Mealybugs on Plants: Causes, Treatment & Prevention

Symptoms

Look first for white, cottony insects on the stems, leaves and roots. You may also find white, cottony egg masses on stems, leaves and in crevices. Check the roots as well as the leaves, since white, cottony insects are found on roots too.

Sticky honeydew can coat the leaves of an infested plant. Black sooty mold can grow on honeydew-coated surfaces. Ants may also be attracted to the plant and tend the infestation. Taken together, cottony insects, sticky leaves, black mold and ants tending the plant all point toward mealybugs.

Mealybugs feed by sucking sap, and that sap-sucking feeding leads to weakened growth. Under a heavy infestation, growth can become stunted and leaves can drop. Some mealybug species live in the soil, and they cause root damage and plant decline. Weakened growth is the general effect of the feeding, while the cottony insects, egg masses and honeydew are the specific signs you can point to. Stunted growth and leaf drop belong to heavy infestations, while weakened growth is the general effect of sap-sucking.

Causes

Mealybugs are favored by warm weather, and they thrive in areas without cold winters. Year-round mild temperatures favor mealybug populations. They also thrive on indoor plants. Indoor plants lack natural enemies, which is another listed cause.

Excess nitrogen fertilizer combined with regular irrigation is also listed as a cause. Nitrogen fertilizer on its own is not the listed cause; the fact pairs it with regular irrigation. Your fertilizer and watering routine is one cause you control directly.

Use of broad-spectrum insecticides that kill natural enemies is another cause. Ants protect mealybugs from predators and parasites. Several of these causes concern natural enemies: indoor plants lack them, broad-spectrum insecticides kill them, and ants protect mealybugs from them.

New plants, tools or pots can introduce mealybugs to your home. Other causes concern warmth, mild temperatures, or arrival on new plants, tools or pots. Two of the chemical options named for treatment, imidacloprid and pyrethroids, are described as harmful to natural enemies.

Diagnosis

Start by looking for the insects themselves. White, cottony insects on stems, leaves and roots are a direct sign of mealybugs. White, cottony egg masses on stems, leaves and in crevices are another.

Weakened growth, stunted growth and leaf drop are the effects of sap-sucking feeding. The cottony insects, egg masses, honeydew and sooty mold are the signs tied to mealybugs on this page. Sticky leaves with black mold on them fit the honeydew and sooty mold pattern described here.

Next, think about where the plant has been. New plants, tools and pots are a recorded way for mealybugs to arrive in your home. Ants on or around the plant are worth noting, since ants are attracted to and tend infested plants. A plant that has been given nitrogen fertilizer along with regular irrigation matches another listed cause.

If the plant is declining, check the roots too, since soil-dwelling species cause root damage and plant decline. Indoor plants without natural enemies and warm, mild conditions also match the listed causes.

Treatments

Inspect plants thoroughly before bringing them into the home or landscape, and discard infested ones. You can hand pick or prune out mealybugs, and you should remove the whole plant if the infestation is serious. You can also spray plants with a strong stream of water, repeating as needed. Avoid unnecessary applications of nitrogen fertilizer on plants that have mealybugs.

Keep ants away from infested plants, since ants protect mealybugs from natural enemies. Clean and disinfect pruning tools between uses with a bleach solution or full-strength isopropyl alcohol. Isolate newly acquired or affected houseplants from your other houseplants to prevent spread. When you choose new plants, pick ones known to be less prone to mealybug problems.

The parasitic wasp Leptomastix dactylopii is sold commercially for greenhouses, citrus groves and interiorscapes. Predators such as the mealybug destroyer lady beetle (Cryptolaemus montrouzieri), lacewings and minute pirate bugs can be encouraged or released, timed to when mealybug egg sacs are abundant. You can dab isopropyl alcohol directly on mealybugs, or apply a more dilute spray solution, and repeat until the infestation is gone. Insecticidal soap, horticultural oil or neem oil can be applied directly to immature mealybugs to reduce numbers.

Dinotefuran is a systemic insecticide that can reduce mealybug numbers on some landscape plants. Imidacloprid plant spikes or granules may reduce crawlers on houseplants, but avoid using them when possible because imidacloprid harms natural enemies. Some pyrethroid products are labeled for certain situations, but they can be devastating to natural enemies. For any of these products, the label is the legal instruction and must be followed for the crop and site being treated.

Prevention

Inspect plants thoroughly before bringing them into your home or landscape, and discard infested ones. Isolate newly acquired houseplants from your other houseplants to prevent spread. Clean and disinfect pruning tools between uses, since tools are one way mealybugs arrive.

Choose plants known to be less prone to mealybug problems. Avoid unnecessary nitrogen fertilizer, because excess nitrogen combined with regular irrigation is a listed cause. Keep ants away from plants, since they protect mealybugs from predators and parasites.

Avoid broad-spectrum insecticides where you can, because they kill natural enemies, which is a listed cause of mealybug problems. Indoor plants lack natural enemies, and year-round mild temperatures favor mealybug populations, so check indoor plants regularly. Warm weather also favors mealybugs.

Mealybugs on Plants

At a glance

Symptoms

Causes

Diagnosis

Treatments

Prevention

Plants most often affected

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