18 February 2000

They had to learn how to live with weeds

in Wilts

LEARNING to live with weeds is becoming more important as cereal margins shrink, according to a Wilts farmer and his agronomist. The key is to distinguish between those which can be tolerated and others still deserving robust control, they say.

David Sainsbury grows winter wheat, oilseed rape, beans and spring barley on 268ha (663 acres) at Castle Eaton, near Swindon.

Main weeds at Manor Farm are blackgrass, some herbicide-resistant, wild oats and cleavers. Knotgrass occasionally causes trouble on riverside land prone to flood.

"We can no longer afford the cosmetic route," says Mr Sainsbury. "But if you try to tolerate too much you can easily regret it, especially with wild oats.

"Our herbicide budget for wheat is £16/acre. Its only £4 for spring barley but it can be much more if we find blackgrass and wild oats."

Having spring barley in the rotation helps overall control, especially of sterile brome, notes Cleanacres James Hynes.

But the big move in easing the task of in-crop herbicides has been wider use of low dose glyphosate on stale seed-beds, he maintains.

"Applying 0.5litres/ha of Stride through a 12m sprayer before drilling is so much cheaper than using a 4m cultivator. And blackgrass levels here are definitely lower than in 1992 mainly because of that policy."

Autumn cereal treatment is based on pendimethalin/DFF/clodinafop mixtures. But newer chemistry is used where it is felt that it will give the edge.

Some blackgrass over-spraying is carried out in the spring. "But we have to be careful not to use the same chemical groups which escalate resistance.

"We hope to live with any broad-leaved weeds surviving the autumn spray. The exception is heavy cleavers but much depends on how competitive the crop is."

Cleavers is the only species which can justifiably be patch-treated, says Mr Sainsbury.

"Spring wild oats in winter wheat are not much of a problem. But they are very different in the spring barley. They are hard to monitor. If we find them we usually spray whole areas rather than patches, otherwise severe contamination can occur."

The trigger is four to five oat plants/sq m with Avenge (difenzoquat) and Grasp (tralkoxydim) the main options, says Mr Hynes. "If its only wild oats we are after Ill use Avenge, but if there is also blackgrass we tend to go the Grasp route.

"Again the trick is to use stale seed-beds to flush out the blackgrass before drilling."

Although either chemical substantially raises the control bill, trimming doses too far is false economy, both men agree. "Its better to budget for £10/acre over a limited area than spend £5 over the whole lot and find it doesnt work," explains Mr Hynes.

However Cleanacres trials suggest 0.75litres/ha of Grasp performs on a par with the full 1.25 label dose provided Output adjuvant is used and conditions are favourable.

Winter beans offer a good chance to clean up, Stomp (pendimethalin) added to simazine boosting grass weed and cleaver control.

"We are having to live with weeds in oilseed rape and generally tolerate wild oats," says Mr Sainsbury.

Pre-drilling trifluralin is seen as a cost-effective alternative to "budget-blowing" Butisan (metazachlor) or Kerb (propyzamide). "Its a useful sensitiser on blackgrass where we have to follow up with Falcon or Laser," says Mr Hynes.

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Manor Farm weeds

* Cleavers patch-treated.

* No let up on wild oats in barley.

* Beans useful cleaning crop.

* Cheap trifluralin basis for OSR.

MANORFARMWEEDS

&#8226 Cleavers patch-treated.

&#8226 No let-up on wild oats in barley.

&#8226 Beans useful cleaning crop.

&#8226 Cheap trifluralin basis for OSR.