Gaps in the rows of germinating crops, germinating host crops show growth deficits, tunnels in cotyledons (seed leaves) of beans, stem (hypocotyl) of pumpkins and squashes is often completely hollow and holds a large number of maggots.
Various species of arable crops preferring warmer temperatures such as maize, spinach, cucumbers, pumpkins, squashes, beans, asparagus… Other species may also be affected under specific conditions.
The flies’ rod-shaped, 1 mm long, white eggs are deposited on germinating host crops. However, cases have been recorded where they have already deposited their eggs on the bare soil during ploughing: apparently, they are lured by unrotten plant material, e.g. during the ploughing in of the spinach leftovers or unripe compost.