Beet Leaf Miner
Beet Leaf Miner, Spinach Leaf Miner, Mangold Fly
A Beet Leaf Miner is a small fly, belonging to the taxonomic family that holds the flies whose larvae mine the leaves of their host plant. They do this by tunnelling through the leaves of the host plant, eating the internal tissues as they mine. Their mines appear as large, irregular yellow-brownish blotches. Eventually, the leaves of the host plant dry out and shrivel. The risks posed by this insect are greatest earlier in the year. This is because plants and crops are less established and more susceptible to damage.
Leaf mining insects can cause considerable damage to foliage as a result of their intrusive way of feeding.
Adult flies are dark brown-grey, reaching about 2mm in length. A female will lay her eggs underneath the leaves of the host plant, they are very small, oval and white in colour. They hatch into creamy white larvae. It's these that cause the most significant damage to plants. Larvae bore into the inside of plant leaves, depleting the internal plant tissue. Mines initially appear pale green to yellow, but eventually, turn brown. Each mine can contain several larvae.
Irregularly sized pale green and dark brown splodges on the leaves of infected plants. Infected leaves soon shrivel and dry. Leafy crops may become inedible.
Europe, Egypt, North America and some parts of central Asia.
It's been suggested to grow plants susceptible to beet leaf miners beneath an insect-proof mesh. It's advised to rotate crops every year, and by doing so, infection by overwintering pupae will be less likely. Pick off any leaves that have been mined or have eggs on them.
Unfortunately, there are currently no chemical treatments available for home gardeners that will give effective control over this pest.