The University of Wisconsin Plant Diagnostic Disease Clinic (PDDC) reports that a Minnesota geranium (Pelargonium) supplier has been infected with Xanthomonas. A grower from central Wisconsin sent seven geranium samples of different varieties received from a Minnesotan supplier and all tested positive for this pathogen. One of the samples looked appeared to be healthy, but upon close inspection one leaf appeared water-soaked along the veins and showed up positive for Xanthomonas.
This pathogen is usually associated with contaminated, fresh or dried leaf material. It can survive on leaf surfaces at low populations and be asymptomatic until environmental conditions suddenly change, the populations suddenly increase and symptoms appear. Symptoms include leaf necrosis and yellow halos.
Overhead irrigation can promote the spread of the pathogen through water droplets. Anything touching contaminated plant debris should be disinfested with 10 percent bleach, 70 percent alcohol or ammonium-containing products. Any infected plants should be discarded and pots should not be reused.
The PDDC is able to perform a fast test for Wisconsin growers who suspect they may have Xanthomonas and results can quickly be made available.
For more information on geranium bacterial blight, click here. For more information on the PDDC, click here.