 15

14b Leaf margin with several egg capsules, soon necrotic after emergence of larvae (procecidia, oviposition scars, not true galls). R. rubrum, uva-crispa: Pristiphora appendiculata

= The yellow gooseberry sawfly Nematus ribesii lays her eggs like pearls on a string along the veins without development of procecidia.

15a Leaf folds or rolls caused by midge larvae; galls lacking additional pubescence => 16

15b Leaf blade often severely disfigured, curved, folded, irregularly hunchbacked, rolled at margins, ± abnormally haired. R. alpinum, aureum: Aceria scaber

15c Less protruding, slight bladder-like archings on leaves of R. uva-crispa: Cecidophyopsis ribis

16a On R. nigrum. Margins of still unfolded leaves ± funnel-shaped to rolled, screw-like; margins of older leaves rolled over upwards to varied extent, also folded. Leaf blade curled. Spaces in between with several, at first whitish, then yellowish or yellow larvae: Dasineura tetensi

16b Similar malformations on other Ribes species. Rolls, especially on younger, developing leaves; on many hosts more densely covered with elongate, ± hair-like structures. Assignment of causer insufficiently known. Unidentified gall midges:

a On R. alpinum: Causer questionably assigned to Dasineura tetensi.

b On R. petraeum; Folds ± thickened and reddened. Abnormal grey to brown pubescence. Containing several white midge larvae.

c On R. rubrum: several white midge larvae. Asphondylia ribesii. Furthermore Stroblophila aberrans which does not induce galls

d On R. uva-crispa: Leaf blades partially abnormally pubescent, containing several midge larvae, at first milky-white, eventually pale yellow are attributed to Dasineura tetensi

17a Pads or bulges bearing yellow to orange-coloured aecia => 18

17b Rotund, sometimes joined, chestnut-brown, yellowish margined weak pads, usually protruding on upper side of leaves, with 2-celled, wart-like teliospores. Frequently also on fruits. R. alpinum, nigrum, petraeum, rubrum, uva-crispa, etc.: Puccinia ribis

18a Swellings minor, almost only on main veins, with joined sori. Aecia lacking peridium, dusty, belonging to the species complex of Melampsora ribesii-viminalis

18b Similar on many Ribes species: Melampsora epitea

18c On several Ribes species also develops: Melampsora epitea var. epitea

18d Swellings always distinct, protruding on leaf underside, usually rotund, up to 10 mm across, yellowish, on upper side often red margined; developing on petioles, young stems and midrib of racemes, oblong, sometimes much larger bulges; young fruits sometimes largely covered. Aecia with cup-shaped opening peridium; often ± circularly arranged on the galls. Ribes spp.: Puccinia ribesii-caricis

19a Leaves ± rolled, curled or weakly arched; often clustered, nest-like, on shoot tips => 21

19b Leaf blades often with several, conspicuous, larger or smaller, yellowish, often deep-red speckled, strongly to broad bladder-like swollen, open, upward archings => 20

20a On R. alpinum: Cryptomyzus korschelti

20b Galls mainly on R. rubrum, rarer on R. nigrum, petraeum, spicatum, uva-crispa and others, also on many cultivated foreign species: Cryptomyzus ribis

21a Disfigured leaves densely clustered, nest-like, on severely stunted shoot tip. Wingless aphids dull on surface, antennae about half the body length => 27

21b Disfigured leaves on often only slightly shortened shoots clustered in nests, or situated distally. Body of wingless aphids glossy, antennae always longer than half the body length, often even longer than the whole body => 22

22a Aphids with club-shaped siphunculi => 23

22b Aphids with cylindrical siphunculi. 2–3 mm, pale-green to green. Siphunculi pale with darker tip, about twice as long as cauda. Antennae of fundatrixes shorter, of fundatrigenia slightly longer than body. Leaves only weakly arched and not discoloured. R. alpinum, nigrum, rubrum, uva-crispa, etc.: Nasonovia ribisnigri

23a Aphid differing from all other aphids on Ribes by its dark brown body. Leaf blades of basal leaves narrower, woody, shaded shoots disfigured, discoloured, soon dropping. R. nigrum, rubrum: Rhopalosiphoninus ribesinus

23b Aphids of different colour => 24

24a Adults with expanded brown to black dorsal pattern. Mainly on seedlings, rolling the brittle leaves but not discoloured, often developing dense nests of leaves. Aphid 2.7–3.1 mm; basic colour green. Tibiae, siphunculi and cauda black. R. rubrum: Hyperomyzus rhinanthi

24b Dorsal body part of apterous aphids lacking pigmentation, or with only minor pigmentation. Siphunculi of apterous aphids pale coloured => 25

25a Aphids pale yellowish-green, difficult to distinguish and only by microscopical examination => 26

25b Aphid green. Leaves ± rolled over their length, also arched; sometimes in loose nests. Venation yellowed or leaf blades yellowing, mosaic-like. Ribes spp., especially on R. nigrum: Hyperomyzus lactucae

= Similar malformations are caused by viruses.

26a Leaves arched, in loose nests. Aphid 2.5 mm long, glossy, pale yellowish-green, siphunculi pale, sometimes darker in the middle and at their tip, rather strongly swollen. Antennae about as long as body. R. alpinum: Hyperomyzus picridis

26b Leaves weakly arched, yellowed at veins. Occasionally in loose nests. R. uva-crispa: Hyperomyzus pallidus

26c Disfigured shoot apices, petioles and curled leaves. Ribes spp.: Hyperomyzus zirnitsi

27a Leaves accumulated at tip, in dense nests. On all wild and cultivated forms of R. uva-crispa: Aphis grossulariae

27b Similar malformations and dense leaf nests on R. rubrum, also on R. alpinum, aureum, nigrum, sanguineum, etc.: Aphis schneideri

= Sometimes the polyphagous, never gall inducing, mite Bryobia praetiosa s. lat., appear as successoria (secondary inhabitants) in early vacated galls of various aphids. From spring onwards in many food plants, especially fruit, partially as important pest, because of suction damage on unfolding, early withering leaves.

28a On fruits => 32

28b On flowers or on inflorescences => 29

29a Flower galls => 30

29b Complete inflorescence disfigured. R. alpinum: Unidentified gall midge

= Various malformations associated with greening, on several flowers of a raceme of R. nigrum, are caused by virus

30a Flowers enlarged, unopened. R. alpinum, rubrum, uva-crispa => 31

30b Flowers transformed into globular- or pear-shaped, whitish or reddish galls. Corolla strongly swollen. Containing one or more yellowish or orange-red midge larvae. R. nigrum: Dasineura ribis

31a Base of calyx succulent, pale yellow to red; corolla and stamens hard. Larvae often gregarious, at first white, then yellow to orange-coloured. Galled flowers dropping after larvae complete development. R. uva-crispa: Contarinia ribis

= The N-Am gall midge Rhopalomyia grossulariae has been recorded on Ribes grossularia

31b On R. alpinum, rubrum. Flowers enlarged, unopened. Unidentified gall midge(s)

32a Galls caused by fungi => 34

32b Galls caused by insects => 33

33a Immature fruits variously disfigured, up to twice the normal size. Containing a single to five orange-coloured larvae. R. uva-crispa: Unidentified gall midge

33b Fruit strongly swollen or elongated and narrowed. R. nigrum: Pachynematus pumilio

34a Fruit wall often with several wart-like pads, a few mm long, on which the telia develop. Ribes spp.: Puccinia ribis

34b Infected fruits often bulging on expanded areas. Many aecia on pads. Sori occasionally also on fruit stalks and stalks of fruiting racemes. Ribes spp.: Puccinia ribesii-caricis

mod 12.xii.2019