Prevention is the best way to control insects which so often infest house plants. Even so, insects do appear. Sometimes they are on the plant when we buy it, or perhaps they are in the soil. Insects also may get onto the plants when we put them outdoors for the summer. They simply are not noticed until the plant is brought indoors again.
If a plant is healthy, however, it is seldom bothered by pests.
Certainly the most common enemies of house plants are plant lice or aphids. Look for them under the leaves where they suck the sap. Tobacco water or soapsuds will get rid of them.
If soapsuds are used, rinse the plant afterward.
The red spider is a very small mite that can scarcely be seen by the eye. Like the aphid, it subsists on the juice of the plant and is especially active when the conditions are dry and warm.
You can control the red spider by frequently showering or misting your plants.
Mealybugs look as if a plant were dusted with flour. They are soft-bodied scales and are often found at rest or crawling where stems and leaves join as well as on the underside of the leaves and along the veins.
If a strong stream of water fails to remove them, try a swab which has been dipped in alcohol.
Another minute sucking insect, and one which is particularly destructive, is the white fly. This pest clusters in large numbers on the undersides of leaves but is rarely seen until a plant is disturbed. Use an old toothbrush and warm water to scrub the backs of the leaves.
Very often scale insects are found on the leaves of palms and ferns, rubber plants and cycads. The most common one is called brown scale. It is one-quarter to three-eighths of an inch long and nearly as wide with a hard, convexed shell which is dark brown in color.
Scales can be removed by applying a spray of whale-oil soap or fir-tree oil.
Thrips eat the epidermis of the leaves. They are brown or black in color and about a quarter of an inch long. To control them use any one of the suggestions already named.
to keep your plants pest free, dust them once a month with a soft cloth. Clean the leaves with warm water, supporting them with one hand as you work.
A number of minor pests are often found in potting soil. Most of them fall into the category of nuisance rather than harm. The worst damage they can do is gnaw at the roots.
A simple answer is to repot th e plant in sterile soil.