Hackberry Aphid
Please see the Pest Notes section of the recent Bohart Museum newsletter (below). It sounds like the Hackberry aphid it describes is the one causing the sticky car mess in our neighborhood. It says that the stickiness is water soluble and can be cleaned off with a strong blast of water. It also describes how to control the aphid population. Maybe this information is adequate to address the aphid topic in the neighborhood.

Robin Kozloff -- Oct 25, 2003

Asian Woolly Hackberry Aphid

The Asian Woolly Hackberry Aphid, Shivaphis celti Das, first appeared in the northern Central Valley last fall. The insect is a pest, not because of the damage it does to trees, but because it secretes copious amounts of a sticky honeydew that drips onto whatever is beneath them. This insect is recognizable by a fuzzy, bluish-white wax that covers the body. It is found on the underside of the leaves of hackberry (Celtis occidentalis, also called sugarberry), a commonly planted tree in the Central Valley because of its ability to withstand heat, drought, wind, and alkaline soils. This aphid is not a pest on other plants.

The Woolly Hackberry Aphid was first discovered in Florida in 1997, and has since spread rapidly across the south and into California. The aphid itself is quite small (2-2.5 mm long) but often appears larger because of the fuzzy wax covering. The antennae have a banded appearance, and the veins of the wings (when present) are slightly darkened.

Like many aphid species, summer adults are all female and parthenogenic (able to produce more females asexually). Summer adults may be winged or wingless. In the autumn, winged males and wingless sexual females may be found, which will mate to produce an overwintering egg. This egg stage allows the aphids to survive the winter when there are no leaves on the trees.

The sugary honeydew produced by the aphids often encourages the growth of a black mold. Everything under infested hackberry trees, such as cars, picnic tables, houses, and plants, may get a gooey coating of moldy honeydew. Luckily, because the honeydew is water soluble, a strong spray of water may be enough to rinse away the sticky substance. Spraying smaller trees with an insecticidal soap may serve double duty, by reducing the aphid population and cleaning the sticky surfaces. However, this control measure may have little effect on large infestations (involving many trees) or on a population on a large tree for which it is difficult to spray every leaf. Natural enemies (such as ladybugs and lacewings) may be most effective at reducing the aphid populations in the long run.

Bohart Museum Society Newsletter
Spring 2003

We have three hackberry trees and Don Schorr of Redwood Barn diagnosed the etiology. He recommended a Bayer product called "Advanced Garden Tree & Shrub Insect Control" that is nearly organic. It is applied to the base of the plant and worked very well.

Craig Blomberg -- Nov 24, 2003

I spoke with Don Shor of Redwood Barn (on 5th between L and Pole Line) today who confirmed that the aphids, while a nuisance due to their sticky secretions, do not weaken or stress the Hackberry trees. Below is what he recommends. More information on this can be found on the Redwood Barn website under the Pest Notes section.

The good news is that beneficial insects (natural aphid predators), especially lacewings and ladybugs, have been observed establishing populations on infested trees, so some level of control may occur naturally. It would be a good idea for folks to learn to recognize lacewing eggs and the larva and pupa stages of ladybugs.

In terms of human intervention, systemic insecticides are the most likely effective control measure. This involves drilling small holes in the tree and injecting the pesticide into them.

Robin Kozloff -- Dec 7, 2003

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