Houseplants Under Lights

Lesson 4: Proper Plant Selection and Care

Insect & Other Critter Pests

Indoor plants may get many of the same insect pests that outdoor plants do. The most common pests are: aphids, mealybugs, scale, white flies and fungus gnats. All but the fungus gnats injure plants by sucking the juices.

Aphids: Tiny soft-bodied insects that may come in several colors including black, gray, brown, yellow and green. You'll find these on the stems and leaves of the plant sucking the juices. They secrete a sticky substance called honeydew. The sooty mold mentioned above grows on the honeydew. Ants are also attracted to the honeydew. Symptoms: Distorted leaves and stems, damaged flowers. Solution: Use insecticidal soap (or make your own as described above). Alternatively, just give the plant a good shower, which should wash off the aphids. This may be done outside in the summer or in your bathroom shower in the winter.

Mealybugs: This soft-bodied insect is oval shape and white colored. You may notice something looking like cotton on your plant's stems. If you pull the plant out of the pot, you may see mealybugs on the roots too. Symptoms: Spotted or deformed leaves, yellowing leaves, white patches on leaves and stems. Solution: Unfortunately, their waxy outer cover repels water. Use a cotton swab dipped in alcohol to dissolve the waxy cover. You may need to spray a solution of water and alcohol on the whole plant if it is badly infected. Be sure to make sure you get all the eggs (white threads attached to the insect's back) and insects or the plant will be reinfested quickly. If you found mealy bugs on the roots, drench the soil with a commercial insecticidal soap.

Red Spider Mites: Spider mites are real spiders (have eight legs) instead of insects (have six legs). If you see the symptoms listed below, hold the plant over a piece of white paper and gently tap the leaves. You'll see tiny dots of red running around the paper. These are the spider mites. Symptoms: Discolored or black flowers, stunted new growth, white mottling on the leaves (looks like spider webs). Solution: Raise the humidity in the area immediately. Spider mites only appear in dry, hot environments. Spray the plants thoroughly with a soap and water spray or use one of the insecticides sold for spider mites.

Whiteflies: Suspect whiteflies if you see tiny white "moths" fly up when the plant is moved. Whiteflies live on the undersides of the leaves. They suck the juices of the leaves and stems. Their larvae also feed on the leaves but are transparent which makes them difficult to see. Symptoms: Mottled and yellow leaves; "moths" flying up when plants are moved. Solution: Use a cotton swab dipped in alcohol to wipe off the leaves and stems. Alternatively, shake the plant and vacuum up the flies! Use yellow sticky traps (see directions below for making your own) to monitor your growing area for both Whiteflies and the Fungus gnats discussed below).

Fungus Gnats: When fungus gnats are present, you may find them being attracted to your television or computer screen when the room is dark. Many people think they are seeing fruit flies. Fungus gnat larvae live in peat or other organic matter in your potting media. The larvae feed on decaying organic matter including rotting roots. There is some debate about how much damage these really do to your living plants because no one is sure if the larvae eat just decaying roots or if they attack living roots too. Symptoms: Gnats fly up from the surface of the soil when the plant is moved. You notice tiny black flies being attracted to lights. Solution: Don't use peat or other organic matter in your potting media. Alternatively, let the top inch or so of the soil dry out before watering again. Use yellow sticky traps. Drenching the soil with an insecticide will kill eggs and larva currently present. You need to repeat this every week due to the short life cycle of fungus gnats.

Making Your Own Sticky Traps

Buy these items to make your own sticky traps:

• A small container of Tanglefoot™ or a bottle of mineral oil.
• Packages of yellow 3"x5" index cards.
• Short pieces of wire or fishing line.

Steps for making them:

• Punch a hole in the top edge of the card (usually the short edge).
• Attach the string or wire to make a hanger.
• Coat one side of the card with the Tanglefoot™ or mineral oil.
• Attach the card to a small pot with rubber bands. Alternatively, mount the card on a stick that can be stuck into the pot. If you coat just one side of the card and have a large pot, lay the card, uncoated side down, on top of the soil.
• Throw the cards out when they are covered with whiteflies or fungus gnats.

If you prefer to buy them, stock up during the summer gardening season or it may be difficult to locate them when you really need them. They do tend to be expensive to buy. Sometimes you can find them on sale at the end of the garden season.

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