Herbicide resistance testing

Herbicide resistance testing

Order your herbicide resistance test

With an over reliance on a much smaller range of herbicide mode of actions the chances of herbicide resistance developing to any giving active is now increasingly higher.

In the UK there are three main grass weeds and three broad-leaved weeds affected by herbicide resistance to a range of different modes of action.

  • Black-grass (Alopecurus myosuroides)
  • Italian ryegrass (Lolium multiflorum)
  • Wild oats (Avena fatua)
  • Brome species (Bromus spp.) - Currently there is no confirmed herbicide resistance in UK bromes, but reports of poorer control are increasing.  Herbicide resistance tests of brome species are currently provided for FREE to better understand this risk (contact Laura.Davies@adas.co.uk for more information)
  • Common Poppy (Papaver rhoeas)
  • Chickweed (Stelleria media)
  • Mayweed (Tripleurospermum inodorum)

ADAS offer herbicide resistance testing for all of these grass and broad-leaved weed species.

For more information on herbicide resistance or the tests that ADAS can offer please contact weeds@adas.co.uk

The Weed Resistance Action Group (WRAG) has issued guidance on the benefits of herbicide resistance testing.

Why have weed from your fields tested for herbicide resistance?

  • To know if herbicides will work on your weeds
  • Avoid potentially wasteful use of herbicides - save money and prevent unnecessary use
  • Help assess the threat posed by resistance on newly farmed blocks of land
  • Monitor the success (or otherwise) of long-term resistance management strategies
  • Samples taken for resistance testing help put the results in a wider context

Resistance testing methods

Grass Weeds

ADAS offers the following resistance tests (however all tests can be tailored to specific requirements, i.e. different herbicide choices and methods, so please contact us to discuss this further and for quotations on specific tests).  Discounts are offered for bulk samples.

Species Test Modes of action When will results be available?
Black-grass Full test

Petri dish: enhanced metabolism using Pendimethalin as an indicator herbicide, ACCase target site using cycloxydim

Pot test: ALS inhibitors (sulfonylurea)

Petri dish: Before post-emergence herbicides are applied*

Pot test: December

Black-grass Pot test ALS inhibitors (sulfonylurea) December
Black-grass Petri test Enhanced metabolism using Pendimethalin as an indicator herbicide, ACCase target site using cycloxydim Before post-emergence herbicides are applied*
Italian ryegrass Full test Petri test: ACCase TS (cycloxydim), ACCase TS (using pinoxaden)
Pot test: ALS inhibitors (sulfonylurea)
Petri dish: Before post-emergence herbicides are applied*
Pot test: December
Wild oats Pot test ALS inhibitors (sulfonylurea), fenoxaprop-ethyl and pinoxaden December
Brome species** Pot test ACCase, ALS inhibitors , glyphosate  

* If seeds are received by the end of July, results will normally be available by the end of September.
**FREE herbicide resistance testing is currently being offered.  Contact laura.davies@adas.co.uk for more information.

Petri-dish assay - Seeds are prepared and then germinated in herbicide solutions.  Seedling growth is recorded after 14 days.

Glasshouse pot test using seeds - Plants are grown in soil, treated with herbicide (at 2-3 leaf stage) and assessed 3-4 weeks later.  This method of testing is used for more effective assessment of ALS resistance.

Each test has its own advantages and disadvantages but to fully understand the resistance status, both tests are necessary for black-grass and Italian ryegrass, and the pot test is necessary for wild oats. 

Broad-leaved weeds

ADAS also offers ALS-inhibitor (sulfonylurea) resistance testing for poppy, chickweed, and mayweed.

(If you would like broad-leaved weeds tested for resistance to different actives, tests can be tailored to specific requirements, i.e. different herbicide choices and methods, different species. Please contact us to discuss this further and for quotations on different tests). 

Discounts are offered for bulk samples.

Order your herbicide resistance test

Why Choose the ADAS Resistance Test?

WRAG guidelines recommend that to be of value resistance tests should:

 
Included in the ADAS Resistance Test?
Use susceptible and resistant reference populations included Yes
State the assessment method and the basis on which resistance is assigned Yes
Incorporate the ‘R’ resistance rating system Yes

 

Interpretation of test results

In addition to all of the WRAG recommended components, each resistance test will receive an interpretation of the results to help guide your resistance management strategy.

Sampling weed seeds for resistance testing

Resistance tests are only as good as the sample collected and the extent to which it represents the suspect population. Follow the guidelines below to ensure your seed sample is suitable.

  • Do not collect from the edge of the field. Collect a representative sample from across the field; across 2-3 tramlines and across an area of 100m.
  • Where patches occur in the field, sample the patches and mix together; the bigger the area the better.

Grass weeds

When sampling grass weed seed for resistance testing make sure the seed is ripe.

Black-grass, ryegrass and wild oat seeds are ready for sampling when seeds are brown and the seeds fall off the panicle on their own when gently brushed with your hand; you won’t need to force seed off the plant.

Best times to sample:

  • Black-grass – 2nd/3rd week of July, when 10-20% of seed has shed
  • Italian ryegrass - early/mid July
  • Wild oats - late July/early August

How to sample

  • Collect a small mug of seed. Collect just the seeds; avoid collecting intact heads as they are unlikely to be ripe
  • When you collect a mug of seed, allow the seeds to dry in a container for a few days.
  • Transfer seed to a paper envelope.
  • Samples are ready for sending.

Broad-leaved weeds

You will need

  • Paper bag/ envelope with the bottom taped up to prevent seed escape.
  • Sharp knife or scissors

To collect poppy and mayweed

  • Cut off mature seed heads
  • Place the heads in the paper bag or envelope.
  • Leave the seeds in a well-ventilated area, making sure the bag remains open to the air to allow drying of the seed heads.
  • Before posting seal the bag/envelope with sticky tape to prevent seeds escaping.

To collect chickweed

Check chickweed plants for flowers and seed heads.  Seed heads will be always be green. 

  • Pull large quantities of chickweed and place in a paper sack. Do not pack it in too tightly but allow enough room for air to circulate.
  • Place the open sack in a well-ventilated area where the plants can dry out. As they dry seed will fall from the heads to the bottom of the sack.
  • When dry remove the chickweed straw from the sack shaking any loose seeds into the sack.
  • When the straw has been removed, tip the seeds into an envelope. Before posting seal the bag/envelope with sticky tape to prevent seeds escaping
  • Alternatively post the sack containing the chickweed plants

Deciding which field(s) to have tested

Ideally fields should be tested every 3 years to coincide with a typical 3 year rotation. Understanding the resistance profile of the grass weed population in the field will help to optimise control measures.

If cost is a prohibitive factor in testing then the following points can be used as a guide when selecting sites:

  1. Fields that have never been tested before
  2. Fields tested 5+ years ago
  3. Fields with continuous cropping (i.e. winter wheat only)
  4. Fields where control of grass weed is poor
  5. Fields where suspected resistant patches are still very small/discrete
  6. Fields with the worst yields

More Information

For more information on herbicide resistance or the tests that ADAS can offer please contact weeds@adas.co.uk

 

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