Herbicide resistance testing

With an over-reliance on a much smaller range of herbicide modes of action, the chances of herbicide resistance developing to any giving active is 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. ADAS offers herbicide resistance testing for all of the following grass and broad-leaved weed species.

• Black-grass (Alopecurus myosuroides)
• Italian ryegrass (Lolium multiflorum)
• Wild oats (Avena fatua)
• Brome species (Bromus spp.) -  Herbicide resistance tests of brome species are currently provided for FREE (2020 only) to better understand this risk (contact sarah.cook@adas.co.uk for more information)
• Common Poppy (Papaver rhoeas)
• Chickweed (Stelleria media)
• Mayweed (Tripleurospermum inodorum)

Why have weeds 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

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

Blackgrass

Example product	Active substance	HRAC group	Resistance indicator
Laser	Cycloxydim	1 - dim	ACCase TS
Stomp	Pendimethalin	3	Enhanced metabolism
Atlantis	Mesosulfuron + Iodosulfuron	2	ALS inhibitors

 

Italian ryegrass

Example product	Active substance	HRAC group	Resistance indicator
Laser	Cycloxydim	1 - dim	ACCase
Axial	Pinoxaden	1 - den	ACCase
Atlantis	Mesosulfuron + Iodosulfuron	B	ALS inhibitors

 

Wild oats

Example product	Active substance	HRAC group	Resistance indicator
Axial	Pinoxaden	1 - den	ACCase TS
Foxtrot	Fenoxaprop	1 - fop	ACCase TS
Atlantis	Mesosulfuron + Iodosulfuron	B	ALS inhibitors

Brome

Example product	Active substance	HRAC group	Resistance indicator
Falcon	Propaquizafop	1 - fop	ACCase TS
Laser	Cycloxydim	1 - dim	ACCase TS
Pacifica plus	Mesosulfuron + iodosulfuron + amidosulfuron	2	ALS inhibitors

Cost for a single test - £120

Cost for each additional herbicide - £60

Book a standard grass weed herbicide resistance test

Problems ordering online? Download the order form.

 

Bespoke grass weed herbicide resistance tests

Example product	Active substance	Group		Example product	Active substance	Group
Axial	Pinoxaden	1-den		Avocet	Pyroxsulam	2-SA
Centurion max	Clethodim	1-dim		Pacifica plus	Mesosulfuron + iodosulfuron + amidosulfuron	2-su
Laser	Cycloxydim	1-dim		Atlantis	Mesosulfuron + Iodosulfuron	2-su
Topik	Clodinafop	1-fop		Broadway star	Pyroxsulam + florasulam	2-su
Foxtrot	Fenoxaprop	1-fop		Stomp	Pendimethalin	3
Fusilade Max	Fluazifop	1-fop		Roundup	Glyphosate	9
Falcon	Propaquizafop	1-fop		Sunfire	Flufenacet	15
Pilot Ultra	Quizalafop-p-ethyl	1-fop		Defy	Prosulfocarb	15

 

Cost for a single test - £120. 

Cost for each additional herbicide - £60

Book a bespoke grass weed herbicide resistance test

Problems ordering online? Download the order form.

What to expect

• 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.

Discounts are offered for bulk samples.

Broad-leaved weeds

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. 

Discounts are offered for bulk samples.

Book a broadleaved-weed herbicide resistance test

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

 

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.

Dr Sarah Cook explaining how to collect black-grass seed for herbicide resistance testing

 

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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