Maize growers should apply the stale seedbed approach that has proved so successful in controlling problem weeds ahead of autumn cereals to get their crops off to the best, weed-free start this season, advises a leading weed management specialist.
Monsanto technical development manager, Barrie Hunt stresses that the grass and broad-leaved weeds than can so badly compromise maize performance in the crop’s first few weeks are easy to let off the hook in the spring. Not only are many well-entrenched in over-wintered ground, they also tend to be growing strongly in warm, moist soils and can be more readily transplanted than killed by cultivations.
“Ironically, their very activity means that most annuals are particularly vulnerable to glyphosate at this time of the year, providing they haven’t moved into stem extension,” he points out. “To achieve the most thorough kill, though, you need to take advantage of their weaknesses rather than playing to their strengths.
“The stale seedbed approach that has become such an essential part of autumn arable weed control in recent years to deal with difficult grass weeds will do just this. As well as hitting over-wintered weeds hard, it will stimulate spring germinators into action so they can be dealt with effectively ahead of planting. This will make early post-emergence control with the limited armoury of herbicides available very much easier and more cost-effective.”
Having left the ground to green-up after any muck incorporation, Barrie Hunt recommends starting the pre-planting weed control programme with Roundup three to four weeks before planned maize drilling. Two or three days after spraying, the ground should be cultivated lightly and consolidated into a false seedbed to encourage rapid weed seed germination.
This will allow a second Roundup spray immediately ahead of maize drilling to knock out the flush of spring seedling growth which would otherwise come through with the crop.
“In addition to the usual broad-leaved suspects like cleavers, chickweed and mayweed, we’re seeing a lot more spring-germinating black-grass in arable ground these days,” observes Barrie Hunt. “And rye-grass, thistles and docks can be especially troublesome when old swards have been ploughed out.
“Perennials are not at the optimum growth stage for glyphosate so will be checked rather than fully controlled by spring applications. However, this suppression can allow vulnerable maize seedlings the extra time they need to establish successfully.
“Application rates need to be geared to weed populations. For established, tillered young black-grass 720 g/ha of glyphosate should be sufficient while up to 1800 g/ha can be used for tougher perennials. Water conditioners can improve performance in hard water areas, but no amount of adjuvant can make up for insufficient glyphosate.
“If you want the greatest reliability and flexibility, use a modern Roundup formulation with particularly good activity under cool conditions, the highest rainfastness and the shortest cultivation interval,” he insists. “Water volumes of around 100 litres/ha and nozzles on the finer side of medium should give you the best coverage.
“It’s also important you take as much time and care in your pre-planting spraying as you would in treating a standing crop. Bear in mind too that if you move as little soil as you can at maize drilling you will stimulate the least weed seed germination and emergence in the seedbed.”