5 reasons ryegrass became the UK’s most difficult weed, and how to optimise control

Here, experts from ADAS and BASF discuss what makes ryegrass so challenging and how to manage it on farm. 

1. Ryegrass is twice as competitive as black-grass: with a competitive index of 1.0 (compared with 0.4). 

 "One of the reasons ryegrass is so problematic is because it is very vigorous and fast growing. As a result, it competes aggressively with crops for light, water and nutrients, robbing yield in the process,” explains Matt Keane, BASF Agronomy Manager. 

2. Prolific and persistent seeds: a single plant can easily produce over 20 heads, resulting in upwards of 5,000 seeds per plant. While the majority of seeds germinate or degrade within 2 to 7 years, some dormant seeds can survive deep in the soil profile for up to 20 years. 

“There is a population level implication of not getting enough control in a single year,” adds John Cussans, ADAS Principal Consultant. 

“With the population able to increase within a single generation, not only are you impacted in the crop that you’re managing right now, your costs in future crops escalate, due to the seed burden return that you’re going to have to manage for several years into the future. Weed control is important for economically sustainable crops.”  

3. Massive yield losses from low numbers: a population of just 1 or 2 ryegrass plants per square metre can reduce winter wheat yields by 5% to 10%. 

 “Black-grass plants can cost you yield, which is significant, but ryegrass impact is even worse. This aggressive grassweed will take hold if robust control is not achieved,” notes Stuart Kevis, BASF Business Development Manager.  

4. Protracted emergence:  The majority of ryegrass seeds germinate between September and November, although some will chit in spring.  

  “While we’d expect around 90% of a black-grass population to have chitted by mid-October, it is likely that only 40-50% of the ryegrass population will have done so,” says Matt.  

 "Delayed drilling and stale seedbeds remain fundamental tools, but the staggered emergence makes them less effective against ryegrass. Autumn is when ryegrass germination peaks, so using the best chemistry, Luximo, at pre-emergence continues to be the most effective strategy." 

5. Widespread herbicide resistance: Italian ryegrass populations develop more diverse herbicide resistance more quickly than black-grass populations do. Today there are populations with resistance to ACCase inhibitors, ALS inhibitors, group 15 chemicals such as flufenacet and/or non-selective chemistry like glyphosate. 

 “Herbicide-resistant ryegrass is much more challenging than black-grass,” says John. “We’re beginning to see a trend towards increased tolerance to the pre-ems in black-grass. But the situation with flufenacet in ryegrass is much more worrying with some populations incredibly tolerant.” 

Effective management of ryegrass 

While the principles of managing ryegrass are the same as black-grass, the weed’s characteristics and behaviour change the risk equation.  

Its tendency for staggered germination, for example, reduces the impact of autumnal activities, though the experts agree, it remains the optimal time for control.  

“Autumn sees ryegrass germination peak,” notes Stuart. “It is also when the plants are at their most vulnerable, so this is best time to control it.” 

“Protracted emergence makes delayed drilling more important, the longer there is for the seeds to chit, the more of the population will be controlled.” 

“We can talk about how challenging ryegrass is in terms of the more staggered germination that we see in this species compared to other grassweeds, but fundamentally it is before the emergence of the weed and the crop that we have that little application window where we’re getting the ‘biggest bang for buck’ from soil acting residual chemistry,” says John. 

Matt adds that using the best chemistry first helps make the most of the opportunity. 

“Looking out at some fields near me, I can already see a strong flush of ryegrass coming through. While ryegrass germination is more staggered than black-grass, the first flush remains the largest, so your strongest chemistry must be first in your programme. This means using Luximo first, in the pre-em position.” 

John agrees, noting that one the best way to reduce risk is to get the strongest chemistry on first, rather than leaving the window open for poor conditions to remove the chance to complete a sequence. He also says that with ryegrass able to develop resistance quickly, applying multiple modes of action is essential. 

“Farmers and agronomists on the ground have to make some decisions about risk. If you’ve got a really tight sequence and miss the second part or even worse, you skip the first part, it is highly unlikely that you will achieve the control needed,” he says. 

Ultimately, ryegrass is the UK's number one weed because its behaviour shifts the balance of risk in ways black-grass does not. Controlling it comes down to recognising that, and paying close attention to the details – the timing, the sequence, and the chemistry you use first.