BACTERIAL DISEASE(S) ALERT IN GERANIUM

Be on the look out for two geranium diseases caused by bacteria. It is early in the growing season and we have already detected an inordinate amount of these destructive diseases. The first disease is bacterial wilt of geranium caused by the bacterium Xanthomonas campestris pv. pelargonii (Xcp). This is the most common disease of geranium and has the potential to be the most destructive. Many cases of this disease have already been reported this seasons. In most years, reports of Xcp on geranium do not reach the levels we are seeing this year until well into the growing season. Because of this, growers should scout the greenhouse regularly and look for the symptoms associated with this disease. Usually the earliest symptom is wilting of a some portion of the affected plant. The entire plant is usually not wilted until the later stages of disease development. Also wilt may be more obvious during the heat of the day or when plants are under some sort of moisture stress. If wilt is seen, check the plant's roots for evidence of root rot. If the roots look healthy, Xcp is a strong possibility. Affected plants should be tested by a university or private testing lab immediately. If the plants test positive, immediate action should be taken to determine the source of the infected material and all plant material from that source should be considered suspect. A representative sample of suspect plants should be tested to determine the extent of the disease in the greenhouse. Since there is no cure for infected plants they should be discarded and copper-based compounds such as Phyton-27 and Kocide 101 should be applied to non-infected plants to help slow the spread of the disease.

If wilted, root rot-free plants are sent to a lab and test negative for Xcp it maybe an indication that another bacterial disease is the cause of the problem. Geraniums can also be infected by the bacterium Pseudomonas solanacearum (Ps). This bacterial-induced disease is not as common in the greenhouse as Xcp, however, it has the potential to be just as destructive. It appears it has reared its ugly head already this season. Plants infected with what appears to be Ps have been submitted to the diagnostic clinics at Ohio State and Purdue Universities. The symptoms associated with disease are very similar to those associated with Xcp and the same types of control measures should be employed if identified. Unlike Xcp, Ps can infect other greenhouse bedding plants such as Impatiens, mums, Gerbera, Zinnia, Petunia, Salvia, and Marigolds.