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The winding trails on leaves are caused by the larvae of a small, dark fly. During summer, the females make little nicks in the leaf surface to lay their eggs. A week later, these hatch into larvae, which tunnel along just under the leaf surface to feed. After 2-3 weeks, the larvae pupate inside the leaves and emerge as adults. The damage is mostly cosmetic but where many leaves are affected, the plant may be weakened or die. Different species of leaf miner fly affect specific plants.
Solution
Organic
Pinch off infected leaves as soon as the first 'wiggling' trails are seen and dispose of them in the bin or burn them immediately.
