Plant Parasites of Europe

leafminers, galls and fungi

gallers on Elymus

Dichotomous table for gallers on Elymus

(incl. Agropyron, Elytrigia, Hordelymus, Leymus, Roegneria, Sitanion, Thinopyrum)

by Hans Roskam

1a On shoots or shoot axis => 2

1b Roots with small slender, crooked or screw-like bent swellings. Elytrigia repens: Subanguina radicicola

= Furthermore, there are records of the cereal root-knot eelworm Meloidogyne naasi

2a On inflorescences or other generative parts => 27

2b On vegetative parts => 3

3a Malformations on culms or leaves caused by smuts => 25

3b Malformations caused by other fungi or by animals => 4

4a Malformations by animals => 6

4b Malformations by fungi => 5

5a Plants with systemic infections, growing rigidly erect, sterile; internodes shortened. Early infected leaves thickened irregularly, ± curved and disfigured; if infected later on the leaf blades are clearly widened; diseased leaf blades often with pale yellow stripes. Elytrigia repens: Physoderma graminis

5b Diseased leaves rolled and twisted, usually thickened conspicuously, pale, later brown and breaking up, exposing chestnut brown, globular naked oospores, 26–33 µm across. Spikes usually stunted, with disfigured, ± succulent, partially blue-green spikelets. Elymus caninus: Sclerospora graminicola

6a Malformation on shoot tips, and terminal shoots or on undeveloped shoots => 19

6b Malformations of culms, leaf sheaths or leaf blades => 7

7a Culm variously disfigured => 14

7b Malformations of leaves => 8

8a On leaf blades => 10

8b On leaf sheaths => 9

9a Leaf sheaths swollen, inhabited by aphids. Elytrigia repens: Laingia psammae

= Grain aphid, Sitobion avenae and/ or Blackberry cereal aphid, S. fragariae, known from many grasses, especially in inflorescences, cause also similar malformations on couch grass.

9b Leaf sheaths thickened above the nodes, usually open on one side. Several spindle-shaped galls inside. Larvae yellow. Elymus s.l.: Tetramesa hordei

10a Malformations of leaf blades caused by aphids => 12

10b Malformations of leaf blades caused by other parasites => 11

11a Leaf blade usually at base with tough, narrow, bulging, usually dark red coloured swellings. Elytrigia repens: Unidentified eelworm

11b Leaves remain unfolded or do not develop completely; discoloured. Elytrigia repens: Abacarus hystrix

= DNA-analysis has demonstrated that “A. hystrix” actually is a complex of a number of species.

12a Leaves rolled inwards by green aphids => 13

12b Leaves ± rolled upwards, often withering early. Aphid about 2 mm long, elongate, narrow, brownish-yellow with pale median stripe. Elytrigia repens: Sipha elegans

13a Leaves rolled upwards, twisted. Aphid 2–2.75 mm long, olive-green, reddish-brown between siphunculi. Elytrigia repens, Elymus caninus: Rhopalosiphum padi

13b Shoot stunted, leaves shortened, tuft-like accumulations. Leaf blades rolled, ± twisted. Agropyron cristatum; Elymus caninus; Elytrigia intermedia, repens: Diuraphis frequens

14a Culm swollen locally, galls contain larvae => 18

14b Inducers are outside galls => 15

15a Larvae in depressions on culm => 17

15b Causers not in distinct depressions => 16

16a Small, blister-shaped protuberances in long brown stripes or as crust-like cover. Elytrigia repens, Elymus caninus: Steneotarsonemus canestrinii

= Steneotarsonemus culmicolus occurs sometimes in the leaf sheaths of couch grass and other grasses and causes facultatively discoloured white spikes. Similar symptoms are also caused by Siteroptes cerealium, occurring on many grasses.

16b Shoot severely stunted. Inflorescence often remains largely hidden in the sheath. Culm at the base of the inflorescence ± swollen. Contains a single larva. Elytrigia repens: Oscinella frit and/ or the closely related O. pusilla

= Oscinella agropyri develops on couch grass without causing malformations.

17a Culm below leaf sheath usually above the upper node and the penultimate node with an expanded weak, usually blackened depression, containing a single orange-yellow to brick-red larva. Elytrigia repens, Elymus caninus: Hybolasioptera fasciata

17b Culm predominantly above the upper and penultimate nodes below the slightly swollen leaf sheath usually with oblong, saddle-shaped depressions, strongly inflated at the ends. Containing single 3–5 mm long bright red larvae. Elytrygia intermedia subsp. trichophora, repens: Haplodiplosis marginata

17c Recorded as inducer of further unspecified slight swelling of stems of Elytrigia repens: Lasioptera calamagrostidis

18a Culm at various places, often above a node or also close to the ground, with spindle-shaped, tough-walled, later on often yellowish-brown galls up to 7 mm long. Occasionally many per plant and fused in variable numbers and in various shapes, forming larger galls bulging from the sheaths as erupting swellings. Each chamber contains a yellow larva. Elymus s.l.: Tetramesa hordei

18b Culm below the often atrophied spikes which remain largely hidden in the sheaths often with several, ± fused, broad spindle-shaped to elongate-oval, very hard swellings, occasionally erupting from the sheaths. Each chamber contains a single larva. Elymus s.l.: Tetramesa hordei

18c Inside a culm or a hardened leaf sheath several ± oval, size of grain of rice size, galls. Culm at outside with irregular swellings, leaf sheath strongly swollen and ripped open. Containing a single pupa or white larva. Elytrigia repens, juncea: Tetramesa linearis

19a Shoot severely stunted already early in development, inflorescence usually not developing => 22

19b Terminal malformation on developed shoots => 20

20a Galls caused by chalcidoid larvae, with tuft of 3 or 4 conspicuously enlarged, increasingly shortened unfolding leaf blades => 21

20b Tip of shoot markedly shortened, swollen. Leaves clustered tuft-like, their sheaths shortened and broadened. The ± reduced leaf blades are usually not broadened and are appressed with their bases against the gall. Gall containing a single maggot. Elymus caninus; Elytrigia atherica, juncea, repens: Chlorops pumilionis

= Chlorops strigulus, C. interruptus, C. marchali and C. speciosus are all non-cecidogenous parasites of Elytrigia repens. – Concerning affiliation of the inducer of malformations on couch grass examination of larvae and rearing of adults is necessary.

21a Malformations, usually distinguished from fly galls by larger size length and width. Larval chamber in pith, oblong, thick-walled, usually extending over 3–4 internodes. Elymus caninus; Elytrigia intermedia, repens: Tetramesa hyalipennis

21b Similar, usually broader galls, up to 40 mm long, on Elytrigia juncea: Tetramesa maritima

22a Leaf blades mostly developed, but plants remain sterile => 23

22b Shoot tips etiolated, elongated, bent, spindle-shaped, enlarged. Elytrigia repens: ? Dasiops latifrons

23a Malformations caused by maggots => 24

23b Young shoots severely stunted; close to the ground ± conspicuously sponge-like swollen to large extent. Leaf blades shortened and disfigured to a varied extent. Elymus s.l.: Ditylenchus dipsaci

23c Short, compact onion-like galls arising from the basal part of young shoots, containing many eelworms: Elymus s.l.: Anguina agropyri

24a Young shoots sometimes, if many larvae or puparia present, slightly swollen. Leaves initially more erect, darker green and more compact than those of healthy plants. Central leaves often withering later on or dying; shoots with sessile, etiolated spikes; culms sometimes slightly swollen and often cracked above the basal nodes. Contain several white larvae and flax seeds-like puparia. Elytrigia repens, etc.: Mayetiola destructor

= Larvae, whitish ± 3 mm long, or puparia of Mayetiola baudysi live within a leaf sheath just above a node, causing a light, often brownish swelling on Elytrigia repens

24b Infected rudiments of shoots severely stunted, sometimes slightly swollen at base. Central leaves soon yellowing and withering. Shoots occasionally developing additional tillers. Elymus s.l.: Delia coarctata

25a Narrow stripes on leaf blades and -sheaths caused by smuts, rarely on culms => 26

25b Patches with smut predominantly on sterile remaining culms which initially grow faster. A number of internodes often noticeably enlarged. Elymus s.l.: Tranzscheliella hypodytes

26a Plants often severely stunted. Stripes long, narrow, ± coalescing, almost black; lacerating the leaf blade if ripped open. Spores slightly dusty, separated, spherical to rotund-oval, about 11–18 µm across. Membrane with blunt, sometimes coalescing warts. Elytrigia repens, more rarely on Elytrigia juncea, Elymus caninus: Ustilago serpens

26b Infected stems at first developing quickly, later on stunted, often remaining sterile, extensively covered with brown-black patches with spores. Elymus caninus, Elytrigia juncea, repens: Tranzscheliella hypodytes

26c Similar infestation. Spores blackish, solitary or aggregated in pairs, however, more rarely with 3–4 together and enveloped by several accessory cells which have a pale yellow membrane. Elymus s.l.: Urocystis agropyri

26d Ditto on Elytrigia atherica, campestris, pungens: Urocystis agropyri-campestris

27a Malformations caused by parasitic fungi => 29

27b Malformations caused by animals => 28

28a Inflorescence usually disfigured over extensive patches. Spikelets according to degree of infestation ± disfigured and greened or discoloured, stunted. Elytrigia repens, Leymus arenarius: Aceria tenuis

= Occasionally this mite is associated with Aceria cornuta.

= Proliferations of flowers of Elytrigia repens are teratological malformations.

28b Flowers greened. Elymus caninus: Inducer not clarified – ? Eelworm

29a Patches with smuts extending to other flowering parts. Elymus caninus, trachycaulus: Ustilago bullata

29b Patches with smuts restricted to ovaries. Smut grains foul-smelling, oblong, grey- to blackish brown, enclosed by slightly spreading glumes. Spores globular, 18–22 µm across; membrane reticulate. Elymus s.l.: Tilletia controversa

= Conspicuously protruding, rough, often bent bodies, black on outside and white on inside, are not true galls, but are sclerotia of ergot Claviceps purpurea, frequent on couch grass. The identity of ergot on Elytrigia juncea has not been clarified

Last modified 1.v.2020