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Damage caused by thrips in onions locally dramatic
When you can recognize damage caused by thrips in a field of onions while driving from the road, you know that yield loss is a fact. When that is also extremely early in the season, the yield loss can amount to more than 30%. Then the risk increases that the storability is compromised.
After all, the application of Royal MH can no longer be used optimally by the crop and, moreover, thrips can enter the storage with the harvested onions.
Why an extremely high pressure of tobacco strips locally?
A problem rarely has one cause. This also applies to the explosive increase in thrips in onions.
host plants – The basic pressure of tobacco strips depends on host crops (onions, cabbages, fodder radish, etc.) in the cultivation plan or the immediate vicinity of the plot. Especially in years with moderate winters, thrips survive not only as a pupa in the ground, but also as an adult on host plants or under crop residues. For this reason, the pressure seems to be increasing nationally in recent years.
Temperature – The rate at which a group of thrips can multiply mainly depends on the temperature. In cool years there are usually only a few generations with few offspring. In that case, leaf damage will hardly be visible. In warm periods, however, the development can increase considerably. In very warm years there are 4 to 6 generations, which together can form millions of descendants!
Crop growth – In a well-growing crop, not only does the less penetration of sunlight result in a somewhat lower temperature, but the crop is also cooler due to higher evaporation. This small effect on temperature can have a major impact on the final population of thrips. In addition, a well-growing crop has an active sap flow. This is an important condition for a systemic agent like Movento to work. Due to the drought in many areas, there was sometimes very moderate growth this year with very limited absorption possibilities.
Control – Thrips hide in the crop when there is a lot of light. For an optimal effect of contact agents (such as Flipper or Decis) on adult thrips, hitting the insect is necessary. This can only be the case in dark weather (cloudy, evening or night) and an application with plenty of water. For optimum control of the small white larvae (which cause the most damage to the suction), the systemically active Movento must be used immediately after the first larvae have been observed. The most optimal recording conditions in a well-growing crop must be used for this. If foliage growth is not or is no longer an issue, then no optimal result can be expected from Movento. Using Movento at this point in the cultivation is therefore no longer an option.
Did Movento actually work?
The answer to this question is without a doubt yes. Year after year, the trials show that Movento is the ideal basis for limiting the population structure of tobacco strips in onions. However, the conditions mentioned above play a major role. Movento must be absorbed by the plant for good effect and carried to the shaft of the onion by the sap flow. This takes a few days in a well-growing crop. By counting, effect can often be established after 3 days. Despite the fact that an effect sometimes takes much longer to appear, Movento is actually working to combat the larvae. In addition, remember that a well-executed application can never work 100%.
One of the reasons for this is the fact that several stages of tobacco strips are present in the crop at the same time. If 50% of a population of, for example, 90 million thrips per hectare is controlled, 5 million individuals will still remain alive. This explains the sometimes disappointing results in the control of tobacco strips.
The graph below shows the average number of larvae per plant from a thrips trial this year in Lelystad. The count of 27 July shows that Movento, applied under good conditions, was able to limit the build-up of the thrips population.
