Aphids are common pests that can stunt plant growth. They can transmit viral disease between plants, promote plant galls, or even cause leaves, buds, flowers, and roots to be deformed. Since we all want our crops and plants free of pests, knowing how to get rid of aphids is of crucial importance.
So, how do you get rid of aphids? Biological methods like the release of aphid predators and cultural processes that include the removal of aphid-habitat plants, removing or pruning the infected plants, and avoiding nitrogen-rich fertilizers are among the safest methods. The use of synthetic insecticides should be a last resort since they negatively interfere with the agroecosystem.
This article gives you extensive knowledge about what aphids are, how you identify them, how aphid infestation starts, and the risks and damages associated with aphids. Most importantly, we give you comprehensive information about how to get rid of aphids and the measures you can take to control and prevent the infestation of these tiny pests. Keep reading to the end.
How to Get Rid of Aphids: Control and Prevention
Mild aphid attacks do not usually have any damaging effects on mature, healthy plants. But large aphid colonies on plants will come with adverse effects on crops and plants, especially those that are still young.
The fact that aphids may not harm mature plants does not mean they should be left to party on plants. Remember that their presence on a plant means fast reproduction and so the large colonies can be created with ease.
Again, even though it is quite easy to control aphids because they do not move at high speeds, these pests multiply fast, and it’s crucial to control them before they begin reproducing, which can happen up to four generations in one season. So, what ways can you use to prevent, control, and get rid of aphids?
Preventive, control, and aphid elimination methods can be classified within four broad categories: the biological, the cultural, the mechanical, and the chemical methods.
Biological methods of aphid control entail the use of natural enemies or predators of aphids. These may appear spontaneously when aphids are found in large numbers on plants. You can also decide to be proactive and introduce aphids to the infested plants.
Some of the most useful predators of aphids include parasitic wasps, soldier beetles, lady beetles or ladybugs, syrphid fly larvae, and lacewing larvae. While these predators make part of the long-term solutions and will work best if they occur naturally, introducing them will solve your aphid problem without waiting for nature to take its course.
For example, you can acquire the convergent ladybugs (Hippodamia convergens) from commercial breeders and follow this procedure to use them as aphid predators.
- Acquire the ladybugs and mist them with water just before the release. This prevents them from flying away as soon as they are freed.
- Mist the surface of the plant where you intend to release the ladybugs to ensure they will stay around.
- Release the ladybugs at the base of the infested plants or the joints of low branches. The ladybugs will start crawling up the plant to look for the aphids. The release is best done at dusk, so the ladybugs don’t fly away. They will do so anyway after a few days, but chances are they will have fed on the aphids before doing so.
Large numbers of ladybugs (around 1,500) are required to control aphids, and you might need to make a few applications before aphid control becomes a reality. Just ensure that every application is made a week apart from the other.
Research by the University of California reported that releasing convergent ladybugs significantly reduced the number of aphids on potted rose plants and chrysanthemums. The study also suggested that this method is one of the cheapest and most widely used in the US to control aphids.
Cultural methods of controlling aphids involve manipulating the agroecosystem so that cropping is less supportive of the establishment and spread of the pest. Several cultural methods can be used to control aphids. They include:
- Removing or pruning affected plants: when aphids are already established and have probably caused negative effects on plants like curled leaves or stunted shoots, the best way to get rid of the pest is to remove the affected plant or prune the branch and dispose of in a way that the aphids do not establish themselves on new plants. Pruning can also serve to aerate inner plant canopies where aphids thrive with ease.
- Getting rid of weed habitats for aphids before planting your crop: certain weeds like the mustards and the sowthistle are good habitats for aphids. Check and remove them from your garden before planting your vegetables or ornamental plant to prevent them from transmitting aphids.
Paradoxically, these weeds can also act as sources of aphid predators. But between the two options, you are better off removing them to avoid aphid transfer.
- Avoiding high quantities of nitrogen fertilizers: high levels of nitrogen in the soil is favorable to the growth of aphids. So, use only the necessary minimum or opt for a less soluble type of nitrogen and distribute it in many small applications throughout the season. Slow-release organic fertilizers would even be best.
- Growing young plants and vegetable seedlings in enclosed spaces before transplanting them: young crops and plants are more susceptible to aphids. Using green covers to enclose them or planting them in a greenhouse will keep aphids away. This will also keep the plants from aphid-transmitted viruses.
- Using silver-colored reflective mulches: these repel aphid colonies and will reduce aphid transmission to the most susceptible crops like melons, squash, and other vegetables. To control aphid spread with silver-colored reflective mulches, follow these steps:
- Remove weeds and cover the beds with the silver mulch.
- Bury the ends of the reflective mulch with soil to firm them.
- Cut 3-4ʺ (7.6- 10.1cm) diameter holes and plant your seed or seedlings.
The silver mulch will not only keep aphids away but will also control weeds and enhance growth. However, these mulches should be removed when temperatures are high to avoid spoiling the crop or plants.
Mechanical methods of aphid control employ physical means that do not harm the ecosystem. One such way is the use of water spray. Aphids are tiny insects and will easily be carried away by a strong wave of water. It will be difficult for them to survive the pressure or return to the plant. It is best to use a hosepipe and avoid a powered pressure washer since the force could also destroy the plant.
Adding alcohol and washing soap to the water can bring a more effective result. Isopropanol (rubbing alcohol) is good enough. Just ensure it has no toxic additives. Usually, you will find the alcohol in 70% strength (sometimes 95%).
To make your aphid spray, mix equal parts of the 70% strength alcohol and water, and a tablespoon of liquid soap. If you use the 95% strength alcohol, it should be 1 part of alcohol to 1.5 parts of water.
Chemical aphid control entails the use of insecticides. However, these should be the last resort considering that they alter the agroecosystem and that most mature and healthy plants can tolerate small to moderate numbers of aphids without any damage. Also, consider that large aphid populations will eventually be controlled by biological factors like predators and hot temperatures. Besides, biological and mechanical options should be tried first.
When insecticides are applied, insecticidal oils and soaps should be preferred. These could be plant oils like canola and neem or petroleum-based horticultural oils. These oils should be applied with high amounts of water. Applications may need to be done more than once since each application takes care of the aphids that are present at the time it is done. Unfortunately, some aphid predators that are present at the time of spray will also be eliminated.
It is vital to apply oil and soap insecticide when temperatures are lower than 90°F (32.2°C). One drawback of these sprays is that they may not destroy aphids that are protected by curled leaves or plant galls.
If you go for synthetic sprays like Acephate and Malathion, use them only on non-food plants. Their use should only be considered when aphids are a real threat to plant survival. This is because they also kill the natural enemies of aphids that provide long-term solutions. Always remember to ascertain that the insecticides you use to control aphids are allowed in your state.
What Are Aphids: Pest Manifestation and Types
If your crop or plants have aphids, you will notice tiny soft-bodied insects, approximately the size of a pinhead. Aphids belong to the Aphididae family and are also called by other names like ant cow, greenfly, and plant louse. Their distinguishing action on plants is that they suck the nutrient-rich sap from plant tissues using their piercing mouthparts. This action can weaken plants and compromise their growth.
The majority of aphid species are winged, even though the adults of some species are wingless. With a close look, you will notice their pear-shaped bodies with long antennae and two short tubes at the hind, known as cornicles. Although you may find single aphids on plants, these pests usually feed in dense colonies that appear stuck to plant stems and leaves. Unlike other pests, aphids are stubborn and won’t escape with a little disturbance.
Aphids can be green or bear other darker colors like yellow, brown, red, and black, depending on the species. It is estimated that there are about 4,000 species of aphids with around 250 of these manifesting on crops and decorative plants. Here are 5 of the most common species:
- The Woolly Apple aphid (Eriosoma lanigerum): manifesting in a purplish color and dark legs and head. Exclusive to the apple tree and produces honeydew that sustains the growth of a woolly white mold.
- The Cabbage aphid (Brevicoryne brassicae): a gray-green aphid that has a powdery wax-like covering. You’ll find it on the underside of cabbage leaves, radishes, Brussels sprouts, and cauliflower and can be responsible for significant yield losses if left unattended.
- The Corn root aphid (Anuraphis maidi radicis): a symbiotic type of aphid that relies on the cornfield ant to store its eggs during winter the carry the hatched eggs to the roots of weeds and then to the corn roots. Corn growth is stunted as a consequence and is likely to turn yellow and wilt.
- The Greenbug (Toxoptera graminum): this aphid is highly destructive to grains like wheat and oat, manifesting as yellow patches on the grain plant. It reproduces extremely fast and can destroy whole crops.
- The Rose aphid (Macrosiphum rosae): appears larger than other types and is green with black and pink marks. Exclusive to garden roses but also hunted by the ladybird and caterpillar larvae.
Other common types of aphids include the Apple aphid (Aphis pomi), the Cooley spruce gall adelgid (Adelges cooleyi), the Eastern spruce gall adelgid (Adelges abietis), the Green peach/spinach aphid (Myzus persicae), the Melon/cotton, aphid (Aphis gossypii), the Pea aphid (Acyrthosiphon pisum), and the Potato aphid (Macrosiphum euphorbiae) among others.
Aphids’ Reproduction and Plant Infestation
You’ll be surprised to know that, even though aphids have several generations in a year, some of the species reproduce asexually through stem mothers. These are wingless females that produce young aphids (nymphs) and not eggs during the summer season. Once the plant that bears the stem mother is overcrowded with nymphs and they develop into adults, they fly to other new plants to set a new feeding base.
Other species, however, produce sexually by mating between males and females in winter or fall. The resulting eggs survive through overwintering in cold climates while in warmer climates, continuous development into nymphs, and then to adult aphids happens. In both modes of reproduction, aphids are reproduced in large numbers.
To set a new base, winged aphids fly to a new plant, and once it is found suitable for their sap-sucking, they leave several wingless young ones on the plant’s tender tissue. The deposited aphids feed and increase rapidly in size and are already mature in 7 to 10 days. That means they can now start reproducing and expand the colony on a plant.
The same cycle is repeated over and over again. This rapid reproduction also means more considerable damage to crops and plants.
Crop and Plant Damage by Aphids
Resistance to aphid infestation may vary from plant to plant. But plants that are sensitive to the parasitic nature of aphids will be negatively affected. This is because the saliva injected by the pest and the continuous sucking of sap from their tissues compromise normal plant processes.
Several forms of plant damage may result from aphid activity. The following five are among the most prominent.
Disfigured and discolored leaves and shoots
Twisted, curled, and wrinkled leaves are all signs of severe aphid infestation on plants. This results from the toxin that some types of aphids inject into plant tissue. The leaves may also turn yellow and eventually wilt or die.
Extreme aphid infestation will also cause stunted growth in shoots, which may also end up dying. In turn, all that compromises the growth of the entire plant.
Some aphid species attack plant roots and are responsible for withered plants that may die in the long run. The buds of infected plants are usually soft and do not develop as they should, which results in lower yields when crop plants are involved. A good example is the Lettuce root aphid that dwells in soil and attacks in spring and summer.
When aphids attack the flower buds, the resulting fruit may be distorted. Honeydew on mature fruits will also cause them to turn black.
A more prominent malformation in plants that results from aphid infestation is the plant galls. These are abnormal growths that form as a result of growth-regulating chemicals released by feeding aphids. These chemicals cause the plant tissues to form a gall, which becomes the new secure breeding space for the aphids.
Ant attraction and fungus growth due to honeydew
Aphids secrete a sticky and sugary fluid known as honeydew. Some of it drops to the ground and can attract ants and other insects that use it as food.
The honeydew can also be a breeding space for sooty mold, a fungus that accumulates on branches and leaves and causes them to turn black. If aphids had not been spotted yet, this fungus could be the first indication of their presence on a plant.
Carriers of plant viruses
Aphids often act as virus vectors. This is facilitated by the structure of their mouthparts, their consistent searching behavior for host plants, and aphids’ high reproduction rate.
Among plant viruses transmitted by aphids is the Barley Yellow Dwarf Virus spread by around 20 aphid types and the group of viruses known as Potyvirus, which is the largest cluster of plant viruses.
Depending on the extent of aphid infestation on a crop, aphids can cause up to a 10% reduction in crop yield. The situation will be aggravated if aphids bring with them the Yellow Dwarf Virus or other aphid-spread viruses.
Considering these and other forms of damages caused by aphids, their control and prevention are imperative.
Despite their tiny size, aphids can damage crops and plants, especially when they infest in large colonies. They can cause plant damage ranging from curled and withered leaves, the attraction of ants due to the secretion of honeydew, the spread of plant viruses, and general plant malformation. All these damages eventually lead to reduced yields from crops.
To avoid the damage of aphids on plants, biological, cultural, mechanical, and chemical methods can be applied. The first three methods are safer and do not disturb the agroecosystem. Instead, chemical methods have a negative impact on the environment and should be considered as a last resort.