A programme to overcome blackgrass peril
A programme to overcome blackgrass peril
By Andrew Blake
LAST seasons tricky autumn threw up a surprisingly successful spray programme for tackling hard-to-control blackgrass in winter wheat in the south of England.
The weed is common on most farms Peter Cowlrick of Chichester Crop Consultants visits. Herbicide resistance is increasing because of a move to contact materials over the past decade, he believes. "In some places we have four to five star enhanced metabolism resistance. Tests have ruled out target-site resistance, so we can carry on using fops. But we have to be careful."
Whatever the scale of the problem, a firm, fine seed-bed is a must for best control, advises Mr Cowlrick. But he admits that is easier said than done on some soils.
Wherever he has resistance, if possible, he starts with Avadex (tri-allate) pre-emergence of weeds and crop. The main point to watch is that seed is drilled deep enough to avoid crop damage, he says. "We like to sow at 1.5in before rolling."
Straight trifluralin has little place in programmes for Sept-sown wheats, he says. "Its not generally persistent enough."
In recent years a Lexus (flupyrsulfuron-methyl)/Hawk (clodinafop-propargyl + trifluralin) mix with oil following the Avadex has given good results, with up to 98% blackgrass control.
Last autumns wet weather meant he did not get as much treated with Avadex as wanted. So he switched to a new strategy of 20g (full rate) Lexus with 2.5litres/ha of Stomp (pendimethalin) at the one to three-leaf stage of the blackgrass, following up with Hawk and oil four to six weeks later where necessary.
"Where we got on before Christmas with the follow up Hawk we had 98-99% control. And in a number of situations we didnt need the Hawk and only had to over-spray for cleavers in the spring. I was also quite surprised with the level of wild oat control we achieved – about 70-80% from the Lexus/Stomp alone."
Pendimethalin has already replaced some of the isoproturon in programmes for downland fields. "We have moved away from IPU on the downlands because its not controlling meadow grass and it can leach quickly after heavy rain." One spin-off is that LERAP restrictions are eased, he says.
The full strategy for dealing with difficult blackgrass is not cheap, Mr Cowlrick admits (see box). "But if you are serious about growing cereals in future it is worth controlling blackgrass now with a belt and braces approach while you have the opportunity, or the problem is only going to get worse."
What it may cost
£/ha
Avadex 22
Lexus 18
Hawk + oil 25*
Stomp 16
TOTAL 81
* Not always required.
Lessons learned last season will benefit weed control, says Chichester consultant Peter Cowlrick.