Plant Parasites of Europe

leafminers, galls and fungi

gallers on Avena

Dichotomous table for gallers on Avena

incl. Avenula

by Hans Roskam

1a On above-ground parts => 4

1b On roots => 2

2a Roots with conspicuous, localised swellings, a few mm long => 3

2b Roots stunted in longitudinal growth, branched bush-like (“hunger roots”). In many cases weakly thickened, sometimes bent, usually darker coloured; inside giant cells. From mid-June onwards with lemon-shaped, at first milky-white, later on brown, soon dropping cysts. Above-ground parts severely stunted. A. fatua, sativa: Heterodera avenae

3a Root tips or young roots swollen and curved. Tissue without particular cavities, containing roundly swollen, immobile eelworms; formation of adventitious roots increased. A. sativa: Meloidogyne cf. artiellia

0b Roots with slender, screw-like bent swellings; inside distinct cavities; containing a few vivid eelworms. Avena spp.: Subanguina radicicola

4a On inflorescences or flowers => 13

4b On vegetative parts => 5

5a On plants with at most rudiments of panicles => 9

5b On plants developing- or with panicles => 6

6a Malformations of stem caused by fly- or midge larvae => 7

6b Leaf sheaths inflated, discoloured. Leaf blade twisted and rolled inwards. Development of panicles often soon stunted, sometimes bleached later on. A. barbata, fatua, sativa incl. ssp. orientalis, strigosa, sterilis: Rhopalosiphum padi

6c Similar, but hardly gall-like malformations may be caused by the following aphids: Sitobion avenae, S. fragariae and Sipha maydis

7a Larvae living between stem and leaf sheaths, without legs, but with sternal spatula => 8

7b Stem stunted at base of the inflorescence, ± slightly swollen. Panicles occasionally severely stunted, often bleached. Larvae feeding on the developing seeds. A. fatua, sativa: Oscinella frit

7c Long conspicuous stripes on chlorotic leaf tissue caused by rust fungus. A. caryophyllea: Puccinia striiformis

8a Stem above a node ± slender, swollen, onion-like, sometimes bent. Under the leaf sheath are several 3–4 (5) mm long, vitreous to greenish-white larvae with arrow-shaped sternal spatula. Caudal part conically tapering. The larva develops into a flattened, flax seed-like, glossy brown puparium. A. fatua, sativa: Mayetiola avenae

8b Stem below the slightly swollen sheaths with several 10–15 mm long, elongated, saddle-shaped depressions, apically rimmed; each gall contains a blood red larva. A. sativa: Haplodiplosis marginata

8c On A. sativa and A. fatua, a similar, but not saddle-shaped swollen, expanded, blackened depressions of the culm, covered by the leaf sheath are possibly induced by Hybolasioptera fasciata

9a Plants usually excessively leafy, ± distinctly swollen at base => 10

9b Leaves of young plants slightly thickened, ± rolled inwards or folded. A. sativa: Anguina tritici

10a Shoots shortened, swollen at base, plants usually excessively leafy. Leaves usually not or only slightly discoloured => 12

10b Shoots shortened, usually less distinctly swollen, at least the inner leaves yellowed; often surmounted by additionally developing, uninfected new shoots => 11

11a Inner leaves yellowed and withered, the outer ones green, central part destroyed; shoot slightly swollen. New shoots often similarly affected, bushy clustered, later surmounted by healthy shoots. Inside is an at first vitreous, then yellowish-white cylindrical maggot, about 3–4 (5) mm long, provided with mandibles [buccal hooks] and tunneling into the root neck; with 2 caudal cone-like spiracles; pupa pale brown. A. fatua, sativa: Oscinella frit

11b Infected shoots usually sessile, at base sometimes slightly thickened. Plants usually very leafy, with many shoots which also become infected later on; leaves yellowing, starting at their margins. Between the outer, later ± browned sheaths are several, 3–4 (5) mm long, vitreous- to yellowish-white larvae or flattened flax seed-like, brown puparia. A. fatua, sativa: Mayetiola avenae

12a Single or several shoots of already developed plants stunted, predominantly at terminal parts; enveloped primordia of plant parts accumulated to ± spindle- or almost cigar-shaped galls. Larvae up to 7 (9) mm long, glossy white-yellow, with mandibles [buccal hooks], with 2 small caudal conical spiracles. Feeding on the central shoot or on upper internode. Pupa yellow-brown, ± flattened. A. sativa: Chlorops pumilionis

12b Plants very leafy, severely stunted, hardly developing shoots; infected shoots ± distinctly swollen at base, onion-like. Leaves short, thickened, undulately curved; becoming yellow and brown prematurely. Containing many eelworms in ± spongy parts. A. fatua, sativa: Ditylenchus dipsaci

13a Ovaries temporarily slightly swollen, soon occupied by a black mass of spores => 16

13b Malformation of large parts or of inflorescence, caused by animal parasites => 14

14a Malformations caused by gall mites => 15

14b Axis of the inflorescence distinctly narrow-undulately curved; panicle clustered; malformations caused by aphids. A. fatua, sativa incl. orientalis, strigosa: Sitobion avenae

14c Flowers swollen, contain yellow midge larvae. Avenula pubescens: Contarinia avenae

15a Spikelets incompletely developed. Panicle often remains largely hidden in leaf sheaths of the generally stunted plant; stalk of inflorescence shortened, ± undulate to screw-like compressed sheaths and the slightly swollen, protruding glumes often carmine- to blue-red. Terminal part of stem or panicle inside the sheath often twisted like corkscrew, covered with many mites which look like crumbly meal. A. sativa: Steneotarsonemus spirifex

15b Spikelets elongated, stalk often surmounting the flower and developing new spikelets. A. sativa: Cause unknown – ? gall mite

16a Diseased shoots develop accelerated longitudinal growth and surmount the healthy ones for a short period; infected spikelets broader and shorter, soon completely destroyed by a black-brown mass of spores, which during eruption turns the unfolding panicle to dust with only the midrib remaining. A. barbata, fatua, nuda, sativa, sterilis incl. subsp. ludoviciana, strigosa: Ustilago avenae

16b From stripes of smut on leaves of A. barbata, sativa incl. ssp. orientalis, Avenula pubescens is furthermore recorded the exceedingly rare Ustilago striiformis

16c Similar infestation, the spore mass, however, develops between two intact valves as a closed, rather compact, non-dusty smut grain. A. barbata, fatua, nuda, sativa, sterilis incl. subsp. ludoviciana, strigosa: Ustilago avenae

Last modified 30.iii.2020