Why Are There White Tunnels in My Spinach Leaves?

Hold a spinach leaf up to the light and you may see pale, winding channels or blistered patches running through the leaf tissue — these are leaf miner tunnels. The beet leaf miner (Pegomya betae), also called spinach leaf miner, is a fly whose larvae feed between the upper and lower surfaces of the leaf, leaving characteristic white or pale green mine tracks that are visible from the outside. This is one of the most common spinach pests and can affect the whole crop in bad years.

How leaf miner damages spinach

The adult fly lays small, white oval eggs in rows on the underside of leaves. Hatching larvae burrow into the leaf and eat the soft green tissue between the two leaf surfaces, creating the distinctive serpentine mines. As larvae grow, the mines expand and can cover large portions of the leaf in a pale blister. Heavily mined leaves look papery, brown and blistered. Individual plants can have most of their leaf area destroyed in a bad infestation. There are typically two to three generations per year, with peak activity in spring and late summer.

Can you eat mined spinach leaves?

Lightly mined leaves are safe to eat once the damaged portions are removed — simply tear or cut out the mined sections and use the rest. The larvae themselves are not a health risk. Heavily mined leaves where most of the green tissue has been consumed are not worth eating and should be composted. Remove badly affected leaves from the plant promptly to reduce the number of larvae completing their cycle and producing more adults.

Controlling leaf miner

Squeezing egg clusters and small mines between your fingers kills the eggs and young larvae before they spread further. Check the undersides of leaves regularly from mid-spring and crush any egg batches you find. Fine insect mesh (enviromesh) over the crop from sowing or transplanting excludes the adult flies from laying eggs — this is the most effective prevention for a crop that is prone to leaf miner each year. Once larvae are well inside the leaf, contact insecticides have no effect; the only management is physical removal of affected leaves. Beet leaf miner has several natural parasitic wasps that attack it — these increase as the season progresses, often naturally reducing late-season populations.

Spinach versus beet and chard

Beet leaf miner attacks all related plants: spinach, beetroot leaves, Swiss chard and perpetual spinach. If you grow any of these in adjacent beds, they act as reservoirs for the fly population. Growing brassica spinach alternatives (such as New Zealand spinach, which is not attacked by beet leaf miner) avoids the problem entirely, though brassica crops have their own leaf miner species.