In the Garden:
Northern & Central Midwest
January, 2005
Regional Report

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1648

These insidious little bumps on a jade plant are mature scales, whose telltale sign is a sticky residue.

Watch out for Houseplant Pest Explosions!

Now that our houseplants have been indoors for several months, they should be finally settling into their new surroundings. Several of my more touchy plants dropped most of their leaves, so I've pruned them back and will see what happens.

Even though I checked my plants carefully and sprayed them with horticultural oil before bringing them in, several of my plants have bugs of one sort or another. Since the plants are inside with no natural predators, this is the time when populations seem to explode.

Spider Mites
Because spider mites are probably the most common insect problem indoors, check for them first. They are too small to see easily, but their damage is distinct. You may notice yellow stippling or fine webbing between leaves and stems. They feed on the undersides of the leaves, but as populations rise, you find them all over. By the time damage is visible, it may be extensive.

Take a piece of white paper, hold it under a leaf, and tap the plant. If the specks that fall on the paper move, the plant has mites. If they don't move, then it's dust. Control spider mites with horticultural oil.

Scale
Looking like bumps on stems and leaves, scales are soft-bodied insects that suck sap from plants and then secrete a hard shell over themselves. A plant with scale will have sticky honeydew and perhaps a black sooty mold all over the leaves. Eggs develop under the hard shell, and later tiny crawlers hatch and move around the plant. At this stage, scales are vulnerable to insecticidal soap and oils. You also can control the adults with oil.

Whiteflies
Whiteflies are flying insects that look like tiny white moths. If you shake the plant, they will fly up in a cloud and then settle back on the leaves. Their damage is similar to that of spider mites. The leaves will be stippled and new growth stunted. The larval stage must be controlled with insecticidal soap or oil. Adults can be trapped with yellow sticky traps.

Mealybugs
Mealybugs are soft-bodied insects that secrete a white, cottony covering. They suck plant sap from leaf axils and branch crotches. New growth on a plant will be distorted, and the plant will be weakened. Mealybugs secrete honeydew like aphids. Control by removing the white masses with a cotton swab dipped in rubbing alcohol or horticultural oil.

Fungus Gnats
Fungus gnats are small black flies similar to fruit flies. Adults are mainly a nuisance, but the larvae can feed on roots and stunt plants. If you see the adults flying, look for larvae when you water. If present in high numbers, they float. Because fungus gnats thrive in damp areas, control them by letting the soil dry out.


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