COVID-19, Ralstonia and Contact Tracing - Updated July 1, 2020!

Published on

An important update as of July 1, 2020: USDA APHIS "has successfully completed actions to eliminate Ralstonia solanacearum race 3 biovar 2 from U.S. greenhouses. This announcement comes just two months after the pathogen was first detected in a Michigan greenhouse in April (NAPPO PAS OPR). In total, the response involved more than 650 facilities in 44 States." Follow this link for the entire announcement:


Background on the Issue (by Beth Scheckelhoff).  In late April of this year, a plant pathogen known as Ralstonia solanacearum race 3 biovar 2 was found in a commercial greenhouse crop of geranium (Pelargonium x hortorum) Fantasia ‘Pink Flare” in Michigan. This pathogen is a bacteria that affects the xylem of plants causing wilting symptoms as seen below. Yellowing and wilting of leaves and stems on geranium alerted the Michigan grower to suspect disease.




Geranium 2

Geraniums exhibiting initial symptoms of Ralstonia solanacearum race 3 biovar 2. Images courtesy of USDA-APHIS PPQ,



Geranium plant infected by R. solanacearum R. 3, B. 2, exhibiting southern wilt symptoms. Image courtesy of:


Why is Ralstonia solanacearum such a concern? R. solanacearum is considered a select agent by USDA-APHIS, meaning it has the potential to significantly threaten public, animal or plant health. This pathogen has five different races (1-5) that together affect a wide range of plants across the world. Geraniums infected with race 3 biovar 2 in the US could transmit this pathogen to sensitive food crops including potatoes, tomatoes, peppers, and eggplant, all with devastating results.


Infection can occur through various means – including contaminated soil, irrigation water, tools, and equipment. Because there are no effective chemical or cultural means of control once plants are infected, all contaminated plant material must be quarantined and destroyed to eliminate the pathogen. Prevention is the key.


This is not the first time this pest has surfaced in US greenhouses. For those that may remember, an outbreak of race 3 biovar 2 occurred in 2004, impacting 24 states and devastating many geranium crops, affecting numerous greenhouses in Ohio.  Since that time, an off-shore certification program for propagators and advancements in tracking plant material allowed for a quick and thorough response to quarantine the pest. 



Tying it all Together (by Tom Dehaas): In response to this finding, the Horticulture Research Institute held a webinar to educate the green industry on the biology and prevention of the pathogen. As I listened to this webinar, I found similarities between how USDA APHIS and the US Health Officials response to the outbreak of Covid 19 are similar. In both cases, the eradication comes from identifying the pathogen, identifying the infected the host, and then separating through quarantine the host from other potential hosts. Obviously the difference is the infected geraniums were destroyed. But the really amazing part of this story is how Ball Horticultural and USDA APHIS were able to trace the variety of Geraniums back to its source in Guatemala and then forward to all greenhouses that had received shipments of the potentially infected geraniums.


This story and Covid 19 reminds us of how important sanitation, supply chain, and labeling/ tagging/ and isolating arriving plant material from other existing plant material is crucial. The quality control tag became the key! In addition, there are Geraniums that may be infected but may not show symptoms but are infected. Testing is the key!


Therefore, whether it is Ralstonia, Boxwood Blight, or Covid-19, sanitation, detection, and separation are key to healthy plants and healthy people.

Additional information from USDA-APHIS can be found in their Pest Alert:


pest alert 1

pest alert 2