Friday, February 1, 2008

Greenhouse - Leafy Gall

The following is an article about a leaf gall being found in annual and perennial plants from the University of Maryland.

A sample of a verbena plant was received in the University of Maryland Plant Diagnostic Lab this week showing abnormal clusters of small shoots and leaves near the crown of the plant. These symptoms are typical of the disease called bacterial fasciation, or leafy gall, caused by the plant pathogenic bacterium Rhodococcus fascians. While this disease has been around for many decades, until recently it was found primarily on geraniums. Recently, the disease has been reported on a number of herbaceous perennials. Symptoms are often compared to those of crown gall, caused by another bacterial pathogen, Agrobacterium tumefaciens. Unlike the crown gall pathogen, which induces galls of undifferentiated callus tissue, R. fascians causes proliferation of green tissue that is recognizable as small stems or leaves. Much needs to be learned about how this pathogen is spread, and how it causes these unusual symptoms. It appears that the bacterium may remain in plants for several weeks or months before symptoms develop, making control difficult. At present, sanitation (removal of symptomatic plants and those plants immediately adjacent to those with leafy gall) is the only management recommendation available. Since similar symptoms may be caused by mites and other arthropod pests, it is a good idea to have plants with leafy gall symptoms checked out by a diagnostic laboratory. Please feel free to contact me at 301-405-1611 ( if you think you may have this disease – we’d like to know how prevalent it is in perennials in our area. Melodie Putnam, plant pathologist at Oregon State University, has been working with Rhodococcus for several years, and more information on the disease can be found at her website

Adapted from the article "Leafy Gall in Verbena" by Karen Rane in the January 25, 2008 edition of the Greenhouse TPM/IPM Weekly Report from University of Maryland Cooperative Extension.

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