Frequently asked questions

What exactly is herbicide resistance?

Herbicide resistance refers to the resistance of plants to the herbicides used. This is a natural acquirement and not caused by using herbicides. However, this characteristic is eventually selected by the repeated use of the same herbicides.

How severe are the problems related to herbicide resistant weeds?

The current situation worldwide

In the project’s database International Survey of Herbicide Resistant Weeds 432 different resistance types were filed by mid 2014. Of these 432 types 145 types

in the United States of America. Additionally, Australia and Canada are considered severely affected countries. In total 65 countries with problems are registered. This phenomenon is also present in Germany. 22 of a total of about 28 known agents/effect mechanisms are affected – which provide the basis for more than 150 different and approved herbicides. They occur on the fields of 82 agricultural crop species.

Source: Wikipedia

The situation in Germany

We have put together data from our monitoring, which we have been carrying out throughout Germany since 2019, in a blog post. In Germany the most prevalent resistances are found in common redroot and wind grass against ACCase-inhibitors (active ingredient 1 or A) and ALS-inhibitors (active ingredient (2 or B).

You’ll find the article here!

How can a herbicide resistance be detected?

Agris42 offers farmers a resistance test which can be used to determine the current level of herbicide resistance. Click here for more information!

LINK to the handout: detecting resistances in the field.

What can be done against herbicide resistance?

Once a herbicide resistance has formed, the farmer can’t use the previously applied herbicides anymore at all. They can’t be applied effectively anymore and there is no way that the plants regress their herbicide resistance in the short run.

We have summarized some practical observations in a separate blog post: Herbicide resistance – once resistant always resistant?

The only option will be to determine the current situation using a resistance test and taking preventive measures to prevent a herbicide resistance. The test will show you which active agents have already lost their efficacy for you and which agents you can still use efficiently in the future.

Why can a herbicide resistance become dangerous?

Once a herbicide resistance has formed, there is no going back. The farmer loses the option to fight weeds with the most effective herbicides. In many cases there are no alternatives to herbicides and all other measures result in financial disadvantages for the agricultural business.

On top of that, there will also be the known disadvantages caused by the large amount of weed; such as loss of yield, reductions in quality, complications during the harvest and the associated financial losses and increased costs.

Which herbicides will the resistance test test for?

Depending on the weed and the used test system, you can choose from different leaf-active agents.

common redroot & ryegrass

Atlantis Flex, Axial 50, Agil-S, Select 240, Broadway

wind grass

Husar OD, Axial 50, Broadway, Agil-S, Select 240


Attribut, Atlantis Flex, Avoxa, Select 240, Maister Power

What do the test results mean for herbicides which were not included in the test?

Our selection of herbicides covers the most popular active ingredients. This also allows us to make a point regarding herbicides of the same active ingredient group. For example the results of Agil-S and Targa Super (both FOPs for i.a. rape) are comparable.

Why don’t you test for soil applied herbicides?

Testing for soil applied herbicides is more expensive than testing for the classical post-emergence herbicides. Since we cannot guarantee that the tests will be completed by the time the seeds are sown, we still don’t offer soil applied herbicides tests. For the 2021 season, however, we are working on a modified test system to be able to offer a test for Flufenacet resistance.

Will you grant a discount if multiple samples are sent in?

Yes, if you send in at least 10 samples, we can offer you a 10% discount. If you send in at least 20 samples, we can offer you a 15% discount.

Can I get tests for a variety of herbicides and application rates?

Yes, if you provide 30 or more samples, we’ll also offer custom testing. We’ll gladly provide you with a custom offer. Please feel free to contact us!

When and how do I need to collect the weed samples?

common redroot:

The perfect time has come once the plant starts to cast its first seeds. This normally happens 1-2 weeks before the regional barley harvest is supposed to begin. You can then easily strip off the seeds from the heads and pack them.


Normally ryegrass does not cast its seeds or if it does, it will happen quite late. However the seeds will be ripe around the same time the common redroot seeds are ripe. This means about 1-2 weeks before the barley harvest. But it can also be collected just before the wheat harvest is about to begin. We recommend packing the whole brittle head in case you can’t strip off the seeds.

wind grass:

Wind grass takes longer to ripen than common redroot. You should wait until about 1-2 weeks before the wheat harvest to ensure that the seeds are fully ripened. Then simply strip off a big tuft from the plant and pack it.

Brome’s seed maturation depends on the brome type. Experience has shown that 1-2 weeks before the harvest is a good time here as well. Then strip off the seeds from the plant as well as possible.


Additional information can also be found here:Resistance testing manual

Can you only test for grass weeds or do you also have offers for weeds such as chamomile, corn poppy, cornflower, and bur-chervil?

In general we can test all weeds, as long as we receive ripe seeds. These are sown according to the same principle as the grass weeds and then tested. Please contact us for individual requests regarding herbicide and application rates.



Additional grass weeds and weeds which can be tested:

  • millet types: barnyard grass (Echinochloa), green bristlegrass (Setaria), smooth crabgrass (Digitaria)
  • chenopod and saltbush
  • knotweed types
  • chamomile types
  • corn poppy
  • cornflower
  • bur-chervil
  • additional ones upon request