Protection of silver onions and first-year onions

"To keep silverskin onions and first-year onion sets disease-free, a comprehensive spray schedule with short intervals is necessary. We need all available resources for this," says cultivation advisor Dick van Kranenburg of ProfytoDSD. Together with his colleagues, he manages approximately 250 hectares of silverskin onions and 300 hectares of first-year onion sets annually, primarily in the Noordoostpolder and Drenthe.

Bayer spoke with Van Kranenburg in mid-May, when most silverskin onions and first-year onion sets were just barely above ground. "So far, everything looks good. And with the predominantly dry weather, there aren't many diseases to worry about yet; so we're off to a good start," he said, describing the current state of affairs.

How different it was last season, when sowing was difficult and delayed due to persistent wet weather. "Especially with first-year onion sets, we saw considerable water damage and loss. Combined with significant disease pressure, this definitely impacted yields. Yields were highly variable, especially in the eastern growing regions—where slightly more rain fell and disease pressure was also higher than here in the Noordoostpolder."

It was also striking that the last-sown plots often performed best, mainly because they were less affected by the bean and onion fly. This also applied to the silverskin onions, which largely avoided the bean and onion fly due to their later sowing date. "So late sowing doesn't always have to be bad," Van Kranenburg emphasizes again. While yields of first-year onion sets were highly variable, those of silverskin onions (in the NOP) were remarkably good. "I think we averaged over 60 tons per hectare. That's easily 5 to 10 tons more than average," the advisor explains.

Tightly-knit spray schedule
According to Van Kranenburg, a well-structured spraying schedule is absolutely essential for controlling diseases like leaf spot and downy mildew. "First-year onion sets and silverskin onions are both very dense crops that often experience a humid climate. As a result, disease pressure is considerably higher than with seed onions. With spraying, you have to be even more vigilant, and you can't afford to make any mistakes."

In order to keep the spraying schedule closed for the entire growing season, all available resources are used, as the advisor shows on a paper printout. Infinite, Fandango and OrondisPlus®/Zorvec Epicaltrin® the three most important agents against downy mildew and Scala®, Luna Experience and Amistar® are the three most important against leaf spot disease.

"With a spray interval of three to four days, we can cover the silverskin onions for eight to nine weeks, which should be sufficient in principle. But as mentioned, with all the increasing label restrictions, we now need all available resources. And with the prospect of the restrictions on resources only increasing, and the question of how long some will remain permitted, concerns are increasing somewhat," says Van Kranenburg, who adds that more or less the same applies to first-year onion sets.

All resources needed
To make the crops "hardier" and more resilient, the program also includes several biostimulants and liquid fertilizers, including manganese, zinc, copper, and silicon. The advisor emphasizes that these are "at most" supplements or reinforcements that can keep the crop more vigorous and therefore slightly less susceptible to disease. "The foundation for combating leaf spot and downy mildew remains a well-designed fungicide program."

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

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