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John Fulton

John Fulton
Former County Extension Director

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In The Backyard

Horticulture columns and tips done on a timely basis

Pest Control for Houseplants - from Dave Robson

Posted by John Fulton -

Houseplants do not thrive during the winter due to adverse growing conditions. However, houseplant pests such as mites, aphids and scales do.

Plants are more likely affected by insect and related pest problems when under stress, states David Robson, University of Illinois Extension horticulture educator, Springfield Center. Fortunately, most insect-related damage is visible even though the pest might not be. Spider mites are not true insects, having eight legs instead of six. Damage from spider mites usually occurs when temperatures are cool and humidity levels are low. The first noticeable sign of mite-infected plants is a speckling of foliage. Leaves will be dotted with yellow spots that slowly turn brown. Careful observation of the underside of leaves might reveal tiny webs, especially between the leaf and stem. Mites can be seen with a sharp eye or a magnifying glass. They are usually reddish, move slowly and can be found underneath leaves and in growing shoots. Mites are most common on palms, scheffleras, crotons, cyclamen and cacti. Aphids, sometimes called plant lice, suck the sap from the leaves, stems and buds. Droplets of sticky sap may coat the plant parts. Most aphids are green, clear or white on houseplants. Like mites, the insects do not have wings and seldom migrate much from their original location. Aphid-damaged leaves appear twisted and distorted. New growth may be small and yellowish. Most flowering plants are bothered by aphids—especially hibiscus. Foliage plants such as palms also seem prone to aphid attacks. Scales are another one of the sap sucking insects that do not move. Brown armor-plated circles are usually found lined up on stems and occasionally leaves. Scales lay eggs beneath this shell. As soon as the young crawlers hatch, they move to another location and start secreting a shell for protection. Ferns are susceptible to scales as are woody-stemmed plants. However, scales seldom appear on the underside of fern fronds. What looks like scales may actually be fern spores, the sign of a healthy plant. Insect and related pest problems can be controlled with regular inspections. Infested plants should be isolated and treated. Insecticidal soaps provide the best control indoors for mites and aphids. Carry the plant to a sink before spraying. Always read and follow the labeled directions. A few aerosols are also available on the market for controlling aphids and mites. Make sure you keep the can at least 12 inches from the plant to avoid "freezing" the leaves with the super cold spray. Scales need more attention. Each should be carefully removed with a toothpick, Q-tip or dull knife. Dab each location with a cotton swab or Q-tip dipped in rubbing alcohol to kill any scale eggs or adult remaining. Wash the dabbed areas within five minutes to prevent the alcohol from drying the plant tissue. Check plants weekly after treating. Repeat applications of insecticidal soap or alcohol may be needed for three or four weeks. When bringing a new plant indoors, keep it isolated from the others for at least a month. Observe it weekly for signs of insects. It may be wiser to discard some severely infested plants instead of trying to cure them, adds Robson. The chance of insects spreading to other plants should always be kept in the back of your mind.

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