By Lauren Krizansky
Cleanliness is the certified seed potato grower’s eternal burden and the mantra of the century old production system.
Certified seed potatoes are not the same as true potato seed. The latter are the berries collected from the potato plant. Seedlings germinated from true potato seed are genetically unique and will produce tubers with different characteristics than the parent plant.
Vegetatively propagated certified seed potatoes are tubers grown for planting that an agency inspects for authenticity and disease. These tubers are started in tissue culture from disease-free plants. Mini tubers are the seed potatoes grown out from these plants in a traditional or hydroponic greenhouse, producing a crop pure in genetics and health. This seed is then grown out for several years before it is sold for final production. As the tuber is reproduced through the generations, environment imposes pressure on the seed to maintain its integrity.
Keeping the seed potato’s wholeness intact is necessary because, ultimately, dirty seed results in substantial table stock and seed production loses. Certification along with breeding programs are the backbone of the seed potato industry. These resources identify and respond to industry needs to keep potato production viable and progressing.
A seed potato grower does everything possible to keep disease off of the farm, and understanding disease and the role of certification is part of the management plan.
Vegetative propagation increases the chance of disease spreading from one generation to the next. Every year, seed potatoes are exposed to soil and air borne pathogens, and insect vectors. These factors can potentially acquire numerous bacterial, fungal or viral pathogens that cause disease. The disease will accumulate in the seed potatoes, resulting in a disease carry over during the subsequent growing season.
The certification system has a steady track record of identifying disease and, in some instances, eradicating the problem. For example, Leaf Roll, a virus, is no longer a threat in many potato-growing regions because of diligent management and decisions that did include multi-season insecticide applications that killed the infected aphid spreading the disease.
“The perfect seed has zero bacteria and zero virus,” explained Colorado Potato Certification Service Manager Dr. Andrew Hauser. “Beyond that, zero pests and zero diseases.”
Certification services conduct summer inspections and post-harvest testing to manage disease. Their findings can knock a seed lot out of the market, which impacts the availability of that seed in the future. The agencies make their annual findings available to the consumer through public reports and documents like the North American Health Certificate.
“The health certificate tells you how much disease, how many problems you are buying,” Hauser said. “My job is to show that there is a quality seed potato crop available. There are a lot of shortcuts that can be made. Seed certification service can choose shortcuts or do our best to make sure those shortcuts do not happen.”
Clean from the start
Certified seed potato rules and regulations are determined state by state. Some states, like Colorado and Montana, enforce programs through their land grant universities while Maine’s program operates under the umbrella of the state’s Department of Agriculture, Conservation and Forestry. In 1914, Wisconsin was the first state to implement certified potato seed guidelines. Maine was the second, establishing certification services one year later. Seventeen states including Montana, Idaho, Oregon, Washington, Oregon, Colorado and Alaska would eventually follow. Today, although the programs are not necessarily harmonious, they do more or less follow the same disease management guidelines. The first guideline: begin with seed that is clean and, when possible, bred for disease resistance.
“Farmers should source certified seed and pay attention to the grower’s opinion,” said Wood Prairie Farm’s Jim Gerritsen, a 40-year veteran seed potato grower in Bridgewater, Maine. “It cuts down risk. It’s like a working farm dog. Pure versus a crossbreed. With the purebred, you will understand the qualities. With the crossbred, there is an unknown, an uncertainty.”
In addition to disease, the absence of variety mix also determines clean seed. Variety mix is identified during multiple summer inspections. If it is present, it is remedied through roguing, a practice that requires walking the fields with a sharp eye and physically removing the unwanted plants.
Cleanliness on a seed potato operation rounds out with constant sanitization and disinfestation of handling, planting and harvesting equipment as well as storages, which certification services also inspect. This is primarily to manage bacterial diseases. Virus and fungal diseases are mainly present in the field.
“Sometimes growers take the risk and plant contaminated seed,” Hauser said. “Most often cleaning that seed up through virus management is challenging and not economic.”
A viral battlefield
Maine’s North Woods nearly envelope Gerritsen’s farm, which is the last of the cultivated lands on his road, six miles from the Canadian border. The woods provide him with isolation from other potato farms and his fields are positioned to the east, preventing the threat of disease laden winds. He chose to plant his seed in a place with an environmental advantage against disease, but it does not grant him immunity.
Potato Virus Y is at home in most growing environments. It finds its way into the wet and humid fields of the northeast and the arid, desert fields of the west. It’s not all the same strain and it doesn’t express in the same ways or at the same time, but every potato field can credit the annual virus spread to aphids.
The USDA defines PVY as a monopartite, single stranded RNA virus that infects mainly Solanaceous plants. In potatoes, it causes a mosaic pattern in the leaves of infected plant. This mosaic expresses as a green and yellow variation, but can also be expressed as a roughness in the leaves, yet most strains do not affect tuber quality. The virus has become predictable in its unpredictability and it is determining what potato varieties can survive in different environments under the most dynamic Integrated Pest Management (IPM) plans.
Every summer, Hauser walks seed potato fields with his band of inspectors under the hot, high desert sun. Most of the lots he inspects are woven between commercial and highly PVY susceptible Norkotah Russet crops. He witnesses many virus management techniques with a great appreciation for the growers’ determination to produce a quality seed potato crop in a place where overexposure to the virus is the norm.
“You have to manage for PVY,” Hauser said. “If you want a seed industry in a place like the San Luis Valley, you have to. Even if you are a commercial grower.”
In a place like Montana, commercial production is scarce, creating an advantage for its seed potato growers.
“Montana has the luxury of being an almost exclusively ‘seed potato’ state,” said Montana Seed Potato Certification director Nina Zidack. “We do not have a significant amount of commercial potato production in Montana which allows us to grow seed potatoes in relative isolation.”
Similar to Gerritsen and his secluded farm in the woods, Montana growers know their isolation does not make them immune to threats.
“Our growers still manage diseases by growing early generation seed potatoes,” Zidack said. “The grow as far away from other seed potatoes as possible, with some farms growing their seed plots in counties that have no history of seed potato production.”
IPM and other considerations
When PVY is present, it does effect yields negatively. Hauser explained in a typical Norkotah Russet crop, 450 hundred weight per acre is considered a good yield. If there is 25-30 percent PVY present in that field, he said, it might drop the yield to 375 or 400 hundred weight, which is not considered terrible.
“This is still an acceptable yield,” he said. “That is the problem. You don’t know that you have that potential. The blame for the acceptable yield is the weather or water or something else, something less provable.”
What Hauser is able to prove, however, is that IPM works. He said insecticides, timing, roguing, oils, and biological practices all have shown to lessen PVY spread in one way or another in the high desert growing environment and elsewhere.
Growers, he said, are applying insecticides like pyrethroids and neonicotinoids in furrow at planting and throughout the season via chemigation systems to kill aphids.
“Neonics are more effective compared to pyrethroids, which excite the aphids and send them hopping from plant to plant,” Hauser said. “The neonics kill more instantly. Overall, the insecticides are not too effective.”
Roguing is a valuable tool for removing plants expressing mosaic symptoms from the field, but it is time and labor intensive depending on varieties and planted acreage.
Planting and vine desiccation timing can shorten the window of vulnerability to infection, which is a serious factor in some organic seed potato production.
“The longer the seed is alive, the more opportunity aphids have to come in and spread the disease,” Hauser said.
Without organic vine desiccant available, organic growers usually either have to wait for a deep frost to kill potato vines or use equipment to beat the vines to encourage skin set. In recent years, a former organic seed potato grower lost an entire operation because of mechanical PVY spread, proving how devastating the virus is when management is neglected.
Bringing additional life in the form of flowers to a seed potato field, however, did reveal that managing the amount of PVY aphids carry is an effective IPM tool. Several seasons ago, Colorado State University supported Hauser in a research project where he planted a diverse flowering border crop around seed potatoes. He found that with the border crop, the spread of PVY was reduced. Since PVY only lives in the aphid for a few hours, it is able to clean its stylus in non-host plants, like the flowers in Hauser’s mix. If the pest enters the seed potato field with a clean stylus, it will not spread PVY unless it feeds off of an infected plant within the field.
The border crop also provided an environment for predatory insects to feed and reproduce. Hauser said he attributed the mitigated PVY spread to the predatory insects the border crop attracted and the alternative food source it provided for all the insects.
Mineral oils are gaining popularity across the industry to battle the virus, and they are especially effective when the grower plants clean seed, Hauser said. It is considered an organic, proactive approach that inhibits the aphid from inserting its stylus. The downside is the expense. The oils cost around $15 an acre and are applied every 5 to 7 days. The management tool also requires significant labor hours and applicator passes.
Gerritsen has found success with mineral oils. This year, he complemented the tactic with a foliar spray that encourages the plant’s natural defense system. Since he is an organic grower, he is working with two certification systems that, for him, have yet to conflict with one another. He said he has found support through both systems to produce a healthy, quality crop, unlike the grower who interpreted organic management as no management at all.
“I abide in the faith, the understanding that the system is right and that there has to be an organic method we can deploy,” Gerritsen said. “I’m not interested in poison, and there have been no restraints. The goal is to grow healthy plants that make healthy tubers.”
Regardless of the management method or certifying agency, quality seed potatoes are available because of the people who understand that the potato is an essential crop and believe in the future of agriculture. Without the checks, the balances, the dedication and the progress, the potato might not grow or even taste like they do today. Farmers, certifiers, breeders, chefs and those who only eat the final product all benefit from the system put in place generations ago to feed many generations to come.
Lauren Krizansky is an agricultural journeywoman. She loves, lives and works with her partner, Brendon Rockey, on Rockey Farms in Center, Colorado.