Storage temperature can determine tuber health
April 13, 2010 By Myron Love
You can’t make a bad potato good.
You can’t make a bad potato good.
|Duane Preston, professor emeritus and retired University of Minnesota Extension potato educator, provided advice to growers on potato storage during Manitoba’s Potato Production Days.
(Photo by Myron Love)
That was the key message Duane Preston, professor emeritus and retired University of Minnesota Extension potato educator, has for potato growers wrestling with storage issues.
“The goal is to keep good potatoes from going bad in storage,” he said.
He recent spoke about hot versus cold potato storage to growers during the annual Manitoba Potato Production Days held in late January at the Keystone Centre in Brandon, Man.
When storage temperatures are too hot – over 18 Celsius (or 65 Fahrenheit) – the main problem is pythium leak, Preston said. Pythium usually shows up in storage. The lesions can be brown, black or grey. It enters the tuber at harvest through wounds and rots the centre of the tuber. A clear fluid leaks from the affected tuber.
“Pythium leak was a problem in the Red River Valley last year,” Preston reported.
Pink rot is often found in the field before harvest, he noted. The tissues of the tuber turn a salmon colour when the potato is cut and exposed to the air. The potatoes infected with pink rot break down in storage and cause problems.
Preston noted that Ridomil used to be great at suppressing pink rot but is losing its efficacy.
Late blight and powdery scab often first show up in the field. The diseases thrive in wet field conditions and Preston recommends that growers shut down their watering early, if possible.
Late blight, he said, shows up as a reddish-brown colouring, with the tuber tissues becoming granular. The potato rots on the outside first.
Fusarium dry rot – which also shows up as Fusarium sambucinum in its wet phase – also enters the tuber through wounds.
Later in the season, chilling and freezing leads to wet conditions in the field. If the tuber isn’t dried out properly, bacterial soft rot can set in and cause the tuber to decay.
Bacterial soft rot thrives in hot temperatures in storage, Preston said. Infected areas of the potato turn cream to tan in colour and may have black borders. The infected areas are odourless at first but develop a strong smell as decay accelerates.
Preston suggests that for pre-harvest management of potato diseases, growers should try to go easy on watering – especially late in the season. They need to keep track of the chemical maturity of the tubers in terms of sugar and glucose levels to help determine storage conditions, and spray early, often and accurately. Workers should try to avoid as much as possible wounding or bruising the tubers during harvest and, once harvested, growers should try to keep all the potatoes below 18 Celsius.
“Rapid cooling can move air and dry out potatoes,” he said.
Preston explained that temperature fluctuations can create problems in storage. For example, piling cold potatoes on warm tubers will create condensation. That can be avoided by cooling the top of the pile overnight.
Growers also need to have a balanced air flow in the storage with consistent temperature, humidity and condensation, he noted.
“This year, start your humidifiers early in the season,” Preston recommended. “And apply air flow continuously to avoid the formation of free moisture.”
If growers see problems in the tubers in the first few weeks of storage, Preston suggested they reduce the temperature as rapidly as possible.
“Soft rot is very active when it’s warm,” he said. “Most organisms are inactive in temperatures below 50 degrees (10 Celsius). But very cold temperatures can result in processing problems. Glucose levels are higher in colder temperatures.”
The temperature levels the tubers are stored at can determine a producer’s bottom line financially, Preston pointed out. That’s because different temperatures affect the quality of the tubers.
“Storage can perform only as well as your design will allow,” he said. “Airflow should be between 25 and 40 CPM per ton. The more air that moves through the potato pile properly, the better off you are.
“A proper potato storage unit is a home, not a hospital,” Preston added.
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