Growers across the country must manage their set aside spraying very much more effectively from this season if they are to keep on top of troublesome grass weeds without compromising their cross-compliance and ELS environmental assets, warns Agrovista technical manager, Mark Hemmant.

"Spray timing is the single thing most growers get wrong with their set aside glyphosate sprays," he stresses. "And, with grass margins, beetle banks and conservation headlands to nurture, everyone is going to have to pay far more attention to minimising spray drift from now on.

"Spray grass weeds during tillering or at full ear emergence and you'll almost certainly get complete control from a single dose of a high activity glyphosate like Roundup Ultra. "Spray too early during stem extension, though, and even the best formulations will give you very variable control. The strong upward sap flow tends to accumulate glyphosate in the aerial parts, giving a good initial kill but allowing tillers to re-grow."

Mark Hemmant acknowledges that it's all too easy to be tempted to spray set aside too early: especially when there's a lot of growth and seed heads are emerging. For every flowering stem in April and early May, he points out that it's important to appreciate there will be many more tillers still in the less vulnerable stem extension phase. Equally, he explains that seeds in early emerging ears commonly take a good six weeks to mature, so there is no rush to spray them.

"The best time to spray grass weeds is once all the ears are fully emerged but while the seed heads and leaves are still green," he insists. "With annuals like black-grass, brome and rye-grass this varies from mid-May to early June. With common couch, onion couch and other perennials it's likely to be later in June or even into early July, depending on the season.

"Spraying in hot weather should be avoided as weed glyphosate translocation can be restricted under these conditions," he adds. "With light intensity also important in governing herbicide movement in the plant, spraying in the morning is always better than later in the day."

For the most cost-effective volunteer cereal and annual grass weed control, Mark Hemmant recommends a single 2.4 litre/ha application of Roundup Ultra, with higher rates for couch and other perennials.

He suggests adding the specialist adjuvant, Companion Gold to the tank prior to the glyphosate to reduce spray drift as well as maximising herbicide efficacy, stressing that boom height, forward speed, spray pressure and nozzle choice must also be spot-on for the most effective spray targeting.

Where volunteer cereal or grass weed growth is excessive, Mr Hemmant accepts that two glyphosate applications may be required - one before the main stem extension phase in late April to mid-May and the other at full ear emergence in June/July. In most cases, however, he considers a single application will be quite effective enough: providing, of course, the spray timing is right.