Downy mildew is appearing early again this year

Downy mildew is showing up early this season. The fungus was already observed at the end of May and not only in the onion sets. The fungal disease is showing itself remarkably early this year, just like last season, when the first attacks also appeared early in the year.

The onion plots within the Crop Tour were sown on average around 20 March this year. That is almost a month earlier than in 2024. Due to the early sowing and varying precipitation distribution per region, the emergence was not the same everywhere, which leads to a more vulnerable crop on some plots. At the same time, growth in many places shows a strong picture.

Hubert Linders from Nederweert (Limburg) is positive: "The growth is great, it's really going fast. Last week the first spraying was done with Orondis Plus. That laid a good foundation considering the weather."

Preventive approach essential
Although the attacks have been limited so far, downy mildew is now observed in several regions. Since the available package of remedies only works preventively, a timely and consistent control strategy is necessary. Curative interventions are not possible. In practice, it is advised to maintain a strict spraying schedule, for example with Zorvec Epicaltrin in combination with Kenbyo FL and a wetting agent, applied at an interval of seven days.

The approach differs per region and situation. Klaasjan Boer from Kortgene (Zeeland) says: "Our best plot has now been sprayed twice. The other plot has not yet, but we will do that this week before the rain." 

In addition to crop protection, hygiene is also of great importance. Onion waste and plant remains must be well covered to prevent the spread of spores. Such material is an important source of infection, especially after a mild winter and with an early start to cultivation such as this year.

Different choices per grower
Not everyone is opting for a chemical approach at the moment. Like Reinder Hogenhout from Kimswerd (Friesland). "At the end of the week I'll just give the onions some Vitalosol Gold (a foliar fertilizer). If I were to start using chemicals now, it wouldn't work out either... There aren't many options." David de Wit from Lepelstraat (North Brabant) sees a strong crop: "The onions are growing very fast, I'm seeing six tubes. No thrips found yet." Last Friday he carried out a preventive spraying against downy mildew.

Vigilance is required
The early pressure of downy mildew emphasizes the importance of close crop monitoring. The fungus can develop rapidly, especially during dew nights and high humidity. By staying alert and taking timely measures, growers can keep the disease under control and guide their crops through the coming weeks in good health.

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