When will phytophthora strike again?

Potato cultivation shows a predominantly positive picture. Growth is going well, partly due to sufficient precipitation and relatively mild temperatures. In many plots the crop is now closed or almost closed. The emergence is generally good and even. On some lighter soils growth has lagged somewhat, especially where there was previously a lack of moisture. With 2024 still fresh in the memory, the question is when phytophthora will strike.

Several growers report a smoothly developing crop. The first flowering is now also starting on sandy soils. The first foliage sprays are being carried out, aimed at, among other things, protection against phytophthora. In 2023, phytophthora was first observed in the first half of July, while in 2024 the first infestations already appeared in the first week of June. This early pressure in 2024 led to great vigilance and more intensive spraying schedules. In 2025, as far as is known, no contamination has yet been detected.

First sprayings
In practice, the focus is now mainly on preventive protection. Growers combine resources to stay on top of phytophthora. The choice and timing differ per region and crop condition. Where no treatment has been done yet, it is often planned for this week, in anticipation of changeable weather.

In Friesland, grower René Mesken from Appelscha (Friesland) reports that he has sprayed the earliest potatoes for the second time now. "I sprayed the last one on Friday just before emergence." His experience is that foliar fertilizers contribute little at this stage 'certainly not so early'.

Brian Salome from IJzendijke (Zeeland) indicates that he has already sprayed three times. "The first two are done, the third will follow tonight." He has already started with foliar feeding. "From the moment the first tubers were formed, we use foliar feeding weekly. I do not use artificial fertilizer, so this is a fixed component." According to him, it is still too early for foliar feeding for the Innovator variety.  

Sander Uwland, crop advisor arable farming at Bayer Crop Science, emphasizes the importance of resistance management."Always two active substances! We know that a number of substances no longer work on certain strains. If you start working with single substances, you run the risk of selecting out again. You don't know which strains are in your plot when! So I don't think it's an option to spray single substances."

Stay alert when faced with disease pressure
The coming period will determine the course of the season. Phytophthora can develop quickly, especially in humid conditions and dew nights. Growers are therefore advised to continue to inspect the crop regularly and to adjust in time. 

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