Start autumn black-grass control pre-harvest

By Rob Jones

09 July 2012

Give yourself a valuable extra edge in tackling serious black-grass and other annual grass weed problems this season by starting your autumn control ahead of cereal harvesting, advises leading independent tillage and weed management consultant, Steve Townsend.

In cereal crops pre-harvest Roundup (glyphosate) is primarily seen as a harvest management and perennial weed control tool. However, he has found it can make a very valuable contribution to reducing black-grass, brome and wild oat burdens, in particular, by sterilising immature weed seed in the head.

“Treatment will destroy the viability of any annual weed seed at the milky ripe stage,” Steve Townsend explains. “And even in later-maturing winter wheat crops where black-grass heads are well into shedding, a good 10% of their seed could be sufficiently immature to remain susceptible.

“This means 10% of weed seed that doesn’t need to be controlled in the stubble or by pre- or post-em spraying, helping to relieve the pressure on hard-pressed in-crop chemistry.

“What’s more, this season we’ve seen very extended grass weed emergence coupled with persistent summer rainfall,” he adds. “So plenty of weeds are likely to be maturing relatively late in the day.”

Substantial weed growth will, of course, make pre-harvest glyphosate especially important this season in ensuring the most efficient, trouble-free and timely combining. As will generally later-maturing crops – courtesy of modern varieties, stay-green chemistry and more-than-adequate soil moisture levels.

Under these circumstances, Steve Townsend sees the annual weed seed control value of the treatment as a completely free bonus.

“You only need to use the standard harvest management rate of Roundup, not the higher perennial weed control rate,” he stresses. “As with harvest management too, go in as early as you can – as soon as grain moisture content drops below 30%. That way you’ll hit the maximum amount of weed seed while it’s still immature.

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“Controlling black-grass is, more than anything else, a numbers game. “And with many growers facing weed seed burdens of 0.5 million/m2 or more after last autumn’s control difficulties, the stakes have seldom been higher.

“Pre-harvest glyphosate has largely been overlooked by many as an annual weed control tool to date. I don’t believe anyone with grass weed problems can afford to ignore it this time around, though. They’ll need to do everything possible to tackle what is almost certainly their biggest threat to next year’s cropping.

“Even if it only takes out 5% of the weed seed, the treatment will be a very valuable contribution when workload pressures, weather conditions and herbicide resistance are all working against you,” concludes Steve Townsend.

“It also means you start next year’s cropping with a completely clean slate, free from any semi-mature weeds as well as seedlings from early shed weed seed that cultivations tend to only transplant.

“Furthermore, by ensuring the most rapid and timely cereal harvesting, pre-harvest glyphosate will give you the best possible opportunity for at least one good stale seedbed ahead of autumn drilling; something that will be absolutely essential to keep on top of grass weeds going into the new season.”