What Are They?
Aphids are tiny sucking insects from family Aphididae. Adult aphids are pear-shaped, measuring less than 1/8" in length. The most common aphids on houseplants are the light green ones (pear aphids), but aphids can also be found colored pink, white, grey and black. Additionally, winged aphids can appear when colonies are established and fly to infect new plants. Juvenile aphids (nymphs) look like smaller versions of the adults.
Aphid infestations tend to develop quickly, and the insects are highly mobile: they rapidly travel from one plant to another. In the outdoor garden, aphid colonies are often tended by ants, which feed on aphid honeydew. Researchers have observed ants transporting aphids to new plants and hypothesized that the ants are "farming" aphids. Indoors, aphids spread through flying or crawling.
Aphids cause damage by sucking sap from new growth. They tend to cluster at the growth end of plants and attach to soft, green stems. As a result, the new foliage may look crinkled or stunted, and the aphids are usually plainly visible around the stem. If the infestation is bad enough, the plant will begin to drop leaves. Finally, like mealy bugs, aphids secrete honeydew that encourages the growth of sooty mold and fungus.
Outside, aphid eggs survive the winter by attaching to woody growth. In the spring, eggs hatch into females. The females give birth to nymphs without mating, and the nymphs rapidly mature into adults (about 10 days). Males are born in the fall and begin to mate with the females to produce eggs in preparation for the long winter. Indoors, however, there is no winter to slow their reproduction, and females can continue to produce nymphs all year without pause. Thus, the aphid population can quickly get out of control.
How to Get Rid of Aphids
Like most pests, the best control for aphids is defensive. Healthy, vigorous plants are less susceptible to infestation than weak, underpotted, and stressed plants. As a general rule, make sure your plants are healthy, and you're less likely to attract these annoying critters in the first place.
If you see aphids on your indoor plants, there are several control options:
- Wash them away. Use a strong stream of water to blast aphids from your plants. You can also knock them off with your fingers or a cotton swab. This is best for light infestations.
- Insecticidal soap. Insecticidal soaps are available on the market (such as Safer's Insecticidal Soap), or you can make your own by using a dish detergent such as Ivory Liquid. Try to find a product free of perfumes and additives that might harm plants. Mix the soap in a weak concentration with water (starting a 1 teaspoon per gallon and increasing as necessary). Spray on plants.
- Neem oil. Neem oil is derived from the neem tree. Use according to label instructions. In addition to its insecticidal properties, neem is also a fungicide and has systemic benefits (meaning the plant absorbs it so it can control insects it doesn't directly contact). According to the Environmental Protection Association, neem is safe for use on vegetables and food plants as well as ornamentals.
- Kitchen insect spray. This all-purpose insect spray was developed by the editors of Organic Gardening magazine and came to me by way of Rodale's Organic Gardener's Handbook of Natural Insect and Disease Control. To make a batch, combine 1 garlic bulb, 1 small onion, and 1 teaspoon of cayenne pepper in a food processor or blender and process into a paste. Mix into 1 quart of water and steep for 1 hour. Strain through a cheesecloth and add 1 tablespoon of liquid dish soap. Mix well. The mixture can be stored for up to 1 week in the refrigerator.