18 February 2000

Dont ease up on blackgrass

By Andrew Blake

BLACKGRASS kills in winter wheat have been better than normal this season.

But growers affected by the weed, particularly where herbicide resistance is a worry, cannot afford to relax, say trade experts.

The next week or so will be the key time to tackle blackgrass survivors, warns Profarmas Stuart White.

Mr White field walks over 4800ha (12,000 acres) and runs product comparison trials on a clients farm near Brackley, Northants. He brands the area as a hot-bed of resistance.

Where applied before the weed emerged, mixtures of Lexus (flupyr-sulfuron-methyl) with trifluralin, IPU/pendimethalin or straight pendimethalin have produced very good kills, he notes. "In eight out of 10 instances we have been getting 92% control. We have had much better results than we ever had with Avadex and Hawk sequences.

Cyanamids as yet unapproved ACH210 was also used in various mixtures in the Brackley trials. "It looks really good," says Mr White.

"The key, not generally recognised, is to get the Lexus on before the blackgrass comes through." Control levels in the trials fell to just 60% where applications were delayed until after weed emergence, he notes.

But even 92% control is not enough for sustainable wheat production. "You wont be able to grow wheat if you do not control blackgrass. You need to get seed return down to the bare minimum."

That means being prepared to follow up with an early spring treatment. For many early-sown crops time is now running out, he believes.

"Once daylight hours extend and blackgrass starts to tiller it gets much harder to kill, and in cases of resistance you can only hope to slow it. It already has three tillers in some fields."

The spring application should include a contact-acting element, he advises. "I would recommend Hawk at 2.5 litres/ha with 1000g of IUP, the maximum you can use with Hawk, and some oil."

Depending on the precise autumn mix the initial cost will have been up to about £28.50/ha (£11.50), he says. His recommended follow up will cost about the same. "So you are looking at about £20/acre. I think people with blackgrass should be reasonably happy with that."

"As soon as the land dries up growers should be thinking about tidying up blackgrass before doing anything else," agrees colleague Simon Pretty who covers south Norfolk and north Suffolk.

Most autumn herbicide programmes worked well, he notes. "But we are seeing fields where recommended residuals did not go on after November rain. Programmes for those will need a contact chemical."

Some treated mid-October sowings also already have tea-plate sized blackgrass after the relatively mild winter, so growers must move in quickly, he advises. "In some places, where we have three-star enhanced metabolism resistance, the sooner the better because the smaller the blackgrass the easier it is to kill.

"There are several options including Hawk, Topik and Puma at various rates to suit the weed size. But for the really difficult blackgrass I would suggest 2.5litres/ha of Hawk with 20g of Lexus and a bit of oil as the Rolls Royce approach." Cost works out at about £39/ha (£16/acre). &#42

BLACKGRASSTIDYUP

&#8226 Generally good autumn control.

&#8226 Lexus mixes particularly useful.

&#8226 Survivors well worth treating.

&#8226 Spring contact element a must.

Herbicides Special

Turn to p66 for our Herbicides Special, providing further detailed guidance on making the most of herbicides this spring.

Dont leave it much longer before bashing blackgrass left over from winter, advises Profarma