How to Identify and Get Rid of Aphids on Outdoor Plants

It’s hard to find something positive to say about aphids. These pesky insects damage food and fiber crops across the world and have killed many an ornamental, vegetable and houseplant. They’re hard to prevent and challenging to treat, and get this — they adapt and become resistant to chemical pesticides.

And did we mention that females can reproduce on their own, and their female offspring are often born pregnant? Entomologists call it telescopic reproduction, which can quickly turn an aphid visit into an aphid infestation.

Let’s look at this garden and crop pest, learn what kind of damage they can do and how to treat and prevent it. We may even find something nice to say about aphids!

What Are Aphids?

Aphids are part of a huge family of sap-sucking insects called Aphidoidea. There are 5,000 or so species of aphids worldwide, and at least 150 are present in North America. (Perhaps hundreds more were brought in as invasives from other parts of the world.)

Because they prefer temperate zones with distinct seasonal changes, they’re prevalent across much of the middle section of the U.S., including areas where soybeans, corn, cotton and wheat are grown.

Left unchecked, aphids can multiply rapidly and do tremendous damage, not only to industrially grown crops but also to home gardens.

Types of Aphids

Aphids are small, pear-shaped insects that measure between 1/16- and 1/4-inch long. They may appear in various colors, including white, green, black, red or transparent. They have six legs and a long piercing mouthpart that penetrates and sucks the sap out of plants.

Here are some of the most common aphids in North American gardens:

• Black bean aphid (Aphis fabae). A major crop pest, this small, black aphid feeds on vegetables and ornamental plants.
• Green peach aphid (Myzus persicae). As the name suggests, this green, sometimes winged aphid feeds on peach trees and hundreds of other plants.
• Pea aphid (Acyrthosiphon pisum). Green to reddish-brown, this crop pest feeds on peas and alfalfa, but also likes garden plants.
• Greenfly (Aphis gossypii). This pest feeds on watermelon, cantaloupe and other low-to-the-ground crops, but also likes hibiscus and citrus.
• Foxglove aphid (Aulacorthum solani). This little green bug likes tulips, legumes and nightshades.
• Rose aphid (Macrosiphum rosae). Ranging from green to pink to reddish-brown, this pest can decimate rose bushes and neighboring plants.

How Aphids Impact a Garden

“Aphids suck plant juices out of a wide range of fruits and vegetables, flowers and ornamentals,” says Josh Matta, senior biologist for Spectrum Brands, which makes lawn, garden and home pest control products. Here is just some of the damage they can do:

• In fruits and vegetables, aphids can weaken and disfigure fruit, leaving it unappealing to eat and possibly affecting taste.
• In all plants, aphids can cause foliage to thicken, wrinkle and turn brown.
• Aphids are vectors, meaning they transmit viruses between plants.
• Aphids leave “honeydew,” a sugary liquid (basically, aphid poop) that attracts ants and other insects. It also can host fungus that turns leaves black.

Signs of Aphids

Matta says that aphids can go after almost anything in your garden, whether it’s fruit, flowering or ornamental. “Unfortunately, they’re not picky,” he says. “You can find aphids on pretty much any kind of plant.” Some telltale signs of aphids include:

• Clusters of them on the underside of leaves;
• Curled, yellowed, misshapen leaves;
• That sticky “honeydew” on leaves and stems;
• Wrinkled, puckered buds on roses and other flowering plants.

How to Get Rid of Aphids

Aphids are most active when the weather is warm but not stifling. So if you have an infestation, spring is an effective time to treat for them.

“This time of year I recommend treating your garden weekly or bi-weekly with a good insecticide formulated for use on edibles,” says Matta. “You can use it on houseplants, ornamentals, flowers, roses and most vegetables, herbs, fruits and nuts up to the day of harvest.”

To eradicate aphids without chemicals, try blasting your plants with cold water from a garden hose, making sure to hit the underside of the leaves where aphids like to hide. This might not be an option for less sturdy plants, though.

Another option is to wash leaves — yep, each leaf — with a mild soapy water solution every two to three days. You can try spraying the solution, too, but you must hit the undersides of the leaves.

How to Prevent Aphids From Coming Back

Matta says frequent inspection and proper insecticide treatment is the best method to keep aphids away. “Some folks try to deter aphids by growing plants with a strong odor nearby, like strong smelling herbs, onions or garlic,” he says. “Also, plants like Nasturtiums or Calendula flowers may attract aphids away from your susceptible plants.”

We told you we’d find something good to say about aphids, and here it is: They attract beneficial insects, like ladybugs, lacewings and parasitic wasps. These love to dine on aphids, as do several species of songbirds, which can eat millions of aphids in a day. You can even buy ladybugs to introduce to your garden — their larvae feed on aphids, too.