This species is very similar to Agriphila tolli and Agriphila inquinatella. It can be distinguished from the first on the basis of the higher distance that separates said cross-lines. Moreover, in A. geniculea the forewings are crossed by a couple of chevrons, while A. inquinatella is longitudinally variably streaked.
The species has one generation. The moth flies at dusk from July to October depending on the location. When disturbed they come to light. The larvae can be found from late September to early May, as they winter in the larval stage. They feed within stems of Festuca ovina and various other grasses. They inhabit silken galleries, camouflaged with excrement, at the base of small grasses. Sometimes they leave these galleries and curl themselves tightly in a coil along the stem-bases of grasses.