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Convention attendees warned of Dickeya on potato seed

By DOROTHY NOBLE
AFP Correspondent

HERSHEY, Pa. (March 21, 2017) — The pathogen Dickeya dianthicola has accounted for blackleg symptoms and severe stand losses of potatoes in numerous states during the past three years.
Extension professor and Extension potato specialist Dr. Steve Johnson of the University of Maine discussed this emerging pathogen at the recent Mid-Atlantic Fruit and Vegetable Convention.
Johnson said, “Without flushing infected seed lots, the disease will become an increasing problem to both potato seed growers and buyers.”
Winter grow-out test data of potato seed lots in recent years show an increase of non-emerged plants. Nonemergence is a symptom of Dickeya infection.
Johnson says that the disease has probably been in the Maine seed system at low levels for over five years.
Further, it may have been present, but its symptoms were attributed to unfavorable weather.
Excessive water and warm conditions favor the spread of this disease.
Johnson outlined the best management practices developed by Drs. Meg McGrath of Cornell and Andy Wyenandt of Rutgers.
Drs. Kate Everts, University of Maryland; Beth Gugino, Penn State; Nate Kleczewski, University of Delaware and Johnson assisted with these recommendations.
An abbreviated description follows:
Select certified seed with negligible contamination potential. Numerous BMPs include investigating past occurrences and their management.
Advice includes talking with the grower and carefully studying certificates. Select seed from farms where the pathogen has not been detected, has tested negative and zero tolerance has been implemented, also where zero blackleg has been reported.
Avoid seed from fields with symptoms even if rogued.
Avoid seed if certificate is unavailable. Request a copy of the certificate, and check the certificate to determine if seed has been increased where Dickeya has been detected.
Also, request PCR testing from an independent lab.
Sample and retest for Dickeya each truckload brought to your farm, and report the findings to your state department of agriculture or potato growers association.
During seed piece cutting disinfest all equipment at least daily and between each lot numbers.
Inspect fields regularly, examining for unevenness, and submit any suspect sample to your local extension office.
Avoid excess irrigation—the pathogen can move in standing water.
While rotation is recommended for most pathogen management, it is not as important for Dickeya because it does not readily spread in fields. Infected tubers are likely to rot in the soil.
Do not apply copper or other fungicide — they are ineffective.
Because the Dickeya pathogen is inside the stems, these treatments cannot reach it.
Although continued development in storage for Dickeya has not been observed, no recommendations are suggested for tablestock potato harvest. However, the experts note that it is prudent to keep storages and pile temperatures cool, plus reduce condensation and encourage airflow and exchange.
Growers are requested to share information about Dickeya occurrence or absence to improve understanding of this disease. The variety, lot number (North American Seed Certificate), field location, and testing results need to be included.