The Q&A Archives: leaf miner

Question: How can I control leaf miners on my citrus trees. I have young seedling and young citrus trees that are infected.

Answer: The adult citrus leaf miner is a moth. The moth is most active from dusk till dawn and rests on the undersides of leaves during the day. The insect only infests young, flushing foliage and does not attack more mature foliage. The female moth lays eggs singly on new shoots and on leaves less than a half-inch in length. The most preferred egg-laying site is along the mid vein on newly emerged leaves.

The larvae, a tiny caterpillar, hatches and begins feeding immediately in nearly invisible mines under the leaf's cuticle. As the larvae grows, its zigzagging path of parallel mines become more noticeable. Its mine has a central trail of excrement that can be used to distinguish it from mines of the native citrus peelminer.

When the larvae matures it moves to the leaf margin where it creates a silken cocoon. As the silk dries the leaf curls over the pupal cell. The larvae pupates within the mine and then emerges as an adult moth.

Since the citrus leafminer is a new pest in our area, the damage it causes may initially be more severe but should decrease in time. Beneficial insects, particularly tiny parasitic wasps, that attack the pest will increase and should provide good biological control in a year or two. Gardeners will need to be patient while this occurs and should not spray mature trees with insecticides that can harm beneficial insects.

Mature bearing citrus can withstand heavy infestation of citrus leafminer with little effect on fruit production. The loss of some new foliage is a minor problem on older trees that have a healthy canopy of mature leaves. Mines in leaves may detract from their appearance, but the green portion of leaves will still produce food for the tree and should not be removed.

Pest control products currently labeled for use on citrus in home gardens are not very effective on citrus leafminer because they do not control larvae feeding inside leaves.

Broad spectrum insecticides that leave a toxic residue on the foliage can do more harm than good. Repeated applications will kill beneficial insects that can result in a buildup of white flies, scale insects and other citrus pests.

The loss of new leaves is a more serious problem on young trees that do not have a lot of mature foliage. The growth of newly planted trees may be reduced by citrus leafminer if the infestation is heavy and prolonged. Treating young trees with insecticide may be justified if it helps protect emerging foliage until new leaves have grown too large for the leafminer to attack.

Before you buy or use an insecticide product to control citrus leafminer, first read the label. Make sure it can be used on citrus and follow all the directions.

A new insecticide product, Green Light Spinosad, is labeled for use on citrus to control citrus leafminer, but only a maximum of six applications can be made per season. Many other insecticides labeled for citrus do not have this limitation, but they may damage tender foliage with repeated application, or if the product is mixed stronger than directed on the label.

Hope this information provides some guidance in controlling citrus leaf miner.

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