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Manage cover crop destruction and weed control with care this spring

Large cover crop canopies that have seen little sustained frosting will need particularly careful management for the most effective destruction, warns Monsanto technical development manager, Barrie Hunt.  At the same time, spring cultivation and drilling must be managed with equal care and attention to minimise grass weed emergence and development in the seedbed.

The scale of many covers coming out of the winter, the lack of sufficient frosts to set them back and the extent to which grass weeds remain below the canopy or are encouraged to germinate before or at sowing puts the onus firmly on good early spring glyphosate management,” he stressed.

Providing spraying is not left until stem extension is underway, the cereal components of cover crop mixes won’t present much of a challenge. Phacelia and mustard will also be relatively easy to destroy. Legumes like vetches and lucerne can be more problematic, though. And large-rooted oil radishes will be especially hard to eliminate without a decent degree of frosting.

Cultivation ahead of drilling will help to hasten the demise of these more difficult components,” Barrie Hunt observed.

But then it or significant soil movement at drilling will stimulate the seedbed germination of black-grass, in particular, which could easily lead to just the sort of early weed competition you don’t want with spring cereals. Nor, in most cases, do you need any unnecessary delay ahead of sowing.

This really puts the pressure on glyphosate at a time of the year when low temperatures invariably restrict plant growth and herbicide uptake. 

Under these circumstances, Mr Hunt insists that growers have to be right first time with their spraying, employing glyphosate formulations that work more effectively in challenging conditions and application regimes giving the best cover crop destruction and seedbed weed control.

Our research shows and spring pre-planting users tell us that Roundup formulations perform better than other glyphosates under tough conditions,” he pointed out. “This is because they get more glyphosate into plants more rapidly and reliably.

Modern Roundups work well at low temperatures and on the frost – providing it doesn’t persist all day. But you have to use the right rates for the job – up to 1440g ai/ha with tougher targets – appreciating that extra adjuvants will not make up for lack of active ingredient.

We recommend a medium spray with around 100 l/ha of water for cover crop destruction, with nozzles inclined towards the rear and travel rates constrained to maximise crop coverage. 

Avoiding spray drift will obviously be important with taller covers, so use formulations proven to reduce drift risk,” advised Barrie Hunt. “And to minimise delays choose those that allow you to cultivate – or drill on-the-green if this is your preferred approach – the next day where conditions are mild or after just two or three days where it turns cold or you have to deal with large-rooted radishes.

Where there are significant under-storeys of grass weeds, he suggests including an approved formulation in the pre-emergence spray, explaining that this will also deal with any weeds transplanted rather than killed by cultivations. Naturally, of course, application needs to be ahead of any crop emergence.

I would always recommend using low disturbance drills for crop establishment after cover cropping,” Mr Hunt added. “The ground is likely to be well-conditioned by the cover and the extent to which grass weeds germinate in the seedbed is directly related to the amount of soil disturbed.