18 September 1998

Big blackgrass threat needs top-notch control

By Charles Abel

BLACKGRASS pressure this autumn could be the worst for years.

To cope with it growers need to concentrate on the financial benefits of good control rather than relying on ipu too heavily in a bid to cut input costs.

So say herbicide specialists after one of the weeds best growing seasons in recent memory. Heavy rain last winter and difficult spring spraying conditions left blackgrass to flourish during the cool, wet summer.

"Seed return will have been very high," warns Novartis herbicide specialist Andrew Cottrell. "People are saying blackgrass infestations were the worst in years, the weed appearing where it has not been seen before. Growers simply cant afford unreliable control this autumn."

ADAS arable technical manager James Clarke agrees. "With such high pressure growers must not be tempted to make input savings."

Heavy reliance upon isoproturon may cut costs, but unless conditions are ideal control from the residual product can be poor, he warns. In ADAS trials over recent years blackgrass control with ipu has varied from 23-95%. "You need 97% control just to hold an average blackgrass population," notes Mr Cottrell.

Dick Neale of East Anglian distributor HL Hutchinson agrees. "IPU does give extremely variable results, there is no question. Growers need to bear that in mind, rather than simply looking at the price on the bottle."

Most of the rising tide of difficult-to-control blackgrass is a legacy of growers choosing the wrong rates of the wrong products and applying them at the wrong timing and in the wrong conditions, Mr Neale maintains.

"This autumn growers need to think about what they spent in the past and what they achieved and think how they could spend that money more effectively. There is a lot of scope with the range of products and sequences available for some cost effective blackgrass control."

Contact acting products like Puma X (fenoxaprop-P-ethyl + ipu), Lexus (flupyrsulfuron) and Hawk (clodinafop-propargyl + trifluralin) could all be particularly useful this autumn.

A lot of people are also missing a good opportunity with green stubbles, he says. "If you look they contain a lot of blackgrass." But wet weather means a total herbicide must be used, particularly if secondary cultivations are being relied on for burial or resistance is suspected. &#42

Rethink cultivations

Too many growers try to cut herbicides costs when cultivations could offer more savings. "Average fixed costs for power and machinery on an East Anglian farm run at £26/t. Average variable costs for herbicides work out at £7/t. Machinery costs clearly offer more scope for savings," says Mr Clarke. Check for over-cultivating and over-capacity, he advises. "If you regularly find yourself completing drilling by mid-October you have probably got fixed cost slack in the system."

WAR ON BLACKGRASS

&#8226 Very high weed pressure.

&#8226 Good year for ploughing.

&#8226 Stubble sprays worthwhile.

&#8226 Beware of ipu weaknesses.

&#8226 Focus on benefits, not costs.