What are onion growers doing about thrips this season?

Due to the recent warm and dry weather, thrips pressure in the north and south of the Netherlands is rising. Good monitoring is required to prevent damage to the crop. Which approach do the Gewastour onion growers opt for?

Thrips can cause significant yield loss and should not be underestimated. In addition, last year it became apparent that thrips can also cause considerable damage in storage, and batches were even rejected. 

Monitoring of thrips
With summer temperatures of 25 degrees, as is the case this week, the life cycle of the thrips is going fast. The higher the temperature, the faster the life cycle of the thrips. It is both the larvae and the adult thrips that cause damage to the crop. Please note: at the end of July you will often find more grain or field thrips in the onion fields. These adult thrips cause damage but do not lay eggs in onions and therefore do not produce larvae.

But finding a number of thrips in the onions does not immediately set off the alarm. "With thrips, it's not about complete control, but about keeping it manageable in the crop," says Mark Ermers, Crop Advisor at Bayer CropScience. "Combating thrips 100% is not necessary and actually impossible. You start by checking the crop, in other words, monitoring it properly. You can intervene on the basis of what you notice. Finally, you check the crop and assess whether the surgery worked." 

Compared to previous years, the thrips pressure is lower this season. The typical Dutch summer is mentioned as the main cause. This is also clearly visible when we look at the control of thrips in onions. Onion growers who have already applied several sprays in recent years are now often given 1 spray with the preventive agent Batavia. Also this year the thrips pressure is traditionally lower in the north compared to the south.

According to Ermers, the effect of Batavia in the last days of July must be taken into account: 'After the last days of July, on average, the plant increasingly switches to generative rather than vegetative growth: the product then goes to the convex instead of the foliage, which means that the deployment of Batavia is no longer useful. Then choose other means, for example Tracer + Attracker.'

Which approach do the onion growers choose?
The Gewastour onion growers monitor their crops, but many have not yet sprayed and, compared to previous years, have not yet found many thrips. Onion grower Klaasjan Boer from Kortgene (Zeeland) now has the Batavia on it: "I sprayed Batavia last week. Normally I spray against thrips earlier, but I didn't come across that much in the crop." Harmjan Hospers from Nagele (Flevoland) also sprayed Batavia: 'We have chosen to spray the onions preventively, partly because there is grass seed and winter wheat around it.'

Last week (week 28) Batavia was sprayed on the plot of Aeres Hogeschool in Dronten (Flevoland). At the other onion growers it is still quiet with regard to the control. A few saw an increase in the number of thrips found this week, so they are keeping a close eye on the crop.

Jesse Torringa

Jesse is an editor at Boerenbusiness and focuses in particular on the arable farming sector, including grain and onions. He also closely follows the fertilizer market. In addition, Jesse works on an arable farm in Groningen with seed potatoes as the main branch.

j.torringa@boerenbusiness. Nl

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