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
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
Dr. Plant Index