4 Ways Aphids Kill Your Plants And How To Stop Them

by | Aphids, Insects

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If you’ve got aphids on your plants, trees, fruits, vegetables, or houseplants, then here’s how much danger your plants might be in:

Aphids can kill plants that are young, stressed, or unhealthy. Aphids don’t often kill a mature, healthy plant, unless the aphid infestation is very bad over a long period of time. But aphids stunt new growth in any plant and stop even mature plants and trees from thriving.

There are several ways that aphids damage and eventually kill your plants and trees. Understanding how aphids feed off plants and what effect this has on plants and trees can help you understand what damage the aphids may cause and why you need to stop them, before the untimely death of your beautiful greenery.

How aphids feed on plants and trees

Photo showing 300 aphids on one soybean leaf
Aphids often feed in large numbers. 300 aphids were counted on this single soybean leaf.
Source: With thanks to Roger Schmidt, University of Wisconsin-Madison, Bugwood.org

If you find one aphid there’s usually more – a lot more, depending on how long the aphids have been around feeding and giving birth to more aphids. Some researchers have counted 300 aphids on a single leaf (see the picture above).

Aphids can attack your outdoor plants or the ones inside your home or greenhouse – click here to find out how aphids get inside.

Aphids are one of the insects that feed on plants and trees. Their mouths are specially designed to puncture the softer, juicier parts, such as new shoots, and then to suck out the sap. The sap that aphids like to eat is called phloem.

Phloem is very important to the plant or tree because it carries sugars, food, and other important nutrients from the leaves to the rest of the plant.

It’s these mouthparts that scientists think aphids might use to pierce human skin – click here to find out if aphids can bite or sting you.

How aphids kill plants

There are four ways that an aphid infestation can kill your plants or trees, or at least stunt their growth and yellow and distort the leaves.

Aphids spread viruses

Photo of the piercing and sucking mouthparts of aphids
Source: With thanks to Kent Loeffler from the United States Department of Agriculture

When an aphid feeds on a plant with a virus, it can pick up that virus on its mouthparts or in its body. When the aphid moves on to feed on another plant, it transfers the virus to the new plant.

Researchers have documented over 150 plant viruses spread by aphids, such as beet mosaic, tomato spotted wilt, and carnation latent. If the plant cannot tolerate or has no resistance to the virus it gets from the aphid, the plant often dies.

In fact:

The majority of viruses infecting plants are spread by insects, and aphids are the most common group of virus vectors or carriers. All potyviruses (the largest group of plant viruses) are transmitted by aphids.

Source: With thanks to Agri-Science Queensland

But how do aphids move around to spread these viruses?

Aphids often fly or crawl from one plant to another, especially when looking for a new source of food to eat. Aphids are also blown around by the wind, and can cross great distances like this without much effort. And sometimes ants carry aphids from plant to plant.  

When aphids suck the sap out of a plant, they release a sweet, sticky substance called honeydew. This is many ants’ favorite food, so ants take care of aphids and farm them to get all their honeydew.

Part of the ants’ job when farming aphids is to make sure the aphids have a lot of sap to drink. If a plant isn’t providing enough sap, or there are too many aphids feeding off a single plant, the ants carry the aphids to another plant to feed.

Aphids kill off many parts of a plant or tree

Aphids like to suck sap from the softer parts of plants and trees, such as stems, new shoots, and flower buds.

This is because it’s easier for aphids to pierce soft tissue with their mouthparts than the tougher, woodier parts of a tree or plant. It’s also where the plant or tree is most vulnerable to the effects of the aphids.

When aphids feed on the most tender parts of plants and trees, they often kill the area or damage it beyond repair:

  • New shoots wilt and stop growing
  • Seedlings or new plantings wilt and often die
  • Leaves become distorted, yellow, and fall off
  • Flowers become deformed
  • Fruit grows abnormally and drops off the tree before maturing

Aphids starve the plant and make it weak

Aphids usually feed on a plant in large numbers, and all these aphids suck out the plant’s food sap and sugars as long as they are there.

When an aphid infestation is very bad, the plant does not get enough nutrients to grow or stay healthy. It becomes stressed and more vulnerable to diseases, and weak plants are often attacked by even more insects, such as other scale insects and cicadas.

All of these weaknesses make the plant more likely to wilt and die.

Aphids cause sooty mold

Photo of black sooty mold growing on healthy leaves

When aphids eat plant sap, they release a sticky liquid called honeydew. This honeydew drops from the aphids onto the plant’s or tree’s leaves, branches, trunk, and stem below.

Many fungi love to eat sweet honeydew, so they start growing wherever the honeydew drops. The fungi look like a black, sticky substance on your plants and trees, which is commonly known as sooty mold.

As the aphids drop more honeydew, more fungi grow, along with more sooty mold.

Because the mold is dark, it stops sunlight from getting to the plant’s leaves, so the plant cannot use sunlight for photosynthesis and to make food. This is especially true for plants that are evergreen and those that grow in shady areas because they need to use whatever sunshine they can get during the day and in the colder months.

When enough sunlight is blocked the plant cannot grow as it should.

Sooty mold won’t kill the plant, but it does harm the plant by blocking sunlight and suffocating the leaves, which die and fall off after some time. If all the leaves fall off a plant, it is very likely that the plant will die.

Even if the plant manages to keep some leaves to feed itself, it slowly becomes weaker and more prone to insect attacks and sicknesses – which could kill it.

What plants do aphids kill?

There are hundreds of different aphids and aphids eat the sap from many different plants. But most aphids will feed on only one type of plant, tree, or vegetable. A few aphids attack different plants at different times of the year.

For example, green peach aphids aren’t fussy and will suck the sap from pretty much any plant. But rose aphids will only eat the sap from rose bushes, and cabbage aphids dine on cabbages.

But there are some common backyard plants that aphids prefer, and gardeners who don’t use chemicals in their gardens often plant these plants as companion plants. The aphids in the yard are attracted to the companion plants and move over to these plants, leaving the rest of the plants in the area alone.

Plants that aphids love and that can be used as companion plants are:

  • Arrowhead plants
  • Asters
  • Chrysanthemums
  • Dahlias
  • Daisies
  • Dumb cane plants
  • Geraniums
  • Heuchera
  • Hydrangeas
  • Mandevilla vines
  • Milkweed
  • Nasturtiums
  • Purple passion
  • Rockcress
  • Roses
  • Schefflera
  • Zebra plants

Best products to get rid of aphids

If your backyard or houseplants are plagued by aphids, here are the top recommended products from Amazon to get rid of these pesky insects:

Bonide Ready-to-Use Insecticidal Soap Spray: This is an option for indoor and outdoor plants, including houseplants, citrus, ornamentals, fruit trees, and vegetables. The spray must make contact with the aphids to kill them.

Bonide Rose Spray: Don’t let the name fool you – this spray isn’t just for roses. It kills all life stages of aphids on roses, flowers, potted plants, indoor plants, ornamentals, shrubs, fruits and vegetables, and more. It also kills sooty mold and prevents fungal attacks.

Houseplant Insect Control Granules: These granules can be used on houseplants, flowers and roses, but not on any edibles like fruits and vegetables. The granules are highly recommended for potted plants or plants in containers and raised beds.

Food-Grade diatomaceous earth: Sprinkle this all-natural, organic product on your aphid-infested plant and around the bottom of the plant or tree. When aphids walk over the diatomaceous earth, it cuts them and kills them, yet this is not harmful to humans. Be sure to use this earth when it is dry, and sprinkle more after it has rained.

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