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Minimizing Bruise Damage

Successful growers share their thoughts on best management practices in potato production.

Minimizing bruise damage is a primary concern for potato growers, not only when harvesting the crop but during handling and storage. We put the question of best management practices for preventing or reducing tuber bruising to three growers from across the country: Randy Visser of Gerrit Visser and Sons in Orwell Cove, P.E.I., Mark Keller of Elk Haven Farms in Brandon, Man., and Mike Wind of Windiana Farms in Taber, Alta. Here’s their take on the best of the BMPs for minimizing tuber bruising.

Potato bruising starts as soon as the tubers are plucked from the ground, so it’s important to monitor weather conditions closely at the start of harvest. Visser, Keller and Wind all agree you don’t want to start digging up potatoes when it’s too hot or too cold outside.

Wind says the hottest they’ll harvest is at about 20 C, and that 10 C is about the lowest temperature at which they’ll consider digging. For Visser, that figure is a little lower:  “You probably want to avoid going below 7 C at harvest time.”

Keller also stresses the importance of making sure the soil is at the right moisture level for digging. “We water our fields before we dig them up,” he says. “We want to make sure the ground is a little bit wet so the potatoes can carry dirt with them.”

Keller adds they also dig deep enough to provide sufficient dirt to help cushion the tubers during handling. “You want to make sure the digger is carrying enough dirt with the potatoes so you’re not handling them by themselves. We make sure operators carry enough dirt all the way to the top of the machine.”

Minimizing Drops

Reducing drops during the potato handling process is another key consideration. Visser says it’s critical to keep a close eye on those drops every step of the way — from harvest to storage bin.

“From the windrowers, to the harvester, to the trucks, to the receiving line, every drop is important to make sure that it’s going to minimize bruising,” explains Visser. This can be done by such means as ensuring drops “deflect the product a little bit so it’s not a hard drop” or by removing the bottoms from conveyor equipment “so the belt actually has got a bit of a spring [and] some give to it, so then there’s not a hard, dead blow,” he says.

Visser adds they’ve found that tuber bruising is also related to how many drops and turns, or transition points, there are in the production line. That’s’ because the damage that can occur in transition points is often cumulative. “Basically, the fewer [drops and turns] the better,” says Visser. “There are ways to manage this, like using one long conveyor belt to cover a distance rather than two shorter ones.”

Keller’s rule of thumb is you “never drop potatoes more than six inches at any time.” He adds it’s also important to ensure your belts are running slowly and are full at all times to minimize the jostling that can contribute to tuber bruising.

Perils of Piling On

Piling potatoes too high can be a recipe for pressure bruising, a primary source of tuber damage in storage.

“How high that you make those piles will make a difference.” says Visser. “It’s variety specific but the more you put on top, the more weight on those bottom potatoes. If you keep it down to 13 feet or less then you’re much better off, I think.”

Harvest time at Mike Wind’s farm in Taber, Alta. Wind stresses the importance of harvesting potatoes in the right weather conditions.

High Humidity

“Humidity’s important in the storage for sure. If you have it too dry in the pile then potatoes will respire and dehydrate. So you want to keep that up as high as you can,” says Visser.

“The only thing you have to be a little careful of is if you get free moisture in your piles — that will open you up to other issues like possible rots,” he says. “So you don’t want it soaking wet in there, either.

“We always say that 95 per cent humidity or plus is fine, as long as you don’t have free moisture in the pile,” says Visser. “The higher the better as far as we’re concerned.”

Visser says his operation is adding new computerized sensors to their storage ventilation systems. This enables relative humidity to be monitored more quickly and in real time.

“We can literally go on the Internet anywhere — my phone, my computer in my office or at home or whatever — and monitor those systems,” he says.

Wind says adequate humidity in the storage bin cuts down on chances of tuber rots setting in, since this helps cool the potato piles down and will also help bruised potatoes heal. “We try to keep it around 95 per cent humidity in there as potatoes come in for the healing process,” he says.

Keller agrees on the 95 per cent benchmark, and says it’s important to have the proper humidity settings from the start. “Whenever possible, you should have the right humidity right off the bat, especially for Umatilla and Russets, so that you’re are minimize bruising the first few weeks going in while they get suberized.”

Differences in Varieties

One of the challenges in bruise management is that some varieties bruise more easily than others. As an example, Wind refers to chipper round white potatoes, which he says are “definitely more susceptible” to pressure bruising than a variety like Russet Burbank.

“First of the all, with round whites you want to make sure you’re putting in a product that’s very clean. You don’t want to put any dirt in the pile because that’ll block your air off,” he says. “I guess with the whole handling procedure, you just have to be more careful.”

Visser says a sensible strategy is to manage bruise damage by focusing on your most susceptible variety.

“Some of these yellow varieties, Yukon Gold for example, can be quite a bit more sensitive to handling. Over the years we’ve grown a lot of Yukon Gold, so we’ve learned a lot about handling from that variety,” he says.

“What you want to do is take your most sensitive variety and use that as your benchmark. If you can take that one in without marking it up or bruising it… it certainly doesn’t hurt the more resilient variety to be handled gently too,” Visser explains. “You take some of your worst case scenarios, or your most susceptible varieties, and build your production around that — that’s kind of what we do.”

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