News on the Grow

Ralstonia Outbreak

Several U.S. growers can now add a new disease to their repertoire: Ralstonia solanacearum biovar 3 race 2. One of the vascular, bacterial agents that causes southern bacterial wilt, R. solanacearum biovar 3 race 2 was recently discovered in a limited number of geranium cuttings that were produced offshore, shipped to U.S. rooting stations and eventually rerouted throughout the Eastern, Southern and Midwestern United States.

Because of its inclusion in the U.S. Agricultural Bioterrorism Protection Act of 2002 as "potentially posing a severe threat to plant health or plant products," this most recent disease importation caused a reaction from Animal and Plant Health Inspection Service (APHIS) and United States Department of Agriculture (USDA) and a temporary quarantine of hundreds of greenhouses.

How it Happened

The disease originated from a minor infestation of seven confirmed 'Americana Dark Red' geranium stock plants in Goldsmith Plants' Kenyan facility. According to Goldsmith's Don Snow, less than 100 cuttings were taken from the contaminated stock plants and unintentionally introduced into the United States in a routine shipment during weeks 44-46 (October 27-November 16) to two U.S. greenhouses, Glass Corner Greenhouse in Michigan and Pleasant View Gardens in New Hampshire. Plants were rooted for five weeks and subsequently shipped to customers during weeks 49-51 (December 1-December 21).

On February 10, the USDA Plant Protection and Quarantine (PPQ) Center officially confirmed the presence of R. solanacearum biovar 3 race 2 in samples collected from greenhouses in Wisconsin, Indiana and Illinois. After the February 13 destruction of approximately 50,000 cuttings (total) at Glass Corner and Pleasant View, both operations resumed shipping cuttings that had not originated in Kenya.

On February 14, the USDA stopped all geranium shipments from Kenya to the United States until further notice. This has impacted Goldsmith, Fischer and Oglevee, which each have stock facilities in Kenya. As of press time, there have been no reported outbreaks at any of the other breeders, and this quarantine is not expected to dramatically impact the 2003 seasons.

The last date of importance is the February 27 release of the USDA/APHIS action plan. At approximately 35 pages long, the action plan gives a detailed account of how to respond to symptoms. As much of this information is of importance only to those greenhouses on the quarantine list, we will not go into the details of the Plan in this article. Those interested can find the Action Plan at any of the Web sites listed at the end of this article. You can also find a 12-page summary of the Plan at the Society of American Florists' (SAF) Web site.

Because of commingling, and possible cross contamination, during rooting and shipping to and from Glass Corner and Pleasant View, the number of greenhouses receiving suspect plants is expected to number approximately 150 but could be as many as 800. While these greenhouses are currently under quarantine, time and testing have revealed relatively few confirmed cases of R. solanacearum biovar 3 race 2.

It is important to remember that the only greenhouses that should be placed under quarantine are those that received geranium cuttings from Glass Corner between November 4, 2002 and January 24, 2003 (weeks 45-4) or from Pleasant View between November 4, 2002 and February 14, 2003 (weeks 45-7).

What Happens Next?

The nearly two-week delay between the first notice of the disease and the follow-up is due to the complexity of the situation and the agricultural security concerns. Ralstonia solanacearum biovar 3 race 2 was placed on the bioterrorism list because it is devastating to important agriculture crops such as potatoes, tomatoes, beans and tobacco, and as such, USDA/APHIS needed to take extra precaution to ensure the protection of these crops.

APHIS has worked with states and scientific authorities and gotten information from the industry (most notably Goldsmith, SAF and the two effected rooting stations) to develop a plan that will be as workable for growers as possible, yet ensure disease eradication. In the interim, the delay has led to uncertainty for both state regulators and the geranium industry.

Fearing that any introduction of Ralstonia on geranium cuttings could damage the U.S. potato industry, some have urged that all imported cuttings be banned -- a move that was introduced last year and one that would cause substantial disruption of the nearly $300 million U.S. geranium industry.

"Long term," explained SAF Senior Director of Government Relations, Lin Schmale, "we are working to get USDA to provide official recognition to the Geranium Bacterial Disease Initiative. Currently, the major breeding companies have voluntarily formed a committee for the self-regulation of clean stock facilities and virus indexing to prevent the importation of diseases such as Xanthamonos and Ralstonia."

"In the future," continued Schmale, "we think official recognition is necessary for the continued importation of cuttings to sustain the geranium market, 50 percent of which originates offshore. APHIS recognizes that the geranium industry is important so they are going to work with us to solve the problem we have right now, and they are going to continue to work with us to set up a system whereby we can ensure that geranium cuttings will continue to come into the United States."

What to Do

Though it is expected that the current outbreak will be contained by publication, growers still need to watch their crops for any geranium or nicotiana plants that show signs of disease under the warm temperatures necessary to finish a good geranium crop.

Symptoms of Ralstonia solanacearum biovar 3 race 2 are reportedly similar to those of Xanthamonas, another strain of southern bacterial wilt, and include wilting plants and abnormal yellowing of leaves. This strain of Ralstonia doesn't spread easily from plant to plant, except through recirculated irrigation water or stem-to-stem transmission via cutting knives or manual cleaning and pinching when the laborer has not sanitized between plants. R. solanacearum biovar 3 race 2 can tolerate much cooler temperatures than other strains, though it remains dormant in the cold. It can also lay dormant in soil and water indefinitely. Growers can easily avoid spreading the disease by simply removing and isolating wilted plants and avoiding subirrigation of geranium and nicotiana plants.

If you suspect you might have R. solanacearum biovar 3 race 2, contact Goldsmith Plants at (800) 549-0158, your local university extension agent or APHIS at (301) 734-3266. Other good sources of information include: APHIS headquarters, www.aphis.usda.gov/ppq; the National Plant Protection Organization's Phytosan-itary Alert Web site, www.pestalert.org; the Society of American Florists, www.safnow.org; American Nursery and Landscape Association, www.anla.org; OFA, www.ofa.org; and Purdue University, www.ppdl.purdue.edu/ppdl/hor03/02-24.html.

--Bridget White