Dichotomous table for gallers on Rosa

by Hans Roskam

1a On above-ground parts => 3

1b On roots or root collar => 2

2a Roots with spindle-shaped swellings. R. canina, multiflora: Meloidogyne sp.

2b On roots or on root collar, expanded, at first succulent, then lignifying proliferations with tuberculate surface. Rosa spp.: Agrobacterium tumefaciens

2c Small solid swellings, often curved and twisted, at tips of lateral roots; other parts of root sometimes thickened; eelworms live externally in soil, not often seen. On Rosa cultivars: Xiphinema diversicaudatum

= The red bud borer Resseliella oculiperda damages rootstocks of cultivated roses and apples when these are grafted with scion buds by “shield budding”

3a Fruit variously disfigured, often ± etiolated. Rosa spp.: Rhagoletis alternata

3b On vegetative plant parts => 4

4a Malformations of various extent caused by fungi, which produce brownish or whitish sori on the gall surface, soon yellowish to orange => 29

4b Malformations induced by other causers => 5

5a Galls on various plant parts, distinguished by moss-like proliferations or swelling of stem bearing bushes of mistletoe => 28

5b Malformations different => 6

6a Galls never closed on all sides, only on leaves; leaf blades folded, rolled, curled, with erinea, or with egg capsules on petioles, leaf blades or between leaf teeth => 19

6b Malformations different; on stems or leaves => 7

7a Malformations closed on all sides, with single or several tough-walled chambers => 13

7b Galls without chambers; only on shoot axis => 8

8a Minor, soon fragile swellings on young shoots caused by egg batches of sawflies (procecidia, oviposition scars, not true galls) => 12

8b Malformations exist for a longer period => 9

9a Causer not recognisable from the outside => 10

9b Bark with small, bulging rimmed depressions, containing causer below a flat, 2.3–3 mm long scale. R. canina, eglanteria, pomifera, villosa, etc.: Chionaspis salicis

9c More expanded malformations bearing Viscum album

10a compact or cancer-like malformations => 11

10b Young lignified shoots slightly swollen over a length of 30–50 mm. The swelling contains a tunnel in the inner bark running in relative narrow turns around the axis. R. x damascena, rubiginosa, x rugosa. spinosissima, etc.: Agrilus cuprescens

11a Axis of older shoots or young stems often with many walnut-size, at first succulent, then lignifying proliferations, mainly close to a node. Rosa spp.: Agrobacterium tumefaciens

11b Infestation sites depressed to varied extent, on reactive young twigs rimmed by flat to almost cauliflower cancer-like proliferations. Proliferations at first dirty-white to yellowish, then browned. “Bark spot disease”. Rosa spp.: Coniothyrium wernsdorffiae

= Similar damage may be caused by the widely distributed, also known from other hosts, equally hardly cecidogenic sac fungus Leptosphaeria coniothyrium

12a Egg capsules arranged in two rows. bark often ripping open and sometimes more or less rimmed later on. Rosa spp.: Arge pagana

12b About 16–18 egg capsules, arranged in one row, just below shoot tip, soon bending, occasionally browning and withering. Rosa spp.: Arge ochropus

13a Galls smaller than 10 mm => 14

13b Galls often larger, usually irregular, bulbous and bumpy, up to 25 (40) mm long. Wall not very tough, yellowish-brown or ± reddened, dark-brown later on. With many long spines, up to 3 (5) mm. Galls on shoots, especially conspicuous at the ends and multi-chambered; with smaller sized galls also on all leaf parts, flowers and hips. Containing a single larva per chamber. Rosa spp.: Diplolepis mayri

13c Galls similar to those of D. mayri, but only in their external morphology, especially when the galls of the last species develop on hips. However, D. fructuum galls are produced by the hypertrophy of seeds inside the fruit, the development of which can finally split the external envelope of the hip. In this case, each seed is modified into an egg-shaped multilocular gall, containing up to 10 larval cells and reaching a size of 15 x 12 mm; one hip can be modified into a large multilocular gall. Galls of D. mayri do not split the external envelope of the fruit. R. canina: Diplolepis fructuum

13d Rounded or elongate swelling in stem, smooth when young, later becoming fissured; containing several orange or orange-yellow larvae in irregular cavities. 6–7; gall splits in 7–8 releasing larvae which pupate in soil. R. spinosissima: Janetiella frankumi

13e Oblong swelling on stem, 80–120 x 20–30 mm, surface slightly fissured. R. gallica: Unidentified microlepidopteran

14a Galls almost exclusively on leaves > 15

14b Shoot axis with acuminate- to oval or elongate spindle-shaped swellings, up to 10 mm long, one- to more-chambered. R. majalis, spinosissima , tomentosa: Diplolepis sp.

15a Galls ± globular, with strongly constricted attachment, only protruding on a single side of leaf => 16

15b Galls on both leaf sides, sometimes coalesced into bumpy groups, surrounded by a ± wide, unchanged leaf margin, variously shaped, rotund or oblong, glabrous or rarely provided with small spines; single galls usually 3–5 mm long, yellow-green, sometimes reddish, one-chambered; on leaf midrib and stalk, ± uneven, more- to one-side, sometimes with several united into larger, almost homogenous gall bodies. On all leaf parts, also on flowers, even on corolla. Containing a single larva. Rosa spp. Diplolepis spinosissimae

16a Outside gall wall glabrous, in some cases tuberculate or provided with short papillae, also with only a few, almost normal spines => 18

16b Galls with many thin or with only a few conspicuous strong and rough spines => 17

17a Galls rotund, 4–6 mm, ± red tinged or spotted, with several strong, sometimes slightly bent, tough spines, star-like; robin’s pincushion. One-chambered, containing a single larva. Aberrant gall form indicates presence of parasites or inquilines. Rosa spp.: Diplolepis nervosa

17b Galls rotund, with many often unequal large slender spines, up to 3 mm long. On leaf-blades or calyx mainly one-chambered; on larger organs often several are united into larger many-chambered, bumpy aggregations. Rosa spp.: Diplolepis mayri

18a Galls glabrous, rarely somewhat tuberculate, up to 8 mm across; one-chambered; thin-walled, mainly on leaf underside, occasionally on upper side and then conspicuously reddened, also on flower peduncles, even on stamens or the tips of calyx leaves or even on attachments of spines, as well as on protuberances of D. rosae galls. Galls containing parasites or inquilines are often variously disfigured and sometimes enlarged and many-chambered. A single larva per chamber. Rosa spp.: Diplolepis eglanteriae

= Periclistus species may be inhabitants of irregularly shaped, also enlarged globular galls of several Diplolepis species. These are commensals developing outside the gall chamber in separate cavities of the gall wall

18b On R. arvensis develops in inconspicuous galls: Diplolepis nervosa

18c Galls similar, but usually provided with short, acute, simple, stiff ± reddened spikes or papillae. Containing a single larva. R. canina, caesia, centifolia, pomifera, etc.: Diplolepis nervosa

19a Leaf blade curled over extensive parts or ± loosely rolled => 23

19b Leaf folded pouch-like, or with pustule-shaped egg capsules or with hair felts => 20

20a Pustule-shaped procecidia (oviposition scars, not true galls) up to 2 mm across => 22

20b Folds or erinea => 21

21a Halves of leaflets narrow pod-like, folded upwards, up to a narrow marginal border strongly swollen, pouch-like; galls sometimes arched, sickle-like. Wall succulent, thickened, brittle, sometimes conspicuously reddened. Containing several orange-yellow larvae. Rosa spp.: Dasineura rosae

21b White to reddish erinea at undefined places. Strongly infected leaflets roll in ± longitudinally upwards. R. rubiginosa: Unidentified gall mite

22a Often with several egg capsules between leaf teeth at leaf margin. Rosa spp.: Arge gracilicornis

= On various occasions also Arge enodis has been reported as producing egg capsules on roses, arranged like strings of pearls. This sawfly normally lives on Salix

22b Pustules, on both sides of leaf, 2–3 mm long, protruding further on upper side, pale yellow to -brown, usually single, usually in petioles, more rarely in basal leaf blade parts, also in stipules. R. canina: Cladardis elongatula

= The female of the sawfly Ardis pallipes deposits her eggs in hardly conspicuous egg capsules in the tips of developing shoots. The thick, yellowish larva up to 10 (12) mm long, eats into pith a 30–40 mm long downwardly directed tunnel, pushing the shoot downwards while it withers.

= Also the sawfly Cladius pectinicornis deposits its eggs in rapidly shrunken procecidia on the petiole surface. Larvae gregarious on leaves, at first eating the parenchyma in between the veins, then producing holes.

23a Leaf blade ± tube-shaped rolled or bent upwards and browned => 25

23b Leaf blades conspicuously curled, variously bent => 24

24a Single or several leaves at stem deflected; their leaflets crumpled, almost nest-like downward converged; at infestation site usually dark green. Containing a single or several froth-covered nymphs. Philaenus spumarius

24b Leaf blades of the terminal leaves curled and ± strongly deflected; usually with several bunched together in loose nests. Rosa spp.: Aphis pomi

25a Leaf blade bent upwards, not thickened; ± discoloured, spotted or browned => 27

25b Rolls of leaf margin => 26

26a Both leaf blade halves tube-shaped rolled downwards to midrib, additionally often twisted. On many wild roses and cultivated forms: Blennocampa phyllocolpa

26b Leaves loosely rolled upwards, hardly thickened, not or slightly discoloured. R. canina: Callyntrotus granulatus

27a On R. alpina, spinosissima: Eriophyes rhodites

27b On R. canina, ? alpina: Callyntrotus schlechtendali

28a Up to 50 (80) mm long, rotund masses with thread-like, ± branched appendages. “Bedeguar”, “Robins pin cushion gall”. Usually many-chambered, very tough, ± reddened. Rosa spp., not on cultivated roses: Diplolepis rosae

28b Stems of R. canina with strong nodular swellings bearing: Viscum album

29a Sori orange-coloured or brownish => 30

29b Shoot tips and expanded parts of ± curved leaf blades covered with a dense, white, or grey mycelium. Rosa spp.: Podosphaera pannosa

30a Young shoot axis, leaf blade, -midrib, stipules, petioles, calyx leaves or young fruits with buckled swellings, their surface eventually covered with orange spore masses. Galls according to response ability of infected substrate. Fungus with all spore forms monoecious => 31

30b Leaves often completely infected, on underside with rotund, often coalescing, dusty, brownish sori of (1) 2 (3) celled teliospores. Leaf blades stay smaller and remarkably thickened. R. acicularis, macrophylla, majalis and relatives: Phragmidium kamtschatkae

31a Aeciospores with loosely arranged spines; wall thickenings of germ pores not substantially protruding inwards => 32

31b Aeciospores with densely arranged, coarse spiny warts; provided with 6–8 germ pores, with wall thickenings protruding hemispherically inwards. Rosa spp.: Phragmidium tuberculatum

32a On R. alpina, majalis and spinosissima. Fungi differ from next species insignificantly and mainly biologically => 33

32b On many other Rosa species as well as on cultivated forms. Teliospores 5–9 celled, often upper half broadened; slightly narrowed at apex, with short papilla. Galls like those of previous species. Rosa spp.: Phragmidium mucronatum

= Mycetophagous gall midge: Mycodiplosis coniophaga

= Almost witches’ broom-like malformations are initiated by unknown causes

33a On R. alpina, acicularis, caesia var. glauca, majalis, pomifera: Phragmidium fusiforme

33b On R. caesia, rubiginosa and many cultivated spp.: Phragmidium tuberculatum

33c On R. majalis, spinosissima, rubrifolia. Teliospores not deep dark-brown as in all previous species, but chestnut-brown: Phragmidium rosae-pimpinellifoliae

mod 13.xii.2019