Mealybugs on coleus

Mealybugs on coleus are a recurring problem in both outdoor summer plantings and overwintered indoor plants. The white, cottony masses in leaf axils and on stems are distinctive once you know what to look for, but infestations starting from a few individuals can build rapidly in warm conditions.

Mealybugs on coleus are a recurring problem in both outdoor summer plantings and overwintered indoor plants. The white, cottony masses in leaf axils and on stems are distinctive once you know what to look for, but infestations starting from a few individuals can build rapidly in warm conditions without being noticed. Coleus brought indoors to overwinter are a common pathway that introduces mealybugs to other houseplants — making identification and treatment before bringing plants inside an important step.

I don't grow coleus outdoors at my Long Island property, so this guide draws on Clemson HGIC, UC IPM, and Penn State Extension research.

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The pest

Several mealybug species infest coleus in outdoor and indoor settings, most commonly the citrus mealybug (Planococcus citri) and the long-tailed mealybug (Pseudococcus longispinus). Per UC IPM, mealybugs are soft-bodied insects (Hemiptera: Pseudococcidae) that feed on plant sap through piercing mouthparts. They produce a white, waxy covering and wax filaments that give the characteristic cottony appearance.

Per Penn State Extension, female mealybugs lay eggs in cottony white ovisacs — egg masses that can contain 300–600 eggs. In warm conditions, generations overlap and populations build rapidly.