The citrus leafminer (Phyllocnistis citrella) attacks all types of citrus trees anywhere in Florida. The adult is a small moth that lays eggs on the undersides of young, tender leaves. The eggs hatch and the larvae burrow into the leaf, creating meandering, silvery lines and causing the leaves to distort. They’re encased inside the leaf; thus, they are hard to kill. Eventually, the larvae will roll a sliver of the edge of the leaf around itself and pupate into the moth. A new generation is produced every three weeks. Citrus leafminer affects growth only on young trees; so many people consider the problem cosmetic on mature trees and ignore the lines on the leaves. If you find the pupating larvae under the leaf curl, you can scrape it out with your fingernail and smash it. Homeowners who want to treat the problem can prune shoots that are heavily infested, reduce the level of nitrogen in fertilizer (because nitrogen encourages new growth) and spray with horticultural oil every 10–14 days until the leaves “harden off” and are no longer tender. The oil makes the leaf less inviting to the moth. Make sure you spray in the early morning, before the air temperature reaches 80 degrees. Follow the label instructions.
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