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PERSISTENCE PAYS IN GRASSWEED CONTROL SUCCESS

Determination, flexibility and, above all, persistence are the three most important ingredients for success in controlling problem grassweeds these days, insists national Grassweed Action co-ordinator, Barrie Hunt.

“Growing challenges from black-grass, ryegrass and bromes, the spread of herbicide resistance and the erosion of our agrochemical armoury means the quick fix of in-crop control from the can has become less and less reliable,” stressed the Roundup technical specialist.

“So our emphasis has had to switch to managing them in a far more integrated way with all the cultural controls at our disposal – including improved stubble management, rotational ploughing, delayed autumn drilling, spring cropping, wider rotations and more competitive varieties.

“At the same time, we have come to appreciate that a very different attitude of mind is essential. First, we have to address these problems with sufficient determination from the outset, making them key priorities in our whole management rather than just another spray decision.

“Then, we need to have enough flexibility in our systems to be willing and able to change the way we’ve always done things. And adapt our whole rotations and management to the needs of individual fields and seasons.

 

“Most importantly of all, we must have the persistence to keep at things over a far longer timeframe than we have become used to. It’s no good, for instance, thinking we’ve solved a bad grassweed infestation just because we’ve had a relatively problem-free season or two. Any failure to keep up cultural control pressures over the long-term will almost certainly come back to bite us if we are not very careful indeed.”

 

By the long-term, Barrie Hunt actually means forever.  His detailed knowledge of the biology of grassweeds and extensive experience of their management means he appreciates just how damaging annuals like black-grass, bromes and ryegrass can reassert themselves wherever they get more than half a chance.

“After all, a single black-grass plant can easily produce over 1000 seeds/year and they can survive in the soil for up to 10 years,” he pointed out.  “So it doesn’t take much for problems to escalate massively and very rapidly.”

Under these circumstances, he insists that a well-planned strategy and continual vigilance is crucial to maintain constant downward pressure on weed levels and nip any seasonal problems firmly in the bud.

“In particular, you need to take every opportunity to stimulate and eliminate weed growth outside the crop each season with the right combination of cultivations and pre-planting glyphosate,” advised Mr Hunt.

“Rotational ploughing can be a good reset if you do it well enough to bury all the weed seed from a depth at which it finds it hard to emerge. But it is unlikely to be effective unless it follows and, in turn, is followed by a good five years of shallow cultivation to concentrate the seed bank in the top layer of the soil plus stale seedbed treatment to erode it.

 

“Later sowing winter cereals is also valuable in allowing as much weed growth as possible to be controlled with glyphosate ahead of drilling, with spring cropping giving even more opportunity here.  But don’t make the mistake of assuming that a year – or even two or three years – of either is necessarily enough to let you go back to an early-sown winter wheat or dramatically reduce your robust pre-emergence herbicide programme.  Nor that you can do so after patch-spraying a badly-infested crop the previous summer.”

“Instead, you need to monitor your fields carefully and plan – and adapt – their management each season to keep bearing down on the grassweeds present.

“You may be able to grow a second wheat if you have low enough weed levels in your first wheat on ground without a recent history of bad infestations. But whenever and wherever you find weed levels increasing you need to step-up your cultural controls without compromise or delay.”

 

Prioritising grassweed control in every break crop is vital too, in Barrie Hunt’s opinion, with the most appropriate use of pre- and post-emergence herbicides through the rotation.

“Although many grass weeds can no longer be reliably controlled with herbicides alone – especially in cereals crops – the activity they still give remains immensely valuable when integrated with the right continual cultural controls over enough time.

 

“Persistence really does pay at least as much – if not more – than either determination or flexibility in modern grassweed management. This is something we need to re-learn from the days before the convenience of modern chemistry. And, indeed, use to protect both the chemistry we have and any new herbicides we get – however effective they may be initially.”