Protecting House Plants From Mealy Bugs

Sooner or later you will come across mealy bugs, which are waxy, woolly-coated houseplant pests. They’re not difficult to deal with, provided you act quickly at the first sign of trouble.

The warm atmosphere of homes provides the ideal environment for mealy bugs to thrive. Though they can eventually build up large colonies on house plants and on plants grown in greenhouses and conservatories, by being watchful and acting quickly you can eliminate them.

Mealy bugs look more like bits of fluff than insects. They’re very slow moving once they’re on your plant. Because mealy bugs cannot flee from enemies Nature provided them with the protective covering of a waxy, woolly coat. Mealy bugs are relatives of scale insects, as well as aphids or greenfly.

Active life

Like most insects, mealy bugs are only interested in reproducing and eating —both of which they do with great enthusiasm. As they’re mainly tropical or sub-tropical insects, they will breed all year long if given a warm environment. Most mealy bugs, however, reach adulthood in summer, and build ups of this pest are worst in autumn and early winter. Females, which hugely outnumber males, lay batches of 100-150 eggs. These are covered by a protective waxy egg sac, and usually hatch in a few days.

For a short time young mealy bugs, known as nymphs, stay in the sac. Eventually they come out, spread over the plant, and feed by sucking the sap. Their protective covering slowly develops until they reach adulthood. They then seek the protection of leaf joints or other sheltered spots where they remain and reproduce.

Effect on houseplants

A mealy bug attack will cause a loss of vigor in the plant and yellowing of its leaves. A serious infestation will result in defoliation. Black fungus will appear on leaves.

Treatment

• If there are just a few mealy bugs, you can easily destroy them by brushing them with a fine, small brush dipped in methylated spirit.
• Spray large established colonies with an insecticide containing malathion, dimethoate or pirimiphos-methyl with pyrethrins, repeating the treatment every 10-14 days, until the pest is completely destroyed.
• Some plants are allergic to certain insecticides. Do not use malathion on ferns, poinsettias, crassulas or pileas. Do not use dimethoate on cinerarias, fuchsias, hydrangeas, Busy Lizzies, calceolarias, primulas or chrysanthemums. Finally, do not use pirimosmethyl with pyrethrins on cacti and succulents.
• Always read the instructions on the label before using a chemical spray, and use it at the concentration recommended.
• Because mealy bugs can be introduced into your home on newly-bought plants, always check them for signs of pests before positioning them among your own healthy plants The best treatment is effective prevention.

What to look for

Every time you water your plants or clean their foliage you should check for mealy bugs.

This pest is easy to identify, as it looks like a small woodlouse. Mealy bugs usually form clusters of adults and young, and have a nasty habit of excreting honeydew. This substance is soon covered with sooty mold, an ugly black fungus. Badly infested, untreated plants are eventually covered with large patches of sooty mold, preventing the leaves from ‘breathing’ Leaf joints and the undersides of leaves are mealy bugs’ favorite hiding places. There they are protected from the drying effects of sunlight and air circulation.

Plants to watch

The large, woody stemmed foliage plants that are so popular with houseplant enthusiasts unfortunately provide mealy bugs with a perfect diet.

Mealy bugs also attack cacti and succulents, but they have a special liking for palms and ornamental figs, particularly the Weeping Fig. Coleus and crotons are other favourites, and ferns, including the so-called asparagus ‘ferns’, are sometimes infested. Flowering plants liable to suffer include fuchsias, hoyas, orchids, jasmines, begonias, hippeastrums (also called amaryllis), chrysanthemums, oleanders, gardenias and azaleas.

Root mealy bugs

These are close relatives of mealy bugs, and attack the roots of pot plants grown indoors, in conservatories and in greenhouses. In severe attacks, plants may die, as the roots can no longer take up water or nutrients.

Cacti and succulents are most vulnerable, because root mealy bugs prefer dry composts, but other favourites include African violets, mimosas, grevilleas, dracaenas, gardenias, pelargoniums and stephanotis.

If a plant stops growing, becomes discolored or wilts for no obvious reason, such as dry or waterlogged compost, excessive heat or sunlight, inspect it for root mealy bugs. Remove the pot, and look for clusters of white, woodlice-like creatures on the roots and on the bases of the stems. Remove as many root mealy bugs as possible, then repot into fresh compost and a new pot. Finally, drench the roots with malathion or nicotine, diluted to spraying strength. You can also use certain systemic insecticides, but check the labels first, as for treating mealy bugs.

The roots may take some time to recover. Place the plant in light shade, and keep it on the cool side and out of draughts for a few days. Regular drenching helps prevent further attacks.