No one is playing pranks and putting plastic shrink-wrap around trees, although it may look like it in one Kansas county.
For the first time in years, webbing, which has been described by some as looking a bit like pantyhose, has been reported in Shawnee County, according to Bob Bauernfeind, horticultural entomologist with Kansas State University Research and Extension.
The web formation is caused by larvae of the Gretchena consitatricana, commonly, but unofficially named the black walnut shoot moth or the walnut trunk webbing moth. Outbreaks of the insect are sporadic, and little is known about its seasonal life history, Bauernfeind said. The strange webbing encases the trunk and large branches of walnut trees. It is thick and in sunlight gives the encased trees a shimmery, ghostly appearance.
"Intense webbing appears to be associated with large established trees growing in woodland areas," he said. "These trees would be capable of supporting the tremendous population of larvae."
Webbing is the after-the-fact artifact of extreme larval populations, the entomologist said. It's formed as mature larvae travel down to the ground, where they seek shelter in the soil to pupate.
The "shrink-wrapped" effect was first reported on trees in Kansas in the early 1990s. In 1991-94 the phenomenon was spotted at Fort Riley in Geary County. In 1993-94 such trees were also reported in Miami County.
In 1995, however, the webbing disappeared and had not been reported until recently from the site in Shawnee County.
It seems this moth is specific to black walnut trees, which are used in lumber production, Bauernfeind said. Except for substantial leaf loss, trees are not damaged.
"However, larvae feeding can distort growth of walnut seedlings and saplings. This is considered a major handicap for the eventual production of straight logs," said Bauernfeind. "In these instances, just a few larvae are cause for concern."
Bauernfeind asks that anyone who sees walnut trees with "shrink-wrapped"-looking tree trunks contact him at rbauernf@oznet.ksu.edu.
