'Basic plan to combat phytophthora overboard'

"What we learned from 2021 is that a season never goes normally. For example, we had to adjust our plans for Phytophthora control very quickly. The pressure was so high that we had to go to the heaviest regime early on."

This is what Ron Peters, owner of the company Agriwerk VOF in Odiliapeel, has to say. Together with advisor Harm Jonkergouw of AgroBuren, he looks back on the potato year 2021. According to Peters, the season went 'moderately to reasonable'. "In terms of yield, 2021 was certainly not the best. For all varieties together, I arrive at an average of 56 to 57 tons per hectare. In a normal year, that is at least 3 to 4 tons higher." – including a strong disease pressure, according to Jonkergouw, the lack of sunlight in particular had a major influence. "I think we soon received a month less sunlight. As a result, not only the potatoes, but also other crops have grown less rapidly than normal.” Peters is positive about the quality of the potatoes. "Despite the wet weather and the high disease pressure, we were able to deliver all potatoes neatly, without rot and with good underwater weights," he says.

Wide variety package
Peters grows about 100 hectares of potatoes every year. On the heavier (river clay) soils these are mainly French fries varieties (Challenger, Fontane, Ivory Russet and Zorba), on the lighter (sandy) soils mainly Hansa (for Peka Kroef). "I like to have some spread in varieties and sales channels. Not only to spread the risks, but also to have the varieties match the available soil as much as possible. With the current range of varieties, that works out quite well. ''

As far as fertilization is concerned, he says he is 'strongly focused on the soil'. "That's where the growth has to come from; not from all kinds of expensive products that you have to put in the sprayer or spreader during the season." Special fertilizers, additives or foliar fertilization are therefore hardly used. it doesn't harm', I'm not going to go along with that'', he emphasizes. "The product prices are simply not high enough for that."

Very high phytophthora pressure
Phytophthora control must also be simple but solid, as far as Peters is concerned. At most, some small (interval) adjustments are made per variety, such as for Hansa, which is less sensitive to tuber phytophthora and therefore needs less protection. Peters discusses the spraying strategy with Jonkergouw in the run-up to the season, after which a kind of basic plan is rolled out. "Last year, due to the high disease pressure, that basic plan was quickly thrown into the wastepaper basket. The pressure was so high that we quickly had to switch to the heaviest regime," the arable farmer looks back. Where in a normal year, usually Revus® , Infinito and Ranman® Top are used, the Infinito product has now been partly saved to have it - in combination with Curzate® Partner - on hand as an emergency remedy in the event of a Phytophthora outbreak.

Harm Jonkergouw emphasizes that saving up does not mean that Infinito can be used 'in between' as an emergency remedy, but that the full blow of the resource must be used immediately. He explains: "If an infection occurs, the Infinito should already be on it. This is especially important for the active ingredient propamocarb: this amount must be built up as quickly as possible in the leaf for maximum curative effect. In the event of an infection, therefore, you must immediately start with the highest dose and continue to the maximum dose of 6,4 liters per hectare."

Whether this method is sufficient in case of a very high disease pressure remains to be seen, according to him. "Last year we more or less got through the eye of the needle. Had the pressure lasted longer, there would certainly have been major damage to the potatoes." Jonkergouw thinks that the block spraying as recommended in the Netherlands has helped to keep the infections under control.” Active substances have therefore been able to build up in the plant; That may have been an important factor that the situation did not get out of hand.”

More eye for crop control
In the 2021 season, both men once again pointed out the importance of good crop control. According to Peters, this has become increasingly compromised in recent years due to the expansion of work. "During the season, I no longer have time to regularly see all the fields. Fortunately, I have assistance from Harm, who has been taking care of part of the crop control for two years now. I am also still trying to do part of the spraying work. so I can see at least part of the plots. But then again: it's actually just too little." Jonkergouw also sees that crop checks sometimes fall short among growers. "The onions, for example, have suffered considerable damage due to the late anticipation of downy mildew. More or less the same applies to Phytophthora in potatoes: if you check your crops regularly and keep the spraying schedules tight, you can save yourself a lot of trouble'', he concludes.

_{Revus® is a registered trademark of Syngenta
Curzate partner® is a registered trademark of Corteva Agriscience
Ranman® Top is a registered trademark of ISK Biosciences Europe NV}

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