Testing for Blackleg and Dickeya in the 2017 Field Season

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By Bryan Swingle and Keith Perry

A destructive form of blackleg disease was reported across the United States in 2015 and 2016, with Long Island and other production areas in the Northeast particularly hard hit. The disease is associated with seed piece decay, uneven and non-emergence, tuber soft rot, yellowing and wilting of plants, and a conspicuous basal stem rot moving upward from affected tubers.

Blackleg disease is managed through a combination of planting clean seed stocks and adherence to sanitation practices. This approach to managing blackleg associated with the pathogen Pectobacterium sp. has proven effective for decades, but a newly emerging pathogen, Dickeya sp., has caused the significant losses seen in the past two growing seasons. There are no commercial potato varieties resistant to the pathogens. Losses occurred in fields planted with certified seed. Addressing this problem is requiring a revision of potato seed certification standards.

Information is key to finding solutions; a Cornell and USDA research team is requesting help from growers by submitted samples. A leading priority is to understand the prevalence of each of the pathogens Dickeya and Pectobacterium, and to determine the level of variability among strains. Are we dealing with one new pathogen or several? Are our diagnostic assays adequate for detecting all isolates? These are the questions we are trying to address.

Samples can be submitted for diagnostics. We will confirm the disease and can determine if Dickeya is present. If you have plants suspected to have blackleg disease, contacts are Bryan Swingle (bryan.swingle@cornell.edu; 607-255-7894) and Keith Perry (klp3@cornell.edu); email is preferred. Growers can also contact the Plant Disease Diagnostic Clinic (http://plantclinic.cornell.edu/; kls13@cornell.edu or slj2@cornell.edu; 607-255-7850). In addition to your contact information, we would like to know the name of the variety, the appearance of the field from where the sample was taken, the county location, and comments on field or environmental conditions.

The sampling and packaging is important. Pull the plant out of the ground and if sizeable, cut off the upper foliage and stems well above any visible stem discoloration or rot. Send us the base of the plant with stems and roots attached. Select plants that have a limited amount of disease; do not send severely diseased plants with extensive rot that will liquefy during shipping. Packaging in paper is preferred; plants in plastic bags will rot with warmer temperatures. Deliver to the Cornell or Geneva campus, or ship overnight. Contact us if you wish to defer the costs of shipping.

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