Icky, sticky, gooey stuff...
Did you experience a clear sticky substance or black mold on your deck, lawn furniture or car last summer? If you did, you may be experienc-ing the symptoms of the Asian woolly hackberry aphid, Shivaphis celti. Middle Tennessee hackberry trees experienced severe infestations during the summers of 2003 through 2006. The aphids mysteriously vanished during the summers of 2006 and 2007 and reappeared again in 2008.
Hackberry, Celtis occidentalis and sugarberry, Celtis laevigata are the host plants for this aphid. The aphids are small, about 2—2.5 millimeters long and are conspicuous due to the large amount of bluish white wax secretion from their abdomen. See Photo. The adults are winged and give the appearance of small pieces of cotton on the undersides of leaves.
Overwintering eggs hatch into females that, without fertilization, give birth to living females. The ability of females to reproduce without mating is termed parthenogensis. This ability allows young to be brought forth throughout the summer, accounting for rapid increases in population. The largest populations usually occur in late July or early August in our area. In late fall, males and females are born. After mating, the female deposits overwintering eggs, and the cycle contin-ues the following year.
During severe infestation the aphids excrete large amounts of honeydew, which coats the lower leaves and drips onto objects below the tree. The honeydew attracts ants, bees and other insects and serves as a medium for the growth of sooty mold fungus. In most cases little injury occurs to the trees; however, staining of wood, painted surfaces or fabric may occur from prolonged exposure to sooty mold.
If you are experiencing staining of decks, lawn furniture or other valuable items, you may want to consider treatment for this pest.
Prevention can be obtained by soil treatment in April or May with a systemic insecticide, such as imidicloprid. Reduction of populations can be obtained by spraying small trees with a contact insecticide or microinjection of larger trees in July through September.