Anyone with a garden, big or small, should be concerned about aphids and the damage these little insects can do. Aphids are small soft-bodied bugs that belong to the Aphididae family of insects, the largest known family of plant parasites in the world. Aphids are usually found in groups although you may find the odd single one too. Also known as plant lice, aphids can suck the life out of a perfectly healthy plant and cause it to wilt and die.
Aphids Have A Pair Of Cornicles That Point Backward From The Abdomen
There are hundreds of species of aphids and most of them are difficult to differentiate from one another. Some aphids are named according to the plant they feed on – for instance, peach aphids and pea aphids. Aphids may be black, brown, green, pink, red, white, yellow, or even mottled. Some species are woolly or waxy too. These little pests have long slender mouth parts that they use to attach to leaves, stems, and any other soft plant parts and suck plant juices, sometimes causing the plants to die. A pair of cornicles or tube-like structures, pointing backward from the back of the abdomen, distinguishes most aphids from other insects. Another distinct feature of aphids is that, unlike most insects, they do not scurry away when disturbed.1
Aphids Thrive In Cool, Low-Light Climates And Feed On Plants
Almost all plants are prone to aphid attack. Aphids generally feed on leaves, flowers, and stems although some are known to suck sap from roots too. Aphids prefer cool, low-light climes, and are usually found thriving in spring and fall. Temperatures ranging between 65 and 80 degree Fahrenheit are most favorable for aphid attack. However, they can survive and grow in any climatic zone and are as common in tropical gardens as they are in colder climes.2 Adult females of many aphid species give birth to live offspring without mating. There are others that lay eggs on a host plant, mostly during fall or winter. This affords a better chance of survival through harsh winters when food is scarce.3
Aphid Infestation Causes The Wilting And Curling Up Of Plant Parts
The most common sign of an aphid infestation is the wilting and curling up of parts of an otherwise healthy plant. Check plants regularly for aphid infestations and take suitable measures to protect your plants.
- Aphids usually hide under leaves. If a leaf is curled up, look closely and you may find an infestation. Some aphids inject a toxin into the plants, which curls the leaves and disfigures plant parts. The curled leaves are, in fact, a sign of advanced infestation and can weaken the plant. The curled leaves also act like an armor for aphids, protecting them from insecticides and natural enemies.
- The young and tender parts of plants, including buds and young fruit, are particularly favored by aphids. This can make the grown fruits and flowers look misshapen.
- If a colony of ants is headed for a particular tree, it could be because of an aphid infestation. Ants are attracted to the sticky honeydew that aphids excrete. And when a sooty mold fungus grows on the honeydew, it turns black and can be easily spotted. In return, ants protect aphids from predators and parasites in an effort to protect their food source.
- You may sometimes spot the white cast-off skins of aphids on the upper surface of leaves.
- The biggest risk to your plants from aphids is perhaps transmission of viruses from other plants. The viruses stunt plant growth, curl leaves, and turn the plants yellow or mottled. Infection can happen even with a small number of aphids. In crops used for human consumption, aphids can transmit yellowing of beets and the yellow dwarf disease in barley. Both diseases are viral in nature and are spread through aphids.4 5 6
Every organic gardener knows that pests and infestation are commonplace if you don’t put measures in place to control them. Parasitism is just one more of nature’s ways of feeding all organisms. However, it is painful to watch your beloved trees and plants slowly die because of parasites. Here are some natural, chemical-free ways to get rid of aphids.
1. Clean Away Aphids
For a minor infestation, use your hands or a soft toothbrush to physically remove aphids from plants. Sometimes a strong spray of water also works. Honeydew gets washed away and dislodged aphids rarely return to the plant. However, a strong spray may knock down a small plant, so choose your method carefully.7
2. Try Biological Controls
Using biological controls is a great way to weed out parasites in gardens.
A very well-known example of biological control involves introducing aphid wasps into gardens. These wasps specifically target aphids and fight their multiplication. The female lays eggs inside the aphid body. The offspring then eats and grows inside the aphid body, killing the aphid, which turns into a brown mummy. If you spot these mummies, you can be sure that your aphid population will decrease soon.8
Aphid wasps can be bought from suppliers that function in integrated pest management programs. Suppliers usually ship the wasps as ready-to-emerge mummies and will advise you about the best ways to release the wasps.
Syrphid flies are another type of biological control that works well on aphids that infest lettuce and other leafy greens. The larvae of this species feed on aphids and other soft-bodied insects, keeping their number in check.9
Syrphid flies are not easy to find commercially but they thrive in most flowering gardens. Lure them and then keep them by maintaining a pesticide-free garden.
Ants treat aphids the way we treat livestock! Aphids provide them with food and ants offer protection. One way to make aphids more susceptible to any treatment is to draw the ants away from the plant. In fact, ant management is one of the most important aphid control methods. A jar of honey placed near the plant can draw the ants away and allow you to clean the plant physically without hurting yourself.10
Some ground beetle varieties such as those belonging to the B. lampros species have shown promise in eradicating grain aphids. However, this is an alternative for large scale farms only.11
3. Use Neem Oil
You can also attempt to remove an infestation by spraying soap solution or neem oil on the plants. Oils kill aphids by smothering them so it’s important to cover the plant parts well. Further, soaps and oils are effective for short periods of time so they have to be sprayed frequently. In fact, neem compounds break down fairly fast (5–7 days) when exposed to sunlight and soil.12
- Make a 2% insecticidal soap by mixing 5 tablespoons of soap in 1 gallon of water. Spray as required. The fatty acids in the vegetable oil or animal fat contained in soap is responsible for the insecticidal properties. Use Castile or some other pure liquid soap for best results.
- Make a neem oil insecticide in a spray bottle by mixing 1 tablespoon of Castile soap with 2 tablespoons of neem oil. Add water as and shake well. Spray wherever needed.
In other studies, a mix of fermented plant extracts of neem leaf and wild garlic were found to be quite effective against aphids.13
4. Try Essential Oils
Vapors of essential oils have shown great promise against aphids. Specifically, oils of cumin, oregano, anise, and eucalyptus have been studied. It has been observed that even at very mild concentrations, the vapors are able to combat several pests, cotton aphids included.14
- To make an effective mix of essential oils against aphids, take about 4–5 drops each of clove, peppermint, rosemary, and thyme oils. Pour this mix into a small spray bottle filled with water. Shake well and spray on infested plants. This concoction works well as a general purpose insect repellent too.
5. Use Garlic
Garlic has a pungent odor and extracts of garlic have been found to be quite effective against some aphids. They effectively inhibit the growth of aphids. When you spray extracts of garlic on plants, aphids avoid settling on them.15 Growing onions and garlic around susceptible plants may also help.
- To make a garlic oil spray, take 3–4 cloves of garlic and chop them finely. Add 2 teaspoons of mineral oil. Let this mix sit for 24 hours. Strain and add the liquid to one pint of water. Now add 1 teaspoon of liquid dishwashing soap. Store this insecticide and use when needed.
- To use, add 2 tablespoons of the mixture to one pint of water in a spray bottle. Garlic is a pretty strong insecticide and must be used judiciously. It is best to use garlic spray in the absence of any beneficial plants in your garden since it can kill both unwanted and beneficial insects.
Aphids Cannot Cause Direct Harm To Humans
Aphids by themselves are not documented to be harmful to humans. In fact, there are probably no studies on their effects on human health. Although they belong to the same class of insects as bed bugs and lice, they are not known to cause or transmit any human diseases. However, some species of aphids do bite, and their bite causes a short-term rash.
That said, the choice of aphid treatment depends on the size of your plants and gardens. For larger gardens with many trees, biological control would be the best. For smaller gardens and a less severe infestation, physical cleaning or using essential oils is better.
|↑1, ↑3, ↑5, ↑7, ↑10||Aphids. Agriculture and Natural Resources, University of California.|
|↑2, ↑12||Controlling Whiteflies and Aphids. The National Gardening Association.|
|↑4||Examples of plant diseases transmitted by insects. University of Florida.|
|↑6||Aphids. The Royal Horticultural Society.|
|↑8||Lysiphlebus testaceipes. Cornell University.|
|↑9||Syrphid, flower, or hover flies. Agriculture and Natural Resources, University of California.|
|↑11||Ekbom, B. S., S. Wiktelius, and P. A. Chiverton. “Can polyphagous predators control the bird cherry‐oat aphid (Rhopalosiphum padi) in spring cereals?: A simulation study.” Entomologia experimentalis et applicata 65, no. 3 (1992): 215-223.|
|↑13||Nzanza, B., and P. W. Mashela. “Control of whiteflies and aphids in tomato (Solanum lycopersicum L.) by fermented plant extracts of neem leaf and wild garlic.” African Journal of Biotechnology 11, no. 94 (2012): 16077-16082.|
|↑14||Tunc, I., and Ş. Şahinkaya. “Sensitivity of two greenhouse pests to vapours of essential oils.” Entomologia experimentalis et applicata 86, no. 2 (1998): 183-187.|
|↑15||Dancewicz, Katarzyna, and B. Gabrys. “Effect of extracts of garlic [Allium sativum L.], wormwood [Artemisia absinthium L.] and tansy [Tanaceum vulgare L.] on the behaviour of the peach potato aphid Myzus persicae [Sulz.] during the settling on plants.” Pestycydy 3-4 (2008): 93-99.|