Passion for seed potatoes

"When I was fifteen, I went along with the selection for the first time. I thought it was such wonderful work back then! I think that is where the passion for seed potatoes was born." These are the words of Tjalling Douma, product manager at potato cooperative Agrico. He has immersed himself in (seed) potato cultivation for no less than 48 years. First five years on a farm in the Wieringermeer, then nine years at the NAK, and subsequently 34 years at his current employer, Agrico. He is retiring in April.

Bayer CropScience spoke with him about developments in seed potato cultivation, and more specifically about the virus problem. "Deep Learning and selection robots will play a major role in the fight against virus."

"So many interesting things are happening in seed potato cultivation right now. We are going to explore the possibilities of AI, the selection robot is on its way. A huge amount of data is becoming available from which we can extract a lot of knowledge. I would quite like to keep playing around with that for a while!" Tjalling Douma has certainly not lost his enthusiasm when it comes to seed potato cultivation. In April, he will retire after 34 years of service at Agrico. As far as he is concerned, it wasn't necessarily necessary yet. "But I want to make room for young colleagues who are just as driven as I am. And yes, a little more time for the allotment garden and for my grandchildren is nice too."

Perhaps we should start by looking back at 45 active years in seed potato cultivation: what wise lessons has this yielded?
"First of all, that there is always a solution to every problem. We have had terrible years with viruses, for example. I am thinking primarily of the year 1976; still a benchmark for older growers. Almost 60% of all seed potatoes were downgraded or rejected back then. There was a huge amount of leaf roll at the time. That certainly caused quite a bit of panic. Nevertheless, we managed to get the cultivation back under control. Primarily through creative and innovative thinking and doing."

Another lesson is that scale and quality do not have to be mutually exclusive. Over the past few decades, acreage and yields have grown enormously. This makes me think back to the 70s: back then, we still had deadlines for haulm destruction – around July 10 – and a yield of 20 to 22 tonnes per hectare was very common. Now we are at double that. At the same time, growers have never lost sight of product quality. They – and the entire surrounding chain – have continued to invest in this. That is why we are still considered everywhere in the world top of the bill are seen in seed potatoes."

Automation has also taken off enormously. I still remember the first discussions about palletizing machines: surely the average seed potato grower didn't need those? But a few years later, almost all of them had one. I see the same thing happening now with optical sorters: they are selling like hotcakes.

Of course, the fact that seed potato cultivation has been highly profitable plays a role; then you can and want to invest. But still: seed potatoes are not just any arable crop; they always stir up an extra bit of passion, both among the growers and the entire industry surrounding them. Perhaps it is a way of life."

Then there is the virus issue. What are the major developments there?
The most striking thing is that leafroll virus is making a comeback. In 2021, after years of absence, we found the first leafrollers again. Since then, the share has grown to nearly 30% now. Is that worrying? Absolutely! Although we dealt with this before in the 70s, 80s, and 90s – when leafroll was also the dominant virus – the situation is different now. At that time, growers still had access to fairly strong systemic agents to kill aphids. As a result, we were able to more or less eradicate this virus, and we haven't seen it for at least thirty years.

"The situation is different now. We have less potent products available, which can also be used much less frequently. As a result, the current leaf roll rates of 30%—and sometimes even higher—are more concerning than they were back then. Growers now have to make do with mineral oil and a limited number of aphicides and pyrethroids. This requires extra vigilance in virus control in the coming years. Or to put it another way: we all need to stay on top of this to the maximum extent!"

Where is there still room for improvement when it comes to combating the virus? Or in other words: where are the weak spots?
An early initial selection is very important. Due to the changing climate, aphids will, on average, be present earlier and earlier. We need to be more vigilant about this in the coming years, especially after a somewhat harsher winter. The rule of thumb is that a first inspection of the crop should be carried out when 40% of the potatoes have emerged. This can be a short inspection round, but if you find even the slightest sign of suspicion, you must immediately focus on the selection.

When 50% of the foliage is above 50%, the first application of mineral oil must also be applied. This remains very important, particularly to prevent the transmission of Y virus. For seed potato growers, this is probably stating the obvious, but I still want to mention it again: mineral oil must be sprayed strictly weekly to protect newly formed leaves.

Furthermore, we will have to be economical with the systemic lice killers still available, such as Gazelle® and Sivanto PrimeThese agents are particularly important in the fight against leafroll virus. This is a persistent virus that must first mature in the aphid's body for 24 hours after being bitten. After that, the aphid is capable of transmitting the virus for the rest of its life. A major advantage of systemically absorbed agents is that they kill the aphid before it can transmit the virus. Therefore, only with aphidicides do you get the chance to kill the aphid before infection occurs.

What about the use of lice netting? When is this useful (and when is it not)?
"Here, too, I would like to go back in time for a moment. Until about the mid-80s, mesh greenhouses were widely used. After that, they gradually fell into disuse due to the rise of strong systemic aphid control agents. With the current virus pressure and the previously mentioned 'weakening' of the agents, I would say: it is good that they are back. Especially for the high-value segment, such as first- and second-year mini-tubers, it is a protection that offers a great deal of certainty. Particularly for susceptible varieties, I see it as a very worthwhile investment."

In recent years, there has also been a lot of attention paid to (visual) confusion techniques, such as covering with straw, sowing grain strips, or whitewashing ridges. What is your view on this?
Although this is still somewhat in the development phase, it is good to continue testing it. Applying straw between the ridges seems to yield the best results at the moment, so perhaps the emphasis should lie there. At the same time, I say: it is not a miracle cure. With high aphid pressure, I even foresee some risks: simply put, such a straw layer should not distract from effective control using mineral oil, pyrethroids, and aphidicides. Confusion techniques can be a supplement against virus transmission, but the basis remains a strict, continuous spraying schedule.

What role does fertilization play in virus control?
With precise fertilization, you can certainly control the protection of your crop. Be aware that too much nitrate makes the plant more attractive to aphids, so limit its use. Potassium, on the other hand, ensures stronger cell walls and thus a more resilient plant. Silicon also plays a role in this. You can apply this during planting or later in the season as a plant strengthener. We do not know everything about this yet, but we do see opportunities here to make the crop more resilient.

Finally, a look into the future: which tools will help us further in the fight against viruses in the coming years?
Then the first thing that comes to mind is the unprecedented – and partly still unknown – possibilities of deep learning and AI. Over the past decades, an enormous amount of knowledge has been built up regarding diseases and pests in potatoes. Consequently, there is a lot of data available with which we can conduct extensive comparative research. By comparing growing seasons in all their facets, patterns can be extracted. We can certainly learn from that.

In the coming years, even more digital information will become available, which we can also analyze very accurately via AI and translate into better, variety-specific control strategies. I don't know exactly how that will work. But *that* It is going to happen, that is certain.

I also have high expectations for the selection robot, particularly during early selection. Thanks to increasingly better algorithms, this machine will eventually be able to detect whether a plant is infected with a virus better, more consistently, and, above all, earlier. That could turn out to be a very important one. game changer be used in seed potato cultivation."

^{Gazelle® is a registered trademark of CertisBelchim}

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