Horticulture Magazine

How To Get Rid Of Aphids On Plants

an aphid infestation on the leaf of a plant

Aphids are among the most prevalent and destructive of garden pests, and they also breed very rapidly.

Aphids suck the sap – the lifeblood – out of plants, thereby quickly debilitating and even killing them.

Fortunately, with some homework and perseverance, you can eliminate these pests.

an infestation of aphids feeding on the sap of a plant

We outline numerous aphid-control methods including manual ones, home remedies, biological controls, and chemical formulations.

Why Are Aphids Damaging For Plants?

There’s good news and bad news about aphids.

First the bad news: aphids can cause horrendous damage to plants and even kill them.

But the good news is that the casual gardener has recourse to numerous methods of different kinds to control, and even eliminate, aphids, commonly called ‘greenfly’ and also ‘plant lice.’

Aphid species number over 5,000 of which more than 500 are found in the United Kingdom. [source] / [source]

magnified view of aphids on the stalk of a plant

Many of them are extremely destructive to some or another set of members of the Plant Kingdom, including agricultural crops, food crops, trees, and all types of ornamental plants, bushes, herbs, and vegetables. 

Many aphids are identified by the particular plants or trees that they prefer to attack, such as Raspberry aphid, Lettuce aphid, and Beech aphid, to name just one example each of aphids that infest a fruit, a vegetable, and a tree.

Many are polyphagous; these attack a large number of plant species. 

No matter what the type of aphid, they have two attributes in common: they breed and multiply very rapidly, and they suck the sap from plants, debilitating them very quickly and even killing them.

close up magnified view of a single aphid

Furthermore, some aphids on certain plants are vectors for viruses which themselves sicken and severely damage plant life. [source]

The present article is written with the goal of covering the topic of controlling and eliminating aphids in the fullest possible breadth; in turn, this means that no one method is discussed in full depth.

We encourage the reader who is interested in a particular method to explore it further.

magnified view of a leaf infested with aphids

Signs Of Aphids

Symptoms of aphid attack include slow growth and stunting, contortion and deformation of leaves, dripping of sap, yellowing and browning of foliage, overall wilting and loss of vigour, and, eventually, death of the plant.

More often than not colonies of these tiny pests are visible on the underside of leaves, but they also occur on their upper surfaces, the stems, and sometimes even on the flowers.

hand holding pepper foliage showing aphids on the underside of the leaves
magnified view of aphids on a pepper plant

They are usually yellow-green but are also brown or black.

Which Plants Are Most Vulnerable?

Some flowers, herbs and shrubs are just more vulnerable than others to aphids.

Jasmine, rose, dahlia, hibiscus, chrysanthemum, tomato, (plain) mint, basil, lettuce, beet, cucumber, peas, and gooseberry are some examples.

Several kinds of trees are also very vulnerable to aphid infestations.

If you have such aphid-susceptible plants in your garden, one of the best steps you could take against aphids is to catch them early.

If you have a small garden, you could make it a practice to inspect different samples of plants (including the undersides of selected leaves at all levels) periodically, say every week or every ten days for aphids.

The beginning of summer is the time to be on highest alert.

Underneath we outline three common methods for dealing with aphids:

1) Typical Treatment

Hibiscus Plant Infested with Aphids

If you spot any, crush the pests and also the eggs.

Hosing off the aphids will remove them but will not kill them.

Instead, spray soapy water, made from a pure organic soap, on the pests which will kill them in short order.

You can wash away the soap residue from foliage in a couple of days.

If you do so, aim for the morning hours on a sunny day. 

Finally, if you catch a localised infestation early (that is before it has had a chance to spread) simply prune or otherwise remove the affected parts of the plant.

Put these on a plastic sheet a safe distance away, spray well and all around with any insecticide that will kill aphids, and promptly remove from your garden.

2) Homemade Remedies

Those who come from horticulturally-inclined families often inherit pesticide recipes from grandparents, great-aunts, and the like.

We list a few homemade recommendations in this section.

Neem Oil
neem oil remedy being sprayed on plants

Neem oil solution is a time-honoured aphid killer.

It should be used in a one to three percent dilution.

Spray it or daub it on aphid-infested parts of the plant.

Pastes, Oils & Powders
lavender essential oils

Solutions of garlic and oregano paste or powder are potent deterrents for most kinds of aphids.

In fact, a solution of both the veg and the herb could be made.

Tea tree, peppermint, eucalyptus, or anise essential oils are also excellent for combating aphids.

A suspension could be made of any combination of these essential oils.

They must be appropriately diluted otherwise they will injure plant life.

A one to three percent dilution is typical.

Rapeseed Oil
a field of yellow flowering rapeseed

Rapeseed oil is a potent pest-killer.

Make a solution of it at a from 1:16 to 1:20 dilution and spray it on aphids, it will kill them within minutes.

If you cannot find rapeseed oil, then substitute with Canola oil.

Diatomaceous Earth
Diatomaceous Earth on a trowel in the garden

Diatomaceous earth kills all kinds of insects but one seldom finds bees or other pollinators on the undersides of leaves which are aphids’ preferred – though not exclusive – nesting places.

Simply prepare a solution – actually a suspension – of diatomaceous earth, and spray it on and around aphids.

After the aphids have died you may wash off the sprayed areas.

Applying Homemade Remedies
homemade remedy being sprayed on pink rose plant

Once treatment with any of these solutions is started, it should be followed up with repeat applications every two or three days until there is no sign of aphids.

Also inspect your lawn, the ground, and other plants in the vicinity in case aphids have sheltered elsewhere.

Only those parts of the plant that are infested with aphids should be treated.

magnified view of pink rose plant infested with aphids being sprayed

You may wish to apply the solution in question to a small part of the plant first to see how well the plant tolerates it.

These homebrew solutions and suspensions have three big advantages over many commercial compounds.

Used in the proper concentrations:

  1. They will not harm bees or other pollinators
  2. They are safe to use on vegetables and herbs
  3. And they are derived from plant life!

Though diatomaceous earth is probably not one of great-aunt’s remedies, we’ll close this section with a mention of it.

3) Using Natural Predators

ladybirds eating aphids from an infested plant

Aphids will be eliminated and will not be able to establish any colonies in your garden if you release and try to nurture green lacewings, ladybugs, aphid midges, and/or parasitic wasps.

Any and all of these beneficial insects, which are a type of biological control, can be bought and released in the garden.

However, as they, especially ladybugs, may decamp quickly, efforts to keep them happy in your garden will be necessary. [source]

Green lacewings and ladybugs feast upon – besides various garden pests – aphids quite indiscriminately, quickly reducing their populations, eliminating them, and discouraging them from establishing any colonies. [source]

Green Lacewings
green lacewing sat on a plant

Green lacewings are far more effective than ladybugs as they are not as affected by wanderlust as are ladybugs, and, per insect, eat up many more aphids than ladybugs and do it much faster as well.

Parasitic Wasps
a parasitic wasp and aphid magnified

Parasitic wasps are specialised to prey upon a specific, somewhat narrow, range of aphids.

However, because of the way parasitic wasps’ eggs are laid and the fact that their larvae prey upon aphid eggs, aphids are exterminated ‘at source’ – they cannot even reproduce. 

Gall Midges
magnified view of a gall midge

While aphid midges, also known as gall midges, do prey upon aphids, their beneficial effects are negligible.

It is actually midge larvae that prey upon aphids ‘in quantity’, so to speak, so it is your midges’ offspring that will do the aphid extermination.

Research has shown that the efficacy of aphid midges through their larvae is strongly dependent upon the presence or absence of other pests, such as thrips.

Retaining Beneficial Insects
ladybird feeding on a greenfly

So how to retain these beneficial insects in your garden, or even attract them?

Apply a solution of sugar and honey to plants affected by aphids, set up this solution close by in insect bait trays or petri dishes, or both.

Doing so will retain ladybugs and may very well even draw them to your garden.

Do not fill the trays or dishes too deeply as feeding insects often get stuck and drown in sticky liquids.

daffodil and scabiosa in a field

To retain and attract green lacewings, keep pollen-producing and/or nectar-rich plants nearby.

Dandelion, fennel, mint, shasta daisy, clover, salvia, hyssop, lavender, caragana, scabiosa, and hibiscus are good choices.

Finally, apply wheast to, or set it up (as described above) close to, aphid-affected plants.

Wheast will retain and also draw ladybugs, lacewings, and other beneficial insects. [source]

Wheast can be prepared at home or purchased from reputable makers.

Do not use chemical formulations, with the exception of targeted applications of Safer Soap, in conjunction with biological controls as most chemicals will repel or even kill beneficial insects.

4) Chemical Formulations

All of the chemical products and formulations mentioned below are organic or are otherwise safe if applied per directions.

spraying leaves of an outdoor plants affected by greenfly

Safer Insecticidal Soap is a non-chemical preparation that is made of potassium salts of fatty acids. It is easy to mix, easy to apply, effectively kills aphids and can be used on all types of plants. We suggest it be your first line of attack on the chemical-controls front.

BotaniGard ES is a chemical product. It is authorised for use but it is potentially toxic to bees and, therefore, it is recommended that it not be applied if bees are nearby. It is also toxic to aquatic life. A 0.4 percent solution of BotaniGard ES will suffice to kill aphids.

Neudorff BugFree Bug & Larvae Killer, Resolva Bug Killer, Provanto Smart Bug Killer, and Provanto Ultimate Bug Killer come in spray bottles and are ready to use – no mixing required. They are all very effective against aphids though they have different active ingredients. They are lethal to different sets of garden pests, and they also have somewhat different properties. For example, one will be longer-lasting while another will kill aphid eggs and larvae, besides the pests. One will be best for a few particular edible plants while another will be suitable for a very wide range of veg and herb.

Neudorff chemical aphid control spray

We suggest that you look into these and use one to see which one works best for you.

Bear in mind that most of these chemical formulations will also have some or another adverse impact on beneficial insects so they should not be applied at all indiscriminately.

They should be applied in a targeted manner.

As well, chemical products and biological controls should not be used at the same time, other than after thorough research on a product-and-insect basis as outlined above.

Why You Shouldn’t Use Pesticides

You may read elsewhere about the efficacy of certain products and compounds.

Well, those products and compounds do indeed very effectively kill aphids; unfortunately, they are at least toxic and are even extremely poisonous every which way to Tuesday, and have been withdrawn or banned either under British or EU regulations.

Withdrawn or not, chemical pesticides have a wide-spectrum action and kill beneficial insects and pollinators, besides aphids and other pests.

multiple dead bees
Effects Of Non-Recommended Chemicals

Keep in mind that approved greenhouse fumigants based on permethrin, a synthetic pyrethroid, are not meant to be used in open gardens.

They may be used inside greenhouses.

For a current list of pesticides that are not permitted in the United Kingdom, please refer to the Health and Safety Executive’s webpage: Regulating pesticides in the UK after Brexit.

HSE also maintains a GB Pesticides Approvals Register.

Ants: Aphids’ Bodyguards

ants and aphids

Garden ants and aphids have a well-known symbiotic relationship, and this relationship may defeat your efforts to eradicate aphids by deploying beneficial insects. [source]

Aphids are (among the) honeydew-secreting insects that are ‘tended’ by ants. 

Garden ants tend aphids by stroking the pests with their antennae to stimulate them to secrete honeydew, which the ants collect.

Ants feed on honeydew, and also carry it to their nest for the queen and the larvae.

ants feeding on honeysuckle provided by aphids

In turn, ants protect aphids, doing so by attacking and killing ant predators including lacewings and ladybugs. 

Obviously, ants’ bodyguard function for aphids can defeat your efforts to control the pests using beneficial insects.

Therefore, prior to releasing or trying to attract such insects, you should determine whether your garden has an ant’s nest or has ants in large numbers.

greenfly and ants working together in a symbiotic relationship

If so, you will probably need to get rid of the ants first as most likely they will already be protecting the aphids.

If not, then after you release beneficial insects, monitor their numbers and stay on the lookout for garden ants that may be preying upon them.

If you spot such ant activity or a decline in the beneficials’ numbers then you should move to eliminate the ants.

Garden ants can be tackled in many ways.

an ant tending to aphids

Preventing Aphids

Water At Soil Level
watering can being used to water at soil level

One preventive course of action that can be taken where aphid-susceptible plants are concerned is never to water from above and always to water at soil level.

If you ever think that the foliage could use a good wash, then water them from above in the early morning on a day forecasted to be dry, warm and sunny.  

Companion Planting

Another preventive step is to grow aphid-repellant plants.

Herbs and shrubs that are odorous and aromatic tend to repel aphids.

These include garlic, onion, shallot, chives, dill, and turnip.

The pungency of spearmint, peppermint, and catnip are also off-putting to these pests.

Potted catnip, lemon balm and peppermint plants

Finally, some flowering plants such as petunias, geraniums, and marigolds are not only resistant to aphids but also keep them away from nearby plants that do not share these properties.

Any of these (or some other) aphid-repellant plants will make a first-rate companion plant for some or another aphid-susceptible plant. 

Though you can pair any of the deterrent plants, named above, with vulnerable plants, some combinations of companion plants will be particularly effective and are recognised to be so.

zinnia and sungold tomatoes being grown as companion plants

For example, garlic with roses, and chives with lettuce. 

Companion plant gardening is a horticultural sub-science in itself.

While companion plants greatly aid in pest control they also serve sundry other purposes. 

Attract Predatory Insects
two ladybirds sat in plant foliage

Finally, try to make your garden attractive to beneficial insects that prey upon aphids.

These include ladybugs, green lacewings, aphid midges, and parasitic wasps (which are not harmful to humans).

A thriving colony of these gardener’s friends will go a long way toward preventing aphid attacks. 

Rid Your Garden Of Aphids!

carrot plants covered in aphids

As mentioned, aphids are very serious garden pests and rapidly destroy plants. And they breed very rapidly as well.

But the fact from which to take heart is that they are not one of those dreadful pests for which lay gardeners have no controls or remedies, further to which they are not even particularly strong.

If you do some homework, try to choose the right aphid-control method, act as quickly as you can, and persevere with your efforts diligently, it is almost certain that you will win your fight against aphids.

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