Mealybugs: A common pest of indoor plants

Plants moved indoors for the winter can be a source of insect pests such as mealybugs, so make sure to carefully inspect them.

Multiple life stages of mealybugs. Photo by John A. Weidhass, Virginia Polytechnic Institute and State University,
Multiple life stages of mealybugs. Photo by John A. Weidhass, Virginia Polytechnic Institute and State University,

Prized orchids, citrus trees, jade plants and many other house plants are moved outside each summer where they benefit from better light conditions and decorate outdoor spaces. Once moved back indoors, plants can fall victim to outdoor pests that were brought into the house with them. Some pests become a challenge to manage indoors and often spread to other indoor plants. One of the hardest to control is the mealybug. It appears as a white, fuzzy substance found on leaves, tender shoots and in the crevices of branches. Like other house plant pests, many find their way indoors on plants they fed on during summer.

You may say, “What is the big deal? If this insect is such a problem, why did it not harm my plant outdoors?” Mealybugs may have not yet built up their numbers to where damage would be noticeable. Outdoors predators and parasites may help keep mealybug populations low. Indoors, without predators and parasites, pest populations can quickly develop and damage plants that we have grown for years.

I was given a jade plant that had been grown outdoors during the summer months. The plant looked great. After a few weeks indoors, I noticed small, whitish creatures moving on the branches. Mealybugs! The adult mealybug is about 0.1875 inch long and covered with a white waxy covering.

This insect damages plants by inserting a feeding tube into plant tissue to feed on the sugary sap. Large numbers of mealybugs weaken the plant and may even kill it. A shiny, sticky sap called honeydew is commonly found on branches and leaves where the insect feeds. This shiny, sugary waste from the insect is also a clue that there are sucking insects on the plant.

Ridding your plants of mealybugs is not an easy task. They thrive in crevices between branches in the interior of the plant where it is hard to spray them. Another issue is that one female can lay up to 600 eggs, quickly expanding their population. Once mealybugs are found on a plant, it needs to be isolated from other plants to prevent the infestation from spreading.

The amount of insects on the plant determines your next step. In some cases, the population may be too high and the better choice may be to discard the plant. With smaller infestations, Michigan State University Extension advises using a cotton swab dipped in alcohol on individual insects, but care must be taken to dab it on the insect and not the plant to prevent damage to plant tissue.

If you choose to spray with an insecticide, make sure it is labeled for indoor use. There are a number of pesticides that can be used to treat for mealybugs. Read labels carefully to see if there are lists of plants that can be harmed by specific products. A good article from the University of Minnesota Extension on pesticides for indoor plants can be found at “Houseplant insect control.”

The jade plant I treated for mealybugs survived for years, but was never totally free of the pest. It is likely I was not controlling the egg stage. I would not see any insects for long periods, but I’d find them back a few months later. I decided to take a number of cuttings from the new growth and start the plant over. The new growth was free of the insect and from it I was able to grow new plants that were free of the mealybug.

The take-home message is to inspect plants carefully when bringing them back indoors. Continue to monitor them through winter to prevent spread of unwanted pests in your indoor garden. If you do find a pest like a mealybug, isolate the plant right away and determine treatment options, potential for taking clean cuttings to propagate the plant, or whether to replace the plant. This will insure a healthy indoor garden and plants that last generations.

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