Blackgrass control vital even if autumn-sprayed

13 February 1998

Blackgrass control vital even if autumn-sprayed

By Robert Harris

PLENTY of big blackgrass is lurking in crops this spring. Spraying is urgently needed on fields which received no autumn herbicide and many that did will need a chemical top-up soon to contain costs.

Up to 20% of heavy land crops remain untreated, reckons Stuart White, Profarmas Banbury-based agronomist. "Blackgrass looks like trees. Most plants have at least three tillers so were probably talking about 90% control at most."

Growers must spray as soon as possible and maintain rates, he advises. In wheat, he recommends either 1.25 litres/ha of Cheetah (fenoxaprop-ethyl) or 150ml/ha of Topik (clodinafop-propargyl), both mixed with 1000g of IPU and oil.

"Adding IPU provides protection against resistance, and takes out some broad-leaved weeds, notably mayweed and chickweed," he says. Puma, a formulated mix of the two ingredients, is more effective, working well on big blackgrass. All three options cost about £50/ha (£20/acre).

Good coverage is vital for a good kill. "Always use 200 litres of water/ha." Weather is also critical. "Avoid long, cold snaps when blackgrass shuts down. The plant needs to be actively growing."

About one-third of crops which received autumn herbicide will need further treatment, says Mr White. "Thats about 50% more than usual." Wet weather is to blame.

Cheap IPU was widely used last autumn. But about 60% of active ingredient has since moved below weed rooting depth. Later emerging plants escaped and now have two to three leaves.

Provided growers treat crops this month, they can use 1 litre/ha of Cheetah or 125ml/ha of Topik, plus 1 litre/ha of a mineral oil like Fyzol. Those treatments will cost about £40/ha (£16/acre). If spraying is delayed into March, rates need increasing by 25%, so adding to costs, he advises.

Clays may have retained more IPU but growers should not bank on that. "Past experience shows dropping rates can reduce control. It is not worth risking that for the sake of a quarter of a litre of product."

Growers must not combine blackgrass and spring wild oat control. "April spraying is far too late to kill blackgrass effectively," warns Mr White.

An additional 0.5 litres/ha of Cheetah or 75ml/ha of Topik with 1 litre/ha of oil should be applied to wild oats at that time. "If they have more than three tillers, or it is droughty, up the rate."

Barleys prostrate early spring growth tends to smother weeds. "It can stand a bit of competition, but dont risk excessive weed return." Tigress (diclofop-methyl + fenoxaprop-P-ethyl) should be applied at 2.5 litres/ha, with 1 litre/ha of IPU. "IPU improves performance, but be sure crops are green and growing well." &#42

A long-awaited fine weather window last week allowed farmer Stephen Adkins to load up with a Hawk/IPU/oil mix to control big blackgrass in wheat at Great Worth Hall, near Banbury, Oxon. Rain and frosts put paid to earlier progress. The spray follows pre-emergence Avadex to help kill fenoxaprop-resistant plants, as advised by Profarmas Stuart White.

SPRING GRASS CONTROL

Wheat:

&#8226 Blackgrass – Cheetah at 1 litre/ha or Topik at 125ml/ha plus oil – increase rates by 25% on big weeds.

&#8226 Annual meadow grass – 3 litres/ha of IPU plus 0.5 litres/ha of Addition (DFF + IPU) pre-tillers.

&#8226 Onion couch – Topik at 125ml/ha or Dagger at 1.7 litres/ha plus 2-3 litres/ha IPU by end March.

&#8226 Ryegrass – 2 litres/ha of Hoegrass plus 1 litre/ha of oil.

Barley:

&#8226 Blackgrass – Tigress plus 1 litre/ha of IPU.