5 Key differences between black-grass and ryegrass

Benefit of delayed drilling

Delayed drilling has been fundamental to farmers’ success in beating black-grass. Drilling wheat in mid-October, means the main flush can be destroyed before drilling the main crop. The same is broadly true in Italian ryegrass although the improvement in control is not as great.

The reason given for this is that ryegrass continues to germinate through the winter and into spring. However, research somewhat contradicts this, a 2010 PhD funded by HGCA, found that that 80% of ryegrass germination takes place in October and only 6% from January – April. This is a very similar pattern to black-grass.

Italian Ryegrass emergence pattern

HGCA Project RD 2006-3206, 2010, R.A Reverte.

Black-grass emergence pattern

The agro-ecology and control of black-grass, Alopecurus myosuroides Huds., in modern cereal growth systems, 1980, S Moss.

There are several potential explanations for this divergence between research and farmers’ experience. But the basic fact is that to control ryegrass, farmers need to consider how to stack some additional control on top of delayed drilling. This may be top-up residual herbicides or a post-em in spring depending on the resistance profile.

Resistance patterns

In black-grass, resistance typically appears in a predictable pattern of post-ems and then possibly pre-em chemistry. This is not the case in Italian ryegrass.

“It’s important for growers to know that they can select for any resistance trait independently. We seem to have this mindset, probably from the experience of black-grass, that resistance appears in a set sequence, starting with ACCase then ALS and perhaps onto residual chemistry,” says John Cussans of NIAB.

But results in the 2021 ryegrass survey and resistance testing showed all possible combinations. For example, populations that were sensitive to both contact-acting herbicides (Atlantis and Axial) but with a significant reduction in sensitivity to flufenacet.

All of this means, that some farmers have more chemical tools to control Italian ryegrass than they think so resistance testing and a willingness to reconsider post-em chemistry, either Atlantis-type products or pinoxaden, may pay dividends.

Spring crop control

In a similar vein to delayed drilling, spring crops tend to not be quite as effective against ryegrass compared to black-grass. “We find that some cultural control techniques that work well on black-grass are not working really differently in Italian ryegrass,” says Mr Cussans. “Spring cropping, which has been a mainstay of black-grass control is much less effective in Italian ryegrass. We’ve had trials last season where there’s more ryegrass in the spring crops.”

Where ryegrass is a problem, don’t sow spring crops to early, wait for spring weather to stimulate a flush of weeds before spraying off with Roundup then drilling. “The danger comes from just assuming a spring crop will fix a grass-weed problem,” says Tom Chillcott of Bayer. “Sticking to solid grass weed principles when you establish a spring crop means there is nothing to fear from ryegrass in the spring.”

Perception of the problem

In recent years, many farmers seem to have developed a system that works for controlling black-grass, this is backed up by research findings. The Rothamsted led Black-Grass Resistance Initiative (BGRI) has monitored over 160 fields since 2014.

“Black-grass levels have definitely come down since the project began, we see far fewer fields with very high infestations and much more at the other end of the scale,” says Weed Ecologist Laura Crook. “Over the same period, we have recorded more delayed drilling, stacking of residual herbicides and spring cropping. These are the main factors behind the change with spring cropping making the biggest single difference.”

On the other hand, Italian ryegrass is thought to be becoming more of a problem. Survey work from 2016, 2020, 2021 all highlighted a perception that it is getting harder to control. Added to that research identifying instances of resistance to key pre-em actives including pendimethalin and flufenacet provides one explanation for increasing problems.

Optimum pre-em stacks

As mentioned above, a small number of popualtions with resistance to pre-em chemistry have been recorded in ryegrass, whereas in black-grass there have been shifts in sensitivity but no out and out resistance.

“Resistance testing focuses on the efficacy of single actives, but farmers typically use mixes and co-forms in autumn,” says Tom Chillcott. “Research conducted in partnership with NIAB found that even where there was resistance to flufenacet. A tank-mix of just Liberator (flufenacet + diflufenican) + Proclus (aclonifen) can almost totally overcome this resistance.”

Farmers are now in a fortunate position of having quite a wide range of actives from different HRAC mode of action groups to use at pre-em. There is scope to rotate actives between seasons and different cereal crops to prevent resistance in ryegrass or black-grass developing.

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