Southern wilt could be devastating to some crops. (Crops & soils).

An outbreak of Ralstonia solanacearum, Race 3 Biovar 2, the pathogen that causes southern bacterial wilt, occurred in one of Goldsmith Plants' geranium production facilities in Kenya recently. Cuttings from Kenya were only imported to two U.S. rooting stations in Michigan and New Hampshire. The geranium cultivars involved in this outbreak include Americana Dark Red, Americana Pink and Americana Violet, shipped as rooted cuttings. Unrooted cuttings of these cultivars are not known to be involved in this disease outbreak.

What is southern wilt?

Southern wilt is a usually lethal disease that affects over 250 plants in over 40 plant families. Susceptible greenhouse-grown ornamentals include, but are not limited to, plants in the genera Capsicum, Cosmos, Cyclamen, Dahlia, Fuschsia, Gerbera, Hydrangea, Impatiens, Lantana, Nasturtium and Pelargonium. Vegetables such as eggplant, pepper, potato and tomato, as well as tobacco, are also susceptible. Southern wilt has recently been detected in geraniums (Pelargonium spp.) in Wisconsin.

Symptoms of southern wilt in geraniums are similar to those associated with bacterial blight (caused by Xanthomonas campestris pv. pelargonii).

Southern wilt is caused by the bacterium Ralstonia (Pseudomonas) solanacearum. This bacterium is commonly found in tropical, sub-tropical and warm temperate climates, but is not believed to survive cold temperatures such as those typical during Wisconsin winters. Several subgroups of R. solanacearum exist, each with a different host range. The bacterium can be moved in symptomless plants or cuttings, or in contaminated soil and plant debris (where the pathogen can remain dormant for many years).

No treatments available

There are no known treatments that will save plants infected with southern wilt. To prevent spread of the pathogen, wash your hands, sterilize equipment, do not carelessly remove leaves/flowers, and observe your geraniums daily for signs of problems. If you see wilted geraniums, do not discard symptomatic plants right away. Isolate symptomatic plants and avoid handling them until a diagnosis is confirmed. Also remove and destroy weeds or weed debris as these can harbor the pathogen. Because the pathogen is easily moved with soil, minimize splashing or any other movement of water or soil from plant to plant when watering. When clipping plants, be sure to clean clippers between cuts (e.g., by dipping in a 10% bleach solution or ammonia). Similarly, disinfect greenhouse benches where infected plants have grown. In the summer, you can disinfect an empty greenhouse by closing vents, turning off air-conditioning and keeping the house at a high temperature for several days. Similarly, you can use a freezing treatment during winter months.

This pathogen is cited on USDA Agricultural Bioterrorism Act of 2002 Select Agents and Toxins List, as a serious pathogen of potatoes, tomatoes, and other solanaceous plants. However, the present introduction seems to have been an unintentional introduction of the pathogen during the routine and normal importation of geranium cuttings from Kenya by a U.S. company.

Additional information can be found on the following web sites:

* USDA/APHIS/PPQ Action Plan for Ralstonia solanacearum, Race 3, Biovar 2 found in nursery facilities (27 February 2003): http://flowers.hort.purdue.edu/ web/USDARalstonia1.pdf

* Present Ralstonia outbreak information: www.growertalks.com/ralstonia/

* Ralstonia on geraniums in Florida 2001: http://extlab1.entnem.ufl.edu/ PestAlert/tmm-0607.htm

* Ralstonia on geraniums photographs: www.state.me.us/agriculture/pi/ pseudomonas.htm

* Information on Ralstonia: www.pestalert.org/Detail. CFM?recordID=70

* Potato Diseases--Ralstonia: www.aphis.usda.gov/ppq/ispm/potato/ ralstonia/

Ed. note: Southern bacterial wilt was first encountered in the U.S. in the 1980s, so it's nothing new. It has just made a re-appearance in the past few months.