The thrips pressure in onions is again high. In the last 2 weeks the thrips populations have developed extremely fast. The combination with the drought is extra disadvantageous for the crop.
In regions where there is little crop, thrips cause extra nuisance; the crop can withstand less there. This mainly concerns the regions of Zeeland and North Brabant. There has the extreme rain caused a delayed development of the crop at the beginning of the season.
These crops are already stressed and are therefore extra sensitive to thrips, says Jelle Westerlaken, crop advisor at Syngenta. "The heat also ensures that the cycle of the thrips goes even faster. Thrips thrive in warm weather."
Early printing
The thrips pressure was present early on, as Johan Bierma of Cebeco Agrochemicals saw. "Larvae were already found in the second-year onion sets at the beginning of June. Initially there was not much damage, but the thrips were dormant. This now results in high pressure in the plots where the correct measures were not taken. are taken."
Westerlaken sees that the onions are showing little development, partly due to the drought. "There is little foliage development and most of the energy is put into the bulb." Last year the situation was even more explosive and the thrips population developed faster. "Some plots were completely gone by July," Westerlaken says.
The crop is generally in better shape in the provinces of Flevoland, Groningen and Drenthe. The crop has been further developed there, but the thrips population is also developing rapidly there.
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Control
It is best to spray late at night. "This is because thrips emerge at night. By spraying as late as possible, you have the best chance of contact. Pyrethroids are also quickly broken down by light and heat, so spraying in the evening has a greater effect," says Westerlaken .
It is important that a good wetting agent and plenty of water are used. Little pressure, so that a large drop is created, is also important. This causes the drop to sink further into the plant, where the thrips are.
June important
According to Bierma, the move (to keep the pressure manageable) should have been made in June. If this has not been done, or has failed, growers may continue to lag behind. This is when the dry weather lasts for a number of weeks.
"Last year, many growers in Flevoland fell through the eye of the needle, because the weather in July was unfavorable for the development of thrips at one point. This is in contrast to Zeeland, where heavy damage was caused by thrips and drought in 2017. "That has made thrips control more difficult," says Bierma.
Main photo: EJ Rampen (@ejrampen).