Spring cereals can only be effective in dealing with problem grass weeds if they are managed with sufficient establishment care and attention. This and the serious damage black-grass, brome, ryegrass and annual meadow grass can all do to crop performance makes a no-compromise approach to early weed management essential.
Although spring barley and oats, in particular, can be highly competitive with grass weeds once growing strongly, they and spring wheat are acutely vulnerable to weed competition during establishment; especially where cold, wet conditions and less-than-ideal seedbeds restrict crop emergence and early growth.
“Letting grass weeds off the hook at this stage in the season is hugely dangerous,” stressed national Grass Weed Action Initiative co-ordinator, Barrie Hunt. “They will compete aggressively with spring cereals, interfering with the rapid, even establishment essential to yields and profitability. The very limited range of in-crop herbicide options available means they will then to go on to produce large numbers of seed heads and a heavy seed return, undermining the key rotational value of spring cropping.
“Unfortunately, it’s all too easy to fail to control these weeds well enough in the late winter and early spring,” he pointed out. “They’re often well-entrenched in over-wintered stubbles and beneath cover crops. Frosting restricts their uptake and translocation abilities. And glyphosate uptake and performance can be markedly reduced under cool conditions and with sudden downpours. Then, as soon as spring warms up they go into stem extension and become that much harder to eliminate.”
Minimise weed emergence
Under these circumstances, Mr Hunt urges growers need to bear down on grass weeds as hard as they can from the very start with an approach that integrates the most effective cover crop destruction and stubble cleaning closely with the best-managed spring cultivation and drilling practice to minimise grass weed emergence in the new crop.
As cover crops will have done their job by February, he sees no advantage in leaving them growing. In fact, he explains that heavy soils are likely to condition better for spring seedbeds if they have a good two weeks – preferably a month – without cover. This also gives the best opportunity to tackle any early weed growth with pre-planting glyphosate.
“The best and safest strategy is to spray-off your covers in late January or early February,” he suggested. “That way you’ve cleared the decks for the most rapid and cleanest spring crop establishment.
For both cover crop destruction and pre-planting weed control, he strongly recommends a modern Roundup proven to get more glyphosate into plants more rapidly and reliably at low temperatures than other formulations.
He also advises using formulations with maximum rainfastness to take advantage of every spray window, and those with the shortest cultivation intervals for the least possible delay ahead of seedbed preparation and drilling.
“It’s equally important to use the right rate for the job,” he insisted. “For established, tillered young black-grass, 720g/ha of glyphosate should be sufficient. However 1,080g/ha may be required for particularly thick and advanced grass weeds. And tough perennials and harder-to-kill cover crop species like oil radish and vetches will need higher rates, often up to 1,800g/ha.
“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 pre-planting applications as a rush job. Take as much time and care as you would with your winter wheat’s T2 fungicide because you have only the one chance to get it right.”
For the most effective pre-planting control, Mr Hunt recommends around 100-litres/ha of water and a spray on the finer side of medium for the best targeting of seedling weeds.
Cultivation ahead of drilling will help to hasten the demise of most weeds in his experience. It can also be a valuable way of minimising the risk of glyphosate resistance development.
However, he warns that 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.
He sees quality seedbeds as far more important than calendar date in spring cereal drilling, insisting that everyone needs to have both the patience to wait for the best possible soil conditions and the capacity to make the most of them when they occur.
“Where drilling has to be delayed for a number of days after pre-planting treatment, consider including an approved glyphosate in your pre-emergence spray,” he concluded. “This can be invaluable in dealing with weeds that can emerge very rapidly with rising soil temperatures. Naturally, of course, application needs to be ahead of any crop emergence.”