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Larry Sagers
Mites, which are plant-feeding spiders, are about the size of a grain of sugar. Some even form webs.

In a perfect world, plants would grow inside our homes without any problems.

At my house, interior plant conditions are less than perfect, and consequently plants often suffer. In past columns we've addressed some of those problems, but we've yet to look at problems caused by insects and biotic diseases.

The creatures that attack our plants include insects and other pests, fungi, bacteria, occasional viruses and a few other creatures that find a niche and proceed to make our prize plants their dinner.

Once pests get started, they seem to flourish with abandon. Inside our home, they seldom have to worry about any of their natural enemies. Lady bird beetles, green lacewings, predatory mites and other creatures that would attack pests are safely hibernating in the snowy outdoors. Inside, pests have what they need to reproduce with fervor — warmth, moisture and food.

The first step in keeping plants healthy is to keep pests out. Start with pest-free plants and keep them clean. In many cases, the problems come from what you drag inside. Be careful about bringing plants inside from the outdoor garden.

The most serious pests are aphids, scales, whiteflies, mealybugs and spider mites. These cause most of the problems and are the hardest to control. They all share a common feeding mode in that they suck the juices from the plants, as opposed to chewing on the leaves.

Unless you are watching carefully, you might not notice the infestation until they are causing serious damage. One common symptom is that when they suck out the juices of the plant, they excrete the excess sugar from the plant sap, making the plants sticky.

Sucking out the plant's sap causes a symptom described as stipling. When pests remove the plant juices, they also remove some of the green-colored chlorophyll. This gives the plant a light or speckled appearance.

Aphids, which are green, yellow, brown, gray, black or blue, can also cause emerging new growth on plants to curl, because they feed on the underside of the leaves.

Mealybugs cause similar damage. They look like tiny bits of cotton and usually congregate in the axis of the leaves or branches. The cottony coverings they create over their bodies resist water and pesticides, so controlling them is not easy.

Whiteflies are not flies but are closely related to aphids. Give them any kind of hold and their numbers explode. Watch for them on poinsettias, fuchsias, tomatoes, Martha Washington geraniums and a host of other plants.

The adults feed on the underside of the leaves, and when you disturb the plant, it appears as if tiny, white butterflies are circling your plant. They reproduce quickly and are aggravating both inside and out.

Several kinds of scale insects can also attack your plants. Many times the infestation is not noticed because the insect's crawler stage lasts only two weeks after the eggs hatch. The pest attaches itself to the leaf or stem and secretes a waxy protective coating over itself that makes controlling them difficult.

The last pests, mites, are essentially plant-feeding spiders. They are only about the size of a grain of sugar, so they are not easy to see. They can produce a new generation every 10 days, so they can get out of control quickly. Some mites form webs, so watch for that symptom.

If you suspect a problem, the first thing to do is find the pest. Keeping plants clean is one of the best controls. If plants are in small pots, take them to the sink, turn them over and wash the back side of the leaves. Use a gentle spray of lukewarm water to eliminate the pests and get rid of the sticky exudates.

If the infestation is severe, or if you are dealing with the scales or mealybugs, you have to try something else. With the plant in the upside down position, spray the back of the leaves with insecticidal soap. Soap coats the pests, clogs their breathing pores and breaks down their protective cuticle layer. They then die off quickly.

An alternative control is to dip a cotton swab dipped in alcohol and touch the insects. This penetrates the cuticle and kills the pests. Horticultural oils are also effective in smothering the pests but wait until it warms up so you can apply it outside the home.

Other sprays are only recommended in extreme cases. Make certain they are labeled for indoor use and follow label directions. Spray several times at biweekly intervals because these sprays only control adults, so any remaining eggs will continue to hatch.


Larry A. Sagers is the horticulture specialist, Utah State University Extension at Thanksgiving Point.