Sticky leaves on Plants

Symptoms

The first sign is usually a shiny, sticky coating on the leaves. This coating is honeydew, a sticky substance that aphids, whiteflies, mealybugs and scale secrete when they feed. Aphids can produce large quantities of it. Honeydew is also described as a sticky exudate.

As time passes, the sticky residue often turns black. The black color comes from a sooty mold fungus growing on the residue. A heavy covering of sooty mold reduces photosynthesis in the plant.

You may also notice ants on the plant, because ants are attracted to the honeydew and feed on it. Curled or distorted leaves can show up when aphids are the pests feeding. Aphids can curl leaves and also produce sticky honeydew.

In short, look for the sticky coating, black sooty mold and ants feeding on the honeydew. Curled or distorted leaves and reduced photosynthesis under heavy mold complete the list. Honeydew is a product of insects feeding on plant sap, so the sticky film points to pests.

Causes

Sticky leaves come from insects that feed on plant sap. The facts name four groups: aphids, whiteflies, mealybugs and scale insects. Each one secretes honeydew while it feeds, and honeydew is the sticky substance you feel on the leaves.

Aphids deserve a special mention. They can produce large quantities of honeydew, and they can also curl leaves. Curled or distorted leaves are a symptom that goes with aphid infestations.

Ants are linked to the problem as well. They are attracted to the honeydew and feed on it. They also protect honeydew-producing insects from predators.

Fertilizer can play a part. Excess nitrogen fertilizer favors aphid reproduction. Natural predators such as lady beetles and parasitic wasps are conserved when broad-spectrum insecticides are avoided.

The black sooty mold grows on that sticky residue, so it appears after the honeydew does. In short, the sticky film on a leaf is evidence of sap-feeding pests, and the pest may be any of the four named.

Diagnosis

A shiny, sticky coating on the leaves is the main sign of honeydew. Honeydew is secreted by insects while they feed on plant sap, which sets this problem apart from a general care fault.

Next, look for the signs that travel with the coating. These are black sooty mold growing on the residue, ants feeding on the honeydew, and curled or distorted leaves when aphids are present. Heavy sooty mold also reduces photosynthesis.

Then work out which insect is involved. The causes named are aphids, whiteflies, mealybugs and scale insects. Curled or distorted leaves point to aphids, since that symptom is listed with aphid infestations. Every cause named for sticky leaves is an insect feeding on plant sap, not a watering, light or soil condition.

Ants on the plant are another clue, because ants are attracted to honeydew and feed on it. If you find a honeydew producer, isolate the plant so the pest does not spread to neighboring plants.

Treatments

Handpick pests or rinse both leaf surfaces with warm water. You can also dislodge aphids and their honeydew with a strong stream of water or by shaking the plant. Prune out infested leaves and stems. Isolate affected plants so the pest does not spread to neighboring plants.

Avoid excess nitrogen fertilizer, which favors aphid reproduction. Manage ants too, including banding trunks with a sticky barrier, since ants protect honeydew-producing insects from predators. Avoid broad-spectrum insecticides so natural predators such as lady beetles and parasitic wasps are conserved. These cultural methods are listed first, ahead of the organic and chemical options.

Insecticidal soap or horticultural oil is applied as a contact spray, covering the undersides of leaves. A plant-derived oil spray, such as neem oil or canola oil, is another organic option. Insecticidal soap can also be combined with a pyrethrin formulation for added knockdown. Insecticidal soap, horticultural oil, neem oil, canola oil and pyrethrins are the organic active ingredients named.

For chemical control, the foliar sprays named are malathion, permethrin and acephate, and acephate is limited to nonfood crops. Imidacloprid is a systemic insecticide that should not be used on plants in bloom or about to bloom, to protect pollinators. Malathion, permethrin, acephate and imidacloprid are the chemical active ingredients named.

The product label is the legal instruction, and you must follow it for the crop and site being treated.

Prevention

Avoid excess nitrogen fertilizer, because it favors aphid reproduction. Keep ants in check, since ants protect honeydew-producing insects from predators. Banding trunks with a sticky barrier is one way to manage them.

Leave natural predators such as lady beetles and parasitic wasps in place by avoiding broad-spectrum insecticides. If one plant shows honeydew, isolate it from neighboring plants so the pest does not spread. Prune out infested leaves and stems when you find them.

Watch for a shiny, sticky coating, ants feeding on honeydew, or curled leaves. Aphids, whiteflies, mealybugs and scale insects are the pests behind honeydew, so these are the ones to watch for. Heavy sooty mold reduces photosynthesis, which is one more reason to deal with honeydew early.

Plants most often affected

No plant page in this build records this problem yet.