The Gardener’s Guide to Aphids: Understanding and Managing These Common Pests

One of the most common problems that you will find in the garden is dealing with pests. Among these, aphids are some of the most frequent pest you will encounter. There have been at least 4,000 aphid species found with probably more undiscovered. In this comprehensive guide, we’ll explore whether aphids are harmful or beneficial, identify the plants they attack most often, understand the damage they cause, examine their life cycle, learn about their predators, and discover effective organic methods to control and/or eliminate them.

Are Aphids Harmful or Beneficial?

Aphids are small, soft-bodied insects that are often considered harmful due to the damage they can inflict on plants. However, their role in the ecosystem is more complex. While they can be destructive, aphids also serve as a food source for a variety of beneficial insects, contributing to the natural balance of the garden.

Harmful Aspects

Aphids are notorious for their ability to weaken plants by feeding on their sap. This feeding can lead to a variety of problems, including stunted growth, yellowing leaves, and reduced yield. Additionally, aphids excrete a sticky substance called honeydew, which can attract sooty mold, further damaging plants and reducing their aesthetic appeal.

Beneficial Aspects

On the flip side, aphids play a role in supporting biodiversity in the garden. They are a crucial food source for many beneficial insects, such as ladybugs, lacewings, and parasitic wasps. These predators help keep aphid populations in check, promoting a healthier garden ecosystem.

Plants Most Commonly Attacked by Aphids

Some aphid species can be picky when looking for plants to feast on. Even so, about 10% of the aphid species will feed on a wide range of plants. Aphids can be blown from plant to plant in strong winds which allows them to travel to each plant helping them to spread out and get the most from their meals. However, certain plants are more susceptible to aphid infestations. Commonly affected plants include:

• Roses: One of the most well-known targets, aphids can cause significant damage to rose bushes.
• Vegetables: Aphids often attack vegetable plants such as lettuce, kale, cabbage, and beans.
• Fruit Trees: Apple, pear, and plum trees are frequent targets.
• Flowers: Aphids will feed on many flowering plants, including marigolds, sunflowers, and zinnias.
• Herbs: Basil, dill, and parsley are among the herbs that aphids find appealing.
• Milkweed: I know that milkweed should be categorized in the flower section but this is the one plant that aphids attack every year in my garden- multiple times through out the year. I always struggle to control aphids on this plant.

The Damage Aphids Cause

The primary damage caused by aphids comes from their feeding habits. Aphids have sucking mouthparts. By piercing plant tissues and sucking out the sap, aphids will deprive plants of essential nutrients. When looking for aphids look under the leaves of the plants. On my milkweed plants the aphids are mostly along the main stems near the tops of the plants and under the leaves. Aphid damage can lead to:

• Stunted Growth: Affected plants may exhibit reduced growth rates and smaller leaves.
• Fruit and Leaf Abortion: Plants will drop their fruit and leaves when there is enough damage.
• Leaf Curling and Yellowing: Leaves may curl, turn yellow, and drop prematurely.
• Deformed Flowers and Fruits: Flowers and fruits can become misshapen or fail to develop properly.
• Honeydew and Sooty Mold: The honeydew excreted by aphids can stick to the leaves of the plants and quickly grow a black, sticky coating on leaves and stems called sooty mold that impairs photosynthesis. Carpenter Ants feed on the honeydew which is produced from aphids. The ants value this honeydew and will protect the aphids while trying to eliminate the natural predators of the aphids. So, if you see ants around the plants that have aphids on them just know that it is a great relationship that benefits both the ants and the aphids.

Aphid Study -Sustainability 2023

Sustainability published a study in July 2023 solidifying widely known information about aphids. Aphids can and will attack over 40 different plant families in North America, Asia, and Europe.

Peach–Potato Aphid Myzus persicae: Current Management Strategies, Challenges, and Proposed Solutions

Aphids Ability To Spread Plant Viruses

While aphids have the ability to spread viruses to other plants it is interesting how they can travel from plant to plant. Some aphids will travel from one host plant to another by way of wind gusts. Strong wind gusts can carry them quite far. However, aphids can grow wings in order to fly to another host plant as it gets crowded or their food source gets depleted. As aphids eat the host plant they will transmit viruses to the plant when they inject their sucking mouth parts into the plant. Crop growers are concerned as this pest can do a considerable amount of damage to their crops being in part as the aphids ability to easily relocate to new plants.

Plants Natural Defenses Vs. Aphids Proteins

Interestingly, plants have natural defenses. Plants send out signals that helps to defend itself. These signals tell the plant to callous at the place of injury, where an aphid is attacking it. However, aphids produce a protein in their saliva that will counteract with the plants defenses. This makes it difficult for plants to defend themselves. In addition, plants struggle to defend themselves against the honeydew that aphids produce as they feed because the honeydew can contain the same proteins found in the saliva of the aphids that prohibit the plants ability to defend itself.

The Life Cycle of Aphids

Understanding the life cycle of aphids is key to effectively managing their populations. Most aphids do give birth to live young, however, root and conifer aphids will only lay eggs. A new generation can take place within 10-12 days. There can be as many as 20 generations in one year.

The most common color of aphids is green, however, the aphids that I encounter here in Texas are mostly yellow. There are dark brown/black aphids that are quite common as well. The aphid life cycle is complex and involves several stages:

• Egg Stage: In colder climates, aphids overwinter as eggs on host plants. These eggs hatch in the spring when temperatures rise.
• Nymph Stage: The hatched eggs produce nymphs, which are small, immature aphids. Nymphs undergo several molts before becoming adults.
• Adult Stage: Adult aphids can reproduce asexually, giving birth to live young without the need for males. The live young are all females at the beginning of the growing season. These females will then become males at the end of the growing season. This allows for rapid population growth, especially in favorable conditions.
• Winged Aphids: When populations become too large, there is too little food, or conditions deteriorate, some aphids develop wings and migrate to new plants, spreading the infestation.

Natural Predators of Aphids

Aphids have several natural enemies that help keep their populations under control. Encouraging these predators in your garden can be an effective way to manage aphid infestations. Please remember that to keep these natural predators in your garden means that you will need to have some of the “bad” bugs in your garden also. The beneficial bugs will not be around if they don’t have a food source. Another thing to mention is that sometimes it may take several days before you see predators to take care of your “aphid problem”. Key aphid predators include:

• Ladybugs: Both adult ladybugs and their larvae are voracious aphid eaters.
• Lacewings: Lacewing larvae, known as “aphid lions,” consume large numbers of aphids. Adult Green Lacewings can be found through out the year. Other Lacewing species only produce one generation of offspring a year. Both the adult Lacewings and the larvae, known as aphid lions are some of the most common insects you will find. I usually see them at night flying around. Their eggs are very interesting, adults will lay their eggs on a small thread-like stalk standing straight. Green Lacewings larvae can eat over 200 aphids in a weeks time.
• Parasitic Wasps: These tiny wasps lay their eggs inside aphids, and the developing larvae eventually kill their hosts. The parasitized aphids will look fat, brown, and will be hard. After being parasitized they are known as “aphid mummies”.
• Hoverflies: Hoverfly larvae feed on aphids, making them valuable allies in the garden.
• Birds: Some bird species, such as wrens and chickadees, feed on aphids.
• Praying mantids: Praying Mantids are great at eating aphids, however, if there are an abundance of praying mantids in the area they will eat each other. They are not picky on what they eat.

Organic Methods to Control Aphids

Managing aphids organically involves a combination of cultural practices, physical removal, and the use of natural predators and treatments. Here are some effective organic methods to control aphid populations:

1. Encourage Beneficial Insects– Create a garden environment that attracts and supports beneficial insects. Planting a variety of flowers with a continuation of blooms, such as marigolds, daisies, and sunflowers, can provide nectar and pollen for egg laying helps these predators. I highly discourage buying lady beetles from garden supply companies or nurseries. The lady beetles will usually fly away and will not stay within your area.
2. Spray With Water- You can easily use a spray from the water hose to get the aphids off of the plants. This method will kill some of them while others that will fall to the ground and get eaten by spiders and other insects that are near the ground. Since spraying with a water hose is a low prep way to control these pest you may need to repeat this method every few days.
3. Companion Planting– Certain plants can repel aphids or attract their predators. For example, planting garlic, chives, or marigolds near susceptible plants can help deter aphids. Conversely, planting dill or fennel can attract ladybugs and other beneficial insects.
4. Physical Removal– For small infestations, physically removing aphids can be effective. This can be done by spraying plants with a strong jet of water to dislodge the insects or by gently wiping them off with a damp cloth (I use my gardening gloves with this type of control).
5. Bacterial Insecticides- There are several bacterial insecticides that have been proven to help control populations of aphids. Bacillus thuringiensis and Saccharopolyspora spinosa (Bosal 10EC and Spinosad) are quite effective in controlling aphids and are safe since they are bacterial in nature and not a chemical derivative.
6. Neem Oil– Neem oil is a natural insecticide derived from the neem tree. It disrupts the hormonal systems of aphids, reducing their ability to feed and reproduce. Apply neem oil according to the manufacturer’s instructions, ensuring thorough coverage of affected plants.
7. Insecticidal Soap– Insecticidal soap is another organic treatment. It works by breaking down the protective outer layer of aphids, causing them to dehydrate and die. Be sure to use a soap specifically designed for insect control and follow the label instructions. I highly recommend that before using insecticidal soap to observe if any aphid predators are in the area, if so hold off on using the insecticidal soap and let the predators do their job. Be patient. Many aphid species are developing resistance against insecticidal soap and other forms of control.
8. Row Covers– Using row covers can physically protect plants from aphid infestations. These lightweight fabric covers allow light and water to penetrate while keeping aphids and other pests out. This is perfect when growing vegetables.
9. Regular Monitoring– Regularly inspect your plants for signs of aphid infestations. Early detection can help you take swift action before the infestation becomes severe.

Pruning, Nitrogen, and the Control of Aphids

An interesting fact is that aphids are attracted to nitrogen. As plants grow they have higher concentrations of nitrogen at the tips of plants where there is new growth or where the flower buds are growing. Nitrogen levels are high when plants are actively growing. Nitrogen levels are lower in the areas of the plants in the middle portion of the stems.

Pruning As An Aphid Control

So how does pruning control aphids on your plants? When we prune plants those plants will begin to encourage growth in other areas of the plant. After close observation of aphids attacking certain plants year after year we can make an educated guess as to what will happen in future years. We can take that knowledge and wait to do heavy pruning for when both the aphids and their predators are within the area. You will want to wait to prune to ensure the predators available to help keep the aphids in control.

Conclusion

Aphids are a common garden pest that can cause significant damage to a wide variety of plants. While they play a role in the ecosystem as a food source for beneficial insects, their rapid reproduction and feeding habits make them a challenge for gardeners. By understanding their life cycle, identifying their predators, and employing organic control methods, you can manage aphid populations effectively and maintain a healthy, thriving garden. Embrace the balance of nature, and let your garden flourish with the help of natural predators and sustainable practices.

Citation: Ali, J.; Bayram, A.; Mukarram, M.; Zhou, F.; Karim, M.F.; Hafez, M.M.A.; Mahamood, M.; Yusuf, A.A.; King, P.J.H.; Adil, M.F.; et al. Peach–Potato Aphid Myzus persicae: Current Management Strategies, Challenges, and Proposed Solutions. Sustainability 2023, 15, https://doi.org/10.3390/su151411150