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(CPM online: 25th August 2010)

Growers should seize the opportunity of the lowest levels of black-grass dormancy since 2006 and the late summer rainfall which has played such havoc with harvesting to really get on top of troublesome grass weeds ahead of drilling this autumn, advises Monsanto technical specialist, Manda Sansom.

“It may have come at just the wrong time for the harvest, but this month’s rainfall has been perfect for pre-planting weed control,” she insists. “Especially so as HGCA-funded monitoring has shown that 2010 black-grass seed has the lowest level of dormancy of the past four years.

“You only have to look at how rapidly this year’s oilseed rape has come through to appreciate how ideal the conditions are for autumn germination. And where the early summer was particularly warm and dry black-grass is likely to have even lower levels of dormancy than the national average. So emergence will be far more rapid and complete than most areas have seen since 2006, setting it up superbly for stale-seedbed and stubble spraying.

“This autumn is especially welcome following a run of seasons which have allowed black-grass populations to build-up alarmingly on many farms,” she stresses. “Two years in which seed dormancy has been relatively high, autumn seedbeds have been very dry and conditions have been far from ideal for autumn or spring post-ems have taken their toll.

“Add to this the rise in resistance to Atlantis and other SUs and most growers can’t afford to miss the golden opportunity this autumn provides to hit black-grass.

“We know the importance of an integrated approach and taking every opportunity to deal with weeds outside the actively growing crop is by far the best economic approach. Well-timed Roundup treatment between harvest and drilling gives you a complete weed kill without the compromises inevitable with in-crop spraying. By eliminating a substantial proportion of the weed reservoir, it helps take the pressure off your post-em programme. And it does so highly cost-effectively.”

So how exactly does Manda Sansom suggest growers take advantage of these better weed control opportunities ? Well, first and foremost she is adamant that no one should rely on cultivations alone, pointing out that full inversion ploughing is essential to achieve a consistent degree of seed burial. And even this is likely to pull-up buried seed from the run of previous relatively high dormancy years.

Instead, she advises everyone to integrate effective glyphosate treatment with their cultivations, regardless of the establishment regime they are employing. At the same time, she recommends as many growers as possible consider adding high compatibility, Roundup formulations to their pre-em sprays to tackle weeds emerging in the seedbed that can so easily present problems for pre, peri and post-em herbicides.

“If you’re min tilling you may well have time to set up and spray off two stale seedbeds this autumn,” she says. “You’ll need to cultivate as soon after combining and consolidate immediately afterwards for the best seed to soil contact. This should enable you to spray weed growth off within14 days in most cases.

“You’ll also have to use a modern, high performance glyphosate with the greatest power and effectiveness under challenging conditions. This means you only need to leave annual weeds for six hours after spraying before you can cultivate again, making it ideal where you want to set up a second stale seedbed.

“It’s equally valuable too for spraying-off stubbles ahead of ploughing or immediately in advance of seedbed preparation – or both, depending on when you cultivate and how strong the weed growth.

“Unlike the majority of glyphosates, Roundup formulations carry label approval for both multiple stale seedbed or stubble treatment and post-planting pre-emergence application,” she points out. “This gives everyone the flexibility they need to make the very most of the season’s welcome autumn weed control opportunity.”
For more detailed information on the use of Roundup in stubbles click here to read our latest Technical Bulletin