There may no longer be any calendar restrictions on spraying to control problem grass weeds in non-cropped land under the new BPS crop diversification or EFA rules but the correct timing of glyphosate applications will be every bit as important as it was under the old Set Aside regime, warns Roundup technical specialist, Manda Sansom.
“Even the most powerful, modern Roundup formulations should not be used on black-grass, bromes or ryegrass during stem extension in April and early May,” she stressed. “Instead, for the most reliable, single application control, all our work shows they need to be sprayed at full ear emergence, which for black-grass is usually in June – the first week of the month is ideal.
“There’s a huge temptation to go in with the sprayer at the first signs of grass weed flowering on uncropped land. But for every flowering stem at this stage there will be many more tillers in stem extension. The whole thrust of their physiology is so strongly upwards that herbicide translocation down to the roots can be seriously restricted. As a result, a good initial kill will be followed by re-growth of later tillers after around a month, necessitating another spray.
“On the other hand, a single spray from full ear emergence in early June until just before the seeds are fully ripe and the foliage begins to die back later in the month will prevent either re-growth or viable seed production.”
Although annual grasses may start flowering in April, Manda Sansom points out that it can take six weeks for the first seeds to mature. What’s more, the earliest heads tend to set few, if any viable seeds. So spraying can safely be delayed until the best time for the most cost-effective control (Figure).
Figure: Black-grass Seed Viability
All the more so with modern Roundup formulations which can reliably be used under challenging summer conditions, are rainfast in just an hour on annual weeds and can be cultivated after only six hours.
“Our extensive trials and field experience show 1080 g ai/ha of Roundup is needed for full annual grass weed control,” she explained. “That’s 3.0 l/ha of a 360g/l product, 2.4 l/ha of a 450g/l, 2.25 l/ha of a 480g/l or 1.5 kg/ha of a 720g/kg dry formulation. It’s important to appreciate too that adjuvants will not compensate for reduced amounts of glyphosate at lower rates.
“Roundup label rates of up to 2160 g/ha for ‘green cover on land not being used for crop production’ give plenty of leeway for tackling tougher perennials in single or split doses. And once cultivation begins there’s approval for a further 1800 g/ha for use on ‘all edible and non-edible crops before sowing/planting’.
“This gives growers the greatest possible flexibility to bring maximum ‘out-of-crop’ pressure to bear on problem grass weeds, providing much need relief for in-crop herbicide chemistry,” concluded Manda Sansom. “To do this in the most cost-effective way, though, demands sufficient understanding and patience to ensure the best summer spray timing.”