Specialty geraniums are becoming more and more popular and with the increased interest in gardening more and more greenhouses are involved in the production of this diverse group of geraniums. Specialty geraniums include geraniums with variegated or uniquely - shaped foliage, a-typical flower shapes and sizes, and a wide variety of scented geraniums. There are scented geraniums that smell like anything from chocolate to lemon.
In growing many of these specialty geraniums the grower needs to be aware of the possibility that these products can be a source of the plant pathogenic bacterium, Xanthomonas campestris pv. pelargonii (Xcp) in the greenhouse. Recently Xcp has been identified in some of the specialty geraniums associated with a special promotional program conducted by a national retailer. The problem was brought to my attention when a grower I was working with had a severe out-break of Xcp in seed geraniums. In working with the grower and trying to identify the original source of the pathogen it became evident that the bacterium had entered the greenhouse on the specialty geranium material associated with this promotion. In particular, one specific type / variety of scented geranium continually tested positive for the presence of Xcp in laboratory tests conducted at The Ohio State University.
In the process of testing these plants it was noticed that very, very few of the infected plants showed any of the classic symptoms associated with Bacterial Blight of Geranium that we normally see in zonal and seed geraniums infected with Xcp. As a matter-of-fact other than a few plants with some yellow leaves the infected plants looked "healthy." There was no leaf spotting and no wilting yet the plants tested very strongly for the presence of the bacterium in leaf and stem tissue. Other geranium varieties associated with this promotion also tested positive for the bacterium, however, they were not as consistent as was this particular scented geranium.
If you are a grower involved in this promotion it is important that you keep these specialty geraniums away from your other geranium material, in particular seed geraniums. Seed geraniums react to the disease more strongly than zonals and can be overcome by the bacteria very quickly. It is also very important that the workers that are handling the specialty material are not allowed to handle the regular geraniums. The scented material is very sticky and the residue that is left on the hands is probably loaded with bacteria, thus allowing Xcp to be spread to other material. If workers must handle other geraniums it is imperative that they wash their hands with warm soapy water prior to contact with other geraniums.
If there is any question about the geranium material you are growing, do not hesitate to have it tested. This disease continues to be a major source of economic loss, and with the introduction of these new geranium products we must continue to be extremely cautious about what we bring into our production facility and likewise how to handle it once we have it in the greenhouse.
