Apotato storage is a home, not a hospital.”
That was the central theme of potato storage specialist Duane “Sarge” Preston’s recent presentation at Manitoba Potato Days.
Preston, a now-retired extension specialist, told growers that getting conditions right before, during and just following harvest would trump anything they could do once the crop was put up – and that any problems would make themselves quickly known.
“If you can store potatoes six weeks, you can store them six months,” Preston said. “Problems appear early.”
“You can’t make a bad potato good – you’ve got to keep a good potato from going bad in storage.”
In many cases, the answer lies in what temperature the potatoes go into storage, says Preston. Too hot or too cold, and certain storage conditions are the result.
Pythium leak is a soil-borne fungus that has at one point or another hit just about every grower in the region, usually in storage, said Preston. It infects tubers through wounds at harvest and is favoured by high pulp temperatures.
Once it’s in a storage it can move quickly and destroy the harvest.
“When it gets to this stage, you’re S-O-L,” said Preston. “That pile can go down in a hurry. I’ve seen 18-foot piles drop to eight feet in a week.”
The key to keeping it out of storage includes halting harvest if temperatures are too high, and minimizing wounds at harvest time.
Pink rot is another common storage problem and it can frequently be found in fields prior to harvest.
“You can tell it’s pink rot if the tuber has a ‘cooked’ texture,” said Preston. “If you cut the tissue it will be spongy or like a bar of soap.”
Pink rot is also a major concern for storage breakdown, though the results won’t be as pronounced as pythium leak. It also enters through skin wounds and Preston says there’s evidence that existing chemical controls aren’t as effective as they once were.
“Ridomil used to be great, but it’s wearing out,” he said. The single greatest contributor to pink rot infections is wet field conditions at harvest time, which are only partially under grower control.
“Shut the water off early and let it dry up – but in the end Mother Nature is the boss.”
Other less common but still dangerous storage issues include late blight, pure blight, fusarium dry rot, chilling and freezing late in the season and bacterial soft rot.
The best time to prevent a storage wreck is while the potatoes are still in the field, said Preston.
“Temperature is number one, followed by overwatering late in the season, then drowning out early in the season or drying out too much late in the season,” he said.
One technique that is really beginning to catch on is measuring the chemical maturity of the crop by testing sugar/glucose levels in the tubers. Less mature potatoes have higher levels of sugars and will respire more in storage.
“It’s being used more and more all the time,” Preston said. “It can really help with the sequence of your harvest.”
Vine killing is another technique that can prevent disease from entering storage. It destroys the green tissue on which most of the pathogens are surviving prior to digging and encourages skin set, which will reduce wounds that provide an entry path. It needs to be carefully managed in short growing season areas, however, to ensure yield isn’t hurt too badly.
Once all the reasonable precautions are taken, however, it boils down to temperature, once again.
“Keep tubers below 65F if possible, and if it gets too warm, stop harvesting,” said Preston.
If the temperatures are creeping up, and your storages have the technology in place, it may be possible to rapidly cool the tubers down.
“New storages have excellent ventilation capacity to move air through very quickly,” he said.
The goal is to prevent the buildup of condensation in the storage, which can provide ideal conditions for infections to grow.
“That potato is like a cold beer sitting on the counter, with water droplets on the side – you have to prevent that water from collecting,” he said.
“In storage you need to control temperature and you need to control humidity.”
Once the potatoes are in storage and are at a stable temperature, it’s a question of balancing that moisture in the bin.
“You need to wick moisture off if it’s wet and humidify if it’s dry,” said Preston. “Avoid the formation of free water, make sure your ventilation system has no plugs and if you are having problems, don’t plan on long-term storage.” [email protected]