18 February 2000

When to weed those wild oats

Prolonged and unpredictable

spring emergence of wild

oats can make control tricky.

Brian Lovelidge reports

THIS springs first flush of wild oats in winter cereals could appear earlier than usual, according to Brin Hughes, UAPs eastern region technical adviser.

That is because the weed seeded during a hot, dry spell, so dormancy is more easily broken, he says. But flushes from older seed are bound to show later.

So growers dilemma is herbicide timing. If control of autumn wild oats was incomplete and early spring germinators threaten significant competition, both Mr Hughes and Roger Bryan, of Kent-based O & N Management Consultants, favour tank-mixing a herbicide with the first growth regulator. Timing is between crop growth stages 23 and 30, usually late February to early March.

"Over-wintered wild oats and early spring germinators have the biggest impact on yield and shed before harvest," says Mr Bryan. "I am less worried about later ones unless there are a lot because they are less competitive. But they can contaminate grain samples."

For early treatment the two agree on product choice and dose. Topik (clodinafop-propargyl) tends to have the edge in wheat at 62.5ml/ha plus oil for oats with one to two leaves. 80-100ml/ha plus oil is needed for larger plants up to tillering.

Cheetah (fenoxaprop-P-ethyl) at 0.3-1 litre/ha, depending on oat growth stage, is the other main option, they suggest. At the lower rates oil can be added below 10C (50F).

Grasp (tralkoxydim) at 1-1.4 litres/ha with Output adjuvant is a useful alternative, which can also be used in barley, particularly if "fop" resistance is suspected, says Mr Bryan. Although a "dim" it can control some resistant populations.

Otherwise Commando (flamprop-M-isopropyl) plus oil or Avenge (difenzoquat) at full rates should be used, he says. "But check wheat varieties for Avenge safety."

Where over-wintering wild oats are absent and there are relatively few early spring germinators, wait until they show above the crop, he advises.

"It is hard to time the treatment accurately because there may still be significant numbers to come." But waiting allows herbicide costs to be cut by spot-spraying patches, he says.

Products and doses are as before, with Topik and Cheetah safe up to GS41, Avenge to GS37 and Commando GS47.

The "no-go" time for treating wild oats is during early, rapid stem extension. That is when they are growing too quickly for the herbicide to be effectively translocated, says Mr Hughes. &#42


&#8226 Early flush predicted.

&#8226 Spray timings dilemma.

&#8226 Waiting game may pay.

&#8226 Full dose advised if resistant.

Playing the waiting game can give cereal growers the chance to cut wild oat control costs, says

Roger Bryan.