Best way to desiccate cover crop on wet soil

Expert view

Dick Neale gives his advice on how to manage cover crop desiccation in a wet season.

Excessively wet soils this year are more likely to be dried by the presence of cover crops than kept wetter. But sun and wind must be allowed to reach the soil surface for adequate drying predrilling.

While many cover crops may have already been dessicated either by glyphosate or grazing, in some situations of late establishment limited growth has been allowed to continue and spray off opportunities have been limited.

Sustainable Farming Incentive rules for overwinter covers also mean that termination is not realistically possible until mid-January – and spraying opportunities and field access even after then has been limited this year.

Some thinner covers may in fact be better left until nearer drilling for desiccation, although this depends very much on species within covers, soil type and following crop and its likely drilling date.

It’s worth remembering too that blackgrass regrowth on bare soil can also be considered under the same rule set as covers with regards to dessication.

Desiccation options

Grazing with sheep is increasingly popular. Hutchinsons Maxi Graze mix is ideal where this is planned. But there are still several considerations to take into account.

It is important the grazier understands that many covers are being grown for soil conditioning and not exclusively sheep grazing. This means the stock will graze the top growth very rapidly and will need moving on before soil surface damage occurs.

For this reason, roughly twice the cover grazing area is required compared to a traditional stubble turnip crop where the sheep are left on to clear all the tubers.

This is what puts condition on the sheep whereas top growth provides a maintenance feed.

Again, this must be clearly understood and accounted for as more work is expected of the grazier – including moving fences, water and livestock – for less weight gain in the sheep. Grazing fees must reflect this.

It is a compromise between soil conditioning, cover crop processing and feed value to the grazier. Only sheep from six months old should graze multispecies covers, do not graze ewes with lambs at foot, as milk taint can occur.

If you go for this option, make sure adequate rates of glyphosate are used – 1000g minimum – with an adjuvant like Spryte Aqua CF. Remember too that low temperatures and shading will impact performance.

Legume species like crimson clover, berseem clover and vetch will often survive treatment.

This is rarely problematic if herbicide in the next crop is effective – or where the following crop is tall like maize or more smothering like peas.

Glyphosate

Kyleo is usually used in mixture with additional glyphosate around 3 l/ha and should be used where surviving brassica or phacelia will impact the following crop. This approach requires expensive post emergence herbicide treatment, if any exists.

Kyleo is helpful where a larger cover bulk needs reducing quickly to improve the drills’ ability to cope with aftermath adding the importance of treatment to sowing safe periods.

Shark can also be a very useful addition to glyphosate for a range of species more tolerant of glyphosate. It is vital where nettles form part of the cover on lighter soils and useful on brassica species – remember the one-month gap before planting a crop.

Cultivation

Cultivation to kill and better facilitate drilling always remains an option in controlling cover crops.

But if a drill will not cope with the situation, then it is better to cultivate as required, rather than risk failure of a crop. Why? Because you only get one chance at establishing a spring crop.

Only do what’s required. Remember the benefit of the cover is largely underground. If ploughing, for example, plough as shallowly as possible or work the top just enough to facilitate accurate sowing.

Remember, the covers are rooted, and drills will often cope well as the residue does not ‘drag’. It is often worth an early run up and down with an empty drill to see if it copes, before cultivations are used.