Honeydew is a sticky, sugary substance found coating the leaves of trees and the surfaces beneath them, such as patios and cars. This residue is not tree sap, but rather the waste product excreted by certain insects that feed on the tree’s internal liquids. Its presence is a clear symptom of a sap-sucking pest infestation actively feeding on your tree. Effective treatment requires a two-pronged approach: immediate cleaning of the mess and eliminating the insect population that produces it. This involves identifying the pests, removing the residue, and implementing targeted pest management.
Identifying the Source of Honeydew
The sticky coating indicates that sap-sucking insects are active, and identifying the specific pest is the first step toward control. These insects feed on the tree’s phloem, excreting excess sugar-water as honeydew. The three most common culprits are aphids, scale insects, and mealybugs.
Aphids are small, pear-shaped insects that often congregate in dense clusters on new growth or the undersides of leaves. Scale insects are less mobile, appearing as small, waxy or shell-like bumps on the bark or leaves; some species are “armored” while others are “soft.” Mealybugs are recognized by their white, cottony coverings and tend to hide in crevices or leaf axils.
A thorough visual inspection of the tree, focusing on hidden areas like the undersides of leaves and branch junctions, will confirm the presence of these pests. Observing the insect’s appearance is important because the most effective treatment method often depends on the pest’s physical characteristics.
Immediate Cleaning and Removal Methods
Addressing the sticky honeydew is necessary to protect the tree and surrounding areas. The sugary residue on foliage blocks sunlight, inhibiting photosynthesis. Cleaning the tree and affected property immediately mitigates these negative effects.
For the tree’s foliage, a strong jet of water from a garden hose can physically dislodge the honeydew and many soft-bodied insects. Directing the stream toward the upper and lower surfaces of the leaves is important. The pressure should be moderated to avoid damaging delicate plant tissue, and this manual rinsing should be performed every few days to prevent accumulation.
To clean stubborn layers of honeydew, apply a mild solution of water and gentle dish soap to the foliage and hard surfaces. Mix two teaspoons of liquid dish soap per gallon of water and spray the affected areas. Allow the solution to sit for a few hours before thoroughly rinsing with clean water. This soap solution breaks down the sticky sugars, making them easier to wash away from leaves and property.
Eliminating the Pest Infestation
Removing the existing honeydew is only a temporary fix; stopping its production requires a focus on eliminating the underlying pest population. The most sustainable and most effective methods involve non-chemical controls that preserve the tree’s ecosystem.
Non-Chemical Control
A non-chemical strategy is the introduction of natural predators, such as lady beetles, lacewings, or parasitic wasps, which feed on aphids and soft scale insects. These beneficial insects provide ongoing biological control and should be encouraged by avoiding broad-spectrum pesticides. Pruning heavily infested branches or leaves can also immediately reduce the pest population in localized areas.
Horticultural oils and insecticidal soaps are low-toxicity options that work through direct contact with the insects. Horticultural oils smother pests by blocking their respiratory openings and are effective against armored scales by penetrating their waxy covers. Insecticidal soaps disrupt the cell membranes of soft-bodied insects like aphids and mealybugs.
Complete coverage is essential for both oils and soaps, as they have no residual effect once dry and only kill insects they directly contact. Managing ant populations is also beneficial, as ants often protect honeydew-producing pests to secure a food source. Applying a sticky barrier product around the base of the tree prevents ants from climbing to the infestation.
Targeted Chemical Control
When non-chemical methods fail to control a severe or widespread infestation, targeted chemical intervention may be needed. Systemic treatments involve applying an insecticide to the soil or trunk, which the tree absorbs and distributes throughout its vascular system. This method is often used for scale insects on large trees where thorough spray coverage is impractical.
Systemic insecticides are effective against sap-sucking pests because the insects ingest the chemical directly while feeding on the tree’s sap. These products must be applied strictly according to label instructions to minimize impact on pollinators and the environment. For complex or recurring infestations, consulting a certified arborist ensures proper pest identification and treatment selection.
Addressing Sooty Mold
The final consequence of a honeydew problem is the development of sooty mold, a fungus that grows exclusively on the sugary waste product. Sooty mold appears as a black, powdery layer on leaves, branches, and surfaces where honeydew drips. Although the mold does not directly infect the tree tissue, a heavy coating shades the leaves, reducing the light needed for photosynthesis.
The solution to sooty mold requires eliminating the honeydew source by successfully controlling the insect infestation. Once the pests are gone and honeydew production stops, the sooty mold is starved. It will eventually dry up and naturally flake off the leaves over time.
To speed up removal, the same mild soap and water solution used for honeydew can be applied to wash the mold off the leaves. This cleaning restores the tree’s ability to photosynthesize more quickly. Regular monitoring for the pests that cause honeydew is the best preventative measure against recurrence.