Ask a Master Gardener
This column is written by the Master Gardeners of Yolo County each month. It provides answers to selected questions recently asked by Yolo County gardeners.
Starting this month, the “Ask a Master Gardener” column is fielding questions directly from Yolo County gardeners and other garden enthusiasts. Previously, the column’s authors were selecting from questions submitted to the University of California Master Gardener – Yolo County Help Desk.
Going forward, questions for this column can be sent to the authors at jmbaumbach@ucanr.edu, with “Ask MGs” in the subject line. People submitting questions will remain anonymous, if desired. When emailing a question, please include as many details as possible. The master gardener authors strongly encourage including photographs, not only to help with finding the correct answer but also potentially to include in the column. Photos can be published credited or uncredited, depending on the contributor’s wishes. We cannot guarantee that we will be able to answer all of the questions submitted, but we will do our best to get an answer for you.
Question: The young leaves on my lemon tree have winding “trails” on them. What can I do about this?
Answer: From your description and the picture you sent, it looks like your lemon tree has citrus leaf miner larvae in its leaves. The citrus leaf miner is a small, silvery moth with a quarter-inch wingspan. Native to Asia, it arrived in California in 2000. It slowly made its way up California and is now found throughout most of the state, including our area. The moth lays its eggs on a citrus leaf. When they hatch, the larvae burrow into the leaf and begin to feed, leaving the tracks you see.
There is no effective spray that is available to the homeowner. The larvae are mining between the outer layers of the leaf, so they are well protected. The good news is that, while unsightly, the leaf miners will not do serious harm to a mature tree. It is best not to remove the affected leaves because they are still able to produce nutrients for the tree.
There are a few things you can do to limit damage. The first is to avoid broad-spectrum insecticides because they will kill beneficial insect predators and wasps that will parasitize the leaf miner larvae. Several species of small wasps may lay eggs on the leaf miner larvae. When the eggs hatch, the wasp larvae will consume the leaf miner larvae. Second, reduce the frequency of pruning. Prune to shape as lightly as possible and remove dead and crossing branches after the fruit has been harvested. Pruning encourages new growth, which is susceptible to the miners. They cannot enter leaves that have matured. While citrus needs additional nitrogen, wait until the new growth has matured before adding fertilizer in the spring.
Here is some additional information: Agriculture: Citrus Pest Management Guidelines - Citrus Leafminer by UC ANR and Savvy Sage Blog article Citrus Leafminer by Peg Smith.
Have a gardening question? Send it to jmbaumbach@ucanr.edu, with “Ask MGs” in the subject line. Include as much detail as possible and pictures if you have them.