Most farmers are familiar with the problem of herbicide resistance. Though many believe that the problem can be solved with long-term use of other herbicides.

Herbicide resistance is threatening more and more acreage in Europe. The dangers from weeds and grass weeds is also threatening more and more businesses in Germany. In some cases no significant success can be recorded in weed control – even if herbicides with different mechanisms of action are used and the treatment intensity is increased. Only proper risk management can protect farmers against financial losses.

Did you know? You can have your acreage tested for herbicide resistance economically!

What causes herbicide resistance?

It is common to treat fields for years with herbicides that have the same effect mechanism. The short-term result is a greatly reduced weed population due to the good herbicidal effect.

However, only weeds that are less sensitive to herbicides can survive. These plants can use their biological advantage and continue to produce their seeds. As a result, the proportion of resistant weeds increases steadily until the entire population consists of herbicide-resistant weeds.

Herbicide resistance is increased by the following factors:

  • Unilateral tillage over several years
  • Corny crop rotations with high levels of weeds that are difficult to control
  • Early sowing in autumn, which leads to a higher density of weeds

Are you affected as well? Let’s test your acreage economically!

Can herbicide resistance disappear again?

If you asked a scientist, you would most likely get a positive answer – with the demur that it would take several decades. For this, however, certain conditions must be met – with factors that are difficult to control in agriculture.

In general, weeds that are not resistant must then have an advantage over herbicide-resistant plants when it comes to survival. However, there are very few scientific studies on this, as it is methodologically very difficult and time-consuming to prove or also to document the biological advantages of resistant and non-resistant plants. This biological advantage can be higher seed production or better resistance to fungal attack. So it depends on whether the plants have better chances of survival than their herbicide-resistant relatives. It can take decades before noticeable effects can actually be seen on the fields.

Herbicide resistance trial Agris42

In many cases it has been shown that existing herbicide resistance can only be combated by the challenging process of changing herbicides. To be able to capture the problem with data from long-term studies, we carried out several studies here at Agris42. We want to prove what happens on the acreage if there is no selection through the use of herbicides with this study.

Our observations always start on fields with strong resistance to certain herbicides.

Example 1

In a conventional field, resistance to Atlantis, Axial, and Maister was found in redroot. When sufficient weed control was no longer possible in 2014, the field was no longer used for 4 years and trefoil-grass was sown in autumn. In 2017 fall wheat was grown again. The resistance situation has remained exactly as it was before the trefoil-grass was sown in 2014. Only the number of seeds in the soil was reduced during the non-productive phase, but not the ratio of resistant to sensitive seeds. Thus, in 2018, when the first wheat was sown after 4 years of trefoil-grass, no sufficient redroot control was achieved. Due to the high level of residual weeds, the seed potential in the soil will soon be back to the starting level of 2014.

Daten: Dissertation Herrmann (2016)

The redroot population, which is herbicide resistant, remains dominant in the fields.

Attention! Only preventive measure can protect you against herbicide resistance! Have your fields tested now!

Example 2

For eight years, herbicides with the active ingredients ALS and ACCase were not used in this field. In this example it can also be determined that no improvement in the resistance situation can be observed over a longer period of time.

Daten: Dissertation Herrmann (2016)

Example 3

In this example, samples were taken from a field that was switched to organic farming four years ago. Herbicides have therefore not been used for control in the last 4 years.

This example shows that even after 4 years of organic farming – and the resulting omission of herbicides – the proportion of resistant redroot plants in the total population has remained the same. A decline in resistant plants, and thus the restoration of the necessary sensitivity for the use of herbicides, cannot be measured after this period.

Daten: Dissertation Herrmann (2016)

Conclusion of this study

Herbicide resistance cannot be reversed once the problem has developed in the acreage. The resistant plants dominate the fields and there is no biological advantage for the non-resistant weeds to become dominant again in the population.

For farmers this means that they will lose the possibility of using certain herbicides for weed control forever (or at least for the next few decades). There is only one way to effectively combat herbicide resistance: by implementing preventive risk management. This is the only way to recognize an impending danger at an early stage so that measures can be taken to counteract herbicide resistance. Otherwise the farmer loses the opportunity to control weeds with herbicides!

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