Andy Wyenandt

Potato seed tubers harboring Dickeya dianthicola are the only confirmed source of this pathogen. It does not appear to be able to survive in soil (including in crop debris) from one growing season to the next. Consequently, rotating with a non-susceptible crop is not a necessary component of the management program. Best management practices listed below are encouraged to minimize potential losses from Dickeya.

1. Select certified seed with negligible potential to be contaminated with Dickeya. This is best determined by talking with the seed grower about past occurrence on the farm and what is being done to manage it. There are growers who have not had Dickeya develop from their seed.
   • Select seed from farms where the pathogen has not been detected and seed marketed in previous years was not associated with Dickeya developing where the seed was planted. Check Certificates before purchase to determine if the seed was increased in previous years on a farm where Dickeya has been detected and so is at risk for being contaminated.
   • Select seed from farms where zero tolerance is being implemented.
   • Select seed with zero blackleg levels reported on the North American Seed Potato Health Certificates or the Winter Grow Out Test results for presence of Dickeya in ANY seed lot from ANY source. Seed lots with field readings of blackleg present should have reports that suspect plant samples were taken for testing and found to be Dickeya free. Check Certificates before purchase and require a copy be provided for your records.
   • Select seed that tested negative for Dickeya. Note that not detecting a pathogen in a sample of seed does not mean the pathogen is not present in the seed lot.
   • Ask for ‘references’ to contact: potato growers who purchased their seed in 2016.
   • Avoid seed lots that tested positive for Dickeya in previous years.
   • Avoid seed if its Certificate is unavailable. All certified seed has a Certificate.
   • Avoid seed from fields where symptoms of Dickeya were observed, even if affected plants were rogued out.
2. Request from supplier (directly from grower or broker) PCR testing for Dickeya dianthicola using an independent laboratory.
3. It is recommended that each truckload brought to a farm operation be sampled and re-tested for Dickeya once delivered. All results should be reported to your State Dept. of Agriculture or Potato Growers Association.
4. All equipment during seed piece cutting should be disinfected on a regular basis (at least daily), and also between lot numbers.
5. While it is recommended to rotate where potatoes are grown to manage most pathogens that can survive in unharvested tubers, this practice is not considered important for Dickeya because this pathogen does not readily spread in fields (thus a few tubers with Dickeya will not result in significant disease outbreak as can occur with late blight) and infected tubers are likely to rot while in soil.
6. Inspect fields for symptoms regularly, starting when skips and affected plants are readily visible. Examine the crop for unevenness (erratic growth) and plants that are unthrifty. Dickeya can be present in a plant affecting growth but not causing its typical blackleg symptom.
7. Avoid excess irrigation that results in standing water as Dickeya can move in this water. Note that surface irrigation water is not considered to be a possible source of Dickeya.
8. Do not apply copper or other fungicide for Dickeya. They are ineffective being unable to reach the pathogen, which is inside stems.
9. Growers are encouraged to submit suspect samples for testing promptly to their local extension office.
10. All growers are requested to share information about Dickeya occurrence and absence in their production fields. This information is needed to improve understanding about this disease. Include variety, lot number (North American Seed Certificate), field location, and testing results.
11. Dickeya has not been observed to continue developing in storage, which is as expected considering high temperatures are favorable, thus there are no management steps to implement after harvest for table-stock potatoes. However, it is prudent to make sure storages and pile temperatures remain cool, also reduce condensation and encourage airflow and exchange.

Prepared by Meg McGrath and Andy Wyenandt with assistance from Steve Johnson, Kate Everts, Beth Gugino, and Nate Kleczewski.

As the potato season is winding down in New Jersey (and other states in the mid-Atlantic region), it is time to begin thinking about sourcing seed for next season. Below is a list of best management practices to help reduce the chances for Dickeya dianthicola in your potato operation.

1. All potato growers are strongly encouraged NOT to purchase those varieties (with lot numbers) which are known to have Dickeya from any source.
2. All potato growers are strongly encouraged not to purchase seed from those growers/brokers with a known history of Dickeya.
3. Potato growers SHOULD NOT rely on Blackleg tolerance levels reported on the North American Seed Health Certificates or the Florida Test results for presence of Dickeya in ANY seed lot from ANY source.
4. Ask the grower/supplier if the field of seed origin was rogued for “Blackleg”.
5. Any grower which rejects a load of seed for suspect Dickeya should report information to your local Extension Agent, Extension Specialist, or Potato Growers Assoc.
6. Request PCR testing for Dickeya dianthicola from supplier (directly from grower/or broker) using an independent lab. Reject any load if no Dickeya test results are available or those seed lots that have tested + for Dickeya.
7. Growers are encouraged that each truckload brought to the farm operation be sampled and re-tested for Dickeya once delivered. All results should be reported to your local Extension Agent, Extension Specialist, and/or Potato Growers Assoc.
8. All growers are encouraged to report every variety, lot number (North American Seed Cert), field (general) location, and testing results each spring so Dickeya can be tracked and that this information be publically available to all potato growers in and out of the state.
9. Fields with a known history of Dickeya should not be planted back into potato for at least 3 years or longer. Avoid planting brassicas and onions in potato rotations, especially in fields with a history of Dickeya.
10. Growers using surface water (pond or stream) should be encouraged to do monthly water testing for Dickeya, especially if water source is near field with known Dickeya infestation.
11. Wash/dump water needs to be displaced in an area away from packing shed, particularly those sheds near any production field or source of ground water that may be used for irrigation.
12. Culled fruit needs to be dumped away from any production field, source of ground water, or any area where contamination of equipment may occur.
13. All potato growers with fields with Dickeya-suspect symptoms need to be sampled and tested during the growing season.
14. Rogue or volunteer plants appearing in fields with known Dickeya infestation the previous year or any prior year need to be removed, and/or sampled and tested if “Blackleg” symptoms present.
15. All equipment during seed piece cutting needs to be disinfested on a regular (daily) basis, and/or disinfested between lot numbers and/or varieties. Quaternary ammonium is a good option for this purpose.

Remember, after doing your due diligence if you as a customer are not satisfied with the seed or information regarding the seed you should seek another source. Dickeya dianthicola has been reported in 16 states (DE, FL, MD, MA, NJ, NY, NC, PA, RI, VA, WV, OH, IN, MO, MI, and TX) on at least nine potato varieties to date in 2016. These varieties include: ‘Reba’, ‘Superior’, ‘Vivaldi’, ‘Norwis’, ‘Snowden’, ‘Yukon Gold’, ‘Beacon Chipper’, ‘Kennebec’, and ‘Atlantic’. Tuber and water test results are still forthcoming. Known sources of infested seed have originated from New Brunswick, Canada and Maine in our state and region this summer. In some cases, multiple varieties of Dickeya-infested seed have originated from the same source. Potato growers, crop consultants, and Extension personnel in states which grow and are still harvesting should remain vigilant by scouting their fields for Dickeya symptoms, particularly those varieties which have tested positive for Dickeya, on a regular basis and by submitting any suspect samples for diagnostic testing.

Dickeya dianthicola has been detected in the US in the past, and because of this, APHIS just recently announced that the pathogen has been designated as a non-reportable/non-actionable pathogen despite its potential to cause 100% crop loss. Thus, any seed originating from Canada or other regions in the US should be carefully vetted. A link to the USDA/APHIS website for information on Dickeya dianthicola detection and control can be found here. Importantly, there is no current policy in place designed specifically for regulating and/or controlling Dickeya dianthicola in potato in the US or Canada.

The best method for keeping your potato operation Dickeya-free is to adopt your own 0% Dickeya-tolerance policy.