Searching for sprouting solutions
Chlorpropham has been used for decades to inhibit postharvest potato sprouting. But with a major potato storage company moving its manufacturing of the chemical compound to the U.S. and the European Union in its fourth year of prohibiting the sale of the gas, questions swirl about chlorpropham’s long-term viability.
CIPC, as the suppressant is commonly known, was first registered as a herbicide and plant growth regulator in the U.S. in 1962. Originally registered for use of a variety of food and nonfood crops to control broadleaf weeds and grasses, CIPC has primarily been used to inhibit sprouting in stored potatoes since 1990.
Toxicity concerns led to its ban in the EU, where sale of the compound has been prohibited since January 2020. EPA studies have found CIPC, a mild eye and skin irritant, to be of low acute toxicity, according to the agency. Slightly toxic by the oral route, CIPC in is the EPA’s Toxicity Category III (the second-lowest of four categories), with the agency urging users to follow personal protection requirements on product labels.
That classification is unlikely to change, EPA spokesman Jeffrey Landis told Spudman.
“The toxicity category for a product is evaluated at the time a product is registered and would only be reconsidered if the agency received new data that would lead to different precautionary statements,” Landis said via email. “EPA does not plan to reevaluate the toxicity category of any currently registered chlorpropham products.”
However, one major pesticide manufacturer is preparing its customers for “not if, but when” CIPC gas is no longer used in the U.S., while researchers are actively working to find commercial-scale alternatives to the treatment.
Time-trusted tactic
One of CIPC’s main appeals is its familiarity.
“CIPC gas is easy. It’s convenient. It’s fairly inexpensive. It’s fairly consistent,” Michael Brewington, product development manager at Drexel Chemical Co., said. “The infrastructure is in place to apply it properly. Folks know how to use CIPC.”
That certainty makes CIPC all the more attractive in an area of potato production that is still being studied, said John Hren, global sales and marketing director for dormancy and sprout control product supplier 1,4Group.
“Everybody spends so much time, energy and care — as they well should — in figuring out the right variety to plant, when to plant, how to protect the seed potato, how to prevent diseases, getting the right nutrition.” Hren said. “The grower winds up, in essence, forgetting about the crop once it goes into storage. It’s almost like putting it in a closet.
“It’s so different than that. It’s really a neglected area of the overall farming operation.”
While colder temperatures generally inhibit sprouting, they can increase reducing sugars, which can affect the fry color of processing potatoes and other potato properties. So sprout suppressors, which provide obvious — if sometimes under-researched advantages — are sent to the rescue.
“If the potato starts sprouting, the quality is decreased and the usability of the product declines,” Brewington said. “Preservation of that quality is paramount, and that’s an annual challenge that we all work towards trying to manage.”
Drexel’s portfolio contains an answer that is anything but new: maleic hydrazide (MH), a chemical introduced into agriculture in the 1950s as a herbicide and plant growth depressant. MH is used in Drexel’s Sprout-Stop liquid formulation.
“We’ve seen a resurgence in interest, use, development and understanding of maleic hydrazide over the last couple seasons,” Brewington said. “Maleic hydrazide has been around for 75 years, but it is a product that’s been used (as) a primary growth inhibitor for other crops, like onions, shallots, garlic, tobacco. In potatoes, we’ve always had other in-storage options.”
Brewington expects one of those options to disappear.
“Domestically, I think the writing is on the wall with CIPC gas,” he said. “The likelihood of CIPC gas being around indefinitely is questionable. The U.S. is behind the European Union as far as recent development of maleic hydrazide and understanding how it fits and how to best use it, but more projects are being taken on, by universities and of course Drexel, trying to prepare the marketplace for not if, but when CIPC gas is taken away as an option for U.S. growers.”
1,4Group registered PIN NIP, its 98% CIPC sprout inhibitor, in 1995, and while Hren said the product remains “a valuable tool in the toolbox for growers,” 1,4Group moved its CIPC manufacturing to the U.S. in April.
Hren said European customers — some of whom he recently visited on a trip to Germany — are not lamenting CIPC’s absence. Instead, 1,4Group product 1,4Sight, which works internally to maximize the dimethylnaphthalene (DMN) naturally occurring in potatoes to delay sprouting and restore dormancy, provides a better return on investment for growers from Belgium to Spain.
“You have more weight because you retain more moisture within the potato by slowing down the respiration metabolism,” Hren said. “This leads to a firmer potato (with) less pressure bruising, which in turn results in not only a storage manager selling more weight — which generates more revenue for them — but it’s a higher grade, a higher quality, a more desirable potato, so you can get a premium on your pricing as well.”
1.4Sight, which can be used in conjunction with CIPC, is sprayed onto potatoes shortly after storage door closure to establish dormancy and in mid- to late-season to extend dormancy and prevent sprouting. MH is an in-season foliar application that Brewington said makes in-storage application of treatments such as natural oils or ethylene more effective. And stored potatoes treated with MH will break dormancy at the same time, he said, reducing “hot spots” in the pile and cutting down on the number of on-storage applications.
While the shift from postharvest to in-season application would be a sea change for some growers, Brewington said it would prove beneficial.
“All of the convenience and consistency that CIPC brings to the table that we would potentially lose can be picked up by the foliar, in-season application of maleic hydrazide preventing the sprouting prior to harvest,” he said. “It does not matter what product you use in-storage as a curative-type product. Maleic hydrazide applied in the field as a foliar application makes all sprout suppressants used in-storage more consistent.”
Researching alternatives
Since 2020, Munevver Dogramaci, a research plant physiologist with the USDA’s Agricultural Research Service, has been searching for ways to optimize potato tuber dormancy and prevent premature sprout growth. Her USDA-ARS research program in Fargo, North Dakota, has several experiments underway to develop alternative management strategies.
The stakes for finding successful treatments are high. According to USDA-ARS, 400 million cwt of potatoes, with an estimated value of more than $2 billion, are harvested each fall in the U.S. More than 70% of the fall potato crop is stored for year-round use, with postharvest losses through physiological and disease-related processes routinely reaching 10-15%.
“Failure to maintain product quality can result in commercially unacceptable product for the processing industry and financial ruin for the producer,” Dogramaci said. “Despite the severity of the losses, the management strategies and technologies employed to control sprouting do not effectively meet today’s consumer and industry demands.”
USDA researchers are utilizing commercial and experimental sprout inhibitors such as DMN, ethylene, essential oils including spearmint and oregano essential oil, and are integrating molecular assays to identify key mechanisms involved in tuber dormancy progression.
MH is part of that research, she said, “but the potato industry was banking on CIPC for so long that the majority of all experiments on dormancy were not at commercial level. That’s what we are focusing on — scaling up experimental projects so that we can see the treatments in real life.”
Projects are also investigating the impact of crop growth environment, agronomical practices and postharvest storage conditions, she said.
While researchers have seen some promising results, “none of these are as efficient as CIPC yet, because they have not been optimized, and there is room for improvement,” Dogramaci said. “While the impact of these compounds on dormancy and sprout growth have been known for some time, they have not been in the real world long enough, and we still don’t completely understand how tuber dormancy during storage is regulated at the molecular level.”
Forward-facing future
The EPA’s Landis said the agency “does stay abreast of the regulatory actions of other countries” but “does not publicly comment on the way other countries choose to evaluate and register pesticides according to their specific legal structure.” The agency also works to promote “the sound management of chemicals and pesticides and, as appropriate, to facilitate trade via decision-making founded in science.”
Drexel’s Brewington sees the international marketplace as another arena where CIPC alternatives will eventually have an edge.
“Some export markets are not accepting CIPC-treated potatoes, and that number is growing,” he said. “Drexel is working with stakeholders to try to prove to those same export customers that maleic hydrazide, when used properly, both provides a solution to the sprouting problem and can be used effectively in a manner that does not result in residues that exceed the MRL (maximum residue limits) that are established for maleic hydrazide globally.”
Brewington emphasized that MH should be applied at the right time (too-early application can impact yield, while too-late application can affect absorption and translocation), onto healthy plants and at the right temperature (less than 85 degrees). Similarly, 1,4Group’s Hren stressed that sprout suppressant programs are multi-faceted and should be tailored to individual operations.
“As technology and AI advances, we’re increasingly realizing that you are putting a living organism in that storage,” he said. “To get that field-fresh quality out of your storage, you really need to think about it, and you really need to strategically plan your storage management strategy.”
Should that strategy not include a long-trusted solution one day, a post-CIPC world is “not a scary place,” Hren said. “It’s a better place.”
