Tips to control a heavier grassweed burden in wheat this season

Some wheat crops are carrying larger weed burdens than normal, and growers are being advised to tackle them as soon as conditions allow to protect crop performance and reduce grass seed return to the soil.

The problem has been caused by a variety of factors, says Agrovista technical manager Mark Hemmant.

See also: Why brome is a rising problem when tackling blackgrass

“There was certainly a temptation to drill earlier last autumn, due to the early harvest and the fact that crops drilled earlier in autumn 2021 generally coped with last year’s drought better than later-drilled ones,” he says.

As a result, some growers with a grassweed problem started drilling too early, and the results are obvious to see.

“Others delayed sowing until mid-October after they had some rain. However, because it had been so dry beforehand, no grassweeds had emerged, so they still had a heavy burden in their crops,” Mr Hemmant says.

In addition, in many cases it was still too dry for pre-emergence herbicides to perform as well as they should have done.

Quite a number of growers have applied second residuals since, which seem to be working well.

However, there are plenty of instances where this hasn’t happened. And some fields may not warrant treatment in terms of protecting crop yield and quality.

But Mr Hemmant says growers also need to take a long-term view on managing seed return to reduce the blackgrass burden within the rotation, and to tidy up ryegrass and bromes, where they have not got resistance.

“Some people think they have resistance, but testing often shows that often poor control is due to some other factor, such as poor weather or less-than-ideal application.”

Post-emergence control

No chemistry offers total control of blackgrass, so the best chance for optimum post-emergence control is to spray when grassweeds are small, rather than waiting for the perfect weather.

February is an ideal month, provided weeds are growing and the ground will travel.

“Going early on if conditions are right is better than waiting – we might have prolonged rain or have an arctic blast for a month,” Mr Hemmant says.

Operators should beware of frosts and dews in winter/early spring, as spray drying times are important, particularly with sulfonylurea products.

Individual fields

“Be prepared to pick off fields here and there, perhaps applying individual tank loads to allow them to dry,” he says.

For those who can go earlier, Horus (mesosulfuron + iodosulfuron) up to 1.2 litres/ha will do a good job in January in the right conditions on blackgrass.

Where ryegrasses, brome or wild oats also need controlling, Palio (florasulam + pyroxsulam) or Broadway Star (florasulam + pyroxsulam + cloquintocet) would be a better option if conditions are suitable.

From 1 February, Pacifica Plus (mesosulfuron + iodosulfuron + amidosulfuron) can be used at 0.4kg/ha.

Treatment can be stepped up further on 1 March when the full rate of 0.5kg/ha can be used, the optimum rate for brome control.

Newer sulfonylurea

However, over the past two years, from 1 February, Agrovista has been recommending Proverb, which contains mesosulfuron, iodosulfuron and thiencarbazone, a newer sulfonylurea active offering better control.

“We recommend Proverb at 0.33kg/ha plus Biopower,” says Mr Hemmant. “It’s not revolutionary, but it provides a useful step-up in control compared with products we have become more used to.”

As with all herbicides, he says good application is key. Apply where possible to young actively growing grassweeds in a fine/medium spray at 200-300 litres/ha water volume, and allow sufficient drying time.

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