New research from Syngenta highlights the role that pre-emergence herbicide Defy can play in helping to control resistant grassweeds.

But further work planned to start this year will focus on finding the best partner products for Defy, as a replacement is needed for trifluralin, which is set to disappear, admits the company's Rod Burke.

"Independent trials have shown that growers can achieve over 70% control of resistant blackgrass with a pre-emergence Defy/trifluralin mix, which is equivalent to the performance of the flufenacet-based products," he says.

"Furthermore, we know it reduces selection pressure on post-emergence sprays, helping to slow the build-up of weed populations with resistance to the sulfonyl­ureas, such as Atlantis. Prosulfocarb has a different mode of action to these herbicides."

Deepak Kaundun, Syngenta's herbicide resistance leader, confirms there have been no reported cases of resistance to prosulfocarb to date. "It's a multi-target herbicide, which makes it less vulnerable to the problem developing," he says.

"It's also a thiocarbamate, putting it in the same chemical group as tri-allate, which means it offers an alternative mode of action and controls both sensitive and resistant grassweeds."

Dr Kaundun's research with prosulfocarb has examined its effectiveness against blackgrass and ryegrass, using weed populations containing both target-site and enhanced metabolism resistance mechanisms.

Very effective

"What we found was that prosulfocarb used alone, and in mixtures, was very effective on both the sensitive and the resistant populations. It controlled weeds with target site and enhanced metabolism resistance, whatever the type."

He also found that the enzymes selected by sulfonylurea and fop and dim herbicides use do not affect prosulfocarb efficacy. "Prosulfocarb is metabolised by different enzymes in the crop, and not degraded by the same one as these other herbicides. It's a lowresistance risk."

This means Defy is an effective tool for controlling and delaying the spread of resistance to existing herbicides, Dr Kaundun maintains.

"It can help with the sustainable use of current herbicides, many of which are increasingly affected by resistance."