Protecting a Delicate Diva

Farmer Stefan Reijntjens regularly checks his seed potatoes. In that way, he can spot dangerous storage diseases early enough to combat them.


Hot, healthy, delicious, that’s how Stefan Reijntjens likes his lunch. Just one look at the steaming potatoes and spinach on his plate and his mouth starts to water.

The dark-haired farmer from Rutten in the Netherlands loves his potatoes, be they on his plate or on his fields. He also is familiar with their great diversity: “There are many varieties, and only some are right for certain dishes,” he explains, cutting his potatoes with a knife. “For this,” he says, stabbing a piece of steaming boiled potato on his fork, “you need a variety like Musica, because it has an appealing deep-yellow color, smooth skin and it’s waxy.”

45 tons

of potatoes per hectare a year are harvested by Reijntjens.

After lunch, Mr. Reijntjens dons his blue winter jacket, pulls on his black work boots and heads for the fields. As long as the potatoes are still in the ground, the farmer walks through the rows of crops at least once a week, his trained eye immediately recognizing damaged or diseased plants, which he yanks from the soil. “By regularly inspecting the plants, we prevent the spread of fungi, bacteria and viruses,” Reijntjens explains.

A day at a potato farm

Fulfilling the high quality standards imposed on his seed potatoes requires great vigilance. A distinction is made between starch, table and seed potatoes. The smaller seed potatoes serve as seed, from which table or starch potatoes are grown. Some farmers, like Stefan Reijntjens, specialize in the production of seed potatoes. He harvests about 45 tons of potatoes per hectare a year from the ground. “We sort them by size and sell them to distributors, who then ship the potatoes all over the world,” he says.

In developing crop protection agents, it is important for us to maintain close contact with farmers.

The small spuds must be free of pests and diseases, “because sub-standard seed potatoes produce poor table potatoes,” Reijntjens explains. For this reason, he takes special care of his fields, for example by planting his potatoes only every six years on the same field. In the interim, he grows onions, chicory or sugar beets on these tracts. This method of crop rotation keeps the soil fertile – and guarantees lush, healthy plants.

All-around protection

Dry rot, black scurf and late blight are the biggest enemies of potato farmers. These fungal diseases can wipe out an entire crop. Late blight, for instance, has already made history. In the mid-19th century, this “potato pest” caused the Great Famine in Ireland, where some one million people succumbed to hunger. Even today, potato disease is a problem worldwide.

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Fortunately, plant researchers in our time have developed powerful counteragents. The product InfinitoTM, for example, acts on all stages of the fungus Phytophthora infestans, which causes late blight. “In developing crop protection agents, it is important for us to maintain close contact with farmers,” explains potato expert Albert Schirring from Bayer CropScience. He and his team help farmers worldwide to care for their crop plants. Fungicides control fungal infection and help to achieve healthy, plentiful potato harvests.

However, the most effective protection begins long before a farmer buries his potatoes in the ground, with a process known as seed treatment. In this step, the seed potatoes are covered evenly all over with a special active ingredient. One effective seed treatment is EmestoTM, a fungicide that uses a new mode of action to stamp out feared fungal diseases such as Rhizoctonia root rot or silver scurf. It further helps the potatoes to get a quick start in the ground. The plants sprout sooner and grow faster than their untreated counterparts.

And the active substance stays right where it’s supposed to. “The substance spreads locally underground, in the potatoes and on the shoots. As a result, very little active substance is required to effectively protect the spuds,” explains Karl-Wilhelm Münks from Bayer CropScience. The substance is already registered in Canada, the USA and other countries, where farmers were anxiously awaiting it. “Farmers held off planting their potatoes until EmestoTM arrived in May,” relates David Kikkert from Bayer CropScience Canada. The substance likewise is to be introduced in China and India, two major potato producers. EmestoTM is the result of several years of intense research in the laboratories and experimental fields of Bayer CropScience.

But sometimes things simply have to go faster, such as in New Zealand in 2009. The zebra chip disease there was causing an uproar among potato farmers. The culprits were bacteria that had been spread over the entire island by jumping plant lice within just a few years. The tiny organisms re-program the potatoes in such a way that they turn their starch into sugar, which causes dark-brown stripes to form on chips or fries when they are fried, hence the name “zebra disease.” What is more, the pathogens weaken the plants and reduce crop yield. Just a few years after it first appeared, researchers at Bayer CropScience succeeded in presenting them with effective protection. The potato experts developed not one but two products to control the insects that caused the disease: MoventoTM and OberonTM. They were registered very quickly in New Zealand and, with their help, the plant disease was soon contained.

Stefan Reijntjens also takes steps to combat pests and disease. Fungi are the greatest risk to this field crop, since they can seriously threaten the quality of an entire harvest. What is more, their spores are hard to control. “I have seen a disease appear on one field, but not another right next to it, despite identical farming methods,” Reijntjens says, pulling a plant with wilted leaves from the ground. “So we have to use various means of prevention.” In addition to regular inspections, the farmer uses crop protection agents to prevent harmful diseases from even emerging in the first place.

Dr. Huub Schepers

Interview with Dr. Huub Schepers, plant researcher at Wageningen University in the Netherlands.

“The most devastating of all potato diseases”

How important is the control of late blight for a potato farmer?
Very important. Worldwide, late blight is the most devastating disease affecting potatoes. It is caused by Phytophthora infestans, a pathogen from the class of oomycetes. Its global damage is estimated at ten billion euros each year. In growing regions with a climate that favors the development of late blight, potato farmers must either protect their plants with crop protection agents throughout the season, or select cultivars from the beginning that are resistant to potato blight. One mistake in selecting the time of planting or potato variety can result in tremendous damage from this disease.

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Why is Phytophthora infestans such a devastating disease?
When weather conditions are favorable, Phytophthora infestans can complete its entire life cycle in just three to five days. During this time, it produces millions of spores, which are easily transported by wind to unprotected plants. In this way, the pathogen can destroy in just two weeks the canopy that is supposed to protect a potato crop. Furthermore, the spores can also get into the furrows and infect the tubers, destroying not only the photosynthetic factory of the leaves, but also the growing potato crop.

Where does late blight occur most frequently?
It is very widespread in wet climates, for example regions with a maritime climate, like northwestern Europe, or mountainous regions with frequent precipitation, like the Andes. In the major potato farming regions the risk of infection is higher. In tropical and subtropical regions, where potatoes are grown at different altitudes, the risk of infection is higher still because potatoes are grown year-round in these areas.

How can late blight be controlled sustainably?
Late blight can only be kept in check with an integrated control strategy based on a number of different methods. First and foremost, sources of infection, such as post-harvest waste and infected seed potatoes, must be reduced. Second, resistant cultivars should be selected to minimize the use of crop protection agents. Third, the strong effect of the substances should be put to the most targeted use possible to exploit their efficacy. And fourth, a database system should be used to compile and organize all relevant information.

What makes this disease so difficult to treat?
The pathogen adapts very easily to a variety of conditions. It increases its aggressiveness by shortening its life cycle, producing more spores, overcoming cultivar resistance and also developing resistance itself to some fungicides. For this reason, the control strategy continually must be adapted to the mutating pathogen.

What is your research team currently working on?
One important part of our work is observing the pathogen in its growth phase. Which single-spore isolates of the pathogen can be cultivated? How aggressive are they? How great is the risk of infection for resistant cultivars? And how resistant are these single-spore isolates to crop protection agents? We exploit the possibilities offered by new technologies to answer questions like these quickly and efficiently. This information can then be used during the growing season to flexibly adapt the control strategy to the characteristics of the pathogens prevalent in a respective region.

Fight against potato blight

Stefan Reijntjens has several divas in his basement. They have names like Lady Anna, Lady Claire or Avarna, and they are potato varieties which the farmer harvested in the fall. The tubers in Reijntjens’s enormous warehouse are stored in crates over a meter high, which in turn are stacked seven meters right up to the roof. What might look simple to a casual observer really requires special skill, because storing potatoes is an art of its own. “We harvest in September and store until spring. A lot can happen in that time,” the farmer explains. “A potato lives on after the harvest.” If conditions are too bright and warm, for example, a potato will sprout and produce the toxic substance solanine. If that happens, the potatoes can no longer be sold. If the humidity is too low, the tubers lose a lot of water, shrivel and again become worthless.

World's leading potato producers

The potato, in other words, is a real diva! And farmers have to humor them so they stay healthy and fresh. “We can only do that with regular quality checks,” Reijntjens explains. With their help, he can spot dangerous storage diseases, such as silver scurf caused by the fungus Helminthosporium solani, and react quickly. “But up to now we haven’t had any problems of this kind,” he reports, while manually inspecting a tuber from this year’s harvest. The potato farmer already starts protecting his plants against disease and pests out in the field, using effective crop protection solutions from Bayer, and he carefully tends his young crop.


different potato varieties exist worldwide.

For farmers like Stefan Reijntjens, worry over the potatoes begins long before harvest and storage, when he has to select the right varieties to plant from among the over 5,000 that exist worldwide. They differ in shape, starch content, skin color and flesh type. These characteristics make them suitable for different purposes: The long Lady Anna is ideal for French fries, the round Lady Claire feels more at home in a bag of chips, and Avarna is the best choice for processing into potato starch. What is more, needs differ by region. The United States demand large potatoes measuring 15 centimeters in length for French frie production, while the French prefer to serve potatoes fresh – small, round and unpeeled.

In other words, a farmer must know precisely what the market wants, and then select new varieties to plant every year. Reijntjens gets information on market conditions from his customers, and grows different varieties of seed potatoes. “Some are good for table potatoes, others for processing into chips or fries,” he explains. This way, farmer Reijntjens always has a good mix to offer the market – and every potato lover has his favorite product on his plate or in his bag of chips!