'Growing onions is going well, but concerns are increasing'

Onion cultivation in the East of the Netherlands has grown considerably in recent years. Quite a few new growers have emerged, particularly on the sandy and valley soils of South-East Drenthe and North Overijssel, but also further south in the Achterhoek. For these newcomers it has been mainly 'good years' with good (field) prices and few major setbacks in cultivation.

"Farmers have now proven that excellent onions can be grown from the eastern sands," is how cultivation advisors Florian Gommer and Wobbe van der Veen of Agrowin BV summarize the developments in their work area. At the same time, their concern for diseases and pests is growing. Nematode control in particular is becoming an increasing challenge, but onion and bean fly and downy mildew are also formidable opponents.

Has onion cultivation in the East of the Netherlands reached its maximum? Florian Gommer thinks about the question for a moment and says: "I think that there will be some additional percentages in my work area. Almost half of my customers grow onions on the sandy and valley soils between Emmen and Hardenberg. Especially since 2018 There have been major expansions here - sometimes even with annual doubling per company. Many are close to the maximum of 1-in-8 in terms of crop rotation, but I still expect some expansion."

For Wobbe van der Veen, who has the Achterhoek as his working area, the cards are slightly different. "Many arable farmers in my work area grow seed and consumption potatoes on a large scale. This is mainly done on leased land from livestock farmers. The business operations are almost entirely focused on potatoes; seed onions do not simply fit in there - both in terms of labor and in terms of harvest time. That is why there are In addition to starters, there are also a few stoppers. Nevertheless, I expect that onion cultivation will continue to grow slowly here.

Nematode control is number one
When asked about the biggest challenge in onion cultivation, both men mention controlling nematodes. By far the most damaging is the root lesion nematode (P. penetrans), but also free-living nematodes (Trichodorus spp.) and root knot nematodes (M. hapla and M. chitwoodi/fallax) sometimes leave significant damage in crops, as Gommer knows. The ban on the drug Vydate will only make nematode control more challenging, he says. "Sampling in advance for nematodes was already very important, but that importance will only increase further. You have to know how the nematodes are doing, otherwise you really don't have to sow onions in some plots."

In order to stay in control of nematodes, Gommer expects that the cultivation of marigolds (marigolds) as nematode control will take on an increasingly important role in his work area. In recent years this was often done as a follow-up crop after the grain harvest, but solo cultivation has now gained the upper hand. "With such a solo cultivation you may miss an entire cultivation year, but the control result of Penetrans eels is much better than with a subsequent cultivation. I therefore expect that more and more fields will turn orange in the coming years."

In the Achterhoek, the problems with nematodes are not yet as great as in the sand valley area, but Van der Veen sees that growers are increasingly having to deal with them. "With the mandatory green manure on sandy soil, the plots are green almost all year round, which makes nematode reduction very difficult. No green manure reduces all types of nematodes, so it is always a compromise. With this knowledge, you can assume that the fight against nematodes will continue in the coming years. It's not going to get any easier."

Concerns about onion and bean fly
Another challenge is combating the onion fly. According to Gommer, the pest pressure is currently still quite low in his working area, but he sees that this can quickly change if (even) more onions are grown. He points to the more northern cultivation areas in Drenthe - the Monden - where the pest pressure has now increased considerably. "It is very important that as many growers as possible participate in the Sterile Insect Technology (SIT), because this allows the pest to be properly controlled. In my work area, it is estimated that around 80% of onion growers participate in the SIT. This means that the onion fly well controlled for the time being." Van der Veen shares the concerns about the onion fly, but thinks that the bean fly is a bigger problem at the moment. "Especially at the start of cultivation, we are increasingly seeing damage from bean fly. This insect not only has many host crops, making it easy to overwinter, but it also thrives on fresh organic material such as incorporated green manure and also liquid manure - something that is Eastern sandy soils are traditionally widely used."

Attacked by downy mildew
As far as fungi are concerned, downy mildew is by far the most dangerous customer. Fortunately, the disease pressure was not too bad in the past two seasons, but 2021 was a real downy mildew year. According to both advisors, the fungus took many (new) growers by surprise. "Because onion cultivation is still relatively new, some growers had never seen downy mildew before. As a result, the disease was not recognized in time everywhere and a number of plots were seriously affected. Downy mildew has a fairly long incubation period, but once it in the crop, it can happen very quickly. This has been a wake-up call for many growers - but also for us. We are now even more alert than before on humid, foggy mornings," says Van der Veen.

New label for Fandango
As far as the available remedies against downy mildew are concerned, the supply is becoming increasingly thinner. Van der Veen points out the remedy Fandango, which next year - with a new label - may only be used twice instead of four times per season. "It is a great pity that such a strong and reliable product will soon be allowed to be used less often. This will make it a bit more difficult to get the spraying schedule properly completed," said the advisor. An additional bottleneck is that the puzzle for good resistance management is becoming increasingly difficult to solve. “To meet the FRAC guidelines, we will have to have maximum variety and we literally need all the resources available,” he emphasizes once again.

Both advisors note that growers' awareness of the theme of resistance management is - fortunately - growing. "The discussions about this are becoming increasingly serious. This indicates that growers are aware that smart resistance management is necessary to maintain the effectiveness of the remaining resources," Van der Veen concludes.

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