Downy mildew plagues the sector

Downy mildew is spreading throughout the Netherlands in the cultivation of planting and seed onions. Crop protection advisor Steven Dorrestijn analyzes the cause of the early outbreak and gives his view on the best approach to the insidious disease.

"The situation is quite worrying. I hear reports of downy mildew from all over the country. And the disease also arrived exceptionally early this year." Steven Dorrestijn has just returned from holiday and he is immediately in luck. "It's all about downy mildew. Consultation with colleagues, phone calls from growers, viewing tests. The sector is currently completely under the spell of the fungus." Syngenta's crop protection advisor knows of examples of growers who had already sprayed twice before July 1 and still got downy mildew. "We are dealing with a combination of circumstances that misled growers and caused downy mildew to quickly spread."

Vulnerable stage
The circumstances that Dorrestijn is talking about are threefold. "To start with, there was pressure from downy mildew from onion onions early on, but that happens more often. Two other things were unusual. Due to the late sowing, many sowing onions were still very small around the longest day and growers thought they were still growing. did not have to start with the downy mildew control. But the bulbing has already started. Because that is a day-long process. You can sometimes barely see it, but at or just below ground level, the onion starts to bulb stage, an onion is very vulnerable to downy mildew." The third factor also has to do with the erratic spring, Dorrestijn continues. "Because they are behind in development, many plots have caught up under the growing weather. This means that the last spraying is more likely to be diluted, so the onions are more vulnerable. All these factors together have ensured that the downy mildew fungus could strike quite easily on many plots of land."

Robust means
With only 3 approved products that work well on downy mildew, onion growers currently need all the sprays that the labels allow. "But it is still important to alternate and also to look carefully at the differences in strength between the products," says the crop protection advisor. “Our fungicide Orondis®Plus Amistar has been the strongest in flushing tests for years. And the practice schedules in which the Orondis Plus Amistar is used early always score highly. These results are due to the high dose of oxathiapiproline; Orondis Plus Amistar is unique in this regard. And that is why we always set the drug at T2 and T5 in schedules so that you benefit from that robust dosage early in the schedule. Because that simply provides better protection. If you add an esterified rapeseed oil to it, the result becomes even better. And because the weather will probably remain moldy for a while, the third spraying with Orondis Plus Amistar can still prove its worth."