NIAB and Syngenta offer advice on managing grass weed

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Growers should not wait to target grass weed already in the crop, according to the latest research from NIAB.

John Cussans, weed biology and management specialist at NIAB, said: “The message for early spring is the weeds you see in the crop right now are the ones that you are targeting; the ones that germinate later and later are less and less of a threat to the crop, and less and less of a threat in terms of ongoing seed return.”

Highlighting the results of the research, which assessed a range of grass weeds germinating at different times through an autumn sown crop, Mr Cussans explained that the individual plants which emerged two or three months after the crop was drilled were about four or five times smaller than the individuals that emerged with the crop.

He said: “When you go through into the spring, to weeds emerging in February or March, we’ve got 10 to 20 times reduction in the number of seed returns and biomass.”

The Italian ryegrass produced twice as much seed and the wild oats had three or four times as much biomass, compared to black-grass.

“There’s a really nice overall picture, that the larger the plant, the bigger the plant biomass, the more the crop competition and more seed return. It’s a beautiful linear relationship,” he added. The differences, in terms of the drop off in the weed size and seed return with the later emergence timing, were even more marked than the NIAB team expected.

“For growers there’s naturally a tendency to think I’ve got this weed that germinates through the season, I’ll wait until every last individual has emerged to target my application timing.

“In fact, we can now see quantitively that you would be better off focussing on rates and timings that get good control of those early germinating weeds, accepting that the smaller number of later germinating weeds may well come into the field. But overall your strategy should be to get that maximum efficacy on early emerging weeds.”

He reiterated that even with changing grass weed species and differing biology, farmers still need to really focus on making sure they get the best possible control of those individual weeds that are germinating alongside the crop in the autumn.

Pete Hawkins & John Cussans

Syngenta field technical manager, Pete Hawkins, advised targetting ryegrass and wild oats when they are smaller and actively growing: “Prioritise fields with larger overwintered weeds and ideally control weeds before fertiliser applications, that will further strengthen their growth. Also consider tank mixing with PGRS and appropriate broad-leaved herbicides to save time and make effective use of application windows.

“And finally optimise application techniques to ensure good coverage of weeds and achieve best possible control.”

Mr Cussans added: “We need to remember that there is a whole load of grass weeds to manage in the future; not just to focus on black-grass. That means we need to look at different aspects of weed biology. Some of these other grass weeds, like wild oats and bromes, have different biological characteristics than black-grass.

“We are repeating the trial this year, where we have added an element of application timing and rates to really complete the whole picture to help growers target these weeds much better.”

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