CAREFUL PLANNING of post-harvest cultivations before sowing oilseed rape will be crucial to maximising the effectiveness of residual herbicides this autumn, growers have been told.

“Herbicide programmes need to take into account the cultivation methods used to establish the seedbed,” said Interfarm’s technical manager, David Stormonth.

While ploughing can bury grass weed seeds beyond germination depth, minimum tillage leaves more seeds near the surface, resulting in potentially good herbicide control, he said.

But he warned growers to be aware that some methods, such as several passes with discs, are not as shallow as often perceived and can spread weed seeds several centimetres through the soil.

Residual herbicides such as propyzamide – to which there is no known blackgrass resistance – do not leach through the soil, but remain effective within the top 2cm. This can make it more difficult to control weeds germinating deeper than this, he noted.

He also highlights the importance of managing blackgrass resistance with herbicide strategies.

“When growing a break crop such as oilseed rape, it makes sense to use the flexibility of different herbicide groups that are recommended in this crop.”

For an in-depth look at crop establishment this autumn, see the Crop establishment feature in this week’s FARMERS WEEKLY magazine (August 5).