Honeydew is a sticky substance secreted by many insects that feed on plant sap. No matter what you see (or do not see), if the substance on your plants is indeed honeydew, it is quite certain that you are dealing with some sort of pest infestation.
If your plants are clearly covered in honeydew but you cannot see any bugs, then there is a good chance that they have been targeted by scale insects, i.e., incredibly small insects that are practically invisible to the human eye.
The only other possible explanation is that the substance you are seeing is not actually honeydew but the result of guttation – a process by which plants exude water and minerals. In this article, I explain all you need to know about honeydew and the nearly invisible vicious bugs that secrete it.
What Causes Honeydew on Plants?
Honeydew on plants is caused by sap-feeding bugs. Honeydew is a sticky and clear substance that many species of sap-feeding bugs leave behind.
The most common sap-feeding bugs that do this are aphids and scale insects. Plant sap is a fluid that contains plenty of sugar but very little protein.
Being bugs that are primarily interested in protein, they need to ingest a considerable amount of plant sap to get all the protein they require – which ultimately causes them to ingest more sugar than they need.
The excess sugar that they ingest ultimately ends up as honeydew when the bugs excrete it.
How Does Honeydew Affect Plants?
Now that you know what honeydew is, let’s discuss how it affects plants.
First of all, if you see honeydew on a plant, it is an unquestionable sign that it is infested. So, should you be afraid of honeydew? The answer is yes and no.
Honeydew is neither toxic nor harmful, at least not in the way that you may think.
There are three key ways in which honeydew affects plants:
- By disrupting the photosynthetic process
- By attracting insects, notably ants
- By creating a breeding ground for fungal infestations
Out of the various fungi that feed on honeydew, sooty mold fungi are probably the most common ones. Sooty mold fungi get their nourishment by breaking down honeydew and are often found on elm, pine, and linden trees – all of which are vulnerable to pest infestations.
As sooty mold colonies expand, they cover every infested part with a thick black substance that prevents the plants from absorbing any sunlight. This ultimately causes their leaves to turn yellow and die – hence the importance of acting quickly.
What It Means If There Is Honeydew But No Bugs
As previously mentioned, where there is honeydew, there are usually also bugs, whether you can see them or not. If your plants are covered in a clear liquid, but you are certain that they are completely pest-free, there are three possible explanations for what you are witnessing:
- Nectar secretions
- A fungal or bacterial infection
Guttation is a process by which plants release tiny drops of xylem sap along the tips of their leaves. Xylem sap, however, is very different from honeydew as it is not sticky and is only found on the edges of a plant’s leaves. If the substance you are looking at is sticky and persistent, then you are most certainly dealing with honeydew.
Nectar secretions are also possible because many plants have special glands that secrete it. Nectar serves a very specific purpose in that it attracts ants so that they may feed on it and, in the process, protect the plant from potential predators.
Fungal or Bacterial Infection
The last possibility worth considering is a fungal or bacterial infection. If your plants are covered in a sticky substance that resembles honeydew but is not honeydew, you may want to conduct a close inspection of their leaves and stems. If you see any cuts, then it is possible that you are dealing with an infection.
That said, not all plants are prone to fungal and bacterial infections. Unless the affected plants are snake plants and/or Swiss cheese plants (monstera deliciosa), chances are fungi and bacteria have nothing to do with your problem.
Also, remember that in each of the above cases, the substance on your plants may be clear and sticky but will not look exactly like honeydew. If you are certain that your plants are covered in honeydew, pests are most certainly behind the problem.
Why You Can’t See Bugs
Honeydew is secreted by different species. If your plant has been infested by aphids or caterpillars, you would most certainly be able to see them, as both of these insects are visible to the naked eye and tend to move around quite a lot. In addition, some plants attract aphids more than others, so you can be prepared for these infestations.
Unlike aphids, scale insects can be very difficult to detect, mainly because they spend most of their lives completely immobile and look nothing like other insects. For these reasons, scale insects often go unnoticed – which may be the case with your plant.
There exist two types of scales, namely:
- Armored scales
- Soft scales
The main difference between the two lies in how they affect their hosts. Armored scale-infested plants often look dehydrated and stressed; in severe cases, plants and trees may even die.
Soft scales operate differently: when they target a plant, they reduce its vigor without actually killing it. Soft scale-infested plants are easily recognizable as they are typically covered in honeydew (like aphids, these insects produce large amounts of this substance).
To see if your plant is actually infested, carefully examine each leaf and see if you can spot any dark bumps. You may need to grab a flashlight and a magnifying glass to get a better view.
How To Deal With Honeydew
To decrease the amount of honeydew on your plants or to remove it completely, you must target the pests secreting it. This can be done using either natural or chemical remedies, depending on your preference and how advanced the problem is.
Keep in mind that most plants can tolerate small amounts of honeydew and sooty mold, so you may be able to improve your plants’ health by simply wiping their leaves with a damp cloth (for particularly sticky secretions, water and soap should do the trick).
Let’s take a look at some of the best strategies to manage honeydew:
- Get rid of the ants. Because ants feed on honeydew, they will do their best to protect the insects that produce it. If you eliminate the ants, or at least most of them, the parasites and predators will quickly take over, feeding on the honeydew-producing insects.
- Prune your plants (but do not get carried away). Carefully prune the most damaged and infested parts of your plants.
- Target the honeydew-secreting insects. Most honeydew-secreting insects are actually pretty easy to eliminate, especially if you are not dealing with a particularly large colony. Get a cotton swab, dip it in rubbing alcohol and dab it all over the affected parts. Rubbing alcohol is very effective in eradicating both scale insects and mealybugs.
- Use natural insecticides. Before switching to heavy weaponry, it is always best to consider the natural route. Natural remedies rarely solve problems in one go, so it may take several applications to disinfest your plants.
- Use insecticidal soap. There are many natural insecticides out there that can help you can rid of honeydew: pick one and apply it all over your plants’ leaves and stems. The good thing about insecticidal soap is that it kills both adult and baby insects.
- Use insecticides as your last resort. Insecticides will most certainly solve your problem as they will kill and keep away all honeydew-producing bugs. Make sure you don’t use anything overly aggressive, and always keep in mind that most plants can tolerate small aphid and scale populations, meaning that you do not necessarily have to see honeydew as an immediate threat.
Now that you have restored your plants’ health, let’s see how you can prevent honeydew-producing bugs from re-infesting your plants:
- Keep your plants well hydrated. When temperatures rise, plants are more susceptible to infestations as they are usually drier and more stressed. Increase the amount of water you give your plants to keep them pest-free.
- Do not over-fertilize your plants. Over-fertilized plants are a breeding ground for bugs, especially aphids. Higher-than-normal levels of nitrogen make it easier for aphid colonies to grow and expand, so make sure to apply fertilizer only when needed.
- Take good care of your plants. Remember that bugs tend to target distressed plants.
You are certain that the clear substance covering your plants’ leaves is honeydew, but you cannot see any bugs – how can that be? Firstly, inspect your plants closely to ascertain that what you are looking at is actually honeydew.
Secondly, get a magnifying glass and see if you can spot any dark spots.
If your plants are indeed covered in honeydew, and you cannot see any bugs, then there is a good chance that you are dealing with soft scales. Follow the tips listed in this article to solve your problem and prevent future infestations.