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MH is used to prevent sprouting. (Photo: Mark VanOostrum)

Growth Regulator Update

Use of the growth regulators MH (maleic hydrazide) and CIPC (chlorpropham) are integral to the potato industry, but there is always room for improvement – and even new avenues of use as the chipping industry evolves.

First, let’s look at how MH works and how it is best applied. MH is effective in preventing sprouting as long as there is enough green foliage to translocate the chemical. It can be applied too early, reducing yields and resulting in plant injury; and too late, so that the interval between MH and the use of a vine killer or occurrence of frost is less than two weeks.

While Mark VanOostrum believes growers are generally very careful to apply it at the right time, he says there is a tendency to be too late with MH application timing compared with too early.

“That curbs the potential benefits, often due to the fact we usually time our MH with a fungicide application on a seven-day interval,” explains the potato supply and quality manager at WD Potato Limited in Beeton, Ont. “I recommend timing its application individually for each field. It may have been only three or four days since the last trip through the field, but you may have to make another separate trip.”

In addition to application accuracy, variety must be kept in mind in achieving proper MH function. VanOostrum notes that within the chipping category, MH is not normally used on Dakota Pearl or some of the shorter-season proprietary varieties that are heavy setters, since the sizes tend to be small and storage does not extend beyond March.

“We typically use it on longer-storage varieties like Waneta and Lamoka for the added benefit of managing large tuber profiles and long-season uniform sprout control when using MH with CIPC,” he says.

VanOostrum adds that during some seasons, with varieties that have rank lush growth, large size and high sucrose/glucose, he and his colleagues use MH to slow the crop down and prepare it for topkill. In addition, on rare occasions, VanOostrum and his team use MH on Atlantic varieties which are not stored, to prevent both large sizes and the likelihood of hollow heart. He says this is preferable to topkilling Atlantics for size control as there is too much risk to stem end sugar defects when the crop is rank.

MH is also used at WD Potato until mid-January for sprout control on some stored short-season varieties. VanOostrum says since the chip industry has almost a zero tolerance for sprouts, they don’t risk using it past that point in time.

“Each year, if frying well enough, we plan to use potatoes that have had MH applied to them by end of December,” he says, adding “we do not recommend MH on drought or heat-stressed potatoes or when canopy is senescing.”


VanOostrum and George Burkholder (president of consulting firm Ag Services in Mitchell, Ont.) both agree that using CIPC in addition to MH can provide better sprouting inhibition success compared to just using MH. “The combination is bullet proof,” says Burkholder. He also mentions Smartblock, a new product that boosts CIPC’s effectiveness through enhancing its distribution into the pile.

“It’s another standalone sprout inhibitor, but also an excellent solvent for CIPC,” he explains. “SmartBlock can be used to treat potato storages that seed has to go back into. After the potatoes are moved out, there will be no residue left to affect the seed performance. Also, on bins that need to be warmed up to bring around good colour that start sprouting, SmartBlock can be used to buy some time and burn off existing sprouts [as a rescue treatment].”

In comparing MH and CIPC as standalone products, VanOostrum notes that MH can provide a more uniform sprout control in some cases when storage ventilation and design do not supply uniform CIPC coverage.

“Often we only think that the cooler the temperature, the more dormant the tuber, and this is true,” he notes. “Respiration rate does decrease as temperature decreases, but we also see that temperature consistency is just as important.”

As an example, VanOostrum presents a comparative situation. Where storage temperature is 46F but it varies within two to four degrees, dormancy will break sooner. However, if the same potatoes are stored at 49F but the temperature doesn’t vary as much, longer dormancy can be achieved. To prevent temperature variation, he advises ensuring adequate insulation is in place. Growers should also consider replacing louvered air intakes with fresh air doors, completely seal any possible air leaks around the storage envelope, and ensure the temperature between plenum and return is no greater than 1.5F. Burkholder agrees the better and more up-to-date the ventilation system you have, the better your in-storage sprout inhibitors will work.

MH Use Going Forward

VanOostrum notes the chipping industry has moved towards a smaller size profile over the last few years. He believes, therefore, that MH could be used earlier, especially for larger-sized varieties, than the suggested timing given on the label for minimum size.

“It’s a scary thought to limit yield,” he says. “But in the future, we will see less tolerance or no tolerance for oversize and maybe an increase in tolerance for small.”

He also notes that every year, his firm has at least one bin of potatoes that is put into a seed storage area on a short-term basis, with no CIPC or MH applied to that point, in the hopes they fry before sprouting.

“This same bin does not fry well enough early, so our only line of defence is to warm up the potatoes to speed respiration and thus sugar burnoff,” he says. “This accelerates breaking dormancy and sprouting. I believe we need to be more proactive and use MH on anything with the slightest chance of sprouting in seed storage.”

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