'Yield and quality of potatoes must increase'

Arable farming and contracting company Witkop in Swifterbant (Fl.) wants to maintain the yield and quality of chips potatoes at least at the same level in the coming years. Or even better: raise it again.

To this end, the rotation will be reduced from 1-to-5 to 1-to-6 and the fertilization strategy will be even sharper and more precise. The fungal control – Phytophthora and Alternaria – remains as it is: complete and without 'holes in the schedule'. "Ultimately we have to earn it on the yield side; then the crop has to be healthy and vital to the end," is their belief.

"To be honest, we've been getting a little further behind in potato cultivation in recent years. Where fifteen years ago we still harvested around 70 tons from a hectare, we're happy with 60 tons these days. We really need to do something about that in the coming years because in the end it is those extra kilos that make potato cultivation financially interesting."

Hendri Witkop of the eponymous arable farming and contracting company in Swifterbant is speaking. Together with his son Toby and advisor Ardon Verschoor of Van Iperen, he sits at a self-built table in the workshop. Because it is still too wet on the land now (early April, ed.), they tinker and weld a bit on a cultivator - and in between there is also some time to talk about the future of potato cultivation on the company. All three men look forward to it with some concern. In addition to the observation that the yields in the Polder have increasingly lagged behind in recent years, they also see that the dependence on this crop - and also the onions - is only increasing. Witkop senior points to the (free) prices for both products – which are particularly high this season. "We received more than 30 cents per kilo for our free potatoes. With that we can take another nice step forward. But you also realize once again: with an extra five or ten tons per hectare, that step could have been even bigger."

Future-proof soil
Witkop senior attributes the declining yields of French fries potatoes mainly to the ever tighter fertilization standards. "Unfortunately, we have to deal with that. The only thing you can do is provide good soil, so that fertilizers become optimally available to the plant. We also have to do more to bring the fertilizers as close as possible to the plants." he says. For this reason, the company will also start fertigation via drip hoses next year. For the time being, first in onions – because there the yield is under even more pressure because of Fusarium. "But who knows, we may also go that way in potatoes," says the arable farmer.

Another measure that should increase the quality and yield of the potatoes is the switch from 1-to-5 to 1-to-6 potatoes. "In this way we bring more peace to the cropping plan and we keep nematodes and other soil-borne diseases under better control. It also gives us more options to distribute animal manure more evenly over the crops," says Toby. He thinks that the potato area will decrease from 15 to 12 hectares next season 'a choice that is worth it'. "Initially we will certainly lose some balance, but we hope to regain that in the coming years with better yields and better quality."

For the same reason, there will also be a change of variety next season. The Markies is now replaced by the King Russet variety (alongside Innovator). "We especially hope that this will clear up a few mixed infestations of nematodes, so that we will be completely clean again," says Toby. All in all, the measures should lead to a balanced, healthy and, above all, future-proof soil, according to father and son. 

Closing spray schedule
While the cultivation plan and the choice of varieties will be shaken up in the coming year, the vision on crop protection remains unchanged. And that means: no risks with Phytophthora and Alternaria and working with comprehensive spray schedules. "If you want to make money on the yield side, the crop must remain healthy and vital right to the end. And that means not taking any risks with disease control," says Witkop senior. Advisor Ardon Verschoor agrees. He sees Alternaria in particular advancing further and further - especially in years with stressful situations in the crop. The relationship with extreme weather conditions (particularly heat and drought) is quickly established, but the increasingly meager fertilization and the disappearance of mancozeb – which not only had an effect against Phytophthora but also against Alternaria – also play a role in this. There are also differences between races. "Particularly varieties that have long and lush foliage - such as Marquis - are extra sensitive to stem breakage and therefore also to a weak fungus such as Alternaria. This also applies to varieties that produce extra leaves at a late stage - such as Agria and Melody. need extra protection at the end of the season, so spraying long enough against Alternaria is important, especially when the crop has to stay green well into September."

Concentric rings
Although most growers are aware of the dangers of the disease, some are still surprised by an early attack, Verschoor notes. "It's not for nothing that Alternaria is called Early Blight – and Phytophthora Late Blight. This indicates that Alternaria is often present earlier than we sometimes realize." He also sees that the fungal disease is sometimes confused with magnesium deficiency or ozone damage, which more or less show the same leaf spots. "In some varieties - such as Innovator - all three phenomena can occur. This makes identification even more difficult. Typical for Alternaria are the slightly angular, concentric rings in the spots that are sharply delineated by the veins of the leaf. When you see that, then it is definitely Alternaria."

Propulse in the base
With regard to the control of Alternaria, the Witkop company agrees with Verschoor's advice. This means that from the start of flowering, an Alternaria remedy alternates with the Phytophthora control. This is usually started with Propulse (based on prothioconazole) and then alternated with Narita® and/or Carial Star® (based on difenoconazole). In addition, an over-fertilization is immediately carried out with nitrogen and potash fertilizers to keep the crop vital for as long as possible.

According to the consultant, Propulse has been given a basic place in the fight against Alternaria almost everywhere in recent years. And that is not for nothing, according to him: "Propulse has clearly proven itself in tests and in practice as the strongest remedy against Alternaria. In addition, it also has a nice side effect against Sclerotinia (rat dropping disease) and also tackles black speckle and Botrytis well. All plus points that help to keep the crop disease-free, green and vital for as long as possible," Verschoor concludes.

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