Infested Southern Hackberries (Celtis laevigata) in a Suburban Park

The Southern Hackberry (Celtis laevigata) is a common tree in the Piedmont of North Carolina, often occurring along rivers and streams, and in suburban parks.  In one large park near Falls Lake, and in the surrounding forests nearby, many Southern Hackberries are visibly discolored and ragged looking, as if someone had tossed a bucket of soot or ash over the foliage of the tree.  The two trees pictured below illustrate this appearance.

Celtis laevigata
Southern Hackberry
Tree With Sooty Mold

Celtis laevigata
Southern Hackberry
Tree with Sooty Mold

Closer examination of the foliage shows most of the leaves covered with a sooty mold.

Celtis laevigata
Southern Hackberry
Leaves with Sooty Mold

Examination of the undersides of the leaves reveals an extensive infestation of Hackberry Wooly Aphids (Shivaphis celti), an Asian species that may have been brought to the U.S. by the importation of Chinese Hackberries (Celtis sinensis).  The Hackberry Wooly Aphid secretes lavish amounts of honeydew, so much that the leaves and twigs become coated with the sticky substance.  The honeydew acts as a perfect substrate for the fungus – usually called sooty mold –  which covers the leaves.  The fungus does not kill the tree, but does cause some leaf drop.  The honeydew, which is rich in carbohydrates, attracts ants ,which do not harm the aphids but instead benefit them by protecting against predators.

Celtis laevigata
Southern Hackberry
Hackberry Wooly Aphid

Celtis laevigata
Southern Hackberry
Hackberry Wooly Aphid

The photos below provide several more views of the leaves covered with sooty mold.  Also seen are orange lady beetles that are present in small numbers on the affected trees.

Celtis laevigata
Southern Hackberry
Sooty Leaves with Lady Beetle

Celtis laevigata
Southern Hackberry
Sooty Leaves with Lady Beetle

The lady beetles are the Asian Multicolored Lady Beetle (Harmonia axyridis), a major predator of the wooly aphids.  They are badly outnumbered on the affected trees and have very little impact on the course of the infestation.  It is ironic that this prey and predator relationship that began in Asia continues in a similar setting on a distant continent where both species were introduced (the aphids by accident; the lady beetles both intentionally and accidentally).

Celtis laevigata
Southern Hackberry
Asian Multicolored Lady Beetle

The Southern Hackberries are also parasitized by Leaf Petiole Galls, caused by the Hackberry Petiole Gall Maker (Pachypsylla venusta).  Petiole is the botanical term for the leaf stalk.  These galls are very common on hackberries and do not kill the trees, even when present in large numbers, as they often are.  Several examples are pictured below.

Celtis laevigata
Southern Hackberry
Hackberry Leaf Petiole Gall

Celtis laevigata
Southern Hackberry
Hackberry Leaf Petiole Galls

There are also small numbers of fruits on the trees.  They can be distinguished from the galls by their smooth, symmetrical surface, reddish tint, and  their position at the end of a stalk.   The galls are always located between a leaf and a twig and are never at the end of a stalk.

Celtis laevigata
Southern Hackberry
Fruit

The leaves on these hackberries, and those in the surrounding forests, are quite variable.  Some have few to no serrations while others are serrated on each margin.  Weakley’s Flora (May 2015) now recognizes the hackberries that have significant serrated leaf margins as Celtis smallii, and it is possible that these trees and others at Falls Lake may fall into that category.

Herb Amyx

 

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2 Responses to Infested Southern Hackberries (Celtis laevigata) in a Suburban Park

  1. Guy MEILLEUR says:

    Great documentation of the ecology around the tree! Not sure the gall-maker (wasp?) is a parasite if the host is not damaged–maybe a mutualist?
    There is beauty in the ugliness. Important to avoid judging the tree ecosystem by the sooty mold.

  2. Thanks for your interest and your comments. The Hackberry Petiole Gall Maker is a psyllid which resembles a tiny cicada. Psyllids are small insects, often called jumping plant lice, that feed on plants. In mutualism, both parties are benefited. So even though the trees and leaves are not substantially harmed, it is unlikely that the tree benefits from the galls.

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