'Handling the resources we have wisely'

With the disappearance of mancozeb this season, an important building block for disease control in onions has disappeared. It was also uncertain for a long time whether the Fandango drug would be available for practice this year.

So uncertain times for Dutch onion growers – who will be more than ever about sensible and future-proof choices. Bayer spoke about this with Mark Ermers, Crop Advisor field vegetables and onions at Bayer.

It was still exciting whether Fandango would be available for this season…
"That's right. In December, a specific additive that is needed for the production of Fandango was not available. Fortunately, this problem was tackled very well together with the sector and Fandango will also be available in 2022."

So good news for Bayer?
"Fandango is indeed an important product for Bayer. But this is also good news for the onion sector. The fungicide schedule in onion cultivation has always been based on mancozeb and mancozeb-containing products in the past. With the disappearance of mancozeb as an active we're just missing four key fungicides, which means we have to build the schedule with far fewer resources. Without Fandango, we would have lost another half of the available sprays against downy mildew. And that would affect the control of this disease , but also for resistance management, for example."

Can you explain that a bit further?
"With resistance management, you try to prevent existing resistant individuals within a population of a pathogen from multiplying unhindered and thereby gaining the upper hand. For example, if part of the population within a fungus is resistant to fungicide A, but you can alternating with fungicide B, such a spraying with fungicide B ensures that the resistant individuals cannot gain the upper hand. Because each spraying affects the composition of such a fungal population, being able to alternate available fungicides is crucial. Against downy mildew in onions, without Fandango we would still have two products that also have the same active ingredient as a basis.

What is the best approach to disease control this season?
"First of all, you will need to know which diseases in your onions are important and under which conditions they can really pose a threat. Where and when can you first find the symptoms of a certain disease in your crop? And in what ways is that possible? If you as a grower do not have an answer to these questions, it will be very difficult to achieve optimal control. Take downy mildew, for example. Some growers think that this disease can also be combated curatively. But if you If you know that after an infection it can take up to sixteen days before you see the first symptoms in the crop, then there can be no question of a curative approach, and the current products only have a preventive effect anyway.

With Fandango it is good to know that in addition to a strong preventive effect against downy mildew, it also works excellently against Stemphylium and leaf spot disease. You can therefore use Fandango without having to add products against other diseases. We know from the past that Fandango can be quite a sharp product. After all, it is originally a grain fungicide that has been formulated in such a way that distribution and absorption must be as optimal as possible. In the fastest leaf growth phase, Fandango can therefore be just too sharp for the onion. The advice has therefore been for years to only apply Fandango solo from the third spraying. Then the fastest foliage growth phase is over and there is no more risk."

Advice schedule onions

• Rudis: Soil application before sowing 0,6 l/ha. Avoid direct contact with seed.
• Fandango: 1,25 l/ha. Apply from spherical formation. A maximum of 4 applications of which 3 consecutive times.
• Luna Experience: 0,5 l/ha. Maximum 2 applications.
• FLIPPER: 5 l/ha. Single contact operation. Hardness of the aerated water <16,8°dH. Add Dynex. Selective for consumption.
• Dynex: Add to FLIPPER(Dynex not in bio). 0,1% per 10 degrees dH (dH 15 = 0,15% Dynex, dH 20 = 0,2% Dynex etc.). Pay attention to mixing order.
• Batavia: 0,75 l/ha. In onions always in combination with Robbester 2 l/ha. Apply preventively. Good growth necessary for transport through the plant. Selective for consumption.
• You decide: 0,3 l/ha. Single contact operation. Not selective for consumption.

What matters do you think are important for the near future?
"A recent forecast has determined that with the current authorization policy we will have about half of the current number of active substances left in Europe by 2025. This means that we have to use the pesticides that we have left wisely and that we have to take steps in other areas that can help us further control leaf diseases in onions. Breeding seems to play an important role in this. With varieties that are tolerant to certain diseases, we may be able to manage with less use of fungicides, but make no mistake: also that tolerance can easily be broken again. There is also an important role for predictive models in the immediate future. When you know better when conditions are favorable for a certain leaf disease, you can also use the limited available resources in a more targeted manner. monitoring there is still a lot to gain."

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