Prioritise Autumn Grass Weed Control Post-Set Aside, Independent Specialist Warns

High levels of poorly-controlled grass weeds in set-aside this year means pre-planting weed control must be a priority for most UK wheat growers if they are to avoid serious and costly in-crop problems over the coming season, warns independent weed management specialist, Colin Stride.

"Set-aside should be the best cleaning opportunity in the rotation," he stressed, "but it has been compromised. In particular, the on-off season we've had this year, with two long dry periods interspersed with persistent heavy rain in May/June, made it particularly difficult to get set-aside spray-timing spot on.

"A lot of black-grass and brome grasses were sprayed either at stem extension when control is notoriously poor or after seed set. This and the very high populations of grass weeds carried over recent years means a substantial reservoir of weed seeds coming out of set-aside in many cases. At the same time, we are also seeing increased levels of poorly-controlled perennial weeds from April/May applications targeted at annual grasses.

"Combined with poor weed control elsewhere in the rotation, this makes it vital to sort things out between set-aside and wheat establishment."

Colin Stride insists that growers need to inspect their set-aside ground especially carefully in the coming two weeks and plan establishment programmes to control their specific weed challenges.

"Use the time you have ahead of winter wheat drilling this season wisely," he advised. "If you have already cultivated your set-aside, work it down as soon as possible with a press or heavy Cambridge roll to create a stale seedbed. Preserve enough moisture and you'll be surprised at how much weed growth you stimulate in the next two-three weeks for a timely dose of glyphosate just ahead of drilling.

"If you've yet to cultivate the ground, establish whether your primary problem is annual grass weeds or perennials. For annuals, rapid shallow cultivation of the collapsed vegetation followed by good consolidation is what you need to produce the best stale seedbed. Mix in the trash, and avoid bringing-up buried seed. Then you can go in with Roundup before drilling - a 6-hour delay is all you need with the most modern formulations.

"On the other hand, it's best to leave the ground uncultivated if perennials like common couch and onion couch, or volunteer potatoes are your main target," recommended Colin Stride. "That way you don't add to your problem by breaking-up the perennating organs and scattering them at different depths.

"Hold-off on spraying for as long as you can, allowing the maximum amount of new shoot growth with at least 2-3 leaves. Once you've sprayed you'll need to wait for two to five days - depending on your weed target and glyphosate formulation - before cultivating and drilling."

Mr Stride insists that effective annual and perennial weed control prior to establishment will pay dividends after set-aside this autumn. As well as reducing early weed competition, getting the best start will minimise the risk of more extensive problems developing later. And it will help combat the increasing amounts of target site resistance being reported in annual grasses.

He stresses that early drilling should not be contemplated wherever grass weeds are a particular problem. "You'll never regret giving yourself time to control them before you sow your wheat," he concluded.