'Fighting downy mildew even more challenging'

The label of the onion fungicide Fandango has been drastically changed. Last year, four applications per cultivation cycle could be carried out, this year (2025) that will be a maximum of two.

According to onion specialist Stefan van Heist, this makes the control of downy mildew even more difficult and uncertain than it already was. "The most important thing is to use all available resources as targeted as possible and according to the applicable FRAC guidelines. In this way, the resources remain effective and we also have the tools to keep the resources on board as much as possible. Furthermore, we must seize all cultivation possibilities to keep the disease pressure as low as possible."

"Yes, it's going to be a big challenge in the coming years anyway," says Stefan van Heist when the fight against downy mildew in onions comes up. Last season it became clear once again how fast, violent and massive this fungal disease can rage through the crop.

"I don't need to tell growers much more about the importance of strict mildew control; that has become very clear in the past year. However, it is good to take a good look at the spraying strategy again, especially now that the basic agent Fandango may only be used twice."

Follow FRAC guidelines?
For this season, in addition to Fandango, the combinations of Orondis® Plus + Amistar® and Zorvec® Epicaltrin + Kenbyo® are available. Both combinations may legally be used three times per cultivation cycle. Together with (maximum) two times Fandango, this amounts to eight sprayings in total. However, if you follow the FRAC guidelines, you will see that both combinations are partly in the same active group.

To prevent resistance formation – and thus decreasing effectiveness – it is strongly recommended to perform a maximum of one third of the sprayings with OSBPIs (Orondis Plus and Zorvec Epicaltrin) and a maximum of 50% of the sprayings with strobilurins (Amistar and Kenbyo). In practice, this means that only three instead of six sprayings can be applied. Together with two times Fandango, this effectively leaves only five sprayings per season.

According to Van Heist, it will be quite a challenge to keep downy mildew under control according to the FRAC guidelines, especially with high disease pressure. "However, we must all strive to prevent resistance formation. Start the schedule on time, alternate, coordinate the choice of agents according to the FRAC guidelines and always adhere to the label dosages; that is the urgent message for this season," says the onion specialist.

Nitrogen and variety selection
As for cultivation measures that can slow down downy mildew, Van Heist mentions nitrogen fertilization first. "Try to do this somewhat sparingly and in doses," he advises. "A massive package of foliage, which usually remains moist for a long time, is an important driver of downy mildew."

Another way to contain the disease is through variety selection. "Here, breeding is mainly responsible for crossing in certain properties for the future. There are varieties that are less sensitive to downy mildew. But targeted control through variety selection is still a bridge too far for many growers, although we should certainly continue to cherish this option for the future," says Van Heist.

Wake-up call
Finally, the onion specialist emphasizes that the label adjustment for Fandango should be a wake-up call for the entire sector. "To avoid even more restrictive measures - or even losing resources altogether - we must do everything we can to prevent emissions to surface water. So do the farm emission scan and take the advice that comes from it seriously!" According to him, the construction of a filling and rinsing area in particular where residues of crop protection agents are collected can reduce emissions enormously.

The same applies to the closed filling system that will be mandatory from next year. "Don't see it as a hassle or a nuisance in advance; it can really help to keep important resources running. Also look at the possibilities of creating an infiltration channel in an uncultivated strip around the plot parallel to the ditch. This ensures that crop protection products do not end up directly in the surface water after a rain shower. Now Fandango is supposedly the victim, but if we do not work more on emission reduction, more resources will follow. Working on emission reduction is no longer optional, it is an absolute necessity," Van Heist states again.

_{^{Orondis® Plus and Amistar® are registered trademarks of Syngenta
Zorvec® Epicaltrin is a registered trademark of Corteva Agriscience
Kenbyo® FL is a registered trademark of BASF}}

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