Honeydew

Honeydew sounds delightful, doesn’t it? To some, its sugary sweetness is like manna from heaven. To a gardener, honeydew sets the stage for countless fungal diseases and pest infestations.

​Honeydew is aphid poop.

Aphid excreting honeydew (Amada44) CC BY 4.0

What is honeydew?​

When aphids feed, they do so by sucking sap from plants. Sap has a lot of sugar in it and the sap within a plant is under pressure. When an aphid pushes its sharp mouthparts into a plant, the sap is actually pushed into the insect! The pressure is so intense (from an aphid’s point of view) that the sap is often pushed all the way through the insect’s body and falls onto the plant. This is honeydew. Eugenia psyllid, whiteflies, treehoppers, leafhoppers, mealy bugs, and some scale insects also produce honeydew. If you notice a trail of ants leading to a soft scale or armored scale infestation, it’s all about the honeydew.

Honeydew as food

Ants love honeydew. They love honeydew so much that they actually farm aphids! Ants herd sap-sucking insects to keep them close to ant nurseries, They will protect aphids from ladybugs, lacewings, and other beneficial predators. Ants even milk sap-suckers for their high energy poop by stroking their bellies! Some bees and wasps collect honeydew and use it to make a strong, dark honey called honeydew honey.

Ant control

This would all be fine except that many of the insects who create honeydew are also vectors for diseases, such as huanglongbing, or citrus greening. As ants feed on the honeydew, they also spread disease. Any honeydew that is left on plant surfaces uneaten provides the perfect habitat for fungal diseases, such as sooty mold. Since ants are the problem in this cycle, using sticky barriers to block their way is the easiest solution.