March 2013
An Ounce of Prevention: Seed treatments can be a cure for healthy yields By Dave Wilkins, Spudman correspondent

A little prevention could go a long way when preparing your potato seed for planting this spring.

It’s already common practice to coat cut seed pieces with bark dust to speed the healing process. Growers should consider a product that also contains some type of fungicide to ward off diseases such as late blight, fusarium dry rot and rhizoctonia.

We recommend that growers who use bark dust use one that has a mancozeb-based dust mixed in with it,” said Jeff Miller, plant pathologist at Miler Research in Rupert, Idaho.

Mancozeb is an old but reliable broad-spectrum fungicide. It provides good protection against seedborne potato late blight and fusarium dry rot.

“The mancozeb component has been a really good component for dry rot control,” Miller said. “Fusarium dry rot is becoming more of a problem. I think some of the new varieties that are being grown are more susceptible to it.”

Fusarium-infected seed pieces are likely to decay, leaving the grower with a poor stand.
Miller has seen that on several occasions when investigating growers’ complaints about dry rot problems. In nearly all such cases, he has found that the seed was treated only with bark.

“Dry rot takes an integrated management approach. There is a lot that needs to be done with that, but using a mancozeb-based seed treatment is an important part of it,” he said.

Mancozeb, which is available only in a dust formulation, is relatively inexpensive by itself, Miller said. Products with added active ingredients may cost substantially more, but offer extra protection. He often recommends Maxim MZ by Syngenta or Moncoat MZ by Gowan. Maxim contains fludioxonil and Moncoat contains flutalonil, and both products provide protection against rhizoctonia.
In-furrow rhizoctonia treatments are available, but are not recommended if inspection reports indicate that high levels of the disease are present in the seed.

“If growers know they have a rhizoctonia problem in a seed lot, then going with the seed treatment makes more sense, even though it costs more money,” Miller said. “The seed treatment is going to be more effective than an in-furrow spray.”

Most of the disease-fighting material applied as seed piece treatments today are primarily targeting two diseases: fusarium dry rot and rhizoctonia.
Growers shouldn’t ignore the threat of potato late blight when planning their seed piece treatments this spring, said Phil Nolte, seed potato specialist with the University of Idaho.

The plant disease blamed for the Great Potato Famine in nineteenth-century Ireland has not been banished. Outbreaks still occur occasionally across North America.

A major outbreak hit the Midwest and Eastern part of the U.S. a couple years ago. It was eventually traced back to tomato transplants distributed by big box retailers.

Seed piece treatments may not necessarily help in a situation like that, but commercial growers need to exercise caution if they farm in an area that includes seed production, especially if they had late blight the year before, Nolte said.

“Even if you haven’t seen late blight in your seed potatoes, some kind of a treatment in that situation would probably not be a bad idea,” he said.

If late blight is present in a seed lot, even at low levels, the pathogen is very likely to be spread during the seed cutting operation. The freshly cut tuber surfaces are vulnerable to infection.

“Seed piece treatments are there to protect those wounds for a period of time … so that the normal process of wound healing can create a new effective barrier,” Nolte said.

Not surprisingly, potato seed piece treatment has become routine. Fifteen to 20 years ago there were still a few growers in Idaho who just “cut and planted,” Nolte recalled.

“That’s a risky practice,” he said.

Commercial growers can easily spend $200 or more per acre on seed potatoes, so spending another $1 or so per hundredweight on a good seed piece treatment to prevent disease only makes sense.

“I don’t know of very many people who are planting without a seed treatment these days,” Nolte said.

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