Aphids are small, pear-shaped insects with sucking mouthparts that feed on a plant’s juices. There are over 4000 species of these little creatures and they’re found all over the world.
They’re able to produce several generations in a season. Whether you know it or not, you have most certainly encountered them living in colonies on stems and the undersides of leaves.
They are a member of the Homoptera order, which includes scale, adelgids, and mealybugs. Aphid species are often named after the plant they like to feed on potato aphid, peach aphid, etc., but they all have similar characteristics.
They attack food crops, roses, trees and shrubs, herbaceous perennials, and annuals. Just about anything you grow can be a host to these little pests.
And…their reproduction rate is simply astonishing!
Aphids are soft-bodied, 1/16 to ⅛ inches (2 to 4 cm) long and have two cornicles on their lower abdomens. These little tubes secrete a defensive substance and can be imagined as little exhaust pipes. These cornicles are the number one way to identify this pest.
Some aphids have a waxy or wooly covering. They do not move or jump or fly when disturbed. Adults and nymphs all feed together in a colony so you will find them in different sizes, all in one group.
Different species are different colors – there are green, white, yellow, orange, red, gray, black, blue, and brown aphids.
Aphids are usually wingless, but winged generations are sometimes produced, allowing insects to start a new colony on other plants. This happens when infestations are large and a plant cannot support the entire colony.
Aphids are easy to see with the naked eye, but they tend to hide in curled up leaves or on the leaf undersides, and they often blend in with their host plant. So take some time to scout them out because populations can explode quickly. We recommend looking for them daily early in the growing season.
They produce a sticky substance called honeydew that you’ll sometimes notice dripping down from trees (and coating your car’s windshield) or on the leaves of your prized hibiscus. This honeydew can be an invitation for a fungus called sooty mold to form. So if your plants have sticky, black-spotted leaves, it’s a good sign you have an aphid infestation.
Another way to tell if aphids are present is the presence of ants. Ants love honeydew, and some ant species even “farm” them. They protect them from predators and will bring aphid eggs into their underground nests to shelter them through the winter.
Aphids overwinter as eggs at the base of plants or on alternate hosts (moving between trees or shrubs to herbaceous plants, for example). The eggs hatch in early spring and the young aphids – known as nymphs or crawlers – begin feeding.
Aphids have an incomplete life cycle meaning there is no pupae stage. All the aphids that hatch in spring are female and all can reproduce asexually, giving rise to many generations in a very short time. They can also give birth to live young, skipping the egg stage of the life cycle entirely. At the end of the season, males and females are produced, eggs are laid, and the cycle begins again.
In mild climates, there is no overwintering stage – aphids keep on reproducing all year round.
Some, like the pine bark aphid, overwinter as females and lay eggs in the early spring about the time Cornus mas (Cornelian cherry) is in bloom.
Aphids will attack all plant parts – roots, stems, leaves, buds, flowers, and fruit, depending on the specific species. Those with alternate hosts spend part of the year feeding on one type of plant and then move to a different plant species, causing damage to both plants.
An aphid infestation can be devastating for a commercial grower’s greenhouse crop, making the plants unattractive and unsaleable. They damage food crops and trees, and can spread plant viruses.
In our home gardens, these pests rarely kill a plant. The population has to be very high for that to happen, but they do cause spotted or curled leaves, distorted and stunted growth, and the sticky honeydew encourages the growth of sooty mold.
They cause plants to look sickly, vegetables to look unappetizing, rosebuds to be discolored and fall off before opening, and foliage to be pale and speckled.
It is impossible to rid your garden of all aphids, and small infestations are not usually a big problem. However, given their ability to quickly reproduce, it’s best to start a scouting program early in the growing season.
Many aphid species are already active when magnolias are in bloom. Look for the signs of damage mentioned above, the presence of ants, sticky honeydew, and the insects themselves.
Controls should be used early, before the populations grow and when the insects are nymphs. That’s the most vulnerable stage.
If you’re not squeamish, you can squash aphids with your fingers. Sometimes they can be blasted away with a strong spray of water from your garden hose.
Small infestations can be pruned out. Destroy or dispose of these plant parts, don’t compost them because the aphids can survive in your compost bin.
Biological control is the term for using natural predators to combat pest problems.
A healthy garden may have pests, but it will also have an abundance of beneficial insects that work to keep the pests in balance. It is important to recognize these friends of the gardener in all stages of their life cycle. Using insecticides might get rid of the pests, but insecticides can also kill the beneficial predatory insects that will do the job for you!
- Adult ladybugs and their larva will eat all the aphids they can find. Everyone knows what adult ladybugs look like, but can you identify ladybug larvae? They are black and spiny, about ½ inch long and have red markings. Take good care of these little guys, because while an adult ladybug will eat up to 25 aphids a day, a single larva can eat 250!
- Aphid Lions, the larva of the green lacewing, are about ½ inch long and are brown and white. They look like little alligators. Aphid Lions eat the eggs, nymphs and adults while adult lacewings eat only nectar and honeydew.
- Parasitic wasps – Aphidius colemani, Aphid parasitoids, and others – are very tiny wasps that lay their eggs in aphid bodies. The larva hatch and live inside the aphid’s body, eventually killing it.
These predators are available for purchase through beneficial insect websites. They offer quantities based on the size of your garden and detailed instructions for release.
For example, when you purchase ladybugs, release them at dusk after the garden has been watered. If you release them during the day, they will just fly away. Ladybugs will stay in your garden as long as there are enough aphids to feed them. They will move on to other gardens in search of another meal when they have finished cleaning up your plants.
Another biological control is beauveria bassiana. This is a parasitic (entomopathogenic) fungus that occurs naturally in many soils. It is the active ingredient in several insecticidal sprays, and it works by entering the insect’s body and poisoning it. Products containing beauveria bassiana are often marketed as “natural” or “safe” alternatives to chemical insecticides. However, keep in mind that it will kill all insects it touches – even beneficial ones – so use it with the same care you would like any other insecticide.
Chemical insecticides do not know the difference between a beneficial insect and a pest. Use care when using these products. Be sure the product is right for the pest, read the label, use the personal protection equipment recommended and follow the directions for use exactly.
Contact insecticides are often sold in spray form. The product must be sprayed directly on the pest and generally kills on contact. These insecticides will also kill any other insect it comes in contact with, so don’t use them when bees are active or other beneficial insects are about their work. It may be challenging to find all the aphids to spray them. They are very good at hiding! And all that’s needed is one female aphid to start a new population explosion.
Horticultural oils and insecticidal soaps are also considered contact insecticides. Horticultural oils smother the insects and insecticidal soaps dehydrate and smother the pests. They may have a different chemical makeup and may be organic instead of synthetic, but they are applied the same way. These products will also harm beneficial insects.
Systemic insecticides are watered into the soil and are then taken up by the plant. This causes the plant to become poisonous to any pests feeding on it, which kills them. Systemic insecticides are a good option for non-food plants and are not harmful to the insects that aren’t munching on your garden.
There are lots of recipes out there for homemade “natural” insecticides, many involving apple cider vinegar, cayenne pepper, dish soap and other household staples. While some of these products may kill the pests, they can also cause harm to plants. We recommend using commercial products that have been developed to deliver the least amount of active ingredient to be the most effective without damage to plants. You’ll protect your garden and save money in the long run.
Eggs overwinter. Ants move aphid eggs to plants to start a new herd. Winged aphids are easily carried on the wind to new plants. They reproduce at an alarming rate: a single aphid can produce 100 daughters in her lifetime. It is unrealistic to expect that aphid infestations can be completely prevented.
But there are steps a gardener can take to help prevent aphids from getting out of hand:
- Search out and use plant cultivars and varieties that are less appealing or more resistant to aphids.
- Avoid lots of nitrogen fertilizer; aphids prefer the tenderest, most succulent growth, which heavy nitrogen applications encourage.
- Keep ants under control to prevent them from defending their herd against predators.
- Invite beneficial predators into your garden by providing the nectar the adults consume.
- Use companion planting – chives, coriander, and nasturtiums have been known to deter aphids.