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Countering a Growing Spring Germinating Grass Weed Threat

Spring germinating grass weeds are being let off the hook in a major way by the increased and  entirely natural emphasis on more robust autumn chemical and cultural control in response to the growing black-grass challenge, believes ProCam national agronomist, Nick Myers.

In the past year, in particular, he has seen a worrying increase in infestations from soft and meadow bromes – not to mention spring-germinating black-grass – across the eastern counties. 

As well as rapid residual degradation in a very mild winter, he puts this down to the extent to which control programmes have been progressively focussed on dealing with difficult black-grass in the autumn.

At the same time, he points out that weeds like bromes and ryegrass continue to be far more problematic than black-grass in many parts of the country. And noticeably more growers have been reporting particular wild oat concerns of late too.

“Five or six years ago we were still getting very good black-grass control from March or April sprays of Atlantis or Pacifica (mesosulfuron + iodosulfuron),”  Nick Myers explained. “This allowed us to use our one permitted ALS inhibitor application to tackle later as well as earlier germinating weeds. These days, however, post-ems need to go on early in the growing season to have any decent effect on many black-grass populations.  So, if we are not very careful with our autumn strategy we are tying our hands firmly behind our backs as far as spring control is concerned.

 “Equally, the sort of post-harvest stale seedbed management that is ideal for stimulating black-grass and sterile brome germination merely serves to induce dormancy in meadow and soft brome seed. Which, in turn, means greater spring emergence. Add to this the fact that some black-grass populations were still germinating well into April last year and there’s a clear need for greater grass weed control balance in many quarters.

“This is underlined by the number of people who went into 2014 thinking they’d done a good job with their autumn grass weed control only to find serious problems developing from the spring.”

Avoiding early drilling and making the best possible pre-planting use of glyphosate remain high on Nick Myers’ list of grass weed control priorities, regardless of the weed threat.  However, he stresses that even this element of the programme needs to be carefully geared to the main problem species. 

Where black-grass and/or sterile brome are the main issues, he recommends light post-harvest cultivation and consolidation to stimulate two or even three cycles of weed growth for spraying-off before drilling.  In contrast, cultivation is best delayed for around a month where meadow and soft bromes are problematic, so the seed is left on the surface to ripen. This helps to break its dormancy for the most effective pre-planting Roundup control. 

“Robust pre-em or peri-em applications are also essential in most cases,” added Nick Myers. “For the best activity, use combinations of flufenacet, pendimethalin, prosulfocarb and DFF. Approved Roundup formulations can be useful in the pre-em tank mix to deal with already emerged weeds in the seedbed if there’s been any delay between the final stale seedbed spray and drilling. Avadex (triallate) is a particularly valuable across-the-board addition too. 

“When it comes to post-ems, though, decisions become more tricky. There’s not much alternative to early mesosulfuron + iodosulfuron if autumn-emerging black-grass is your Number One threat. But in many cases now even this doesn’t do much of a job. And it will seriously limit your spring spraying options. 

“So where you don’t have a lot of black-grass coming through early-on or you’ve been having more problems with soft or meadow bromes you may be better off holding back on your ALS inhibitor until the spring. That way you’ll be able to make the best possible use of the brome herbicide Monitor (sulfosulfuron) or more general grass weed killers like Pacifica, Broadway Star (pyroxsulam + florasulam) or Broadway Sunrise (pyroxsulam + pendimethalin).  All these options should also be able to deal with spring emerging black-grass.

“A big emphasis on early autumn grass weed control remains crucial,” Nick Myers concluded. “But everyone really needs to keep a close eye on the increasing threat of spring germinators and flex their management carefully to address it over the coming season. Or they could be facing even more intractable problems this time next year.”