Theme Day Onions
'Start thrips control as early as possible'
The infestation of thrips kept the onion sector busy last season. At the Onions Theme Day in Dronten, Johan Bierma of Cebeco Agrochemie told more about the very harmful insect, how you can prevent the pest and how you can combat it.
Damage from thrips was frequently observed during the 2017 growing season. Still, according to Bierma, it is not a new phenomenon. However, knowledge development has come to a standstill. “The views haven't changed much since 2004,” he says. "Characteristic for last season was that the thrips pressure was very high early in the season."
host plants
According to Bierma, thrips cannot be prevented, but we can make the plague manageable. First of all, more knowledge is needed. "In the past it was thought that thrips overwintered in the ground. We have now come to different conclusions. Thrips survive as larva or adult animal in a host plant. Lucerne is such a plant, but also green manures, which are increasingly used in winter. frost is the biggest enemy. At an average day temperature of 10 degrees, it starts laying eggs. The first flight occurs in June/July. Depending on the circumstances, 1 animal can lay 50 to 300 eggs. The larvae then eat to the leaf: the suction damage. Larvae pupate in the soil. Depending on the temperature and environment, several populations can be built up in this way."
Last year it became clear that the problems are area dependent. Groningen and Friesland suffered the least, Zeeland and the southwest had the highest pressure. "In very good conditions, 1 thrips can lay 300 eggs. The time cycle then goes from 30 to 10 days for building a population," Bierma explains. "In the most extreme case, more than 1 million thrips are multiplied in 8 season. You do not experience this quickly in practice. With Dutch temperatures, reproduction is often less large-scale. If it is cold, it does not go further than 2.500 insects. We therefore see the biggest problems in greenhouses."
Integrated Control
In practice, thrips are often detected too late. Due to the rapid development, damage can quickly occur. Timing the spray with the right product is essential. "If you interrupt the first cycle, you slow down the population build-up for the entire season," says Bierma. "An integrated approach is required to tackle the problem. This sounds woolly, but it is not. It involves the joint use of chemical and biological agents, working with natural enemies and having good knowledge and skills as background. That starts with prediction modules."
Look at the environment
Cebeco Agrochemie works together with the Belgian company IPM Impact to see which crop protection products are effective and to maintain the natural enemy population. "Beetles, predatory mites and lacewings do extremely useful work," says the Cebeco man.
"We therefore have to move towards a system that retains the enemies. That starts with improving the basic system. Look at your environment and situation. Which crops are nearby? The initial population is high due to host plants. Crop strips in onions are also looked at. to lure natural enemies. The organic sector is already experimenting with this." Trips is not very mobile. They have wings but need the wind. They spread out a maximum of a few hundred meters.
Field edges
In addition to alfalfa, Bierma is also resolute about field margins. "The flowers are beautiful, but they are also host plants for thrips. In practice, we notice that they dive into the crop from the edge. Natural enemies are also abundantly present, but they do not come out of the edge because they have sufficient food. Controlling aphids is a different story. Then there are definitely benefits. Check your crop carefully at all times. There is no damage threshold. If you find larvae, react immediately. Early combat works best."
Control
If you decide to combat, opt for selective means. "Do not use pyrethroids. Preferably not in the entire cultivation and cultivation plan. They do a lot of damage to beneficial insects," says Bierma. A comment that can lead to a lot of reaction from the audience. Certainly among growers of onions and seed potatoes.
"Determine the right injection time for your agent," he continues. "Many agents work well in dark weather. That is why a lot is sprayed at night. Attracting thrips with attracting fructose works well. The available package of agents consists of pyrethroids, the biological agent Flipper, Movento and Tracer. The latter 2 work best. pyrethroids is only 30% on thrips. That also applies to Flipper. The rest is systemic and the effect is longer. In the soil, we see that there is a difference in the presence of natural enemies in the presence of natural enemies, depending on the agent you use."
Bierma: "Movento and Tracer need good growing conditions. That is why the spraying in Zeeland worked so poorly. Movento works best with the first flight in June and Tracer early after finding the first infestation. Flipper is only suitable for checking the population controllable. If spraying is not possible, opt for irrigating. This means less pupation in the soil. If we have a wet season, the thrips pressure is lower. Interrupting the cycle at an early stage has an advantage at the end of the season. the growing season."
Strategy 2018
Winter 2018 had little real winter weather for the time being. It stayed with a single night frost. Bierma recommends starting with soil quality as a strategy for the coming season. "That means more natural enemies. A good structure, a higher content of organic matter, more air in the soil and better permeability ensure this. When combating, the right selective agents must be used, administered at the right time. However, he also indicates that there are still more questions than answers, especially in the area of resources and the use of natural enemies."
Cover photo: Erik-Jan Rampen (@ejrampen).
Niels van der Boom
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