15 November 1996

Look out for crop safety in rush to use herbicides

By Robert Harris

MORE autumn cereal crops than ever will be sprayed with herbicide this autumn, according to a recent survey. But growers must take care not to compromise crop safety or weed control in the rush, say advisers.

"Growers have considerably raised their spraying targets since mid-October," says Cyanamids Tony Billings. "They now say they want to treat 93% of their drilled area compared with the record 80% at the same time last year." Good results last autumn are the most probable reason, he suggests.

Many growers are well on the way to achieving that figure. Recent rain has encouraged rapid crop emergence, helping patchy crops even out. It has also moistened soils and broken down cobbly seed-beds. As a result, most winter cereal crops are at an ideal stage for spraying.

Mr Billings estimates 30-50% of crops have been treated. But patchy crops are still a headache for some. "A lot of people have been waiting for crops to come through. It will now be clear which will make it and now is the time to strike," says ADASs Jim Orson. Preference should be given to fields where blackgrass is approaching the three-leaf stage, he advises. "If residual chemicals have given good control in the past, it is best to stick with them in accordance with resistance guidelines."

Where weeds have begun tillering, additional contact treatments like Cheetah Super (fenoxaprop-P-ethyl) or Hawk (clodinafop-propargyl + trifluralin) may be needed to boost control.

That also applies to blackgrass emerging from depth. Roots are often 5cm of more below the surface, so although plants appear small, they are often well-tillered and may escape initial treatment, he adds.

Most growers in Harrogate-based Yorks Arable Advices area have got on well, says Andrew Fisher. "We had a keen frost last week which hardened crops off. Most growers have picked their days and have done up to 75%."

Mr Fisher is basing most treatments on an IPU/diflufenican mix, adding CMPP where larger oilseed rape plants are a problem. "IPU/ Stomp mixes have been a bit pricey this season. And we have quite a few spring-germinating wild oats in this area, so I am not keen to use contact materials now."

Growers with patchy crops should wait until they get healthy, even growth, especially if a hormone weedkiller is needed to remove broad-leaved weeds like oilseed rape, says Lincoln-based Agrochem Souths John Bayes.

Weeds may then be too large for CMPP or HBN materials. "I would then use something like Quantum. It has a very good broad spectrum activity, is safe to the crop and takes out big weeds." It may pay to apply this before tackling grass weeds – big rape plants can shelter blackgrass, he adds.

Pendimethalin and diflufenican, with or without IPU, are favoured choices on evenly-emerged crops where blackgrass remains easy to control. The diflufenican portion can be cut to 25-35% on small, soft weeds, he advises. &#42


AUTUMN WEED CONTROL


&#8226 Farmers aiming to treat 93% of drilled area.

&#8226 Up to half already sprayed.

&#8226 Patchy crops evening out.

&#8226 Treat soon – tackle big weeds first.

&#8226 Use residuals if possible – add contacts for tillering or deep-rooted blackgrass.