Marin Master Gardeners
University of California
Marin Master Gardeners

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Pest of the Month - Mealybugs

Mealybugs... indoors and out.

Mealybug sign

It’s that chilly time of the year when we gardeners daydream about the upcoming spring, plant seeds for cool season veggies, start pruning shrubs and roses, and dust our oft-forgotten houseplants – those splashes of green that enliven an interior window sill or cozy corner.  Taking a closer look at our indoor greens may bring about a surprise or two, especially when dust isn’t the only thing you find.

Nestled in the cracks and crevices of plant stems you may spy some fluffy white material - like tiny pieces of cotton hugging growing tips, stems, leaves, leaf axils and the flowers of your plants. You might notice stickiness on the plant, some blackish mold and even ants.  If you do, looks like you’ve discovered mealybugs. 

Feeding on a wide range of outdoor plants like gardenia, chrysanthemum, geranium, gladiolus, grape, apple, peach, pear, plum, maples and yews, mealybugs are also serious pests of orchids and other indoor plants - African violets, begonias, ferns and palms, just to name a few.  Though not true bugs (hence the one word name) these insects are related to aphids and scale in the Order Homoptera, all of them having sucking mouthparts and producing honeydew.  That sweet waste product attracts ants and supports the growth of sooty mold; and if that’s not bad enough, their sucking can result in a decrease in plant vigor and weakening or loss of leaves, buds and flowers.

Mealybugs
The elongated and segmented soft-bodied, grayish adult insect is about 0.05 to 0.2 inch long, and may have wax filaments radiating from the body. The slow moving, wingless females are covered with whitish, mealy or cottony wax.  They may lay eggs or bear live young. The nymphs or crawlers, appearing as diminutive adults, are the most active stage and can move between plants in search of feeding places. They are adept at hiding on roots and rhizomes deep in soil or potting media and under the lips of pots. These pests congregate in large numbers, and under optimal conditions, can produce several generations each year. 

Mealybugs can be easily confused with the wooly apple aphid, both sporting the unusual waxy coating.  Their body shapes, however, are quite different – all aphids are pear-shaped with long legs and antennae with their telltale cornicles on the hind end of the body.

Outside, mealybugs have a host of natural predators – parasitic wasps, brown and green lacewings, lady beetles and the mealybug destroyer (Cryptolaemus montrouzieri), as well as weather, especially heavy rains, to keep their numbers low. Indoors, they can be difficult to control. Management of the pest is essentially the same as it is for aphids, starting with a blast of water to knock them off the plant.  A solution of rubbing alcohol (70% isopropyl) can be applied directly on the pest either with a light spray, a cotton-soaked swab or soft infant’s toothbrush, and repeated once or twice at weekly intervals to ensure removal of recently hatched crawlers.

Moving up the integrated pest management ladder, an insecticidal soap or narrow-range horticultural oil can be effective in smothering the little beasts, and if none of these methods work, a systemic insecticide may be effective.  If you’ve got mealybugs on your houseplants, be sure to sanitize the entire pot and treat the surface of the soil.  Also manage for ants.

Now, back to daydreaming about spring and planting those vegetable seeds.

By Nanette Londeree

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