Regional Gardening Reports :: National Gardening Association

In the Garden:
Upper South
January, 2009
Regional Report

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Whiteflies and spider mites have invaded this Italian parsley.

Houseplants Invaded

They seem to appear from nowhere and are particularly attracted to certain plants, while others seem to be immune. Even so, insects can spread like wildfire through your indoor plants. They may have entered the house from plants either recently purchased or brought in after the summer outdoors. Some lie dormant or as eggs until the conditions are just right. But no matter how they arrived, they can do some serious damage before you even realize they're there.

It's important to watch plants carefully for development of insect problems as they can be easily corrected if detected early. If ignored or unnoticed, insect problems can become quite difficult to control and can eventually destroy plants. Insect infestation can reach large populations in a short time indoors because there are no natural controls, such as weather or predatory insects.

The most important preventions are to keep plants from being stressed by regularly watering and feeding and maintaining proper humidity and temperature levels. Although garden writers often mention giving your houseplants a weekly shower, I always found this daunting. If it works for you, go for it.

Fortunately, there is only a small group of insects that harm indoor plants. The most common are mealy bugs, scale, whiteflies, and spider mites.

Mealy Bugs
Mealy bugs are soft-bodied insects and are usually covered with a white, powdery material. They feed on the plant with a piercing-sucking mouthpart that extracts plant juices. Mealy bugs are usually found clustered along leaf veins, on the underside of leaves and in hidden areas at leaf or stem joints. Their excess waste is excreted from the body in a form that is referred to as honeydew, as it contains a high amount of sugars and is very sticky. Many times, this sticky substance is discovered on the leaves before the insect has been detected. Some methods to control mealy bug include attempting to remove them using a cotton swab dipped in rubbing alcohol or by dislodging them with a strong stream of water.

Scales are small, soft-bodied insects that are covered and protected by an outer waxy coating. They have piercing-sucking mouthparts and damage the plant by sucking plant juices. Scale can be found on both sides of the leaves, especially along the veins, hidden in the crevices of stems or leaf axils, and on the twigs and stems. As with mealy bugs, scales excrete honeydew, and this is often the first sign that people notice. Another sign is that leaves begin to yellow or wilt. Scales can usually be rubbed off the plant with your fingers as well as with a soft toothbrush or cotton swab dipped in rubbing alcohol. Heavily infested plant parts should be pruned and disposed.

Whiteflies are, well, teeny white flies. They fly off the plant when it is disturbed. Whiteflies also have piercing-sucking mouthparts and are more closely related to scale and mealy bugs than flies. Their damage is similar to mealy bugs and scale as they also remove plant juices, causing the plants leaves to be mottled and yellow. They are one of the most difficult to control of indoor insect pests. If indoor plants are infested, you might consider disposing of the plants or using sticky yellow traps. If plants can be kept alive until outdoor temperatures allow, whitefly populations will be killed by outdoor weather conditions and predatory insects that feed on whitefly.

Spider Mite
Extremely small and difficult to see, spider mites are not insects but rather belong to a class that contains ticks and spiders, all of which have eight legs rather than the six of insects. Spider mites reduce plant vigor by sucking plant juices, with the leaves turning yellow and dropping. Sometimes a fine webbing may be seen on the undersides of leaves. When a leaf or branch is tapped over white paper, small specks appear as moving pieces of pepper or dust.

Organic Houseplant Insect Controls
Besides the other methods previously discussed, there are organic insecticides that can help to control these houseplant pests. These include neem, insecticidal soap, and horticultural oil. Be sure to read and follow manufacturer's directions. It's also important to thoroughly wet the plant with the spray and to repeat at least every two weeks.

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