'Focus on phytophthora, don't forget alternaria'

"Of course I am extra focused on phytophthora this year. But that other disease - alternaria - can also cause a lot of damage, so we should certainly not forget about it." This is what arable farmer and contractor sprayer Jan Willems says in Wanroij (North Brabant). Together with advisor Maarten van Erp from Willems Balgoy, he is looking ahead to the coming potato season.

It's early April and the weather forecast promises quite a bit of rain in the coming weeks. However, for Jan Willems it is no reason to worry. He was able to sow his spring wheat, sugar beets and Japanese oats all neatly; only the potatoes still need to be planted. "Last year the potatoes only went into the ground at the beginning of May and that ultimately resulted in a very reasonable harvest. So let's not rush and wait until the weather dries up; there is no point in getting muddy now," he says while pouring a cup of coffee in the kitchen.

From pigs to arable farming
Willems' company was originally mainly a pig farming company, but has slowly been transformed into an arable farm since the early 90s. The second branch - contract spraying - was also added during that period. "That started as a hobby, but has increasingly become a permanent part of the company. I now spray about 1.800 to 2.000 hectares of crops every year. I can just about do that with my arable farm," says Williams.

Within the crop plan, potatoes are the most important crop. In recent years, Willems mainly grew Ivory Russet (for fries) and Hansa (for the fresh market). This season, however, he is switching completely to Isa, the new variety from potato processor Peka Kroef and supposedly the successor to Hansa. Willems has followed the 'test period' of the breed closely and expects Isa to do well on his soil. Van Erp also does not see any issues that will complicate cultivation for the time being. "In terms of cultivation and crop protection, Isa hardly differs from Hansa. And because we now know Hansa inside and out, I do not expect any significant problems with the transition to Isa."

Seen way too much phytophthora
When asked about things that could cause problems this year, both mention phytophthora. Willems says that he had to spray quite intensively last season to keep the disease under control. This did not work out completely on one plot and the disease was very prevalent, he remembers well. "Fortunately, we managed to stop the infection, but after years of low disease pressure, it was yet another signal that you should never underestimate the fungus." 

Maarten van Erp recognizes this image all too well. He says he saw 'far too much' phytophthora last year and is extra alert to it this year. According to the advisor, the South-East of the Netherlands is in any case a 'hot spot' for phytophthora. "Favorable conditions for the disease often come together here, such as balmy nights with little wind, a lot of irrigation and also - we must be honest - relatively large amounts of potato storage that are not controlled or not controlled enough. All these factors together form a very fertile ground for the fungus." Last season, Zorvec and Revus were also initially sprayed solo in a number of places - products to which it is known that phytophthora strains can become resistant and that these products then no longer work. "That obviously did not help to keep the disease under control," says Van Erp.

To prevent early infections, potential sources must be eliminated as early and as completely as possible, Van Erp emphasizes. These are not only uncovered waste heaps, potato storage and infected seed potatoes, but also the few hundred hectares of potatoes in the area that are (still) in the ground. "If they are not dug up - or if they are properly cultivated and the emerging plants are controlled with Roundup - then this can be a very large source of infection for phytophthora. We must prevent this at all costs."

Don't forget Alternaria
Although the focus this year is clearly on phytophthora, according to both men, alternaria should not be forgotten in disease control. Van Erp calls alternaria a silent killer that can quickly swirl through the crop at the end of the season and cause a lot of damage unnoticed. "In my opinion, those spots at the end of the season are still too often taken for granted. But they often cost an unnecessary amount of kilos. Not everyone realizes that."

According to him, the mindset surrounding the disease still plays a role. "Alternaria mainly occurs in drier seasons; you do not always associate it with fungi and danger. In warm and humid weather this is very different; then everyone knows that phytophthora is lurking and everyone is on alert - especially this year ." He also warns against 'stressful transitions' - such as sprinkling with cold water during hot weather. "These are those moments when the crop weakens for a moment and alternaria can strike very easily."

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