How to Identify and Manage Aphids

Aphids are one of the most troublesome garden pests around the world. With a few hundred species ready to attack almost every plant in your garden, spotting an infestation can be overwhelming. To make matters worse, their rapid reproduction means a small problem can quickly get out of hand.

Although we all deal with these pests at some point, it doesn’t have to be a disaster to fix. Understanding how they operate and employing control and prevention methods can help reduce risk and protect your plants.

What Are Aphids?

Aphids are pear-shaped, soft-bodied insects with piercing, sucking mouthparts that feed on almost any plants in the garden. If you’ve planted it, a species of aphid probably wants to eat it.

They are members of the family Aphididae, which contains 4,400 species – about 250 of which are quite damaging to plants. Most species are specialists, meaning they feed on one particular genus or species of plants. A few species are generalists and feed on anything they see.

Most adults don’t have wings, but a few species do. They congregate in large masses and feed on all parts of the plant by sucking the sap from the leaves and stems. Most species you’ll find in your backyard like to gather and feed on the undersides of leaves, making them easy to miss in the early stages of infestation.

Reproduction

Reproduction is largely asexual, with multiple generations born per year. Immature aphids are called nymphs. Nymphs go through at least a few cycles of shedding their skin (usually four) before they mature. 

High numbers in moderate climates are generally the result of live birth by adult females via parthenogenesis at rates of a massive 80 offspring per week in active seasons. Parthenogenesis is just a fancy word for asexual reproduction, meaning the egg doesn’t need a sperm to produce an embryo. In other words, aphids spread quickly because the females don’t always need males to reproduce.

While most aphid species reproduce asexually, some colder-climate species mate and lay eggs in fall or winter. This helps overwintering eggs develop hardiness to survive more intense elements without leaf tissue on their preferred host plant.

Some females lay eggs on one host plant and move to another when the weather warms. Many multiply quickly and can move from nymph to adult in seven to eight days. This is why aphid colonies are so large and can quickly get out of hand if not controlled.

Why Are They Bad For Plants?

While a small amount of aphid damage may not cause many problems in the garden, infested plants can experience leaf curl and yellowing. Some aphid feeding can stunt plant growth. Essentially, the longer you ignore the problem, the worse the symptoms will get.

Aphids also secrete a substance called honeydew, produced as the bugs feed. Honeydew secretions attract ants that feed on the substance and can cause sooty mold on plants that further impact growth.

Some more dangerous species inject toxins into plants as they feed, which distorts and eventually destroys leaves. If uncontrolled, this can end up killing your plants.

While most tend to feed on leaves and shoots, there are also root aphids. Lettuce root aphids, for instance, feed on underground parts of lettuce plants, causing stress and creating conditions for full lettuce head dieback. Other types that feed on crowns and roots may cause root veggies to lose their tops when pulled.   

One of the most important reasons aphid control should be a priority in your garden is they are often vectors for plant viruses. Look out for an aphid attack on squash, cucumber, pumpkin, melon, bean, potato, lettuce, beet, chard, and bok choy. These are the plants where infestation could mean the beginning of a viral disease.

Viruses transmitted by aphids cause mottled and curling leaves and stunted plant growth. Because the viruses transmit in just a few minutes, prevention is key. It takes longer to control populations with insecticide than it does for viral transmission to take place. Many diseases that aphids are vectors for also have no cure, such as mosaic viruses.

How To Identify

Aphids tend to live where they eat, and what they eat depends on the aphid species. They can be found on most fruit and vegetable crops, on some flowering plants like roses or chrysanthemums, on trees, and in some bushes.

Often, the wingless aphids remain hidden on the underside of leaves, but it’s very easy to spot a large infestation as they cluster together in large quantities.

Characteristics

Aphids are small bugs that can be tough to see individually. They have soft, usually pear-shaped bodies with longer legs and antennae. Sizes vary between species and life stages, so it can be tough to tell whether you have an aphid problem.

Different species come in various colors, including green, yellow, pink, and black. Understanding the visual differences between types can help with identification, making the problem easier to treat. Alternatively, you can look at which plant they are feeding on, as several species prefer certain plants.

Some aphids also have a fluffy or waxy coating, similar to mealybugs. Woolly apple aphids are one example, creating a fuzzy white cover when grouped together that protects the bugs from damage.

Signs of Damage

If you don’t spot aphids immediately – perhaps because they’re hiding out in clusters on the undersides of leaves – you can also identify them by the damage they leave behind.

As sap-sucking pests, you’ll likely notice issues in the leaves first. These include curling, shriveling, and discoloration at the colony’s site. If the infestation is severe, you may also notice stunted growth in the leaves and stems, indicating internal damage.

The next thing to look out for is sooty mold. If you notice any black fungi on leaves or stems, it could be caused by the honeydew they left behind. Alternatively, you can look for ants that feed on the honeydew.

Finally, signs of disease do not always indicate an aphid problem, but the two issues often go hand in hand. Aphids can transmit various viruses to plants, leading to patchy discoloration, stunted growth, and possible defoliation. If you spot any diseases, also check the undersides of the leaves for potential aphids.

8 Ways To Manage and Remove

Once you’ve spotted an issue, it’s important to act quickly. Aphids aren’t always deadly, but their rapid reproduction can turn a small issue into a big one in just a few months. These bugs are also impacted by the seasons, but it’s far better to deal with a problem soon than ignore it and risk the health of your precious plants.

Hand Removal

For those who aren’t squeamish, picking aphids off plants by hand and squishing them between your fingers is possible. This is only possible for small colonies unless you want to spend hours picking single tiny bugs by hand.

For hand removal to be effective, it’s essential to investigate plants thoroughly, especially for tiny species. Aphids are good at hiding underneath leaves and in any stem crevices, so check each area carefully when picking so you don’t miss any large clusters.

Since getting all the bugs the first time is tough, you’ll need to check back again and pick off any new bugs you see. The more vigilant you are, the less chance they will have to reproduce.

Pruning

If you have a larger aphid problem that makes hand removal unfeasible, you don’t have to reach for insecticides immediately. Your pruning shears can also be helpful in this situation.

Because aphids congregate in groups, selectively pruning leaves and stems can help remove large sections at once. This is helpful for established plants that won’t mind losing a leaf or two but can be trickier for new seedlings where aphids are feeding on the new and vulnerable growth.

Use a sharp knife or a pair of quality Felco 2 pruners to remove the entire leaf and destroy it. If you have to remove more than one-quarter of the plant to eliminate the aphids, opting for another control method to avoid stressing the plant further may be better.

Water Sprays

One of the most common recommendations for removing aphids is to spray them off your plants with a strong jet of water. At first, this may seem useless, but there is a method behind the madness.

Aphids that are washed off a plant quickly won’t simply climb back on the plant to continue eating. Since they settle in and suck the sap of leaves or stems, spraying them off with a strong nozzle separates their mouthparts from the rest of the body, killing the bugs.

As with hand picking or pruning, this won’t always remove all the bugs. You’ll need to keep at it, regularly inspecting your plants and spraying continuously to limit spread.

A blast from a hose is usually enough, but you don’t want to spray your plants so hard that you damage the leaves. Using water in the morning is also helpful so the plant has ample time to dry out in the sun. Excessively spraying plant foliage with water could lead to other issues like powdery mildew.

Natural Predators

One of the most effective ways to eliminate aphids without constant maintenance is by employing their natural enemies.

Aphid predators like adult lady beetles, lacewings, and parasitic wasps eliminate aphids or consume them as a food source. Predatory mites also feed on aphids. Broad-spectrum pesticides will kill aphids but can also harm other insects, including our beneficial ones, so this is a far friendlier control method for the garden and local environment.

Start by providing an environment to draw in beneficial insects that feed on aphids. Purchasing lady beetles or other beneficial insects may be possible at a nearby nursery, but they won’t be effective without the right environment.

Parasitic wasps (particularly Aphidius coleman) are predatory insects that will come to your garden through encouragement by planting host plants like yarrow, Queen Anne’s lace, fennel, and dill. They’ll then lay their eggs inside aphids, and the aphids will be parasitized as the egg hatches and the larval wasp feeds.

Syrphid fly larvae, also known as hoverflies, are another helpful natural enemy. The larvae of these hoverflies prey on newly hatched aphids and adults.

You can dramatically decrease aphid populations without extra effort by considering your natural predators and planting plants to increase your beneficial insect population. Get them to stay with a permanent rotation of companion plants, and you’ll have fewer aphids season after season.

Here is more on How to Plant a Biocontrolled Garden to Regulate Pests.

Remove Ants

One of the most important biological controls is ridding your garden of ants. It may sound crazy, but ants can actually “farm” aphids like cattle.

While ants aren’t the worst thing to have in your garden, they feed on the honeydew aphids secrete. In return, the ants protect the aphids from predators, exacerbating both problems. In other words, control ants, and you’ll also have better control of aphids.

As you monitor your plants for aphids, look for ants as a sign they’re around, and check the undersides of leaves to see if the ants are harvesting aphid honeydew. Ant bait traps or citrus sprays may help control ant populations, simultaneously reducing your issues with aphids.

Horticultural Oil/Insecticidal Soap

Aphids can be killed using insecticidal soaps, neem oil, or horticultural oils if you want to go the spray route. Make sprays your last vector of control, as they can sometimes damage plant tissue and deter beneficial predators. 

Neem oil, horticultural oil, and insecticidal soap can be sprayed once every 7 to 10 days until the problem subsides. Spray them before the sun rises and in the evenings. Avoid using dish soap as a quick fix, as it can cause significant damage to plants.

All sprays should applied cautiously. Wear gloves, eye protection, and a face mask to prevent accidental inhalation, and don’t apply a spray in high wind conditions.

Beauveria bassiana

For a more biological spray solution, try Beauveria bassiana. This fungus is often used for biocontrol insect management. Spores reproduce inside host insect bodies, draining them of nutrients and eventually killing the bugs, causing white muscardine disease in the insect. The fungus spreads on contact, so you don’t need to rely on the aphids consuming the spores for the treatment to be effective.

It is possible to purchase products that contain this fungus, slowly ridding your plants of aphid infestations. After mixing, spray the plants as soon as possible, as spores will slowly die off over time.  It’s best to spray the leaves directly in the evenings, as intense sunlight can make the treatment less effective.

Diatomaceous Earth

Diatomaceous earth is another treatment that can be dusted on plants to control aphids. This fine microscopically sharp dust, used to target many pests, is good at scratching up the soft bodies of aphids, which causes them to dehydrate and die and prevents them from attacking plants.

If it rains or is windy, you’ll have to reapply, so ensure you monitor conditions frequently until the infestation subsides.

How To Prevent Aphid Infestations

Aside from planting those plants that natural predators of aphids will flock to, you can do things to prevent aphids altogether. None of these are foolproof, but they will reduce the risk of damage, limiting the need to use control and removal methods.

Improve Soil Health

Start with the foundation of plant growth – the soil. Planting in the right soil conditions will improve root growth, limiting stress and improving overall health. Since aphids are more attracted to damaged or stressed plants, maintaining healthy soil is a great way to discourage aphids from settling in.

Start by choosing the right plants for your soil type, whether sand, clay, or loam. Also, consider pH levels and nutrient availability before you plant. Finally, amend the soil with plenty of organic matter to boost microbial activity and structure.

Water Consistently

Another important part of care is watering, specifically watering consistently. One of the easiest ways to stress your plants is to water too little or too much. Underwatered plants are particularly attractive to aphids, and combatting dry conditions can limit your need to employ other controls.

Check the soil often and water your plants before they show signs of stress like wilting or yellowing. Adjust your watering schedule as temperatures increase in summer when the soil dries out much quicker.

Avoid Overfertilizing

Fertilizing can help boost growth in plants and ensure they have all the nutrients required to grow successfully. But when it comes to feeding, too much of a good thing will cause more harm than it helps.

Feeding constantly encourages the plant to continue pushing out new young growth – the tasty parts of the plant for aphids. Fertilizing is still an important part of care, but it’s also essential to give your plants a break and only feed when absolutely necessary.

Plant Trap Crops

If you just want to keep aphids away from certain plants, you can use trap crops to your advantage.

These plants are placed near plants susceptible to aphids to draw them to that plant rather than the others. If there are any issues, that plant can be pulled and sacrificed to keep your garden aphid-free and your precious plants untouched.

Nasturtiums are great for this purpose, but you can try a few others depending on the plants you want to protect.

Use Row Covers

Newly planted seedlings are at their tastiest and, therefore, the most vulnerable to aphid problems. For those with consistent issues with aphids season after season, it’s best to eliminate the option completely by protecting your seedlings with row covers. However, this does prevent pollinators from reaching plants while keeping the aphids at bay, so you may need to hand-pollinate plants that start to flower under the row covers.

You can also keep susceptible plants inside a greenhouse, monitoring for any signs of infestation. Note that aphids can still strike inside of a greenhouse, but it’s easier to reduce pest pressures this way!

Final Thoughts

Aphids are one of the most common pest issues gardeners will deal with, but they don’t have to be a nuisance. Follow the preventative tips and closely monitor plants to control infestations as soon as you spot them.