Plant Parasites of Europe

leafminers, galls and fungi

gallers on Avenula

Dichotomous table for gallers on Avenula

(incl. Avenastrum, Avenochloa, Helictochloa, Helictotrichon)

by Hans Roskam

1a On inflorescences or flowers => 8

1b On culms, shoot tips or leaves => 2

2a On leaves or shoot tips => 4

2b On culms => 3

3a Upper internode of culm with one-sided, hard, reddish swelling about 10 mm long and 3 mm wide. Avenula pubescens: Tetramesa sp.

3b The diseased culms develop early, usually over their complete length, because of increased growth above all the basal internodes and have smut patches on their culms ± protruding from the leaf blades on all sides. Spores clustered with 1–2 (4) per ball, enveloped by a layer of many auxiliary cells. Avenula pubescens; Helictochloa versicolor: Urocystis avenastri

4a Malformations caused by animals => 5

4b The shortened, narrowed and often setose leaves on the often rigidly erect, soon stunted shoots with rows of often coalescing, later on erupting smut sori releasing black spores. Spores solitary. Avenula pubescens, Helictochloa pratensis: Ustilago scaura

5a Malformations on ± distinctly stunted shoot tips => 6

5b Leaf blade with less than 10 mm long, often purple, narrow cylindrical swelling. Helictochloa pratensis: Unidentified eelworm

6a Galls caused by larvae of insects; occurring inside => 7

6b Malformations caused by aphids occurring on the outside. The terminal leaf sheaths ± inflated and discoloured. Leaf blade variously twisted, curled or ± rolled inwards. Avenula pubescens, Helictochloa pratensis: Rhopalosiphum padi

7a Tuft-like accumulation of leaves on the upper internodes of the ± thickened shoot tip. Containing a single larva in pith. Avenula pubescens: Tetramesa sp.

7b Development of young shoots stunted while still close to the ground. Stems from their base onwards slightly swollen and excessively shortened towards the tip. The leaves close to one another, but not clustered into a tuft; their bases and sheaths often conspicuously reddened. Avenula pubescens, Helictochloa planiculmis: Chlorops pumilionis

8a Various malformations of spikelets, dependent on the reactive ability during infestation, often associated with leafiness and greening of the spikelets, eventually atrophying of all parts resulting in bleaching. Avenula pubescens, Helictochloa pratensis: Aceria tenuis and/or A. cornuta, Aculodes dubius

8b Ovaries disfigured often in many or all flowers of a panicle, soon destroyed and replaced with a black, dusty spore mass. Avenula pubescens: Ustilago avenae

Last modified 24.iv.2020