5 January 2001

Herbicide spray is top job…but keep it legal…

By Arable reporters

HERBICIDE spraying should be the top priority for cereal growers, say agronomists. But the temptation to exceed label doses must be resisted, they stress.

With fieldwork largely on hold after a flurry of activity in the brief dry spell before Christmas, concern is growing that blackgrass could gain the upper hand.

Only 50% of winter cereals drilled have received any herbicide, estimates north Lincs-based AICC agronomist Philip Ranby.

"The position with resistant blackgrass is getting desperate. Much of it is past the critical three-leaf stage and some has received no sensitising. It is going to be really difficult."

But Peter Taylor, chairman of the Association of Independent Crop Consultants, cautions against exceeding label rates. "Some blackgrass plants are well tillered and getting very big; and where there are carpets some growers, especially those with resistance, may be tempted to use higher than label rates."

Quite apart from the illegality of applying herbicides at doses beyond label maximum, there is no evidence that doing so will provide any better control, says Mr Taylor. "There is also an increased risk of crop damage."

Main weapons at this stage of the season on well developed blackgrass are Hawk (clodinafop-propargyl + trifluralin) and Lexus (flupyrsulfuron-methyl) mixtures, he says. "The full rates are 2.5 litres/ha and 20g/ha and my advice is to stick to them, but dont cut."

There may be a case for doubling the amount of adjuvant oil used in such mixes, he adds. "Some of us have always felt there is anecdotal evidence that 2litres/ha works slightly better than 1. But the manufacturers have never claimed it."

In Hants, where resistant blackgrass is less of a problem, growers can wait for better conditions, says Alan Bide of Hampshire Arable Systems.

"We are always reluctant to advise spraying in January or February unless conditions are ideal, because herbicide performance tends to be lacking."

In oilseed rape Mr Ranby recommends growers with resistant blackgrass get an application of Kerb (propyzamide) on as a matter of urgency, possibly making use of a frost to travel. "Warmer temperatures degrade Kerb more rapidly. It should be on by the end of this month."

Other graminicides such as Laser (cycloxydim) or Falcon (propaquizafop), suitable where resistance is not a concern, can wait until early spring if needed, he adds. "They need a dry leaf – its better to wait for good conditions."

East Yorks-based agronomist Sam Lawrence echoes Mr Ranbys comments and urges growers not to forget aphids. "It hasnt been cold enough to kill them. Anything that was there will still be there."

HERBICIDE QUANDARY

&#8226 Blackgrass control concern.

&#8226 "Above label" dose temptation.

&#8226 Illegal and risk of crop damage.

&#8226 Growing conditions key.

Patchy drilling

Stark differences in cereal drilling progress are being reported. In East Anglia up to 80% of drilling is finished, say independent agronomists. But in Sussex only 30% is done and many fields are again flooded, says Laurence Power of Chichester-based merchant Bartholomews. In the sodden south-west Profarma agronomist Arthur Hulls records an even gloomier picture. "I have four customers between Yeovil and Taunton, with areas of up to 450 acres, who have not managed to sow any winter wheat at all."