Only 30-40% of the usual supplies of the cereal herbicide, IPU, will be available in its last season of use before being withdrawn, Bayer CropScience‘s Tim Holt said.

It meant the forthcoming season would see the biggest change to growers’ herbicide programmes as a result of the withdrawal. “Not every farmer has thought through the implications,” he suggested.

Against annual meadowgrass and broad-leaved weeds growers would either have to use a pre-emergence or early post-emergence residual herbicide, such as a flufenacet product, prosulfocarb, or chlorotoluron.

That could need a change of farm policy, he suggested, because all these residuals needed to be applied much earlier than the traditional IPU timing. “Not everyone is kitted up, or has the mindset to change.”

Residual herbicides also required good seed-bed conditions and moisture to work most effectively, he noted.

An additional tank-mix partner might be needed to strengthen broad-leaved weed control. In the Bayer wheat demonstration plots with key drilled weeds, 0.3litres/ha Liberator (flufenacet + diflufenican) had left some mayweed, chickweed and cleavers.

The low rate of Liberator reduced the amount of DFF in the mix, Mr Holt explained. “So you might need to top up with Hurricane if you want more broad-leaved weed control. Alternatively you could use Firebird, which contains 60g/ha DFF.”

For bigger meadowgrass and for those not keen to spray early the only option was Bayer’s Othello, he claimed. “It controls tillering meadowgrass and a range of broad-leaved weeds.”

Containing mesosulfuron-methyl + iodosulfuron-methyl + diflufenican it was specially formulated in a new Odesi (oil dispersion) liquid formulation. “It adds on the broad-leaved weed side – you get more out of the DFF than you might expect,” Gordon Anderson-Taylor of Bayer said.

It did cost more than a residual, Mr Holt said. The full rate of 1.0 litres/ha cost around £30/ha including the adjuvant Biopower compared with £16/ha for 0.3 litres/ha Liberator. A lower 0.8 litres/ha dose could also be used where appropriate.

A test market this season had proved very successful. “A survey of 50 growers scored annual meadowgrass control at 4.71 out of five.”

Ideally the product should be used in the autumn in the classic IPU slot of late October, early November, he advised.

But with its strongly contact activity Bayer’s seed treatment manager, Adrian Cottey, suspected it might get delayed to around a typical Atlantis timing in blackgrass.

That, or a move to pre-emergence timings, would increase the need for a Deter (clothianidin) insecticide seed dressing, he suggested. “The loss of IPU could well intensify the use of Deter as a management tool because annual meadowgrass timings will become similar as those for blackgrass.”

In blackgrass areas the pre-emergence, followed by later post-emergence Atlantis (mesosulfuron-methyl + iodosulfuron-methyl) approach meant growers needed to apply a solo pyrethroid spray for BYDV control, he explained. “That application cost is around the same as using Deter. Quite simply the Deter option is a lot simpler.”

Another advantage of Deter was it protected the crop as soon as it emerged. “Even where a pyrethroid is sprayed in mid-October for a mid-September sown crop you can get a little BYDV showing in the crop. The only logical explanation is that has got in the crop before it was sprayed.”

That could explain why pyrethroid-treated crops didn’t seem to reach their yield potential, he suggested.