Saving lime trees from damaging scale: Ask the Ground Crew

We have a lime tree that we winter indoors. In March, the tree developed about 60 limes. Also during that time, the tree developed scale insects. We purchased a nontoxic solution, which somewhat worked. The limes were slowly growing, then suddenly the tree started losing fruit. Bottom line: The tree lost all of its limes.

We have now moved the lime tree, still in its pot, outside for the summer. Because the tree had a second fruiting last year and we were able to harvest three limes, we’re hoping it sets limes again. What can we do to completely eradicate the scale? I think this is contributing to the loss of limes. Also, what is the ideal watering schedule for a potted lime tree? — Laura Cannon, Lakewood

Brown soft scale is a common problem on citrus trees, including lime trees. Scale insects appear as small, waxy or crusty bumps on leaves, stems and sometimes fruit, and they are one of the most challenging plant pest problems to control. There are two different types of scale: armored scale (very difficult to control) and soft scale.

Scale attacks leaves and stems by attaching to and sucking plant sap from new, tender growth. As scale feeds on the plant, the insects exude a honeydew substance that causes a sticky film to settle on surrounding plant parts and surfaces near the plant.

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If your lime tree is indoors, the floor under the potted plant may become sticky. Also, honeydew may cause a plant disease called sooty mold.

If left unattended, scale insects can cause leaves to yellow and plants to weaken and become stressed. Overall growth of the lime tree may be adversely affected, and the pests could certainly cause weakened flower or fruit production.

The first thing you should do is clean your lime tree. Move the potted lime to a shady area outdoors and use a soft flow of water (not a jet stream) from a garden hose to rinse the honeydew off the leaves, stems, trunk and container. Do this on the lawn, sidewalk or driveway, away from other landscape plants. Allow time for the tree foliage to air-dry.

Next, take a cotton ball, douse it with rubbing alcohol, and gently wipe away the scale insects on leaves, stems, trunk and fruit. Wipe firmly to remove the scale yet gently as not to damage the plant parts. It is important to wipe both the upper and under sides of the leaves as well as all of the stems and trunk. Change cotton balls frequently. You may want to wear latex or rubber gloves while doing this.

Now use a horticultural oil or insecticidal soap (neem oil, for example) and thoroughly spray the entire plant and container. Before spraying, read the entire label on the oil or soap container and follow the directions exactly. It is important that the spray solution cover all plant parts to suffocate any scale insects and eggs that you may have missed.

Wait until the plant is completely dry before moving it back to its growing location.

This may sound like a daunting task, and depending on the size of your lime tree, it may be a bit of a challenge. But this method will give you the best chance of eradicating the existing scale and preventing more from attacking your plant.

Most scale insects are active from late winter to early summer — this is the time to spray your lime tree with oil or soap to prevent scale from returning. Also, if you closely monitor your lime tree, you may be able to spot the scale development very early and quickly eradicate the insects by just using your cotton ball and rubbing alcohol.

The best prevention of scale is to keep your lime tree growing in its optimum environment.

By Paul Pfeifer, Draime Estate Gardens

Pfeifer is managing director of Draime Estate Gardens of Kent State University.

Got a question for the Ground Crew? Send it to [email protected], with Ground Crew in the subject line. Or, mail a letter to Ground Crew, Inside and Out, The Plain Dealer, 1801 Superior Ave., Cleveland, Ohio, 44114. Include your name, address and daytime phone number.