Better ryegrass control with multiple actives
This battle has become an increasingly difficult challenge to meet because of rising levels of resistance to the current arsenal of herbicide active ingredients. Growers therefore must employ cultural and chemical controls to ensure arable crops are adequately protected.
Ryegrass species
Ryegrass is a common arable weed in many parts of the UK, with Italian ryegrass (Lolium multiflorum) widespread in the Midlands and South and usually more problematic than Perennial ryegrass (Lolium perenne).
One of the key reasons for the prevalence of Italian ryegrass is the simple fact that its seed can survive for more than five years in favourable conditions.
Ryegrass is also exceptionally vigorous and can be more competitive than black-grass: a population of just 5 plants/m2 can reduce cereal yields by 5%, with higher infestation rates known to cause yield losses of up to 89%.
Ryegrass also tillers more liberally than black-grass, with each plant capable of producing more than 20 heads and 5,000 seeds. As a result, populations can build up very rapidly.
Herbicide resistance
Herbicide resistant Italian ryegrass was first detected in the UK in 1990 and is now present in at least 33 counties in England. The first case of ryegrass resistance to ALS inhibitors was confirmed in 2012. In comparison, herbicide resistant black-grass was known to be present in 35 counties in 2017.
The main mechanism conferring resistance is enhanced metabolic non-target site resistance (NTSR) which can reduce the efficacy of most ryegrass herbicides.
ACCase (FOP, DIM and DEN) and ALS (sulfonylurea) target site resistance have also been confirmed in ryegrass species.
Cultural controls
In addition to the use of a robust programme of well-timed, accurately applied, target-specific herbicides, cultural controls are also essential in the fight against ryegrass.
As with all weeds, machinery hygiene is key to preventing the spread of ryegrass seeds: all cultivation and seeding equipment should be thoroughly cleaned to reduce the movement of weed seeds between fields.
The creation of stale seedbeds, delaying drilling and using spring-sown crops will all help to reduce the ryegrass burden, but these techniques are less effective versus ryegrass than they are against black-grass.
Increasing the seeding rate of cereal crops can also be used to increase competition for light and nutrients, thereby enabling the crop to thrive at the expense of the ryegrass population.
Boosting control with ADAMA’s herbicides
Practical ryegrass control programmes need to consider the germination profile of the field population in question, and the sensitivity of that population to different herbicide actives.
Recent glasshouse trials of post-patent herbicides carried out on behalf of ADAMA have shown that our three-way herbicide, TOWER® (250 g/l chlorotoluron, 40 g/l diflufenican & 300 g/l pendimethalin) performs well on all strains of Italian ryegrass, giving a 98-100% reduction in fresh weight.
The same trials also indicated that while no populations of ryegrass were completely resistant, straight pendimethalin and straight prosulfocarb showed a reduced efficacy in each population, indicating a degree of herbicide insensitivity. Meanwhile, straight diflufenican showed more effect on insensitive strains of ryegrass, although it was the least effective residual active ingredient when used alone.
Various strains of Italian ryegrass showing herbicide insensitivity to several post patent active ingredients
Efficacy of post patent herbicides against a range of UK Italian ryegrass populations: UK22HE3POTSO901A NIAB Code: GH23-02613
In contrast, most of the efficacy exhibited by TOWER can be apportioned to the inclusion of chlorotoluron: it is reassuring that chlorotoluron is not obviously affected by any of the known resistances in UK species of Italian ryegrass and that TOWER will therefore be a useful component at the pre- or early post-emergence timings.
The trial work clearly indicated that among post-patent herbicides the following applications at weed peri-emergence gave the best levels of ryegrass control:
- Peri-emergence treatment: TOWER plus prosulfocarb
- Peri-emergence treatment: TOWER followed four weeks later by TOPIK® (240 g/l clodinafop-propargyl & 60 g/l cloquintocet-mexyl)
- Peri-emergence treatment: TOWER followed four weeks later by TOPIK plus mesosulfuron and iodosulfuron.
Because ryegrass seeds have the potential to germinate over a wide period of time, it is critical to adopt an herbicide strategy that maintains effective levels of control for the entirety of this period. Typically, this requires a sequence of applications to be made, starting from the pre-emergence stage and carrying on through until the early post-emergence timing. At each of these various stages, two to four different herbicide active ingredients should be used to boost the level of weed control.
Key ryegrass control tactics
- Delay drilling to create stale seedbeds
- For heavily infested land, consider a switch to spring cropping
- Ensure all cultivation and seeding machinery is kept clean to reduce weed seed migration
- Increase seeding rates to enable the crop to out-compete weeds
- Select a programme of appropriate target-specific herbicides
- Ensure herbicides are applied accurately and at the optimum timing
TOWER®: an exclusive three-way co-formulation
TOWER is an exclusive co-formulation of three active with complementary modes of action for optimal grass weed control and resistance management.
In addition to providing excellent control of annual meadow grass and broadleaved weeds, TOWER also provides good activity against grass weeds in winter and spring wheat, winter and spring barley, winter rye and winter triticale.
Three active ingredients:
- 250 g/l chlorotoluron
- 40 g/l diflufenican
- 300 g/l pendimethalin
With a flexible product label, TOWER can be used as a pre- and/or post-emergence treatment in winter cereals and spring wheat and spring barley.
