One year later perhaps than Syngenta was hoping, the firm’s pre-emergence grassweed herbicide Defy will be available on farm this autumn. Its approval arriving just too late for the current season.

Active ingredient prosulfocarb is from the same thiocarbamate group as Avadex, but that’s where the similarities end, Syngenta’s Iain Hamilton says.

For a start it is a liquid (800g/litre EC formulation) that doesn’t need specialist equipment to apply, it has low volatility, and while Avadex is strong on wild oats, Defy isn’t.

Instead it is being aimed at the increasingly important blackgrass and ryegrass pre-emergence markets.

“It was developed because we identified a need for more choice of actives in the sector,” Syngenta product manager Rod Burke says.

“We don’t anticipate any new modes of action in the next five to 10 years.”

Currently the grassweed pre-emergence market, which has doubled in size in the past three years, is dominated by two products – Crystal and Liberator – plus trifluralin, which is commonly used a mixture partner, Mr Burke says.

“Three actives – pendimethalin, flufenacet and trifluralin – account for 95% of the market.”

Defy has different chemistry from those, Mr Hamilton notes, although Syngenta will be recommending it is tank-mixed with trifluralin when targeting blackgrass.

“It means we have two different modes of action and broadens the range of other weeds.”

Similarly Defy will be recommended with either chlorotoluron or pendimethalin against ryegrass.

Trials evidence indicates the mixtures at least match the performance of full rate current pre-emergence standard Crystal (flufenacet + pendimethalin), Mr Hamilton says.

“Across 22 comparisons in independent and Syngenta trials the difference between the two was only 1%.”

Defy appears to be more consistent. In 10 TAG trials in the past two seasons control ranged from 65-100% with Defy compared with 30-100% with Crystal.

“In particular Crystal didn’t seem to work as well in the dry season two years ago.”

But it is Defy’s apparent crop safety margin that could tempt growers to switch over.

In four seasons of trials at pre-, peri- and post-emergence over a wide range of seedbed conditions no significant crop effects have been seen, Mr Hamilton says.

Despite that, Defy will still carry a 30mm seed soil depth restriction, similar to Crystal and Liberator’s (flufenacet + diflufenican) requirement for 32mm of soil covering the seed. “On paper they do look similar, but in the field they differ.

You have significantly more safety margin with Defy than other materials, particularly if heavy rain falls afterwards.”

mike.abram@rbi.co.uk