Frit fly (Oscinella frit) larvae are yellowish-white in colour and can grow up to 5 mm long.
There are usually 3 generations per year, and the third generation which emerges in late August/early September is the most damaging.
Eggs are laid on or near grass plants and the larvae tunnel into the centre of grass and cereal plants causing dead-hearts. They may then move to another tiller or plant, even if the field has been ploughed.
Leaving a gap of 10 weeks between the previous grass crop or grass stubble will reduce the risk significantly.