Cultivation immediately after harvesting has become standard practice for growers wanting the best control of problem grassweeds ahead of winter cereal drilling – but that might be the worst thing they could do after oilseed rape.

That’s the experience of national weed management specialist, Barrie Hunt, who runs the Roundup technical support service and he said this is the best time to deal with both.

His proven way of overcoming their conflicting management needs is based on better understanding both OSR and grassweed biology. “Volunteers are inevitable consequence of oilseed rape growing,” he insisted. “A small amount of seed loss is unavoidable, even with the best pod shatter resistant varieties, combining technologies and harvesting practice.

“This wouldn’t be a problem, but for two things. First, every 10 kg/ha lost is typically more than one and 0.5m seeds – or around 170 seeds/m2. And second, a proportion of these can remain viable in the soil for a good 10 years.

“So, as well as getting in the way of your first wheat and providing an ideal environment for slugs, volunteers can seriously interfere with the management and productivity of your future oilseed rape crops. They’re also a prime culprit in the erucic acid contamination of ‘double lows’ on land once used for HEAR growing.

“On the plus side, we’re dealing with seeds specifically bred to germinate readily and reliably when at or near the soil surface. Often – as autocasters will testify – a combination of chaff and dew are sufficient.

“This means we can stimulate the vast majority of shed rapeseed to grow by not burying it to anything more than a couple of centimetres. Cultivating it down any deeper will only encourage dormancy and future trouble,” he argued.

Using a simple ‘twin-track’ approach, leaving OSR stubbles uncultivated for up to four weeks, then spraying-off volunteers and low dormancy black-grass, he recommended light tillage and consolidation to set up a stale seedbed to brings on grassweeds for spraying ahead of drilling.

“If you have bad black-grass, ryegrass or brome you shouldn’t be drilling wheat until mid-October at the earliest,” he added. “So with OSR coming-off before the end of July, you have plenty time for this approach. The great beauty of this is that it enables you to deal with both volunteers and grassweeds in the best possible way, without compromise.

“On one hand, you leave any shed rapeseed open to predation by birds and mammals and get a maximum flush of volunteers vulnerable to glyphosate. On the other you achieve the surface cover needed for a maximum flush of black-grass, ryegrass and sterile brome to control."