The USDA announced yesterday that a single cultivar of geranium in a Michigan greenhouse has tested positive for the bacterial pathogen Ralstonia solanacearum Race 3 Biovar 2 (RSr3b2). This particular strain of Ralstonia solanacearum causes a serious wilt disease in geraniums, and can also infect solanaceous vegetable plants such as eggplant, peppers, tomato, and potato. The full text of the announcement may be found here:
Symptoms of RSr3b2 on geranium are very similar to those caused by Xanthomonas pelargonii. The main difference is that Ralstonia will cause wilting along with leaf yellowing and necrosis, whereas Xanthomonas can cause small round leaf spots as well as wilt. Ralstonia is spread primarily within diseased cuttings. The pathogen can be transmitted from root system to root system by water movement, so any ‘bottom watering’ method such as recirculating sub-irrigation systems can facilitate spread. Ralstonia is soil-borne and is not expected to be spread by overhead irrigation unless there is puddling around pot bases. The time between infection and symptom development is temperature dependent; for example, at 81°F days and 68°F nights it takes 13 days for symptoms to appear, while at 75°F days and 64°F nights it takes 23 days.
Monitor geraniums and solanaceous vegetable starts carefully for symptoms. If you are concerned that you have symptomatic plants in your greenhouse, do not move them, as movement facilitates the spread of the bacterium to uninfected plants. If you are in Massachusetts or Connecticut, contact the office of the State Plant Health Director at 203-741-5644. Growers in other states should contact their respective State Plant Health Regulatory Official (SPRO).
For additional information, refer to our RSr3b2 fact sheet at https://ag.umass.edu/greenhouse-floriculture/fact-sheets/southern-bacterial-wilt
General tips for preventing spread of bacterial diseases:
- Isolate new shipments of geraniums from other crops.
- Keep batches from different propagators separate from each other.
- Keep cultivars separate from each other.
- Keep seedlings, perennial geraniums and zonals separate from each other.
- Do not grow ivy baskets over seed or zonal geraniums.
- If possible, do not keep vegetable transplants in the same greenhouse as ornamentals.
- Work in blocks to prevent spread.
- Wash hands or wear and change gloves often.
- Angela Madeiras, Extension Educator and Diagnostician, UMass Extension Plant Diagnostic Lab