P&PDL Picture of the Week for
January 18, 2010

Southern Wilt in Mandevilla

Gail Ruhl, Sr. Plant Disease Diagnostician, Dept of Botany & Plant Pathology, Purdue University

Mandevilla is a flowering vine grown in Indiana greenhouses for use in containers and hanging baskets. This plant can be troubled by several insect pests as well as several fungal leaf spots. Growers should also be aware that it is susceptible to Ralstonia solancearum, the bacterial pathogen that causes southern wilt.

Ralstonia solancearum is divided into several different races and biovars. A biovar 3 strain of R. solancearum can infect and cause disease of Mandevilla. Please note that the biovar 3 strain, which causes disease on Mandevilla, is distinct from the strain classified as a select agent (race 3, biovar 2). The strict regulatory guidelines associated with the presence of race 3 biovar 2 DO NOT apply to biovar 3.

Infected plants may remain symptomless for a period of time, especially during cooler environmental conditions, however all infected plants will eventually die from this systemic bacterial disease. Symptoms of R. solanacearum infection on Mandevilla include yellowing and browning of the lower leaves, leaf drop, wilting, and eventual plant death. Management relies on good sanitation practices that include removal and destruction of pots with infected plant material. In pots with multiple plants avoid removing an infected plant and replacing it with a "healthy" plant. Even though the remaining plants in the pot may appear healthy the bacteria is still in the soil and will eventually infect through injuries in root systems and cause more plant death.

Symptomatic plants should be tested for R. solanacearum. Testing can be done at a diagnostic lab or in the greenhouse with commercially available ImmunoStrip tests. Identification of the specific biovar requires more involved laboratory testing. Please contact the Purdue Plant and Pest Diagnostic Laboratory if you desire additional information on biovar testing.

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Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service