Match Cultivations To Weed Control Needs

August 2006 - Providing you safeguard soil moisture, you should be able to control weeds and volunteers very effectively ahead of drilling this autumn. But cultivating immediately after harvesting without sufficient thought could easily compromise the control you actually achieve. It all depends on what weeds you need to get on top of.

This is the timely warning from leading agronomist, Bob Mills of Frontier who urges growers to plan autumn tillage and glyphosate spraying carefully field by field to meet their particular weed control requirements.

"With just enough moisture in the soil surface and an early harvest, most growers will have a great opportunity to seriously deplete weed and volunteer populations in stale seedbeds or stubbles," he points out.

"This will really help counter the increased weed threat resulting from the past spring's poor control at minimum cost as well as being particularly valuable in tackling resistance problems in wild oats, ryegrass and black-grass.

"After the hot, dry summer black-grass will be especially vulnerable as the seeds should have little, if any, dormancy," explains Bob Mills. "So rapid shallow tillage as soon after combining as possible with immediate rolling or pressing will set-up a stale seedbed with sufficient moisture and good soil to seed contact. With soil temperatures as they are, this should stimulate a strong flush of weed seedlings for spraying-off with a highly economic 1.2 l/ha Roundup Ace within 7-10 days.

"Because you can cultivate after only 6 hours with our modern glyphosate formulation you can then till the ground again lightly to produce and spray-off a further flush of seedlings comfortably ahead of mid-September drilling," he adds. "This will stand you in particularly good stead in tackling serious annual grass weed or volunteer problems."

Bob Mills advocates precisely the same strategy for the most effective control of sterile and great brome, annual meadow grass, wild oats and volunteer cereals and oilseed rape, stressing the critical importance of shallow tillage as opposed to deep discing or ploughing with OSR volunteers in particular.

However, he insists this approach will be completely wrong with meadow, rye or soft bromes, couch, thistles or volunteer potatoes.

"These bromes respond to a stale seedbed but need a period of after-ripening on the surface to encourage good germination," he notes. "So it's best to leave the stubble undisturbed for 3-4 weeks before setting it up with cultivation if they are your main problem. Again you'll be able to spray within around 10 days, then cultivate just 6 hours later if you use Roundup Ace.

"Equally, about the worst thing you can do with common and onion couch, thistles and volunteer potatoes is to cultivate before spraying-off. With all these weeds the greatest possible amount of new growth is what you need. And with couch your problems will only be increased if you chop and spread the rhizomes with a cultivator.

"If you really want to control perennial weeds and volunteer potatoes, therefore, you should leave the stubble for 3-4 weeks, spray off with up to 3.2 l/ha of Roundup Ace and only then cultivate," recommends Bob Mills. "You'd also be wise to leave 2-5 days before cultivating for maximum effectiveness.

"You'll need to leave more time between harvesting and drilling wherever these more difficult-to-control weeds pose problems," he accepts. "So it would be wise to leave such fields for later autumn sown crops. Doing so may conflict with your desire to get drilled-up as early as possible, but it will invariably pay dividends in avoiding serious crop losses."