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Growers should seek to control grass weeds sooner rather than later this spring – rather than waiting for more to emerge, suggests NIAB research. Trials shine spotlight on early weed control

• Early weeds are bigger threat

• Seed return and biomass key

• Look at spray application rates

Growers should seek to control grass weeds sooner rather than later this spring – rather than waiting for more to emerge, suggests NIAB research.

Farmers should focus on weeds with potential of a high seed return, not just from a crop competition point of view, says John Cussans, a NIAB specialist in weed biology and crop management.

“The message for early spring is the weeds you see in the crop right now are the ones that you are targeting,” says Mr Cussans.

“The ones that germinate later and are less and less of a threat to the crop, and less and less of a threat in terms of ongoing seed return.”

The trials assessed a range of grass weeds germinating at different times through an autumn-drilled crop. Weeds which emerged two or three months after drilling were four or five times smaller than weeds emerging with the crop.

Less biomass

Compared to blackgrass, Italian ryegrass produced twice as much seed and wild oats had three or four times as much biomass. But weeds emerging in February or March had 10-20 times fewer seed returns – and much less biomass.

“It’s a really nice overall picture,” explains Mr Cussans. “The larger the plant, the bigger the plant biomass, the more the crop competition and more seed return. It’s a beautiful linear relationship.”

The reduction in weed size and seed return with later emergence was even more marked than the NIAB team expected, says Mr Cussans. This is another reason for getting on top of weeds sooner rather than later.

“For many 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.’

Rates and timings

“In fact, we can now see that you would be better off focusing 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.

Conducted in association with Syngenta, the trials reinforce the role of Axial Pro in early grass weed control. Overall, the strategy should be to get that maximum efficacy on early emerging weeds, says Mr Cussans.

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 germinating alongside the crop in the autumn.

Tank mixes

Syngenta field technical manager Pete Hawkins says the advice from the trial for Axial Pro application this season is to target ryegrass and wild oats when they are smaller and actively growing.

Growers should prioritise fields with larger overwintered weeds and control weeds before fertiliser applications further strengthen their growth.

Tank mixing with growth regulars and broad-leaved herbicides can save time and make better use of application windows, says Mr Hawkins.

Application techniques

Optimising application techniques will ensure good coverage of weeds and achieve best possible control.

“We need to remember that there is a whole load of grass weeds to manage in the future; not just to focus on blackgrass,” explains Mr Cussans.

That means growers and agronomists should consider the different aspects of weed biology.

“Some of these other grass weeds – such as wild oats and bromes – have different biological characteristics to blackgrass.

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