Substantial increases in spring cropping across the country this season should do much to address black-grass, brome and Italian ryegrass problems. But only if sufficient care and attention is put into their control ahead of and at sowing.
This is the view of Monsanto technical development manager, Barrie Hunt who insists that failing to take full advantage of this particular opportunity can seriously compromise both the weed control value and performance of spring crops.
“It’s all too easy to achieve less-than-ideal control of problem grass weeds in the late winter and early spring,” he pointed out. “They’re often well-entrenched in over-wintered stubbles and uneven or poorly-established cover crops. Frosting tends to restrict their uptake and translocation abilities. And glyphosate uptake and performance can be markedly reduced under cool conditions and with sudden downpours.
“Letting difficult-to-control weeds off the hook at this stage in the season is particularly inadvisable. They will compete aggressively with spring crops, interfering with the rapid, even establishment essential for the best performance. Having done so, they will go on to produce large numbers of seed heads and a heavy seed return, defeating one of the main objects of spring cropping.”
Under these circumstances, Barrie Hunt sees a no-compromise approach to early weed management as vital this spring; an approach that prioritises the most effective destruction of cover crops and first class stubble cleaning, closely integrated with the best-managed spring cultivation and drilling practice to minimise grass weed emergence in the crop.
“Some cover crop species can take a lot of killing if they haven’t been dealt with sufficiently by frost,” he explained. “Vetches, oil radish and lucerne can be particularly problematic. So too can well-established grass and perennial broad-leaved weeds. At the same time, research shows that some glyphosate formulations are much better at coping with challenging cool and wet conditions and difficult weeds than others.
“So for both cover crop destruction and stubble cleaning ahead of planting I’d strongly recommend a modern Roundup performance-proven to get more glyphosate into plants more rapidly and reliably under just such conditions. You also need a formulation with maximum rainfastness to take advantage of every spray window and one which has the shortest cultivation interval for the least possible delay ahead of seedbed preparation or drilling.
“It’s equally important to use the right rate for the job,” added Barrie Hunt. “For established, tillered young black-grass 720 g/ha of glyphosate should be sufficient while up to 1440 g/ha may well be needed for grass weeds already into stem extension as well as for covers containing vetches, pulses and oil radish, and volunteer OSR.
“Water conditioners can improve performance in hard water areas, but remember that no amount of adjuvant can make up for insufficient glyphosate. And whatever you do, don’t treat spraying over-wintered stubbles as a rush job. Take as much time and care as you would in treating a standing crop of wheat because you have only the one chance to get it right.”
Mr Hunt recommends a medium spray with around 100 l/ha of water for cover crop destruction, with nozzles inclined towards the rear and travel rates constrained to maximise crop coverage. For seedling weeds he suggests similarly low water volumes and application practice with nozzles on the finer side of medium.
Cultivation ahead of drilling will help to hasten the demise of most weeds in his experience.
However, he warns that it or significant soil movement at drilling will stimulate the seedbed germination of black-grass, in particular, which could easily lead to just the sort of early weed competition you don’t want with spring cereals.
“To minimise delays choose glyphosates that allow you to cultivate – or drill into covers on-the-green if this is your preferred approach – the next day where conditions are mild or after just two or three days where it’s cold or you have to deal with large-rooted radishes,” he advised.
“Where there are significant under-storeys of grass weeds in previously-treated cover crops or drilling has to be delayed for a number of days after cultivation, include an approved glyphosate in the pre-emergence spray too. This will deal with any weeds sheltered from the pre-planting application by cover crop canopies or transplanted rather than killed by cultivations. Naturally, of course, application needs to be ahead of any crop emergence.”