Spray priorities more important this springtime

19 February 1999

Spray priorities more important this springtime

As sprayers venture on to winter cereals, we open this

special focus with views on how to cope with the backlog

left by the saturated autumn. We include advice on keeping

pulses and oilseeds clean, clearing out cleavers, killing

volunteer rape and home in on an allegedly rare weed giving

trouble in East Anglia. Edited by Andrew Blake

CONSIDER carefully which fields merit herbicide treatment first this spring, say Bob Mills of Banks Agriculture and Hutchinsons Andrew McShane.

In the rush to catch up with spraying and other fieldwork, priorities must be set to ensure weed control, especially of blackgrass, slips no further, they say.

"It was the worst autumn for some time and I have felt far less in control of events than usual," says Mr Mills. But only 10% of early sown wheats remain untouched and to date few yield losses have been sustained, he believes. His main concerns are for Avadex (tri-allate) treated crops which did not get follow-up residuals before the weather closed in, and blackgrass in unsprayed winter barley.

"Where you have resistant or difficult blackgrass the interval between Avadex and the following residual needs to be quite tight to get the best effects," he says.

"With unsprayed barley the problem is that we do not have as good an armoury as we do for wheat. The choice really comes down to Tigress Ultra or Corniche, Grasp and Hoegrass, and in terms of blackgrass control you have to say that even now they all need ipu added. They are not in the same league as Hawk, Topik and Lexus which cant be used on barley."

Higher than normal populations of cleavers after poor control last season could justify early use of more modern products like Eagle (amidosulfuron) and newcomer Lotus (cinidon-ethyl) rather than waiting to apply CMPP (mecoprop) or Starane (fluroxypyr), he adds. "Early removal may be of more benefit this year. The advantage of Lotus is that it has a slightly broader control spectrum, and it has done well in trials when temperatures are low."

A wide range of mainly residual materials and mixes was used last autumn, most of which performed satisfactorily where seed-beds were good, Mr Mills reports. Spring germinating wild oats are likely to be the main consideration in subsequent treatments.

"But for some later applications which went on in less than ideal conditions and where blackgrass has come up from depth there may need to be a more specific follow up with contact products."

Growers without blackgrass may still need to get the sprayer out before long. "Broad-leaved weeds in later drillings are no problem yet. But speedwells and especially cranesbill in early drillings have come through with a vengeance, possibly because we have taken our eye off the ball a bit." Like cleavers, cranesbill is costly to control in oilseed rape and more easily tackled in cereals, he says. "One of the best options is Ally."

Wheat growers still have plenty of treatment flexibility, says Mr McShane. But blackgrass in barley merits urgent attention. "You must sort it out before it gets too big because the options are very limited. In some unsprayed fields there is already well-tillered blackgrass." Even with the addition of ipu, Tigress Ultra (diclofop-methyl + fenoxaprop-P-ethyl) and Grasp (tralkoxydim) will not give consistent control of blackgrass beyond mid-tillering, he notes.

In order of priority he suggests concentrating first sprays on blackgrass in barley. Untreated wheats with high levels of the weed should come as soon as possible thereafter, followed by top-up treatments where blackgrass survived autumn applications. "Growers can then move on to lighter land and late sowings. I am surprised at how clean some late drillings are."

In contrast to Mr Mills experience in Bedfordshire/Suffolk, autumn cereal programmes in Cambridgeshire and other parts of East Anglia gave mixed results, says Mr McShane. So individual field assessment is vital to help plan spring programmes.

Dose rate, too, needs choosing carefully. For products like Puma X (fenoxaprop-P-ethyl + ipu), the label dose may be 3, 4 or 5 litres/ha depending on the extent of tillering and the size of the blackgrass. "It is easy to misjudge it when plants are small," he warns. "Those with three tillers may not look much different to those with only two at first glance.

"Where nothing has gone on at all so far, there is great scope for false economies. It is no good relying on high rates of ipu alone to deal with blackgrass. You must have some contact graminicide included."

In the absence of blackgrass 1000g/ha of ipu, rather than the full 2100g/ha spring rate, should give good control of early tillering annual meadow grass. "But you have got to watch out on lighter soils where wheat and barley are not well established because there is a risk of crop damage."

It is also worth remembering that products normally used in the autumn may have growth-stage or date cut-offs, he adds. "Read the label carefully," he says.

lIn Scotland, where sprayed fields are the exception, pressure to treat is much less than in the south, according to Keith Dawson of CSC CropCare.

"We do not have blackgrass for a start, and weed growth was not high last autumn. My message is do not panic. There are still plenty of opportunities and good chemicals." Products like Javelin Gold(diflufenican + ipu) and Quantum (tribenuron-methyl) can be used quite late, he notes. But early sown winter barley definitely merits treating first because weeds are more competitive.

His main worry is that once growers can get on, the temptation to tank-mix too many products risks crop damage, especially if the weather is frosty. &#42


&#8226 More unsprayed crops.

&#8226 Programmes disrupted.

&#8226 Priorities need setting.

&#8226 Barley scope limited.

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