SOME SPECTACULAR weed growth has continued throughout the winter, so a spring herbicide regime will be best applied early before weeds get even bigger and tougher.

Neil Thomson, of Bayer, who has a good overview of the situation from travelling the length of the country updating agronomists and farmers this winter, told The SF: "Unsurprisingly, the situation is a bit of a mixed bag depending on where farms are and the weed problems they've faced in the past."

He reckoned that most winter barley crops had been treated with a residual herbicide, like Liberator (flufenacet + diflufenican) and that farmers also completed a pre-emergence programme on more than three-quarters of the wheat area.

"A lot of people who've gone with a pre-em will be quite pleased, as the residual herbicides have done a good job with most weeds. Annual meadow-grass control seems to be good, brome control has also been good, although brome is generally tougher than meadow-grass so some of it will need tidying up this spring."

Crops which ended up with a peri- or post-emergence spray of residual herbicides have seen noticeable lower control so may also need looking at, added Mr Thomson.

Andrew Gilchrist, of Scottish Agronomy, agreed: "On our patch, most of the winter cereals got an early post-em and control's been pretty good. There's a chunk of later-sown wheat that will definitely still need a herbicide, possibly Othello (mesosulfuron + iodosulfuron + diflufenican), to mop up annual meadow grass. Unfortunately, there aren't any options for barley crops that missed out on the pre-em."

Brome problems are likely to be found on min-tilled land and that tends to be in the south of the country, according to Mr Gilchrist. These fields will have received a robust pre-em spray and wheat crops should be followed up with contact material this spring.

"The unique thing this winter is that the weeds haven't really stopped growing," added Mr Thomson. "Before Christmas, soil temperatures were a relatively high 8°C, they dropped to 4°C but are picking up again, so the weeds have carried straight on."

With weeds bigger than normal, going out early to control them will be more important than ever this year. Mr Thomson thinks that grass weed control will need to kick off in early March to get good results as long as the weather remains reasonably mild and the land dries out.

Wheat crops that didn't get treated in autumn may have high meadow grass levels, the best treatment for this is Othello. If there are broad-leaved weeds in the mix, adding a partner based on florasulam will beef up control. For wheat suffering from brome, Pacifica (mesosulfuron + iodosulfuron) is a good option.

But, with Pacifica, timing is crucial, said Mr Thomson: "We did trials last year and saw a big drop off in effectiveness when we applied it later in the spring - control dropped from 96% to 57%. We do the work in a field with a moderate to high sterile brome population, so the untreated plots are a good guide to show the extent of the issue - in fact I was astounded by how much there was in this particular trial.

"All plots had a pre-em application of Liberator in the autumn followed by Pacifica in the third week of March with the other plots receiving treatment in early May and the difference was huge. With 96% control in this high pressure situation, growers can feel confident they are able to keep on top of brome but if you delay and that control's reduced you'll allow too many seeds back to the soil," concluded Mr Thomson.

Apart from grass-weeds, there are also the broad-leaves to consider, these vary a little more from place to place, but the warm conditions will mean that cleavers, mayweed and chickweed will all be fairly large. Mr Gilchrist noted that cleavers are becoming a nuisance for a lot of people in cereals but fluroxypyr products can usually mop this up.

The other thing to think about is spring barley and Andrew Gilchrist thinks there has been a change in weed management in recent years. "People have moved away from sulfonylureas at post-em and now use pre-em products. A typical programme will include 0.3l/ha Liberator backed up with pendimethalin or some diflufenican.

"The pre-em generally works out a little cheaper without the resistance issues of sulfonylureas - there were difficulties controlling chickweed, mayweed and pansy. The other advantage is that a pre-em can control annual meadow-grass and altogether I'd say you get between 80-90% total weed control," said Mr Gilchrist.