Aphids are one of the biggest enemies of most farmers, gardeners, and plant-lovers. These small plant-eating insects are known for their incredibly fast reproduction cycle, the devastating damage they can cause to any garden or potted plants, as well as the host of additional indirect problems they bring with them.
Aphids are notoriously difficult to get rid of once their infestation grows to a large enough size. This makes aphid prevention and control methods extremely important for anyone interested in growing a healthy vegetable or fruit garden or just having a nice set of pot plants at home.
Fortunately, there are also quite a few ways to achieve aphid prevention, as well as to deal with an already existing infestation of any size. Some of these methods are physical, some are biological, and a few of them are chemical. In this article, we’ll go over the curious specifics of the aphid insects, which makes them so undesirable, and how exactly to deal with them in the best possible way.
In this article:
- About aphids
- What damage do aphids cause?
- Aphid control
- Methods for long-term aphid prevention
Aphids are a diverse species of herbivorous phloem-sucking insects that feed on the young leaves of cultivating plants and destroy them. Phylogenetically, aphids are classified under the Class: Insecta, Order: Hemiptera and belong to the Family: Aphididae, which houses approximately 4,500 different species of aphids.
What do aphids look like?
Commonly known as plant lice, aphids are soft-bodied, pear-shaped pests that primarily infest plants growing in the temperate regions. Aphids measure approximately 4-8 mm in length and have distinct morphological features. Head portion of these insects is made up of a pair of antennae, and 2 compound eyes, each containing a protruded extension called ocular tubercle. Enclosed inside the mouth are stylets, which function like a syringe-needle and are used to pierce into the plant’s body and suck the sap inside the phloem. Aphids possess a pair of siphunculi or cornicles that are tube-like structures protruding from the posterior side of the abdomen. These cornicles discharge a wax-like fluid called honeydew or cornicle wax, which is used either to alert the surrounding aphids or to attract symbiotic insects such as ants. Aphids also possess a tail-like structure near the rectum known as cauda, which is used for secretion of pheromones. Aphids have long legs that are thin and contain two jointed and clawed tarsi.
Polymorphism in aphids
Aphids exhibit tremendous polymorphism in their body color ranging from green to white, red, black, yellow or brown. Some species of aphids may even be colorless. This variation in body coloration arises due to reasons such as genes, pigments, or color-changing bacteria. For example, pea aphids can synthesize its own red or yellow-colored carotenoids and appear red or green. Presence of melanin renders black or dark brown color, while aphids are polycyclic quinone molecules that are responsible for other colors. Body coloration is also controlled by factors such as hormones, light, temperature, host plant, and parasites. Coloration helps aphids’ dissuade their predators. Additionally, body colors likely influences other biological functions on aphids such as reproduction, and adaptation to harsh climatic conditions.
What do aphids eat?
An aphid’s diet is primarily made up of plant sap extracted from the phloem, which is rich in sugars, amino acids, minerals and essential nutrients that aphids need to grow and multiplicate.
Aphids use stylets to penetrate and consume plant sap from the xylem cell. This xylem sap suffices their hydration needs and balances the negative osmolarity inside their stomachs. Interestingly, aphids have a special type of cells called bacteriocytes, which harbor endosymbiotic bacteria responsible for the synthesis of essential amino acids that cannot be obtained from the plant’s sap.
Where do aphids come from? Aphids life cycle
Adult aphids have an average lifespan of one month. These insects have a complex lifecycle characterized by alternating cycles of asexual and sexual reproduction, which revolves around availability of a host plant and favorable environmental conditions. Most aphids (for example cabbage aphids) infest only on a single species of host plants on which they complete their entire life cycle making them monophagous. However, about ten percent of aphid species (for example green peach aphids and potato aphids) alter between 2 or more host plant species during their sexual and asexual phases.
Offspring turnover rate of aphids is exceptionally prolific and faster than any other insect. In the harsh and cold months of winter, aphids survive as overwintering eggs. At the onset of spring, aphid eggs hatch releasing wingless female aphids known as fundatrices. These female aphids reproduce asexually (also called parthenogenetic reproduction) during spring and summer months and give birth to least 80-100 wingless daughter clones of the mother aphid. As the fall months, approach and temperatures drop, mothers give birth to winged male forms that facilitate sexual reproduction, resulting in a production of fertilized overwintering eggs. These eggs are then deposited on new leaves and repeat the aphid lifecycle.
Aphids can alter between wingless or winged (alatae) forms depending on the availability of food, space and seasons. This is an evolutionarily adaptive behavior scientifically known as polyphenism.
What damage do aphids cause?
Aphid bug infestation is the worst problem encountered by agricultural and horticultural crops. If left untreated, these infestations induce stress and premature plant death, leading to lower crop yields and huge economic loss. These bugs can even infect ornamental plants and directly affect their development.
Unlike other insects, aphids have evolved with an exceptional survival advantage as they can increase their population rapidly. Dual reproductive strategy together with shorter generation times and short maturation period for the nymphs to become adults (approximately 5 days) produce a large number of offsprings, And the ability to convert from wingless to winged forms allows aphids to disperse rapidly and contributes to their abundance and colonization of host plants over a large area. Aphid-mediated damages to host plant can be broadly classified into 2 categories – direct and indirect aphid damage.
Symptoms of aphid infestation
The most common signs of an aphid-infestation on plants include discoloration of leaves, abnormal formation of young shoots, stunted growth, necrosis or tissue destruction on leaves and other body parts of the plant, premature falling of leaves, and formation of galls or outgrowths. During an aphid infestation, one can even observe the presence of a black sooty layer of fungus growing on the plant. This fungus grows on the sweet and sugary honeydew secreted by aphids, which coats the plant foliage, branches, and stem.
However, symptoms of aphid infestation and the extent of the detrimental effects of aphids on plants may vary based on the type of host plant and the aphid species. For example, aphids lower the concentration of lycopene and other carotenoids in tomatoes. As a result, fruits appear pale and distorted. In the case of potatoes, an aphid infection can cause a brown discoloration inside the potatoes, formation of dead rings on the skin of the potatoes and can diminish their quality. Aphids infecting cabbage and broccoli feed on the flower stalks and contaminate the crop by infecting the plant with a mosaic virus that leaves the leaves distorted in both color and shape. While an infestation of aphids on roses and other ornamental plants such as hibiscus affects the formation of healthy buds, which means that the buds don’t form into flowers and therefore the plans don’t bloom as they should.
Direct aphid damages
Here are some of the damage caused to the host plant directly due to aphid infestation:
- High aphid density on the leaves blocks sunlight and prevents chlorophyll synthesis causing chlorosis.
- Aphids ingest plant phloem’s sap using stylets, which are used to pierce through different plant tissues layered on top of the phloem. In this process, they cause a nutritional imbalance in the host plant leading to symptoms like rolling and wilting of leaves and tissue necrosis.
- Aphids also manipulate their host by blocking the export of essential nutrients to various plant tissues. For example, aphids divert nitrogen and sugars to the gall and promote protein breakdown so that there is an increased flow of essential amino acids in the phloem. These changes prevent nutrients from getting to the newly formed young shoots leading to their malformation, and premature death, yet increase the nutritional quality of the aphid feeding zones.
- And saliva released by aphids while feeding is phytotoxic and impairs the plant’s overall immune system.
Indirect aphid damage
Notable indirect plant damage caused by aphids include transmission of plant viruses and attracting infestations from unrelated insect species such as ants.
- Transmission of viruses – Because of their feeding behavior, aphids are the most efficient carriers of plant-infecting arboviruses as they can deliver them directly to the cells or the plant tissues. Aphids transmit approximately 300 different types of plant viruses, the majority of which affect crop yields and induce plant death as plants succumb to the infection. For aphids, however, viral infections are highly useful. For example, the concentration of essential amino acids in the sap of virally infected plants is significantly higher than uninfected plants. Additionally, viruses also lower the plant’s defense mechanisms, which makes it easier for aphids to live and multiply on that particular plant. Research suggests that viruses can ensure that aphids have prolonged feeding time and improved reproductive cycles, which allows them to survive in their environment even longer. However, viral infections are detrimental for the host plant since they not only worsen the disease symptoms caused by aphids but also can’t be eradicated via conventional insecticides. And winged aphids can also spread these infections from infected plants to other healthy plants causing an outbreak of the disease and killing even more plants.
- Aphids and Ants – Aphids use their honeydew to establish a mutualistic co-existence with ants, thus adding another layer of indirect damage to the plant. Ants feed on these sugary secretions for their nutrition, and provide protection to aphids from predators and parasitoids, apart from eliminating their competitors such as spider mites. Furthermore, interactions with ants help aphids in their reproduction, maturation of nymphs to adults, maintenance of color polymorphisms and dispersal of overwintering eggs. However, when it comes to the plant studies suggest that ant-aphid interactions have a negative effect on the production of fruits and seeds meaning that this symbiotic relationship between aphids and ants is another major way how aphids indirectly damage plants.
A number of physical, mechanical, chemical and biological methods can be used to control the aphid population. However, the efficacy of these methods depends on the extent of the infestation and the type of host plant. For instance, physical methods such as water spraying or cutting off infested leaves are useful only when the aphids have colonized no more than 2 to 3 percent of the buds or young leaves. Biological methods are useful when the colonization is 5 to 15 percent of the entire plant. And chemical methods such as insecticides should be used when the aphid colony is very large.
Similarly, physical and biological methods are routinely employed for treating small-scale aphid infections on garden plants, and horticultural crops. And for immediate and effective eradication of large-scale aphid infestations on agricultural crops, chemical methods are the most suitable. If you want to know how to get rid of aphids, use one of the strategies enlisted below or combine several of them for even better results.
DIY control methods
Also called physical aphid management method DIY aphid control strategy is highly popular and can yield impressive results if implemented correctly and properly. DIY methods are routinely used on home gardens and ornamental plants. And the reasons for their popularity is the fact that they are economical, safe, non-toxic, easy-to-implement, do not require any special training or equipment, and don’t harm the flowering parts of the host plant. Here are some of the most common DIY aphid control methods.
1. Removing aphids from the infested areas with a cloth
Periodical monitoring plants help in early detection of aphid infestations. And that infestation can be controlled by physically removing these pests from the infested plans using a soft damp cloth and which is then disposed directly into a recycling bin.
- Doesn’t require you to purchase and use chemicals or any other additional products.
- Virtually costless method of removing aphids.
- The aphids should be removed from the plants extremely carefully to avoid spreading them to nearby healthy plants.
- Physical removal using a damp cloth is a laborious and time-consuming process, which demands intense focus and astute observational skills.
- This strategy is only useful for plants housed in a very small area.
2. Cutting infested leaves and branches
Aphids prefer to hide from their predators and multiply inside the curled portion of leaves and inner canopies. Such infested leaves and branches should be pruned periodically using a pair of small garden shears to make the plants less inhabitable for aphids.
- Highly useful in preventing the spread of aphid infection to other parts of the plant.
- Basically costs nothing.
- Pruning infected leaves should be done carefully to prevent them from landing on adjacent healthy plants.
- Pruned leaves should be immediately discarded in a waste collection bin.
- This method is also a short-term fix and will be best for aphid removal in small areas.
3. Spraying the plants with water
Aphids are highly sensitive to harsh climatic conditions such as cold and rain. So spraying a jet of cold water simulates these conditions and dislodges the bugs from the plant shoots and leaves, without affecting the flowering parts of the plant.
- This is the simplest do-it-yourself aphid removal method.
- The process can be repeated often to achieve maximum aphid extermination. Also, spraying with a water jet is the most effective when done in the morning, as it allows the leaves to dry throughout the day.
- Water spraying also helps in clearing the sugary honeydew coating from the surface of the leaves and therefore is useful against black sooty mold coverings.
- You have to be careful when using this method so you don’t damage the plants when praying them with the water, especially the plant buds and shoots.
- Overwatering plants by spraying them with water too often can also have negative effects on the plants.
4. Making homemade soap spray
Another commonly used home remedy for aphids is to spray the plants with a 1 to 2 percent home-made soap solution. These solutions are prepared by mixing 1 part of vegetable oil, 1 to 2 parts of any dishwashing soap and 1 to 2 cups of water. Alternatively, a soap concentrate can be bought in a store and diluted with water to obtain the desired concentration. Then using a spray bottle the soap solution is thoroughly sprayed onto the affected leaves and other parts of the plant. Periodical application of soap solution is required to achieve the most thorough aphid control.
- Killing aphids with soapy water is an easy and inexpensive strategy that anyone can practice in their home gardens. It does not require specialized tools or skills.
- Strong soap solutions can be harmful to the aphid host plants. Therefore, it is always advisable to test the soap solution on a small area of the plant first and wait for 2 to 3 days to see if the soap has any negative effects.
5. Simulating tropical conditions
Even though aphids demonstrate the highest fertility in the summer, they are also susceptible to excessive heat. Heat destroys the bacterial endosymbionts and affects aphids’ fertility. So if you have a small aphid infestation in your greenhouse, it is possible to increase the temperature gradually for a brief period of time to simulate tropical conditions which will kill the aphids helping you rid your greenhouse of the infestation.
Aphid control products
Apart from physical methods, a number of anti-aphid products are commercially available and have been used successfully to counter aphid infestations.
1. Diatomaceous earth
Also known as DE or diatomite, diatomaceous earth can be described as a white powder derived from naturally-occurring sedimentary rocks that are rich in silica, alumina, fossilized diatoms, and minerals such as iron dioxide. DE is highly abrasive, granular and porous. And due to these properties, diatomaceous earth powder can easily penetrate the outer sheath of aphids and their larvae and destroy them. Furthermore, DE also interrupts with the feeding and breathing patterns of aphids. How to use it? Fill a sieve or strainer with a scoop of DE and sift it on top of the infected leaves so that a layer of DE coats their surface. Or mix it with water and spray the mixture onto the affected plants. DE should also be adequately applied to the plant base so that it can destroy aphids that fall on the ground. As for when to use diatomaceous earth to kill aphids, DE aphid treatment should be done early in the morning. Moisture inside the dew will help DE adhere better to the leaf surface and therefore the treatment will yield better results.
- Using DE is an eco-friendly and organic aphid control strategy that does not damage the environment.
- Diatomaceous Earth should be handled carefully. Safety goggles, respiratory masks, and gloves should be used while applying DE because the fine powder can irritate the lungs and eyes if accidentally inhaled.
- DE is effective only in humid conditions. And you shouldn’t apply DE when it’s raining or windy because it will just be washed away. In such a scenario, DE should be reapplied as soon as the rain stops and the wind dies down.
2. Neem oil
As an insecticide, neem oil is considered as the best aphid killer. Neem trees are evergreens that are indigenous to tropical countries of South-East Asia such as India, Pakistan, and Srilanka. Neem oil is pressed out from the seeds of the Neem tree and used extensively in Ayurvedic medicine and cosmetics because of its inherent medicinal properties. The active component of Neem oil is known as azadirachtin. As an insecticide, azadirachtin disrupts the hormonal systems of the insects, interferes with their reproduction and disturbs their entire lifecycle. A commercially available concentrated form of Neem oil should be diluted with water and this diluted form is then sprayed thoroughly on the aphid-infested plants including the underside of the leaves, branches, and base of the plant.
- Low to medium exposure of Neem oil is harmless, even if humans, kids or pets accidentally come in contact with it.
- Neem oil is also non-toxic to plants, fish and other aquatic species.
- It is easily available in most grocery stores.
- The Neem oil only works against pests such as aphids. Beneficial insects such as ladybugs and bees are not affected by Neem oil unless they feed on foliage that has been sprayed with Neem oil.
- Heavy exposure to Neem oil can cause irritation to eyes and skin in some individuals. It can also cause an irritable bowel reaction.
- Neem oil, when sprayed on cats as flea treatment, has been reported to cause symptoms such as nausea, sluggishness and impaired motion, excess salivation, convulsions, and even death.
- Neem oil, if applied in excess, can clog the pores on the surface of leaves and therefore interfere with the breathing pattern of the plant.
3. Natural aphid sprays
Apart from Neem oil, a number of other organic substances can be concocted and sprayed as aphid repellants. Some of these include tomato leaf extract, garlic oil, and hot pepper spray. Tomato leaf spray is prepared using chopped tomato leaves soaked overnight in a cup of water. The extract is further diluted using another 2 cups of water and sprayed on the stems and foliage of the infested plant using a spray bottle. Alkaloids present in the tomato leaves are effective aphicides. To prepare garlic oil extract, finely minced garlic cloves are mixed with mineral oil and incubated for 24 hours. Following incubation, a teaspoon of dish soap and a pint of water are added to this mixture and sprayed on aphid-infected plants. Garlic oil is rich in sulfur, which acts as an effective bug repellant. Hot pepper spray is prepared by mixing 1 part of hot pepper sauce, 1 part of dish soap and one pint of water. The mixture should be allowed to sit overnight and then sprayed onto the plants. The active insecticidal ingredient in peppers is known as capsaicin, and it causes an extreme reaction in aphids. And aphids can also be killed by spraying a diluted solution of vinegar onto the plants that have aphids on them as it causes these bugs to convulse.
- Natural aphid sprays is an organic and safe way of getting rid of aphids and limits the need to use harmful and synthetic chemical sprays.
- Ingredients required for the preparation of natural homemade aphid spray are easily available in most grocery stores.
- Natural aphid sprays can cause skin and nasal irritation in individuals allergic to tomato plants, garlic or pepper.
- Garlic oil and hot pepper are non-selective insecticides that can also harm beneficial bugs.
- Excess use of natural aphid sprays can cause damage to the plants that they are sprayed on, therefore, caution must be exercised.
4. Sticky traps
Due to their limited eyesight, aphids are usually attracted to bright colors such as yellow. Whenever aphids are found on plants, it is a good practice to place yellow sticky traps at several places in the garden to lure the winged aphids to these traps. These traps are available as squares or strips and coated with an industrial-grade super-sticky adhesive. Once the aphid lands on the trap, it gets glued to it and, unable to get away, the aphid will die from starvation.
- This is an inexpensive anti-aphid product and is wildly available.
- The use of sticky traps is very effective in preventing the spread of an aphid infestation.
- These traps are not specific to aphids. Due to their bright color, these traps can also attract the natural enemies of aphids and other insects and therefore can have a negative effect on their numbers.
5. Aphid insecticides
Chemical control of aphids by spraying insecticides on the plants infested by them is one of the oldest and most popular strategies used for controlling aphid outbreaks. Prior to World War II, nicotine extract and lead arsenate were routinely used for killing aphids. However, these compounds were discontinued due to their toxic effect on human health. Some of the best insecticides for aphids control include neonicotinoids, organophosphates such as Malathion, pyrethroids such as Cypermethrin, keto-enols such as Spiromesifen and anthranilic diamides such as Flubendiamide. Neonicotinoids are approved for treating seeds in some European countries prior to sowing. However, aphid insecticides should be used in a rational manner and only as a final step of pest management when all the other aphid control strategies have failed.
- Insecticides are highly effective and fast-acting
- They can be used for removing aphids on a wide variety of crops and in a large area
- Potent toxins are extremely hazardous if used without adequate care and safety equipment
Chemical insecticides are also highly carcinogenic
- They are the most expensive aphid control method on this list
- Broad-spectrum use of insecticides can also kill beneficial insects
- Chemicals used as insecticides do not break down easily in the soil leading to a residual build-up
These toxic insecticides can also cause damage to the local ecosystem by leaching into nearby ponds and poisoning native flora and fauna. The emergence of insecticide-resistant aphids has been a major concern associated with intense use of insecticides. And chemical aphid insecticides are the most effective against persistent viral infections.
6. Natural enemies that eat aphids
Biological control of aphids by exposing them to their natural enemies or predators was developed as an eco-friendly alternative to chemical aphid control methods. Currently, this is one of the most widely-used aphid management strategies worldwide, particularly when the host plant is an agricultural crop of economic importance.
Aphids are a highly preferred dietary choice for various birds (for example the American goldfinch, vesper sparrow and passerines), insects (for example spiders, ladybugs, ground beetles, lacewings, soldier beetles, hoverflies, and damsel bugs), fungi and microorganisms. Natural aphid predators can be broadly categorized as generalist and specialized predators. Generalist predators feed on a wide variety of prey, including aphids. On the other hand, specialized aphid predators such as parasitic wasps and aphidius wasps prey only on aphids by becoming their parasites. Studies demonstrated a significant reduction in aphid density by the hand of lady beetles and other parasitoids over a long period of time as they disturb the feeding patterns and reproductive cycles of aphids. However, generalist predators were found to be effective only if they were introduced during the spring season when the aphid larvae hatch from their eggs. Aphid predators can also be categorized as flying insects (for example hoverflies, and parasitoid wasps) and ground dwellers (for example ground beetles) based on their ability to fly. Flying insects are more effective in controlling aphid population than ground dwellers. Introduction of new predator species or employing methods to enhance the growth of locally available natural aphid enemies can be a tremendously effective both as a short-term and long-term aphid control method.
Methods for long-term aphid prevention
Aphid infestation on crops and plants is a serious problem as it can inflict severe damage to the plant health leading to their death. And sadly getting rid of an aphid infestation is not only extremely challenging but can also be an expensive endeavor depending on the extent of the infestation and the type of aphid you are dealing with. Additionally, aphids also introduce plant viruses that are difficult to treat. Therefore, it is imperative to have prevention strategies in place so that aphid infestation can be avoided over a long period of time.
- Controlled use of fertilizers – Aphids thrive on soils high in nitrogen and other essential minerals. Once an aphid infestation has been identified, avoid feeding your garden or crops with a fertilizer containing high-nitrogen content. But if you need to use fertilizer, one alternative is to use fertilizers specially-formulated to release nutrients slowly into the soil.
- Grow pest-repelling plants – There are several herbal plants that repel aphids and other pests. Examples include onion, garlic, bay leaves, lemon grass, mint, lemon thyme, chives, basil, oregano, parsley, and rosemary. Essential oils released from these herbs act as potent bug repellants and can keep the garden aphid-free. So planting these strong-smelling herbs as companion plants within your crops can keep aphids at bay for a prolonged time. This strategy is known as intercropping.
- Plant nectar-producing flowers that attract beneficial enemies – Another mode of intercropping for aphid management is to grow flowering plants such as calendula near the vegetables. Flowering plants produce nectar that attracts natural aphid enemies like ladybugs, bees and hoverflies hence there is less chance of a wide-spread aphid infestation.
- Remove attractive weeds – Weeds are highly invasive plant species that can alter the ecological balance of a particular area. They compete for sunlight, space, and food with other plans, and are difficult to control. Additionally, attractive weeds such as sowthistle also form feeding grounds for aphids, which thrive on them. Therefore, it is essential to remove all weeds from your garden to avoid the growth of aphids.
- Install bug-eater bird houses – Birds are the chief aphid-predators. And since installing birdhouses will attract aphid-eating birds, it will help you get rid of an aphid infestation before it becomes a chronic problem. Additionally, they can also keep the pests at bay for a long time letting you keep your garden aphid-free for many seasons.
- Use special cover cloth – And another useful strategy for preventing an aphid infection in your garden is to grow plants under the cover of an all-purpose garden fabric. This cover prevents the landing of winged aphids on your plants keeping them safe and healthy.
As you can see, aphids can be quite a problem when left unchecked. They can destroy large quantities of leaves and plants in record time, they bring hundreds of potential diseases with them, and they even have significant symbiotic connections with other pests. Their fast life cycle, the alteration between sexual and asexual reproduction, as well as the switch between flying and non-flying development helps them to spread like a literal plague when left unchecked.
Fortunately for us, there are multiple ways to “check” aphids, to deal with them, as well as to execute effective prevention against them. In the easiest scenarios, you can use simple physical DIY methods such as soapy water, hand cloth cleaning, or cold water spraying to deal with aphid presence. You can also employ various natural biological methods or resort to chemical solutions if need be. You can even make your garden attractive to some of the aphids’ natural predators such as ladybugs or spiders.
Which method you choose should be based on an accurate reading of the severity and the type of the infestation. Hopefully, our article has made this easier for you.