Plants in the genus Dracaena are grown both indoors and outdoors for their interesting foliage and exotic appearance. These spindly plants are often grown as houseplants, but can be integrated into the landscape in U.S. Department of Agriculture Plant Hardiness Zones 10b through 11. In either conditions, they tend to be very hardy disease-resistant plants, with their biggest problems coming from insect pests. When a fluffy white, mildew-like substance appears on the surfaces of dracaena plants, it's far more likely to be mealybugs than mildew.
Mealybugs are sap-feeding insects that use their mouths to penetrate and extract the contents of plant leaves and stems. These tiny insects are covered in a waxy coating and move very slowly, giving the appearance that they are simply a fungal growth underneath leaves and in other hiding spots on dracaena. When they move or die, very white waxy or cottony secretions are often left behind.
Mealybugs feed directly on leaves; high populations cause leaves to yellow and drop and new tender growth is often distorted. These insects also exude honeydew, a sticky clear to white substance, as they feed. Honeydew attracts sooty molds and ants to the plant, resulting in further damage. Ants that are actively farming mealybugs for food may also move the mealybugs to uninfested plants as populations expand.
Mealybugs on indoor plants are fairly easy to control, since they are usually isolated populations. Handpicking the insects from your dracaena, being careful not to damage the plant, may eliminate a light infestation. Removing particularly stubborn mealybugs requires a blast of water. A swab dipped in alcohol might also work, with care to only smother the mealybug, since alcohol can burn the plant. Always check dracaena for insect pests when moving them indoors.
Heavy mealybug infestations, or those on outdoor plants, may require chemical intervention. Ants that are protecting the mealybugs before attempting to destroy the colony are first baited away from the plant. With the ants out of the way, predators may be able to keep future mealybug activity in check. Horticultural oils or insecticidal soap may work, but test a small spot at least 2 days in advance of treatment in case your particular dracaena has a photophobic reaction that increases its sensitivity to the sun. Drenching the soil around your dracaena with imidacloprid will eliminate any mealybugs that might have escaped the foliar drench.
- University of Florida IFAS Extension: Dracaena Deremensis
- University of Florida IFAS Extension: Dracaena Production Guide
- Penn State College of Agricultural Sciences: Disease and Arthropod Management in Greenhouse Floriculture
- University of California Statewide Integrated Pest Management Program: Mealybugs
- University of California Statewide Integrated Pest Management Program: Foliar-Feeding Mealybugs