Cultivations and rotations are set to become more important in the battle against problem grassweeds such as blackgrass. Luke Casswell reports.

Ploughing and a switch to spring cropping will be vital in blunting a three-pronged attack from blackgrass, ryegrass and brome this autumn.

These troublesome grassweeds can be reduced by introducing ploughing into the rotation and by using spring cropping for more than one year.

Stuart Jackson, herbicide specialist at Dow AgroSciences, says cultivations and rotations will be vital to get the most out of their herbicide programmes to control grassweeds.

“We are seeing more pressure being heaped on our spray programmes so growers must do everything they can to maintain their efficacy and get on top of weed problems,” he says.

Trial work carried at the company’s research and development site in Wellesbourne, Warwickshire, has shown that ploughing is one of the most effective measures to prevent these three problematic weeds.

These grassweed rotational trials began at the site in 2011 and have looked at a mixture of wheat and oilseed rape rotations using min-till techniques with cultivations down to 5cm and ploughing down to 25cm.

Results showed that control of blackgrass was higher in the plots that were continually ploughed or where there was a mixture of min-till and ploughing.

Plots using a permanent min-till approach showed higher populations of grassweeds, indicating the important role the introduction of a plough can play in the rotation.

The correct plough set up will be vital in order to get a full inversion and bury the seed, with growers on heavier, more challenging land having to pay particular attention to ensure this is achieved.

“If you can’t plough properly it is going to be closer to a min-till effect. So full inversion with the skimmer set to push the trash to the bottom and going slow enough for the trash to fall to the bottom is important,” Mr Jackson adds.

While cultivations are important, work at Wellesbourne has underlined the introduction of crops such as oilseed rape, as even in continuous min-till establishment systems this does lead to improved grassweed control in the next cereal crop.

Grassweed concerns should also prompt a closer look at using spring crops for more than one year, according to Mr Jackson who says the 2012-2013 season showed that where growers were forced into spring cropping for one year, it was still not enough.

“Turn the new three-crop rule to your advantage. A spring crop will allow grassweeds to germinate throughout the winter, so be sure to use a stale seedbed before drilling as the options for grassweed control in spring cereals are far more limited,” he says

For autumn-sown crops, herbicides will need to be used in unison with cultural techniques to battle the grassweed threat.

In winter cereals, Mr Jackson advises the use of a pre-emergence treatment of flufenacet and pendimethalin-based products, and where seedbeds are dry at drilling growers should ensure tri-allate is also used.

For post-emergence weed control, Mr Jackson says growers should consider his group’s pyroxsulam-based product, Unite, which he points out is as effective as other post-emergence products and offers a wide range of broad-leaved weed control as well.

Meanwhile in oilseed rape, propyzamide-based products such as Kerb give some of the most effective weed control.

However, to get maximum effect on blackgrass, Mr Jackson says the weeds needs to be coming from the top few inches of the soil.

Good ploughing can be a useful tool in the big battle against blackgrass.