We've written about quite a few of the insects that produce honeydew in our blog, so here is a list of the possible culprits that may be causing the mess this time of year:
Aphids
The hackberry woolly aphid is a major pest on hackberry trees. The aphid's honeydew drips all over, leaving behind a sticky mess. Read more about this pest in What's that Sticky Stuff on my Car?
Many other types of aphids suck plant juices and create honeydew on other plants. Visit the UC IPM Pest Notes: Aphids to read more about them, their host plants, damage, and management.
Asian Citrus Psyllid and other psyllids
Psyllids are another pest that produce honeydew, and there is one psyllid in particular that you may have heard about: Asian citrus psyllid (ACP). ACP is infamous for its ability to carry huanglongbing, an incurable disease that kills citrus. Learn how to check your plants for this pest, read the post Invasive Spotlight: Asian citrus psyllid and huanglongbing disease.
Leafhoppers
Read about these small, wedge-shaped pests that hop around and feeds on a variety of plants in our blog article, Leafhoppers on plants.
Mealybugs
This pest is often mistaken for cottony cushion scale, woolly aphids, and even soft scales and whiteflies. They can be found outside in the landscape, but also indoors on houseplants. Learn more about this pest by reading the post New Mealybugs Pest Note!
Scale
Scales can be difficult to identify, since sometimes they may not resemble insects. Once they reach the immobile adult stage, they look like bumps on leaves and stems. The presence of sticky honeydew and sooty mold can be a clue that something is amiss, but this does not occur with every kind of scale. Read the post Scale Insects: Recognizing and Managing for help.
Whiteflies
This tiny pest is fairly easy to identify since it is white and flies around when disturbed. You can find whiteflies on a wide range of host plants, usually living on the underside of leaves. Our post Whiteflies Resource-Newly Updated! has more information.
Ants
Along with the pest, honeydew, and sooty mold, you may also notice an abundance of ants climbing all over your plants. Ants don't produce honeydew, but they are attracted to it. There is an easy solution to this problem you can learn more in the video we discussed in the post Using a Sticky Barrier to Keep Ants Out of Trees.
- Author: Karey Windbiel-Rojas
Around this same time last year, I posted an article called "What's this sticky stuff on my car?".
Well, it's that time of year again when we see the sticky, messy drippings from many different kinds of trees that are infested with a honeydew-producing insect.
I won't repeat the information again, but we've been getting questions from the general public on the droplets and sticky messes they see on sidewalks, plant leaves, and their cars, so I figured it was worth sharing again.
The pests that make this mess will soon go away when the weather changes, but for now, read the article and learn what you can do to reduce the pest numbers and the damage they cause.
![Hackberry woolly aphids. [Credit: Jack Kelly Clark] Hackberry woolly aphids. [Credit: Jack Kelly Clark]](/blogs/blogcore/blogfiles/55422.jpg)
- Author: Karey Windbiel-Rojas
If you are like me, you try to park your car under a tree in parking lots and on the street for some shade, especially with the hot weather we've had lately. Maybe you choose to park under a big hackberry tree, but when you return to your car, you notice droplets on your windshield and sticky stuff on the sidewalk, other cars, and the parking lot. What is this?
The sticky substance is called honeydew. The honeydew is excreted by a number of sap-sucking insects such as aphids, whiteflies, mealybugs, certain scale insects, and few others. On hackberry trees (widely planted in some cities), an insect called the woolly hackberry aphid produces a large amount of honeydew which drips from the leaves onto surfaces below.
If you examine the tree's leaves, you may see bluish-white masses that are actually this insect in disguise, coated in a pale wax that makes them appear fuzzy. In addition to the mess caused by the honeydew, you may also notice a black, sooty mold growing on the leaves. Although honeydew and sooty mold can be a nuisance, no long-term or serious damage to hackberry trees has been found, even after years of aphid infestations.
To learn more about the woolly aphid, see the UC IPM Pest Notes: Hackberry Woolly Aphid. If the sticky tree you park under is your own, the Pest Notes will help you find solutions to manage the aphid population should you choose to do so.
Another pest that also attacks hackberry trees and excretes honeydew is the citricola scale. As you can see from the photo, it may be very difficult to see when inspecting your tree. To learn about this pest, read the UC IPM Pest Notes: Scales.
Other shade trees can also get different types of aphids, scales, and other honeydew-producing pests. Find information about these other plant sucking pests and their damage and management at http://ipm.ucanr.edu/PMG/invertebrates/menu.aphidsthrips.html.
![Aphids suck on plant sap and excrete honeydew. Aphids suck on plant sap and excrete honeydew.](/blogs/blogcore/blogfiles/46595.jpg)
![Hackberry woolly aphids and honeydew on leaves. Hackberry woolly aphids and honeydew on leaves.](/blogs/blogcore/blogfiles/46596.jpg)
Hackberry woolly aphids appear as fuzzy, bluish white masses on leaves and other tree parts and are about 1/10 of an inch or less in diameter. Not all the aphids have wings, but those that do have distinct black borders along the forewing veins and their antennae have alternating dark and light bands. As the aphids suck out plant juices, they excrete the sticky honeydew. Sometimes blackish sooty mold grows on the honeydew and creates a sticky mess on leaves and surfaces beneath infested trees.
Before initiating any management methods, inspect hackberry tree leaves for signs of the aphids and make sure they are the culprits of the sticky honeydew and not another insect that also attacks hackberry trees and excretes honeydew: the citricola scale.
For information about other pests and problems on hackberry trees, visit the UC IPM home and landscape web page.