What is honeydew?
Honeydew is a sticky sap found on plants. It is not produced by the plant itself, but is left behind by various plant pests. These pests suck the sugary plant sap and excrete the excess. Honeydew is therefore the excretion of aphids, scale insects, or other sap-sucking insects. If you discover honeydew on your plant, it is a clear indication that it is infested with such pests.
Appearance and characteristics
Honeydew is clear and transparent like dew, yet thick and sticky like honey. Over time, it can form a glossy, almost lacquer-like coating on the leaves. If it remains for an extended period, dust and dirt particles accumulate in it, making the plant appear dull. Furthermore, honeydew provides an ideal breeding ground for sooty mold fungi, which colonize the surface, eventually leading to the formation of a black layer on the leaves.
How does honeydew form?
Honeydew is excreted by insects that feed on plant sap. Since plant sap is rich in sugar but low in protein, these insects must consume large quantities of sap to meet their protein needs. However, they cannot fully utilize the excess sugar. This excess sugar is excreted as honeydew, which then remains on the leaves.
Is honeydew harmful to the plant?
Honeydew itself is not directly harmful to the plant. However, its effects can cause significant problems. Firstly, the sticky layer that accumulates on leaves and shoots impairs photosynthesis . The leaves become coated, absorb less light, and the plant appears weakened overall. Secondly, honeydew is always a clear sign of pests. These pests constantly extract sap from the plant, causing it to lose valuable nutrients and water, which weakens its growth and makes it more susceptible to disease.
If your plant is outdoors, the sugary sap can also attract other insects, especially ants. They use the honeydew as a food source and therefore stay close to the pests. This allows the pests to remain undisturbed for longer and reproduce more rapidly, further exacerbating the infestation.
Here's how you can combat honeydew
Honeydew cannot be directly controlled. It's important to combat the pests that cause it and thoroughly clean the plant at the same time. If you discover honeydew on your plant, proceed as follows:
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Identify pests : Specifically search for aphids , scale insects , or whiteflies that excrete honeydew.
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Separate the plant : Place the affected plant away from others to prevent the spread.
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Wash the plant : Rinse the leaves with lukewarm water to remove honeydew and any initial pests.
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Use plant protection products : In case of severe infestation, use suitable products such as potassium soap, neem or rapeseed oil preparations.
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Use beneficial insects : Support natural pest control through beneficial insects such as lacewings or parasitic wasps.
To prevent honeydew from forming in the first place, you should keep your plants strong and healthy. Ensure sufficient light and air, water the plants evenly without waterlogging , clean the leaves regularly, avoid over-fertilizing, and inspect new plants before adding them. This will keep your plants more resilient and make it harder for pests to thrive.
