gallers on Trisetum

1a On above-ground parts => 2

1b Roots sometimes with minor swellings, from which cysts erupt up to 1 mm long, lemon-yellow later on. Trisetum sp.: Heterodera avenae

2a On vegetative organs => 4

2b Galls on ovaries => 3

3a Ovary transformed into an oblong gall protruding far outside the spike. T. flavescens: Anguina agrostis

3b Ovaries within the unopened, not disfigured, glumes strongly elongated, abnormally thin, sometimes conspicuously curved. Each floret containing a pale brick- to orange-red larva. T. flavescens: Dasineura triseti

4a Malformations caused by animals on culms or leaves => 6

4b Leaf blades, rarely sheaths, culms and parts of spikes with several long parallel stripes of smut => 5

5a The long stripes of smut contain a black spore powder. Spores 2–8 in balls, completely enveloped by many sterile auxiliary cells. T. alpestre, flavescens, spicatum: Urocystis triseti

5b The smut mass consists of 8–12 μm single spores. Trisetaria panicea, Trisetum spicatum: Ustilago striiformis

6a On culms => 7

6b Leaf blades ± thickened, longitudinally upwardly rolled inwards and curved, screw-like. T. flavescens: Unidentified tarsonemid mite

7a Culm slightly swollen at base of the ± stunted inflorescence. T. flavescens: Oscinella frit

7b Culm, with weak, slightly rimmed depressions underneath the sometimes slightly arched leaf sheaths, usually close to a node; each containing an orange-yellow larva. T. flavescens: Lasioptera calamagrostidis