Chrysanthemum Leaf Miner
In the garden: Chrysanthemum, Gazania, Senecio and Asters
Throughout UK and Europe, commonly found in greenhouses
Small dark coloured flies 2-3mm in length. The female flies make small puncture marks usually around the edges of plant leaves in order to feed and lay eggs. Eggs hatch into maggots that burrow under the leaf surface creating tunnels as they feed and grow. At the end of their mining, the maggots will turn into small dark brown pupae at the end of their tunnels.
Chrysanthemum leaf miner larvae feed on the cells within the host plant leaves and create silvery lines across the leaves. In low numbers, the damage is usually cosmetic, however severe infestations will reduce the photosynthetic capabilities of the plant and weaken it resulting in loss of flower buds. Host plants that have small leaves will often lose their leaves completely when chrysanthemum leaf miner larvae infest them.
Regular observation of the leaves of susceptible plants for small white dots around the edges will indicate when the adult flies are egg laying.
Leaves displaying the larval mines can be removed and destroyed. Pupae that have formed at the end of tunnels can be crushed. Parasitic wasps can also be purchased and released around affected plants when they are grown in greenhouses.
Early identification and treatment of an infestation can allow healthy plants to develop through to the end of summer.