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Weed Management

Darren Adkins

Weedy Stubbles Demand First Class Spring Cereal Management

The weediest stubbles for many years, courtesy of few, if any, windows for early winter cultural or chemical control make first-class early spring cereal management vital this season.

Spring cereals are an excellent rotational aid to managing difficult weeds like black-grass, ryegrass and bromes as well as annual meadow grass, wild oats and a range of broadleaves. But much of their value here lies in the extra opportunities they offer for effective weed control over the winter; opportunities that have been sadly lacking in the wettest early winter in living memory for many.

Although spring oats and barleys can be highly competitive once growing strongly, they and spring wheats are acutely vulnerable to competition during establishment; particularly where cold, wet ground and less-than-ideal seedbeds restrict early crop growth.

“Early weed competition seriously compromises the performance of spring cereals with their short growing season and limited ability to compensate,” points out Bayer technical manager, Darren Adkins. “At the same time, large numbers of seed heads/weed and a heavy seed return in more open crops will undermine the whole rotational value of spring cropping.

“On top of a lot more ground to sow this spring, we have very well-entrenched weeds in most stubbles and in some decidedly thin cover crops. Black-grass revels in the wet. And the mild conditions have meant it has continued to germinate and grow strongly through to the New Year. The earlier germinators are especially well-established with seven or eight tillers apiece.

“We fail to deal with these effectively ahead of sowing and give our spring cereals the best possible chance to grow away from the challenge of continued weed germination at our peril.”

Under these circumstances, Mr Adkins recommends a robust dose of the most active glyphosate as soon as the ground is fit to travel this spring. He sees patience as essential to give the treatment enough time to work. Equally, to ensure the soil is fit enough for a decent seedbed, good pre-em activity and rapid early crop growth before drilling. Moving as little soil as possible at drilling – together with high enough seed rates and sufficient attention to early crop nutrition and plant growth regulation – is also crucial, in his experience.“Glyphosate uptake and performance is markedly reduced under cool conditions, and there have been serious questions over the performance of some glyphosates following the withdrawal of tallow amine formulations,” he stresses. “So, make sure you use a modern Roundup formulation proven to get more glyphosate into plants more rapidly and reliably at low temperatures; and use it at the right rate for the job.

“For established, young black-grass 720g/ha of glyphosate should be sufficient. However, 1080g/ha may be required for particularly thick and well-tillered grassweeds, with tough perennials needing even higher rates, often up to 1800g/ha.

“Water conditioners can improve performance in hard water areas. But remember that no amount of adjuvant can make up for insufficient glyphosate. And whatever you do, don’t rush your stubble applications. Take as much time and care as you would with any pre-em because you don’t have a second chance to get it right.”

Soil conditions are far more important than calendar date in spring cereal drilling, in Mr Adkins’ experience. He insists that the worst thing is drilling into a cold, wet seedbeds that are too rough for much in the way of pre-em activity. The fact that spring barley and oats can be sown into April means that most growers should have plenty of time to sow into seedbeds that are fine and warm enough for the best establishment and residual weed control.

“Moving as little soil as you can at drilling will wake up the least amount of weed seed,” he adds. “If you need to cultivate, top-down working will be best for most soils so you don’t bring-up clods and I’d work as shallow as 5cm wherever possible. This should help ensure seedbeds that give the best activity from your Liberator (flufenacet + diflufenican) pre-em.

“Where you’ve gone in early with your pre-planting treatment and held-off on the drilling we’ve found including an approved glyphosate with the pre-em works wonders too. Even when we couldn’t see any emerged black-grass in the seedbed, including Roundup with the Liberator made a staggering difference to the control we achieved.

“If the seedbed is a bit cloddy and soil temperatures are rising rapidly it’s all too easy for grassweeds to have emerged and be beyond residual control before they are immediately visible. Of course, the glyphosate must be on before there’s any chance of crop emergence,” he concludes.

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