This fall might be a tough one for a few Manitoba potato growers battling rots like pink eye, bud-end decay, late blight and leak in storage. Generally, these diseases are present in storages but the levels are not abnormally high, so a caution is warranted.
According to Vikram Bisht, Manitoba’s provincial plant pathologist, leak and late blight infected tubers have already been found in some Manitoba storages. “There was a late season incidence of late blight disease, probably following September 4 to 6 thunderstorms and rainfalls,” he says. “Foliar late blight symptoms appeared soon after the rains and were first reported from Carberry, around September 8 and 9.”
Neil Gudmestad, a distinguished professor of plant pathology at North Dakota State University, says growers in North Dakota, Minnesota and Manitoba will also face issues with pink eye and leak in storage this fall due to late-season rains.
Storage infections are always a risk for potatoes because they damage relatively easily, he says. “Potatoes are much different than cereal or true seed crops because what you put into storage is a fairly fleshy thing. It bruises very easily and the bruises made during harvest are infection courts for pathogens.”
Gudmestad emphasizes pink eye as a disease to watch. Though specific causes of the disease are still unknown, it is fairly easy to identify severely infected potatoes by pink to brown blotches of pigment under the tuber skin. In recent years, growers in potato growing regions have seen an uptick in pink eye incidence — particularly in years with excess moisture prior to harvest.
Late season rains increase soil water saturation and, as a result, soil microorganism activity. “Potatoes are a living breathing entity, and when you have soil saturation you end up with a film of moisture around the tuber,” says Gudmestad.
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In storage, the potato tubers continue to respire and that process builds up carbon dioxide. “When you have a film of moisture around the tubers, that’s like putting a plastic bag over a human’s head — the carbon dioxide builds up and the tubers suffocate,” says Gudmestad.
Excess moisture is a double threat, as it also helps deliver bacteria to damaged tubers — infection that often does not appear until potatoes are in storage, and liable to infect other potatoes.
“We have a lot of pink eye and bud end decay this year in the North Dakota region. I’m talking 1.5 per cent. That might not seem like a lot, but if you are losing five bags an acre at the current prices, that’s a $40 to $45 per acre loss or more. It isn’t a bank breaker, but as those tubers are being harvested, a couple of things happen — tubers are wounded and smear on other tubers, and you get secondary infection after you put them in the bin,” says Gudmestad.
Pink rot and leak are hard to distinguish, he says. Tubers that are severely infected with leak will literally leak clear liquid when squeezed.
Fortunately for growers, there are a variety of wet and dry potato rots to watch for in storage, management strategies are similar for all rots.
Good cultural practices that start at the very beginning of the season are integral to mitigating the risk of rots in storage, says Gudmestad. Managing moisture availability is an important component of these practices. “We depend on the water moving through the soil profile,” he says. “So really good pre-plant tills is really important to make sure there aren’t areas where the water gets trapped.”
Growers who use irrigation systems should ensure fields are properly watered prior to harvest, he says. “Carry adequate soil on the primary and the digger to reduce bruising,” he says. “Make sure the soil is pre-watered and the tubers aren’t dehydrated because dehydrated tubers will bruise more, which causes infection.”
Bisht says growers should harvest low-lying areas last, particularly if excess moisture is visible in these areas.
Gudmestad says a warm harvest also presents risks for growers. If possible, warm tubers— with tuber pulp above 18 C —should not be put in storage, as it increases infection efficiency.
For non-seed potatoes, Bisht and Gudmestad both recommend applying a phosphorous acid treatment as tubers are going into storage, which helps control late blight and pink rot.
Once tubers are stored, the most important rot management strategy is bringing in fresh air and good ventilation. “If higher than normal rot is expected in storage, running lots of air through the potatoes helps desiccate the rotting tubers, which helps reduce leakiness in storage,” says Bisht.
“After suberization, it is important to bring down the storage temperature to as low as the possible for the grade of potatoes. Seed potato storage temperature can be brought down to close to 36 F (2 to 3 C), while the processing potato storage could be brought down to around 47F (8 to 9 C) for long-term storage. For higher levels of rots, it is best to get the potatoes processed as soon as possible. For temporary storage potatoes, with high priority for processing, do not go below 53 F (12 C), else the fry colour will be unacceptable,” he says.
Bisht says airflow is crucial to minimizing storage rot losses. “Storage ceilings have to be kept dry with circulation fans,” he says. Condensation dripping onto potatoes from ceilings provides moisture that promotes bacterial rot in the piles. Constant monitoring of storages is recommended.