With an over-reliance on a much smaller range of herbicide modes of action, the chances of herbicide resistance developing to any giving active are now increasingly higher.

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

We offer testing for:

  • Black-grass (Alopecurus myosuroides)
  • Italian ryegrass (Lolium multiflorum)
  • Wild oats (Avena fatua)
  • Brome species (Bromus spp.)
  • Common Poppy (Papaver rhoeas)
  • Chickweed (Stelleria media)
  • Mayweed (Tripleurospermum inodorum)

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Why have weeds 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

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

We offer both standard and bespoke herbicide resistance testing.

Standard grass weed herbicide resistance tests

Costs for a standard test

Cost for a single test is £120. Each additional herbicide will cost £60.


Example productActive substanceHRAC groupResistance indicator
LaserCycloxydim1 – dimACCase TS
StompPendimethalin3Enhanced metabolism
AtlantisMesosulfuron + Iodosulfuron2ALS inhibitors


Italian ryegrass

Example productActive substanceHRAC groupResistance indicator
LaserCycloxydim1 – dimACCase
AxialPinoxaden1 – denACCase
AtlantisMesosulfuron + IodosulfuronBALS inhibitors


Wild oats

Example productActive substanceHRAC groupResistance indicator
AxialPinoxaden1 – denACCase TS
FoxtrotFenoxaprop1 – fopACCase TS
AtlantisMesosulfuron + IodosulfuronBALS inhibitors



Example productActive substanceHRAC groupResistance indicator
FalconPropaquizafop 1 – fopACCase TS
LaserCycloxydim1 – dimACCase TS
Pacifica plusMesosulfuron + iodosulfuron + amidosulfuron2ALS inhibitors


Discounts are offered for bulk samples.

Order a grass weed standard herbicide test 

Bespoke tests

Cost for a single test is £120. Each additional herbicide will cost £60.

Discounts are offered for bulk samples.

Order a bespoke grass weed herbicide resistance test

What to expect after you have sent in your sample

  • ADAS will acknowledge receipt of your sample
  • As most grass weeds have a dormancy period testing will not begin until 2-4 weeks after seeds arrive. Tests take 8-10 weeks to complete with tests being sown every 2-3 weeks.
  • Samples with poor germination may result in delayed or failed tests.
  • Results will be sent as soon as they are available with an interpretation of the results to help guide your resistance management strategy.

If seeds are received by the end of July, results will normally be available by the end of September.  Samples must be received by 1 October to guarantee testing in the year of collection. Contact sarah.cook@adas.co.uk​ for more information.

Broad leaved weeds testing

We also offer 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.

Cost for a single broad-leaved weed resistance test is £150.

Discounts are offered for bulk samples.

Order a broad-leaved weed resistance test

Sampling weed seeds for resistance testing

Resistance tests are only as good as the sample collected. 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 taking samples of 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.

Black -grass stages

The ideal time to collect black-grass seed for herbicide resistance is when the plant is at 10-20% shedding


Grass weed testing months

Suitable months to collect your grass seed sample

How to sample grass weeds:

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

Collecting 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.

poppy and mayweed

To collect chickweed

Check chickweed plants for flowers and seed heads.  Seed heads will 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

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