Seize 2004 Opportunity to Repair Two Years of Poor Autumn Weed Control

July, 2004 - With staggering amounts of brome plaguing cereal crops in many areas and serious ryegrass and black-grass problems in others, leading agronomists are urging UK growers to take full advantage of the excellent opportunity they have this autumn to repair the damage caused by two consecutive years of poor establishment weed control.

"Brome problems have more than trebled in some areas in the past season," stresses Dr David Ellerton of ProCam. "Both barren and meadow brome have caused particular headaches. And they have been widespread across whole fields rather than just confined to headlands and clear crop foci.

"Specialist spring brome killers proved a godsend, but we had to use three times more of them than ever before. So much so that UK supplies actually ran out before the end of the spring spraying window.

"Although nowhere near as dramatic as the upsurge in brome, we have also seen significant increases in infestations of both ryegrass and hard-to-kill black-grass," he adds. "All-in-all, this season has been one of the single most challenging for grass weeds in recent memory. After two years of decidedly poor autumn control, weed seed populations have built-up to disastrous levels in many cases."

"Two very dry autumns in a row are undoubtedly part of the reason for this year’s widespread weed problems," confirms Bank Cargill’s Bob Mills, "linked to the increasing trend towards minimum tillage. "There simply wasn’t enough moisture in the ground to allow most people to get any reasonable flush of stale seedbed weed growth for spraying-off ahead of drilling in either year. The weed seedlings just sat there to emerge and establish within the crops once the rains actually arrived.

"The brome and other annual grass weed seed populations that built-up over 2002/3 couldn’t be tackled effectively last autumn. Which meant problems really came to a head over the past season when conditions proved just right for brome in particular.

"Thankfully, we should have plenty of moisture in the ground this autumn," Bob Mills continues. "The pre-harvest storms may have battered many cereal and rape crops, but they also gave a timely top-up to soil moisture levels. And the moisture will have been held securely in the ground under the canopy of the ripening crops rather than either being transpired or burnt off."

Both agronomists see this autumn giving growers the ideal opportunity to get back on top of their current grass weed problems. Equally, they stress that, with present weed seed populations, failure to take full advantage of it could be disastrous for many.

"The past two seasons have really underlined how much we depend on good out-of-crop weed control these days," points out David Ellerton. "If we fail to hit our troublesome annual grass weeds effectively with glyphosate between harvesting and drilling again this year, we are really in the mire. Especially so with resistance, not to mention in-crop herbicide bills, going through the roof." With soil moisture conservation unlikely to be so critical for most this autumn, Dr Ellerton believes a combination of ploughing and pre-drilling Roundup will prove particularly beneficial in tackling barren brome and black-grass problems in many cases.

"Burying brome and black-grass seeds below the depth at which they can emerge is a very effective way of depleting the weed seed bank," he explains. "But you need to follow the plough with a good press to preserve moisture and induce the greatest possible pre-drilling emergence of any weeds seeds not buried sufficiently deep.

"Plough and press as soon after harvesting as you can. Then wait 10-20 days for a good greening-up, go in with 0.75-1kg/ha of Roundup Max and you’ll hit the annual weeds for six. What’s more, you can work up your seedbed and drill just six hours after spraying, so you’ll be able to get your next crop in without further delay."

Where minimum tillage is practised, Bob Mills also advises cultivating as soon as practicable after the previous crop has been removed and consolidating well to create the best conditions for annual weed seed germination. Thereafter, he suggests two stale seedbed options.

"Either wait as long as you dare for maximum weed seedling emergence before going in with the Roundup," he recommends. "Alternatively, go in with the sprayer as soon as you see a reasonable greening-up, then wait a further week or so and spray-off a second flush of weed growth before drilling.

"If you have the time, a two-flush strategy is likely to give you better control. It’s not something we’ve seen for three or four years, but with sufficient moisture in a stale seedbed you can stimulate a matt of weed growth so dense that many seedlings will be shaded from the glyphosate. Also a major initial flush of germinating grass weeds tends to inhibit the germination of other seeds, which will then emerge once the inhibiting effect of the first germinators is removed.

"In either case, I’d use 1.2 l/ha of Roundup Gold for its rainfastness, speed of action and short 6 hour cultivation interval."

Where grass weed problems are especially serious or good pre-drilling control has proved impossible, Bob Mills and David Ellerton point out that Roundup Gold and Max can both be tank-mixed with a modern pre-em like Crystal to hit early emerging seedlings in the cereal seedbed.