Dutch Crop tour Onions - week 28
Alarm bells are ringing because of thrips in onions
The warm weather gives thrips the perfect conditions to develop and cause damage to the onions. Damage has already been observed in several plots and the thrips pressure will only increase with the warmer weather.
Onion growers are detecting thrips earlier and earlier in the growing season. That was the case again this season. Where the insect used to be mainly found in the warmer south of the Netherlands, the plots in the far north are also covered by it. Several fields have already been affected and thrips can be a threat to onion cultivation for at least 6 weeks.
In addition, another well-known from last season has also been observed in onion cultivation: Downy Mildew.
Youngest leaves most susceptible
According to Mark Ermers, Cropadvisor at Bayer, you have to keep monitoring the onions throughout the season and act on what you see. "With cool, damp weather and a growing crop, the chance of damage is smaller and you have more time to apply crop protection under better conditions. If the weather is warm and dry, the population of thrips can increase enormously within a few days. According to the weather forecast, it will be so hot that the onions will be under stress and growth will come to a standstill. The youngest leaves in particular are therefore more susceptible to thrips."
Several growers have already carried out the second treatment with Batavia, which is intended to protect the crop against the larvae of the thrips, the greatest danger. Batavia is absorbed by the plant and works against immature sucking insects. Tracer + Attracker or Benevia can be used to combat adult thrips. Make sure to use the correct DRT conditions.
Irrigation against thrips
A rain shower also does the onions good in terms of thrips control. If you start counting trips after a few rain showers, you will count less than before. An artificial rain shower by reeling also hinders the thrips but is not sufficient to protect the crop. Irrigation helps the crop in several ways:
- Disturbing thrips feeding on a plant. Thrips don't like humid conditions
- You ensure that the plant will grow again. Because the plant grows, thrips always strike at a different place on the plant. This does less damage than multiple times in the same spot.
- The applied agents can do their job better because the transport within the plant is active.
Thrips will not be killed by irrigation. "If you open an onion pipe, you can see how deep the shaft is. You can never fill it completely with water, there will always be some air in it," explains Ermers.
Robin Winter
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