10 September 1999

TOUGHER TACTICS THIS SEASON

HIT them earlier and harder. That is how Luke Chamberlayne plans to tackle burgeoning blackgrass and meadow brome at Maisemore Court on the outskirts of Gloucester this season.

Early post-emergence, full rate isoproturon/trifluralin mixtures have long been the mainstay of autumn weed control on the 324ha (800 acre) family farm. But rising populations mean more robust, albeit more expensive, tactics are needed to allow winter wheat in particular to reach its full yield potential.

The farm has a range of soils from river terrace gravels and silts to heavy clay with various rotations to suit. About a third, in the flood plain of the River Severn, is increasingly being sown to spring crops because of the risk of not being able to apply autumn herbicides or even losing the crop.

Grass weeds all too easily eat into wheat output. "In places the blackgrass can look like lawn turf," says Mr Chamberlayne. Meadow brome seems to be spreading fast from hedge bottoms. "We get a few plants showing one year. The combine spreads them down the field and the following year it is all over.

"Our yields are not particularly high anyway. We rarely get above 4t/acre and some second wheats can be as low as 2. I reckon meadow brome in the worst spots this year took off at least 0.5t/acre and bad blackgrass at least 1t." Wild oats have gradually succumbed to follow up treatments with contact herbicides and sterile brome has never been troublesome.

"In the past ipu/Treflan has done what we anticipated and given reasonably good results on blackgrass – sometimes better than expected." The main problem is that contact follow up treatments with Cheetah (fenoxaprop-ethyl) or Hawk (clodinafop-propargyl + trifluralin) have proved increasingly disappointing. "They have worked in the past but now seem to be less reliable."

No resistance tests have been carried out. But the fact that Laser (cycloxydim) alone in field beans failed to control blackgrass, whereas simazine followed by Laser did, suggests fop/dim resistance may be present, says Mr Chamberlayne.

Pendimethalin/ipu mixtures have given variable results and always needed a follow up, he notes.

Meadow brome is an even tougher challenge as few currently available herbicides have much effect on it. "We have tried ploughing it down and that didnt make any difference. I have even tried weed-wiping with glyphosate. That took out wild oats but had very little effect on the brome."

SEQUENTIAL APPROACH TO CONTROL

THIS seasons campaign began with increasing attention to stale seed-beds. "Where we have time we are using a sequential approach, discing and rolling first and then going back with a cultivator press to try to get a second weed flush before spraying off with Sting."

Second wheats will be drilled late, probably not before the end of October, to avoid encouraging blackgrass.

When it comes to selective autumn chemical treatments the emphasis is shifting to earlier control.

Pre-emergence Avadex (tri-allate) granules applied with a Kuhn pneumatic spreader ahead of ipu/trifluralin has usually worked well against blackgrass in winter barley, though it has done little to improve brome control.

"The slight problem with it is that it really needs to go on within two days of drilling and the weather can prevent this." Wind and wet field patches can also reduce its effectiveness, he says.

That said, the full 15kg/ha rate is being introduced to boost overall grass weed control in the wheats this season. "Its not cheap, at about £24/ha, but probably well worth trying."

Beyond that, and especially where the Avadex cannot be applied in time, Lexus (flupyrsulfuron-methyl) is likely to figure for the first time depending on price. "Based on last years £16-17/ha I shall definitely be using some. We are certainly going to move away from contact-only products."

Mr Chamberlayne does not employ an agronomist, relying instead on ADAS bulletins and information gleaned from a range of sources. Promising trial results mean he is also likely to try some Lexus/pendimethalin mixes for the first time.

As for the meadow brome he is pinning his hopes on early UK approval for sulfosulfuron to allow it to be applied from next Feb. "It is already used as Monitor in Ireland and no doubt will increase our total spend. But it does also have some effect on broad-leaved weeds which will have to be taken into account." &#42