The female leafminer lays eggs on the leaf surface of chard, spinach and beet leaves. When the egg hatches, the larvae travel into the leaves and do this damage. Our solution is to remove and destroy damaged leaves. We also plant host plants such as parsley and dill nearby to attract predatory insects such as parasitic wasps.
Turning up the soil in late autumn exposes the leafminer to the wasps and also freezing. Luckily chard puts out enogh leaves that we can still harvest a good crop.