Dickeya: A New Potato Disease

Dickeya: A New Potato Disease

Dickeya early symptoms for web

These potato plants are showing early symptoms of Dickeya. Photo credit: Margaret McGrath

Known as Dickeya blackleg because symptoms are similar to blackleg, or just Dickeya, this disease is causing trouble for potato growers in the Northeast and particularly seed producers in Maine. An aggressive pathogen, the bacterium Dickeya dianthicola thrives in hot temperatures, which many areas in the Northeast are currently experiencing.

Margaret Tuttle McGrath, a plant pathologist at Cornell University, says the greatest losses last year occurred in the Mid-Atlantic region and farther south.

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She adds that some growers lost entire fields in 2015. The disease has been documented in potato fields this year, too.

What To Look For

The symptoms growers need to be wary of begin with poor emergence resulting in scattered blank spots in the fields. Contaminated plants that are able to emerge typically wilt and have black stems.

“Because the bacterium thrives in heat, as the temperature increases, we will see more plants dropping out,” she adds.

Wetness may also be an issue as rainwater may help move the pathogen adjacent plants. She adds, however, that any movement wouldn’t be far.

Initial stem symptoms for web

This stem shows initial symptoms of Dickeya, a new potato disease. Photo credit: Margaret McGrath

The problem, McGrath says, is the Dickeya pathogen is in the seed, making management in a production field difficult.

Unfortunately, McGrath says fungicides cannot fight this bacterium and there are no resistant varieties available. One thing researchers do know is the bacterium isn’t known to live in the soil for long periods.

“From what we know, it doesn’t survive in the soil for long enough to be an issue for the next potato crop in a field, except in unharvested infested tubers,” she explains. “This is good news for growers but it puts more of the onus for management on the seed producer.”

Monitor Field Conditions

McGrath encourages growers to monitor what is happening in their potato fields and pay attention to which varieties are affected.

Using potato seed that is free of Dickeya is the best management practice, she says. The problem with this practice, however, is symptoms often don’t develop in cool temperatures, which are typical in seed-producing areas.

Is there a test available to determine the presence of Dickeya on seed? McGrath says not yet, and infected seed can appear healthy, further complicating the issue.

What about Disease Tolerance?

In addition, she says an agreement has not been reached regarding tolerance for the pathogen in seed.

“There are differing opinions about whether there should be no tolerance for Dickeya, similar to bacterial ring rot, in certified potato seed, or whether a low percentage of contaminated seed can be tolerated as is the case with other diseases such as late blight,” McGrath says. “A major difference is that there are resistant varieties and effective fungicides for managing late blight.”

Stay tuned to GrowingProduce.com for additional details on Dickeya.

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Amanda Coombs says:

We are a potato grower in NJ and were devastated by this disease last year. We lost 70 acres of our 200 acre potato crop. We believe we have been receiving “bad” seed for a few years now and our losses were repeatedly attributed to our wet, humid weather. The seed we received looked fine coming and was certified by the state of Maine so we never suspected the seed was the problem. It wasn’t until last year that we received the official diagnosis of dickeya and unfortunately we were not alone. This disease ABSOLUTELY needs a zero tolerance policy. Maine’s seed certification rules..even the updated version…are not going to cut it. They are not requiring anyone in Maine to test their seed lots for dickeya (even the ones they know had issues for growers such as myself). And even if the seed grower did test their lot and get a positive result, they don’t have to report it to anyone and they can continue to ship that “bad” seed to other growers. Farming is hard enough without being doomed from the start with dickeya infested seed. Maine seed growers and all potato seed growers need to be testing their seeds lots for dickeya and not passing the disease on to their buyers….or they won’t have buyers for long. As a side note, when I was looking for guidance on how to handle the loss of last year, I was told repeatedly that we should have had crop insurance….fair enough….however, I learned this year that dickeya is not covered by crop insurance. So, you can’t see the disease in the seed, you can’t spray anything for it and you can’t get insurance to protect yourself in case you receive a bad load. The ONLY option is to require more stringent seed testing and that needs to happen now…not next year year..not slowly. Put the zero tolerance policy in place now. I understand testing costs money and there would be a financial impact to the seed growers, but if they don’t do something and do it soon, they aren’t going to have customers left to ship their seed too.

Kris says:

I’m a tablestock grower in eastern PA for 20 years. I believe this disease has been with us longer than we think at least since 2012. I agree that a zero tolerance is an absolute necessity. We’ve had losses that cut yields in half, no one seems to care. Soon no one will buy Maine seed. We have purchased most of our seed out of canada with no issues yet.

John notdgaard says:

Yes, Dickeya is a very serious disease. I have confirmed losses for 3 years along the Eastern seaboard and the pathogen is deeply ingrained in the seed system. I fully support zero tolerance in FY1 and FY2 seed.

Nate says:

All you have to do is require a dormant tuber test for dickeya as part of your seed purchase agreement. I believe all seed producing areas are able to provide this, or at least send a sample to an approved lab.