Getting a potato crop this far this season has been no mean feat. Flooding wiped out several crops, while blight did for a few more. And those crops requiring storage are far from being out of the woods yet. The heavy mid-summer rain is likely to cause problems in stores for a large number of growers all across the country, Jeff Peters of the British Potato Council’s Sutton Bridge Experimental Unit says.
“Broadly there are three main issues for growers – rotting, physiological problems caused by water logging and internal defects.” The key to improving the chances of successfully storing potatoes will be making sure crops dry as soon as possible, Dr Peters says. But before crops are even harvested growers should be preparing. “Inspect samples now to get a clear idea of crop quality,” he advises. “Look out for tuber blight, blackleg, blown lenticels and growth cracks.”
To accurately assess rot risk put 300 tubers in a hot box at 20C for up to a week to see if breakdown occurs. “Remember the critical level for rots is as little as 1-2%. If you’ve got over 2% you have to question whether to store at all.” Use the pre-screening to help prioritise storage. “The best crops destined for long term storage should go in first.”
When harvesting don’t forget to minimise damage – it lets in disease, he adds. Crops should be graded before storage where possible but avoid smearing wet rot over unaffected tubers. “If there is any smearing make sure you hose down the grader and completely dry it before doing the next batch.”
But the key for storage will be to make sure crops are dried as soon as possible once in store. Positive ventilation, where air is passed through the crop, will be more effective than passive systems where air passes around the boxes. “The latter is a perfectly adequate system provided there are not any short circuits but it will take longer.”
Stored crops should then be cooled – aim for a curing temperature of around 10-12C for 14 days to ensure wound healing. Temperature pull-down will need to be done slowly where potatoes are still being loaded into stores to avoid condensation. Store temperatures should be monitored daily for the first four to six weeks and at least twice weekly thereafter for variations in temperature and for conditions that might allow condensation to form. “Soft rot bacteria lies dormant in lenticels when dry, but will exploit moisture to cause breakdowns.”
Any hot spots will spread if nothing is done about them, he warns. “Action, such as removing boxes or the crop, will need to be taken immediately in that case.”