The news last week that resistance has developed to glyphosate in Italian ryegrass in Ireland has many people asking questions on what it means and what needs to be done.
Glyphosate is a non-selective herbicide. It has been a game changer for weed control on farms across the world.
When we think of weeds like scutch grass it has helped to take control of it and so many other difficult weeds.
It also plays an important role in the use of cover crops and minimum-tillage practices.
Many people using reduced tillage and low-input tillage systems are dependent on glyphosate in their farming systems. However, that dependency can also start to cause problems.
We chatted to Dr Vijaya Bhaskar (pictured) who is the lead researcher on the Teagasc EVOLVE project. VJ explained that: “Modelling studies predict that glyphosate resistance could develop within 10-15 years in no-till systems where glyphosate is relied on for pre-sowing weed control, which would equate to a single application each season to the same field.
“In general, factors that accelerate resistance in grass weeds include: herbicide selection intensity, frequency of resistance present in populations, the biology of grass weeds and population pressure.”
While many farmers are now concerned about resistance development and rightly so, they can do things to prevent it.
VJ noted: “Glyphosate resistance evolves relatively slowly compared to ACCase/ALS herbicides [e.g. Axial/Pacifica] which are both considered a high resistance risk, because they are applied early in the season when fewer weeds are present, exerting less selection pressure.”
Basically, if you rely on a herbicide to control weeds without any rotations, cultivations or alternation of chemistry, the risk of resistance development will
be higher.
Another risk is the use of insufficient glyphosate rates.
If rates which do not give control are continually used then weeds will develop resistance.
Applying in poor conditions will also help resistance to build up.
VJ said crop establishment is “a crucial component of an integrated weed management (IWM) strategy”.
He noted that in non-inversion tillage systems where no ploughing occurs “these systems rely on the use of glyphosate and ALS/ACCase herbicides” to control grass weeds.
“This reliance may increase pressure for resistance in early-germinating grass-weeds (e.g., bromes, Italian ryegrass, blackgrass, annual meadow grass).
Vijaya Bhaskar is the lead researcher on the EVOLVE project.
“Non-inversion tillage growers typically establish winter crops with a single stale seedbed practice, where post-harvest stubble cultivation is followed by glyphosate use pre-sowing of the cereal.
“In some situations, min-till growers may use multiple stale seedbeds (two or rarely three), with glyphosate used each time, to tackle weeds like sterile brome.
“If scutch or other weeds are present in the crop prior to harvest, glyphosate could be used pre-harvest too resulting in the product being used multiple times per season.
“To minimise selection pressure and resistance risk, even if multiple stale seedbeds are warranted, glyphosate may only be needed once with cultivation alone being adequate in the intermediary stage,” VJ explained.
He also commented that diverse rotations allow for alternative chemistry to be used to control weeds in oilseed rape and beans for example.
Cover crops are increasing in popularity and VJ commented that this is resulting in spring cropped land now being exposed to an annual application of glyphosate, even though autumn-germinating annual grass weeds are less problematic in these fields.
VJ noted that in a plough-based system cover crops could be controlled with glyphosate every three to four years, but annual use could help to build up resistance.
“Even with min-till, cultural alternatives to glyphosate use should be considered such as rolling in frost or cultivation with elements that deal with these type of vegetation (perhaps blade rollers, etc.),” VJ added.
Glyphosate needed for control
VJ noted: “This case does reiterate the fact that we should no longer take glyphosate for granted.
“Glyphosate remains an important component of IWM and we should protect it.
“While it may be a one-off or a rare occurrence, the news of this resistance should be seen as an important opportunity to increase awareness.
“This may lead to more suspect cases needing to be analysed, which may not necessarily be resistant but Teagasc has put systems in place to complete this work if, and when required.”
If you suspect resistance
If you suspect you have a weed resistant to a herbicide on your farm contact you agronomist or Teagasc and they will discuss next steps. The weeds can be brought to seed and then tested for resistance in a lab.
You will also receive advice on what to do with the weed and how to stop it spreading and how to control it. The resistance testing service is completely confidential.
Contact VJ on Vijaya.Bhaskar@teagasc.ie.
In short
Glyphosate is an important herbicide for weed control. Herbicide resistance happens where the product is not applied at the right rate or in poor conditions over a period of time.Resistance develops in a field to the specific plants in the field.If resistance develops the seed of those plants if spread can spread resistant seeds.Resistance can develop in any plant in any field.If you suspect resistance talk to your adviser and collect seeds for testing.You can hear more from VJ on the Irish Farmers Journal Tillage Podcast wherever you get your podcasts.
The news last week that resistance has developed to glyphosate in Italian ryegrass in Ireland has many people asking questions on what it means and what needs to be done.
Glyphosate is a non-selective herbicide. It has been a game changer for weed control on farms across the world.
When we think of weeds like scutch grass it has helped to take control of it and so many other difficult weeds.
It also plays an important role in the use of cover crops and minimum-tillage practices.
Many people using reduced tillage and low-input tillage systems are dependent on glyphosate in their farming systems. However, that dependency can also start to cause problems.
We chatted to Dr Vijaya Bhaskar (pictured) who is the lead researcher on the Teagasc EVOLVE project. VJ explained that: “Modelling studies predict that glyphosate resistance could develop within 10-15 years in no-till systems where glyphosate is relied on for pre-sowing weed control, which would equate to a single application each season to the same field.
“In general, factors that accelerate resistance in grass weeds include: herbicide selection intensity, frequency of resistance present in populations, the biology of grass weeds and population pressure.”
While many farmers are now concerned about resistance development and rightly so, they can do things to prevent it.
VJ noted: “Glyphosate resistance evolves relatively slowly compared to ACCase/ALS herbicides [e.g. Axial/Pacifica] which are both considered a high resistance risk, because they are applied early in the season when fewer weeds are present, exerting less selection pressure.”
Basically, if you rely on a herbicide to control weeds without any rotations, cultivations or alternation of chemistry, the risk of resistance development will
be higher.
Another risk is the use of insufficient glyphosate rates.
If rates which do not give control are continually used then weeds will develop resistance.
Applying in poor conditions will also help resistance to build up.
VJ said crop establishment is “a crucial component of an integrated weed management (IWM) strategy”.
He noted that in non-inversion tillage systems where no ploughing occurs “these systems rely on the use of glyphosate and ALS/ACCase herbicides” to control grass weeds.
“This reliance may increase pressure for resistance in early-germinating grass-weeds (e.g., bromes, Italian ryegrass, blackgrass, annual meadow grass).
Vijaya Bhaskar is the lead researcher on the EVOLVE project.
“Non-inversion tillage growers typically establish winter crops with a single stale seedbed practice, where post-harvest stubble cultivation is followed by glyphosate use pre-sowing of the cereal.
“In some situations, min-till growers may use multiple stale seedbeds (two or rarely three), with glyphosate used each time, to tackle weeds like sterile brome.
“If scutch or other weeds are present in the crop prior to harvest, glyphosate could be used pre-harvest too resulting in the product being used multiple times per season.
“To minimise selection pressure and resistance risk, even if multiple stale seedbeds are warranted, glyphosate may only be needed once with cultivation alone being adequate in the intermediary stage,” VJ explained.
He also commented that diverse rotations allow for alternative chemistry to be used to control weeds in oilseed rape and beans for example.
Cover crops are increasing in popularity and VJ commented that this is resulting in spring cropped land now being exposed to an annual application of glyphosate, even though autumn-germinating annual grass weeds are less problematic in these fields.
VJ noted that in a plough-based system cover crops could be controlled with glyphosate every three to four years, but annual use could help to build up resistance.
“Even with min-till, cultural alternatives to glyphosate use should be considered such as rolling in frost or cultivation with elements that deal with these type of vegetation (perhaps blade rollers, etc.),” VJ added.
Glyphosate needed for control
VJ noted: “This case does reiterate the fact that we should no longer take glyphosate for granted.
“Glyphosate remains an important component of IWM and we should protect it.
“While it may be a one-off or a rare occurrence, the news of this resistance should be seen as an important opportunity to increase awareness.
“This may lead to more suspect cases needing to be analysed, which may not necessarily be resistant but Teagasc has put systems in place to complete this work if, and when required.”
If you suspect resistance
If you suspect you have a weed resistant to a herbicide on your farm contact you agronomist or Teagasc and they will discuss next steps. The weeds can be brought to seed and then tested for resistance in a lab.
You will also receive advice on what to do with the weed and how to stop it spreading and how to control it. The resistance testing service is completely confidential.
Contact VJ on Vijaya.Bhaskar@teagasc.ie.
In short
Glyphosate is an important herbicide for weed control. Herbicide resistance happens where the product is not applied at the right rate or in poor conditions over a period of time.Resistance develops in a field to the specific plants in the field.If resistance develops the seed of those plants if spread can spread resistant seeds.Resistance can develop in any plant in any field.If you suspect resistance talk to your adviser and collect seeds for testing.You can hear more from VJ on the Irish Farmers Journal Tillage Podcast wherever you get your podcasts.
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