Aphids

What are those little green bugs on your plants? They're probably aphids! Here are our best tips on how to identify and control aphids in the garden.

What Are Aphids?

Aphids seem to find their way into every garden. They are small, soft-bodied insects that feed by sucking the nutrient-rich liquids out of plants. In large numbers, they can weaken plants significantly, harming flowers and fruit. Aphids multiply quickly, so it's important to get them under control before reproduction starts. Many generations can occur in one season.

The good news is that they tend to move rather slowly and aphid control is relatively easy.

Identification

Identifying Aphids

Aphids are tiny (adults are under 1/4-inch), and often nearly invisible to the naked eye. Various species can appear white, black, brown, gray, yellow, light green, or even pink! Some may have a waxy or woolly coating. They have pear-shaped bodies with long antennae; the nymphs look similar to adults. Most species have two short tubes (called cornicles) projecting from their hind end.

Adults are usually wingless, but most species can develop a winged form when populations become crowded, so that when food quality suffers, the insects can travel to other plants, reproduce, and start a new colony. Aphids usually feed in large groups, although you might occasionally see them singly or in small numbers.

While aphids in general feed on a wide variety of plants, different species of aphids can be specific to certain plants. For example, some species include bean aphids, cabbage aphids, potato aphids, green peach aphids, melon aphids, and woolly apple aphids.

What Does Aphid Damage Look Like?

Nymphs and adults feed on plant juices, attacking leaves, stems, buds, flowers, fruit, and/or roots, depending on the species. Most aphids especially like succulent new growth. Some, such as the green peach aphid, feed on a variety of plants, while others, such as the rosy apple aphid, focus on one or just a few plant hosts.

• Look for misshapen, curling, stunted, or yellowing leaves. Be sure to check the undersides of leaves; aphids love to hide there.
• If the leaves or stems are covered with a sticky substance, that is a sign that aphids may have been sipping sap. This "honeydew," a sugary liquid produced by the insects as waste, can attract other insects, such as ants, which gather the substance for food. When aphids feed on trees, their honeydew can drop onto cars, outdoor furniture, driveways, and so on.
• The honeydew can sometimes encourage a fungal growth called sooty mold, causing branches and leaves to appear black.
• Flowers or fruit can become distorted or deformed due to feeding aphids.
• Some aphid species cause galls to form on roots or leaves.
• Aphids may transmit viruses between plants, and also attract other insects that prey on them, such as ladybugs.

Control and Prevention

How to Get Rid of Aphids

• Try spraying cold water on the leaves; sometimes all aphids need is a cool blast to dislodge them. Typically they are unable to find their way back to the same plant.
• If you have a large aphid invasion, dust plants with flour. It constipates the pests. 
• Neem oil, insecticidal soaps, and horticultural oils are effective against aphids. Be sure to follow the application instructions provided on the packaging.
• You can often get rid of aphids by wiping or spraying the leaves of the plant with a mild solution of water and a few drops of dish soap. Soapy water should be reapplied every 2-3 days for 2 weeks.
• One variation of this soap-water mix includes cayenne pepper: Stir together 1 quart water, 1 tsp liquid dish soap, and a pinch of cayenne pepper. Do not dilute before spraying on plants.
• Diatomaceous earth (DE) is a non-toxic, organic material that will kill aphids. Do not apply DE when plants are in bloom; it is harmful to pollinators, too.

How to Prevent Aphids

• For fruit or shade trees, spray dormant horticultural oil to kill overwintering aphid eggs.
• Beneficial insects, such as ladybugs, lacewings, and parasitic wasps, will feed on aphids. Supplemental populations of these insects can be ordered online and should help keep the aphid populations controlled from the start.
• Companion planting can be very helpful to keep aphids away from your plants in the first place. For example:
  • Aphids are repelled by catnip.
  • Aphids are especially attracted to mustard and nasturtium. Plant these near more valuable plants as traps for the aphids. (Check your trap plants regularly to keep aphid populations from jumping to your valued plants.)
  • Nasturtiums spoil the taste of fruit tree sap for aphids and will help keep aphids off of broccoli.
  • Garlic and chives repel aphids when planted near lettuce, peas, and rose bushes. 

Using Alcohol to Control Aphids

Isopropyl alcohol (also called isopropanol or rubbing alcohol) works fine and is easy to find, but be sure it doesn’t have additives. Ethanol (grain alcohol) seems to work best. Alcohol usually comes in 70 percent strength in stores (or 95 percent strength purchased commercially). To make an insecticidal spray, mix equal parts 70 percent alcohol and water (or, if using 95 percent alcohol, mix 1 part alcohol to 1 ½ parts water). 

You can also add alcohol to a soapy emulsion to make it more effective. For example, in a spray bottle, combine 5 cups water, 2 cups alcohol, and 1 tablespoon liquid soap.

Caution: When applying an alcohol or soap spray, or a combination, always test a small area first, and apply in morning or evening, when the sun is not beating down. Watch the plant for a few days for any adverse reactions before applying more. Plants can be sensitive to alcohol and soap. Also, some soaps have additives that can damage plants—select the purest form.

Check out this video to learn more about how to get rid of aphids. 

Do you have more tips for controlling aphids? Let us know in the comments below!