CARBERRY, Man. – A hundred potatoes, each sliced in half, line the table in front of Phil Northover.
All the potatoes show some sign of soft rot. They had been healthy less than a week earlier.
Northover, a plant pathologist with Manitoba Agriculture, wanted to demonstrate the importance of sterilizing equipment used by growers when cutting seed potatoes before planting in the spring. He had cut through only one potato infected with soft rot and that was enough to infect the other 100 potatoes that were cut immediately afterward.
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To alleviate the risk of infection when planting potatoes, growers should, at the very least, disinfect their seed cutting equipment between seed lots, Northover said. He suggested using a disinfectant of diluted ammonia solution.
“It’s literally as common as dirt,” said Northover, describing the prevalence of the bacteria, Erwinia carotovora, which can cause soft rot in potatoes. And he noted that it is only one of several bacteria that growers need to guard against.
The discussion was part of the potato diagnostic school held at the Manitoba Crop Diversification Centre near Carberry Aug. 13-14, which was supported by Manitoba Agriculture, the crop diversification centre, Agriculture Canada and the University of Manitoba.
Soft rot flared up on a handful of potato farms in Manitoba this year, mainly in the southwest part of the province. Some fields were lost to the rot, but the problem did not become widespread. However, Manitoba Agriculture potato specialist Bill Moon said some producers were concerned that it could.
Erwinia soft rot likes warm, moist conditions. Planting cold potatoes into warmer soil can be a contributor, since that can cause moisture to condense onto the skins of the tubers, Northover said.
Seed potatoes left in a pile can also be attractive for the bacteria if there is moisture in the pile and a scarcity of oxygen, which is another condition conducive to soft rot.
Moons said this year’s outbreaks could not be linked to specific seed lots. There were different fields planted from the same seed lots, and not all of them encountered problems.
Other preventative measures suggested by Northover include sterilizing storage areas before bringing in new seed lots.
And he said growers and workers should wash their boots between visits to different potato fields. The bacteria can be transferred in the mud on boots, even after the mud has dried.
He recommended making sure custom pesticide applicators clean their tires between fields.
Yellowing or wilting plants that are more easily stressed by heat are among the symptoms of soft rot. However, Northover said they could also be signs of other problems, so a more thorough investigation is advisable.
Soft rot can cause an unpleasant odour in potatoes in storage and the tubers can degenerate into a rancid pool of slime.
