An attack of sciara fly can be noticed when the 2-3 mm long black flies come up when the plant is moved. The adults do not damage the plants, but the larvae do. They are around 5 mm long, glassy, legless and with a black head. They are most dangerous in seed trays, as the young plants need constantly moist conditions which are ideal for the larvae.

If there is an outbreak in a seed tray, the best solution is to remove undamaged seedlings, taking care no soil goes with them and replant afresh, for safety watering with a contact insecticide. New egg-laying can be avoided by covering the surface of the soil with a thin layer of sand. The sand dries quickly and discourages the female sciara from laying her eggs in the soil. Adults can be trapped using the yellow sticky strips.