In the last of our series on cultivations, Mike Abram looks at how they can be used to improve control of grass-weed species.
For most grass-weeds the simple fact is ploughing, when looked at in isolation from other factors, is the most effective cultivation system for reducing grass-weed pressure.
Black-grass, ryegrasses and bromes all struggle to emerge from depth, so effective ploughing and burying seeds at depth can often help reset problem fields, when used as part of an integrated approach.
But we do not live in a perfect world and there are other factors to consider, from cost to carbon release and impact on soil biology and structure, to just whether you might be ploughing up seed previously buried.
Where ploughing is not the preferred system or even an option there are other aspects of weed biology that can be used to help tailor management, says Craig Simpson, commercial technical manager for Bayer in Scotland.
“For example, there are differences in when grass-weeds typically emerge which impacts how effective delayed drilling will be.” Most black-grass emerges in autumn, with a relatively small percentage in spring which is why delaying autumn drilling until after that peak to allow it to be tackled with Roundup (glyphosate) pre-drilling has been a successful tactic, he says.
“With ryegrass you tend to get an early autumn flush, less through winter, and then more again in spring.
There is still an argument for delayed drilling or spring cropping with ryegrass, but it isn’t quite as effective as with black-grass.” Using cultivations to encourage a chit pre-drilling can be helpful, but the timing of that cultivation depends on environmental conditions – if it is dry it can be better to wait for moisture.
“With black-grass it is especially important to get pre-emergence on because of the high autumn emergence.
“The mixture of Liberator (flufenacet + diflufenican) plus Proclus (aclonifen) with its extra persistency can help control later flushes.” That mix has also been helpful for ryegrass where some resistance issues have emerged with flufenacet in some populations, he says.
While brome species fall into two broad camps – either anisantha or bromus species – it is important to know which species even within those groups you are dealing with as the biology changes management.
“For example, rye and soft brome heads look quite similar, although rye brome has v-shaped seeds when you cut them in half while soft brome seeds are more saucer shaped.
“Soft brome germinates in spring as well as early autumn, while rye brome germination can be delayed into early winter so control from pre-emergence herbicides isn’t that strong, but spring applications work well.” Bromus species’ seeds generally require a period of ripening on the soil surface and require light before they will germinate, whereas sterile and great brome germinate in the dark and exposure to light triggers dormancy.
“If you’re looking to get a chit of sterile brome before drilling, cultivate immediately after harvest, while for bromus species leave around four weeks before tickling the surface.”
Emerging threat rat’s tail fescue has relatively low dormancy and appears to be mostly autumn-germinating, Mr Simpson says.
“It’s shallow rooting so is more of a problem in min- or no-till situations.
“Deeper cultivations will help control it and from what we’ve seen flufenacet works well, although it’s not on the label.”
Managing 1,440 hectares split across three sites in North Yorkshire, West Yorkshire and north Lincolnshire, Matthew Copley needs a clear strategy for weed control in different soil types and flexibility in his cultivation and establishment regimes with all operations carried out by contractors.
Discussions with his contractors begin before harvest to discuss straw management for different crops, especially ahead of oilseed rape where longer stubbles are left to help with cabbage stem flea beetle control, while wheat straw is chopped and barley straw is removed.
“We also start discussing if and where we are going to plough.
I’m a big believer in the benefits of rotational ploughing if it is done well to get the black-grass buried.” That decision is made partly on cropping, partly on history.
“If we’re starting to get in a mess with grass-weeds and it hasn’t been ploughed in the past few years, we’ll plough to press the reset button.
If it has been ploughed we’ll start to think about spring cropping.” Where ploughing isn’t needed on heavy land, cultivations tend to be a little deeper than on the lighter land, he says.
“Typically we’ll go with a primary cultivation straight after harvest, press about a month after and then spray off and drill a month later.
“I do think we need to loosen to a reasonable depth, but within dry soil to avoid smearing.” On lighter land where the rotation is more diverse with spring cropping, which helps keep on top of black-grass, they typically tickle the surface, let it green up before spraying off and drilling.
Some decisions, especially on the farms away from where he is based, are left to the contractors, he says.
“We have some strict rules, such as if you can’t spray the pre-em then don’t drill, but it is in the interests of the contractors for it to go in well.
Well-sown is half-grown.” Hybrid rye has been introduced on some fields where ryegrass is becoming a problem.
“The ryegrass retains its seeds when the rye is harvested, which means it is removed from the field.”
Whether you’re using a tine or disc cultivator, setting it up to run parallel to the soil so all the tines or discs work to the same depth to get the same finish across the width of the machine is important, says Ed Worts, product specialist for manufacturer Kuhn.
But that is particularly crucial for minimum tillage, such as when cultivating to a depth of 2-3cm in stubbles to encourage weed chits, he explains.
Fortunately, with Kuhn machinery that is pretty straightforward.
“Most of our cultivators can be set up for a little bit of lateral movement so it can contour the ground a bit better.”
Adjustments on the springtine based Prolander is through just one lever, while the discbased Optimer is a little more involved as it requires moving the spacers and each packer to get the correct working depth, explains Marcus Ainley, sales specialist for Kuhn.
“But both machines are very easy to adjust, which makes it more likely users will do it,” he says.
Both the Prolander and Optimer can be used for postharvest stubble cultivations to prepare stale seedbeds.
The Prolander can be fitted with duck-foot tines to move the whole soil profile to a depth of 2-3cm, together with a double U-packer which provides a firming effect to help germinate weed seeds.
“It’s probably most suited to lighter soil types.
It can be used for stubble in autumn, but is also good for working deeper in spring.” Working speeds are around 8-13kph for the tine, while the disc-based Optimer can go a bit faster at 10-15kph.
“The Optimer gives more of a chopping effect, so you get more weed destruction to the same working depth.” It can be fitted with discs with small notches compared with standard discs, which helps it to work accurately at shallow depths, while a lightduty, full-width packer gives good soil firming across the profile and means you get the seed germinating in the first flush, he concludes.
Deciding on the most appropriate method of cultivation is currently one of the most debated topics in arable production.
The reality is there is no right or wrong answer. Numerous variables come into play when decision-making and there are pros and cons to all approaches.
This series will look at all aspects of the debate from machinery and engineering through to crop protection and nutrition.
Visit the series homepage for more information