Aphid Honeydew: What Is It, What Causes It and How Do We Get Rid Of It?

Gardeners everywhere know that anything strange found on a plant can be a sign of major problems. One of the most common symptoms is the presence of a white sticky substance on the leaves or running down the stems.

For a lot of gardeners and plant enthusiasts, this warning sign is immediately recognizable as aphid honeydew.

Ant collects honeydew from aphids grouped on leaf
Ant collecting honeydew from aphids | vvoennyy-DepositPhotos

Aphids are one of the most common and destructive plant pests, finding their way to both indoor and outdoor plants.

But once you start seeing honeydew, aphids can soon become the least of your problems.

Knowing how to identify honeydew, its related risks, and how to get rid of it is a vital key to keeping all of your plants healthy.

What Is Aphid Honeydew And What Causes It?

Aphid honeydew is perhaps the most common form of honeydew you’ll find on plants.

It’s created when an aphid pierces the plant’s phloem ducts with its mouthparts, creating enough pressure that the sap passes straight through the aphid’s body and escapes as excrement.

Plant sap is filled with sugars that aphids and other pests love to feed on but is kept under pressure, much like the blood in your arteries.

Once the initial pressure has abated, the aphids are free to feed.

There are several other honeydew-producing insects and pests such as cicadas, scale insects, and even some species of caterpillar.

Meanwhile, species of bees and wasps actually harvest the honeydew and use it to create a type of honey, which can also lead to a decreased pollination of flowering plants.

What Damage Does The Aphid Honeydew Cause?

Honeydew, especially from aphids, is both a symptom and a direct threat.

This sticky substance will begin dripping down once aphid infestations become severe, leaving sticky residue on walkways, walls, and windows.

It can attract pollinators, who use it to make honey, but will also become exposed to any pesticides present and put local bee colonies at potential risk.

A wide number of pests are attracted by the honeydew, which signals that the plant is an easy meal.

Honeydew also attracts ants, who protect and harvest aphids as cattle, taking the honeydew back to their colony.

A direct result of honeydew production is the damage done to the host plant. The aphids severely weaken the plant, which can no longer absorb light as efficiently due to the loss of chlorophyll.

Even worse, the honeydew is a perfect breeding ground for sooty mold.

Finally, aphids can transmit a range of plant-based diseases, which infect the weakened plants through the lesions an aphid creates while feeding.

How To Control Aphid Honeydew?

Taking care of honeydew is a two-step process. First, you must get rid of the pest creating it, and then ensure there are no traces of honeydew left on your plants.

Preparation

Isolate the affected plant or plants, and always sterilize any tools before, during, and after the treatment to prevent cross-contamination.

Carefully prune off the most damaged leaves and put them in a sealable plastic bag for safe disposal. It’s important to prune only what’s necessary, as the plant may already be severely weakened.

(In the event you’re treating a large outdoor plant, isolation may not be possible, so you will have to also treat any nearby plants.

Eliminate Any Ants

As mentioned, ants not only harvest aphid honeydew, they’ll actively protect their aphid populations.

This is especially problematic for outdoor infestations, as it can limit the number of natural options for controlling the aphids themselves.

Set ant traps or deterrents around the base of the host plants.

Diatomaceous earth works extremely well without harming your family or pets.

Natural Options

Without ants to protect them, outdoor aphids become easy prey for natural predators such as blue tits, lacewings, ladybugs, and wasps.

While this won’t necessarily eliminate an aphid infestation, it can help bring it under control, especially when the infected plants are trees.

Smaller or indoor plants can be thoroughly cleaned with insecticidal soap or neem oil to kill the aphids and is especially effective if repeated every other day for about ten days or until there’s no remaining sign of the aphids or their eggs.

Chemical Options

Broad-spectrum insecticides specifically marked to kill aphids are a good option when the natural route doesn’t cut it.

Avoid using any pesticide containing carbaryl, which has been known to speed up reproduction in some pests.

A pesticide containing acephate or chlorpyrifos will prove much more successful, as it affects the aphids’ nervous systems.

However, the best option, especially for trees, is to use a systemic pesticide.

These are pesticides that are absorbed by the plant and travel through its circulatory system, much like antibodies or vaccines do in humans. 

What makes this option best is the fact that it won’t harm the plant or any beneficial insects.

Instead, aphids and other sap-sucking insects will unknowingly ingest the pesticide, killing them.

Cleaning Up

Once the aphids are gone, it’s time to give your plant a gentle bath with a soft cloth or paper towel.

Be sure to wipe away any traces of honeydew and clean the entire surface of the plant.

For trees and large shrubs, you will only be able to reach part of the plant, but a good hose-down will help until the next rain comes.

You can remove the final traces by scrubbing down your car, sidewalk, or anything else that was coated in honeydew.

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