The withdrawal of trifluralin will leave a gaping hole in the herbicide armoury for some field vegetables. So what else is available?

Trifluralin is the mainstay for controlling broad-leaved weeds in brassica leaf and root vegetable crops. And because it is the only pre-emergence herbicide with grass weed activity, for some it is essential for effective blackgrass and annual meadowgrass control.

Not only that, but the soil-incorporated product is very reasonably priced, making its impending withdrawal from the market very unpopular, says independent herbicide specialist Cathy Knott.

About 40 specific off-label approvals will be recalled, although the vegetables most affected will be transplanted brassicas, winter field beans, and some roots. Some alternatives exist for the first two, but with simazine gone for beans, growers will be left with no cheap weed-control option. Kerb controls resistant blackgrass, at a cost. Stomp has off-label approvals for use at low rates, and is good against polygonums, says Ms Knott.

Of particular concern is the fact that trifluralin is incorporated and therefore compatible with mechanical weeding – the alternatives are not, because hoeing disturbs sealed soil surfaces. The options are limited for transplanted crops.

“The Horticultural Development Council is funding some herbicide screening trials in vegetable crops but there is no government funding to seek out alternatives when effective herbicides such as trifluralin are withdrawn,” she adds. “That will severely disadvantage UK growers.”

But the crop that will suffer most is the swede, warns Neil Potts, independent agronomist for Matford Arable Systems, based in Devon, who advises a quarter of the 12 or so growers of consumable swedes in the south west.

“The situation is serious for swede growers because there really isn’t anything to step into trifluralin’s shoes. If there was, growers would readily pay five or six times the price they pay now,” he says.

The problem is that once the nets go on, small weeds are very difficult to reach with sprays. And swedes must be covered with nets soon after drilling to prevent damage by cabbage root fly, whose larvae devastate yields and reduce quality. Soil-incorporated trifluralin is just the job, says Mr Potts.

Solutions

There are one or two pre-emergence alternatives, but they can be harsh on the crop, he points out. Ramrod and Dacthal pose a greater risk to good establishment than Butisan S, which must be used at a low rate to avoid crop loss.

Although those products control a reasonable spectrum of weeds, they are not as good against the range of cruciferae and polygonums as trifluralin is, he stresses. And because growers often don’t know what to expect in the way of weeds because they commonly produce swedes on rented land, the outcome could be poor.

And it’s a matter of fingers crossed when forced to recommend post-emergence treatments, he adds. His advice is to split applications to improve the chances of weed kill through nets.

“For grass weeds, the only real option is Fusilade, though it doesn’t control annual meadowgrass. And the only crop-safe product for broad-leaved weed control is Dow Shield, which is expensive at £60/ha, but what can you do?”

Taking the sprayer in early after emergence will be crucial to success. Where weeds such as fathen and knotgrass get a hold, he has seen misshapen roots and swede yields halved. If the quality of UK produce falls, supermarkets will source outside the EU where trifluralin use is still permitted, Mr Potts warns.

Not only would that reduce UK growers’ income, it would be a set-back for the food miles campaign.

“Swedes are something we can grow well here, and no one in the West Country, or indeed in Scotland, wants to give up on them,” he adds. “We shall hope for a revocation of the restrictions on trifluralin use for vegetables, though we realise it would involve investment in further research.”