You brought your houseplants back indoors a few weeks back and everything is going pretty well, except one plant seems covered with small white dead skins. Examining it more closely, you see that its stems and leaves are covered with small plump insects: aphids! What can you do?
Know Your Enemy
There are thousands of species of aphids and they can come in almost any color: black, purple, orange, red, yellow, white, etc. However, the aphid that is most often found on houseplants is the green peach aphid (Myzus persicae), an insect that, despite its name, is not limited to peach trees, but is instead rather a generalist, affecting many plants outdoors and in. This aphid is usually a translucent pale green in color, although it can occasionally be yellowish or pinkish.
It is usually introduced on a plant that was not thoroughly cleaned before coming indoors, but sometimes too hitches a ride on a pet or human coming inside. Although usually wingless, there is a winged generation, usually in the fall, but aphids remain weak flyers and are therefore unlikely to find their way indoors on their own.
It only takes a single female aphid to produce thousands of babies, and in just a few weeks at that. No male is required: the female produces replicas of itself by parthenogenesis (reproduction without fertilization) and its babies begin to produce babies just days after birth. Imagine the speed at which they can multiply!
Damage to Plants
Aphids damage plants by piercing their cells and sipping the sap that flows out. This weakens the plant, often leading to the yellowing and eventual death of affected stems and leaves. Affected flower buds often abort. A seriously infested plant may die.
You’ll often see honeydew on the plant’s lower leaves or on furniture the plant is set on. It’s a sweet, sticky excretion that aphids give off and drips down to the lower parts of the plant. Sooty mold often forms on honeydew and covers the leaves with what looks like black powder, reducing the plant’s ability to absorb light.
Aphids can also affect your plant’s health indirectly by transmitting plant viruses and other diseases.
Finally, aphids can also spread to nearby plants. They’re not very selective: almost any plant can be infested.
Outdoors, predators such as ladybugs, lacewings and hoverflies often come to the rescue of the plant and stop the infestation in its tracks. Indoors, however, these predators are absent. So it’s up to the plant owner to react and thus limit the damage.
The first step is always to isolate the affected plant so the infestation can’t spread.
The easiest and often the most effective treatment is to carry the plant to the sink and rinse it thoroughly with a strong jet of water. If the plant is too big for the sink, try the shower. For this to work, you have to be able to reach all parts of the plant, including the undersides of the leaves. It may be necessary to repeat the treatment several times, because if even one aphid survives, the infestation will start up again.
Neem is an excellent pesticide for controlling aphids, as it not only kills many of them instantly, smothering them in oil, but also has a longer term effect, since it contains hormonelike substances that prevent them from reproducing. Insecticidal soap, an organic product readily available in garden centers, is another good choice. Horticultural oils and pyrethrum-based insecticides can also be effective.
Dilute the product chosen according to the manufacturer’s recommendations and apply it to the affected parts with a small hand sprayer, also being careful to reach the less visible parts, like the underside of the leaves. Repeat as needed every 4 to 5 days.
Beware of using dishwashing liquid to treat aphids. Although this product was once often used by gardeners to control insects, today’s brands often contain additives (colorants, perfumes, stabilizers, etc.) that can be toxic to plants. Plus modern dishwashing liquids are usually detergents, soaps, and detergents are not much more effective against insects than plain water!
Keep At It
I’m not going to deny that aphids are difficult to control. You often have to repeat the treatment several times before you finally get them all. But if you are persistent in your applications, you will be able to free your plants from aphids.