It doesn’t just matter what happens in the fields, disease management in potato storage is just as important for a successful potato crop.

When it comes to producing top notch spuds, it’s not just about what you do in the field, the storage season is just as critical. Potato diseases can attack your spuds while they’re sitting in storage and there are things you can do to protect them.

“The most important thing you can do is avoid injuries and damage at harvest time. Because those pathogens need injury to enter the tuber,” Gary Secor, a professor in the plant pathology department at North Dakota State University, said during a presentation at the Alberta Potato Conference and Tradeshow in November 2022.

Gary Secor
Gary Secor, a professor in the plant pathology department at North Dakota State University

Handling during harvest and into storage is paramount when it comes to disease prevention, Secor said. A lot of storage diseases are caused because the potatoes were injured during harvest.

“It needs to be vine killed for maturity so you get a good skin set, so you don’t end up with a sticky stolon and pulling it off during harvest, that makes an injury that soft rot bacteria can enter or Fusarium,” he explained.

All potatoes have soft rot bacteria in the lenticles, and when you damage the potato skin, the bacteria will multiple and infect the spud causing disease. One of the best management practices is to avoid wetness and blocking oxygen on potatoes as the bacterium can survive without oxygen.

“(Soft rot is) more important as a secondary disease following other diseases. So, it follows late blight, pink rot, ring rot, dry rot, pinkeye — those make the injury that allow the soft rot to enter,” Secor explained. He added it can cause meltdown in a potato storage.

Fusarium dry rot on the other hand survives in soil and seed and can cause problems in both the field and storage. In the field it causes seed decay, wilting of plants and it’s a component of the early dying complex of verticillium, nematodes, and black dot. In stored potatoes it causes dry rot.

“It’s the most serious disease of potatoes when they’re stored for a long time. So, it develops slowly, the longer they’re in storage the worse it gets,” Secor said. He added it may be hard to diagnose as its symptoms are internal, but it is easy to culture and diagnose if a test is taken.

Another disease to watch for is leak, which causes the water to leak out of your spuds. Leak is a soil borne disease that’s present in almost all agricultural soils, but a wound must be present on the tuber for it to get infected, Secor said.

“Leak doesn’t occur in the field; it only occurs after harvest. And it only occurs in tuber pulp temperature above 20 degrees Celsius. So, one of your best friends to carry in the field at harvest time is a pulp thermometer,” he explained. Adding that you should stop harvesting potatoes if the pulp temperature reaches 18 C.

To reduce risk of leak you can reduce damage at harvest and don’t harvest if the pulp temperature is too high, Secor said.

Keeping Seed Potatoes Disease Free

Potato disease reduction isn’t just about what you as a grower do, it’s also about the seed that you plant. For seed growers, they need to watch out for some of the same storage diseases.

“Your buyer customers wants good seed and if you sell them good seed, they’ll come back year after year after year — that’s important,” Secor said. He added that if you sell bad seed then you’re going to get blamed every time something goes wrong in the field.

Good seed is important to get a full stand establishment. When you have a poor stand it leads to things like pink eye, heat runners, and verticillium, Secor added.

“Best management practices should be followed whether you use cut seed or whether you don’t cut seed, whether you use a seed treatment, or you don’t use a seed treatment,” he said.

The seed you sell needs to be physiologically young to middle aged, disease free and meet certification requirements. The trucks and handling equipment need to be sanitized before the seed touches them, and the seed needs to be stored cold.

If seed is pre-cut, store the seed under high humidity at 90 per cent or more, temperatures of 10 to 12 C and makes sure there’s lots of air, Secor cautioned. He added that these are the same conditions you should store seed in if you are healing wounds. For cut seed you also want to make sure your storage piles aren’t too high. If the seed is too wet from harvest or a mancozeb-based seed treatment was used, then you should watch for bacterial seed decay.

Seed treatments can help with management of Pectobacterium diseases as they manage Fusarium which can be an entry spot for the soft rot bacterium, Secor said. Liquid seed treatments should be applied at ultra-low volumes and then allowed to dry. Best management practices for soft rot are to keep your seed dry as they can’t survive without water, don’t plant in wet soils, and avoid seed with Fusarium dry rot.

Seed treatments should be used for management of rhizoctonia, silver scurf, Fusarium, or late blight. These diseases are seed borne and seed treatments are part of an integrated management plan for management, Secor added.

Options for non-seed treatments include using a bark seed dressing to manage the cutting juice, dry the seed, and favour wound healing. Secor explained bark seed dressings don’t have a fungicide in them as they’re an organic matter which allows good flowing of the seed.

Header photo — A pile of potatoes in storage. Photo: Terence Hochstein

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