Step-up Pre-Planting Weed Management for Maize and Root Crops
Posted 6 years ago
24/04/2020
Maize and root crop growers will need to step-up their pre-planting weed management efforts this season to safeguard establishment in the face of particular grassweed challenges; especially so where they are planted well into April or early May.
Black-grass, ryegrass and bromes have all developed strongly where conditions have prevented much, if any, winter or early spring control. The mild winter has enabled them to become firmly-established and tillered. What’s more, by mid-April they and difficult broadleaved weeds will be well into stem extension, making them challenging to control with even the best glyphosate formulations.
“Knowing how vulnerable maize, sugar beet and potatoes are to early weed competition, we must step-up our pre-planting cultural and chemical control efforts to combat these threats,” warns Bayer technical specialist, Roger Bradbury. “And we’ll have to do this at a time when workloads are even more stretched than usual with such a backlog of winter and late-sown spring cropping fieldwork.
“Warmer soils will help delayed sugar beet and potato sowings get out of the ground and away more rapidly,” he adds. “But well-established weeds will take even greater advantage of them. So, they and maize will need the cleanest possible start ahead of their main in-crop sprays.
“If crops don’t get this, growers will struggle to control weeds, compromising plant establishment, restricting yields and leaving a damaging legacy of weed seed return to deal with in the rotation.”
To achieve the cleanest late-sown spring crop start while adding as little to workloads as possible, Mr Bradbury recommends careful integration of cultivations with the most effective glyphosate treatment.
Specifically, he advises an early glyphosate spray as soon as ground conditions allow, hitting weeds before they get too far into stem extension. This should be followed by the most appropriate cultivation for the soils concerned once they are fit, and a second glyphosate spray immediately ahead of sowing, if needed, to deal with newly-emerging weeds.
For sugar beet and potatoes, this follow-up spray can be replaced by an approved glyphosate as a pre-em for extra workload flexibility.
“It will be more important to use a modern Roundup formulation performance-proven under challenging conditions to deal with weeds already into stem extension,” he stresses. “All the more so given the lower levels of performance we’ve recorded from the most popular phosphate ester replacements for tallow amine glyphosate formulations withdrawn from use in 2018.
“Rainfastness from just one hour and a cultivation interval of as little as six hours with modern Roundups also gives the greatest possible leeway to deal with uncertain weather and valuable extra flexibility to fit-in with very tight workloads.”
Mr Bradbury insists it will also be vital to use the right rate for the job and appreciate that no amount of adjuvant will make up for insufficient glyphosate. While 720g/ha of glyphosate in a modern formulation is normally sufficient for well-tillered grass weeds, where stem extension is underway he recommends increasing this to 1080g/ha. Of course, rates can be reduced to 540g/ha for the second application which will only be dealing with seedling weeds.
“Taking sufficient care in glyphosate spraying is equally essential,” he adds. “For the greatest efficiency, water rates as low as 100 litres/ha will be fine. I’d also suggest a forward speed of no more than 12km/hr with a boom height of around 50 cm and a medium to coarse spray for the best coverage.
“Coupled with enough patience to cultivate and sow only when the ground conditions are right, this pre-planting approach should provide the best possible foundation for pre-em sprays of Emerger (aclonifen) and Artist (flufenacet + metribuzin) in potatoes or post-em Betanal mixes for sugar beet and MaisTer (foramsulfuron + iodosulfuron-methyl-sodium) for maize.”