Tank-mixing Roundup (glyphosate) with pre-emergence herbicides is one option growers could consider if they are struggling to achieve two good cycles of stale seed-bed treatments, says Manda Sansom of Monsanto.

An increasing number of growers have been inquiring about the technique, she says, interested in minimising the pressure on post-emergence sprays, but concerned about their ability to achieve good stubble and stale seed-bed grassweed and volunteer control.

“Growers want to get drilled up as early as possible, but at the same they are worried about extended blackgrass emergence in a relatively high dormancy season.”

Including glyphosate has proved successful in eliminating early emerging seed-bed weeds, she says. “By taking out weed seedlings germinating in the seed-bed as well as those transplanted by cultivations, pre-emergence glyphosate minimises the spread of in-crop weed growth stages, making it easier to achieve optimum post-emergence timing.”

Growers need to be careful with the timing when using the technique, Will Foss, a UAP agronomist in Suffolk, stresses. “Make sure the crop is not coming through or close to coming through.”

Cloddy seed-beds can also cause problems. “With better seed-beds you are less likely to spray any seeds exposed between clods.”

Make sure any green material is actively growing, too, he adds. “And beware if there is soil covering any transplants – glyphosate is deactivated by soil.”

In an ideal world fields will be sprayed before drilling, Peter Riley of TAG says. “That would be best practice. But mixing glyphosate could be useful if you haven’t managed to kill blackgrass before you drill and weeds are still there.”

Not all glyphosate formulations are approved for post-planting, pre-emergence use, Ms Sansom stresses, so check labels before applications. But newer Roundup formulations are compatible with almost all commonly-used pre-emergence herbicides, including Crystal (flufenacet + pendimethalin), Liberator (flufenacet + diflufenican), Defy (prosulfocarb) and trifluralin.

Stubble spraying seed beds

Those who have not sprayed off stale seed-beds with glyphosate pre-drilling can consider using Roundup mixed with the pre-emergence spray, says Monsanto.

GLYPHOSATE PRE-EMERGENCE
  • Use where cannot spray pre-drilling
  • Takes out transplants and early germinating weeds
  • Care with timing
  • Make sure green material is actively growing