Winning against grass weeds – Tillage & Soils

In the search for answers and better guidance for farmers, Hutchinsons has been testing a range of ideas at South Sea Farm, Kingston, Cambridgeshire for some years.

Their particular target has been Blackgrass, although the company’s Dick Neale says other weeds may also require attention:

“We are seeing meadow and soft brome sneaking in, so we will have to do something about them as well”.

Their work has tested multiple approaches. But it all starts with sound planning, he told open day audiences:

“We aim to locate where Blackgrass is a problem and where we need to spend time and money treating it, and where we can save

time and money”.

That includes assessing soil types and identifying areas of heavier soil that tends to lie damper – the sort of conditions that Blackgrass prefers.

Techniques they have tested include stale seedbeds, which have proved effective, having reduced populations after five years:

“We have largely exhausted that September germinating population. Blackgrass populations are around 10% of what they used to be:

“They have fallen from between 400 and 600 plants/square metre to between 40 and 60 plants. But those plants that remain tend to be larger and have very strong tillering ability”.

Experimenting with drilling dates can help, with November drilling backed up by one pre-emergence treatment producing a clean crop.

But he accepts that it is not always practical to leave drilling that late:

“We do see less Blackgrass by drilling later, but its germination tends to be more protracted. We can spray it off every two weeks but more emerges.

“An alternative option would be to drill a bit earlier and ensure a stronger crop that could out-compete the Blackgrass”.

Another tactic they are trying is growing blends of multiple different wheats together to see whether their different rooting characteristics might help crowd out the Blackgrass:

This year’s combination of Group 4 varieties includes Gleam, Champion, Dawsum and Inistor, the seed being mixed in the drill:

“We started doing this before SFI was launched, and it so happens that SFI does reward us for doing it. We are using it rotationally along with cover and companion crops.

They are also trying zero tillage establishment and cover crops, which contain at least six different species:

“We are using winter and summer cover crops whether we are being paid for it by SFI or not because it is the right thing to do”.

Improving drainage at the farm has been another priority, and they have seen instant benefits from restoring mole drains on areas of some fields that had previously laid wet.

When relying on chemistry to control the weed, he advocates using complete treatment sequences:

“You can’t get away from sequencing herbicides. You can’t just drill and make one application a few days later and get away with it.

“You have to follow the full sequence to get good control”.

And he reminded growers that there is no ‘silver bullet’ to controlling Blackgrass:

“There is no single thing I can see that does the job. It may be a lot of little things you need to change, but taken together they can make a big difference”.

John Cussans, Weed Specialist with ADAS, echoed his point about the surviving Blackgrass plants getting larger, and the importance of effective spray sequences:

Larger plants are just part of evolution, he said:

“Since the 1990s to the current day, output from the field has increased as crop protection, fungicides and nutrition have all got better.

“What we see in crop yields is mirrored in weed populations and seed return”.

Weeds may also exploit any move to drilling crops in wider rows as it leaves more inter-row space for them to populate.

“They may be present in relatively low densities but there is potential for seed return due to the system change”.

Well-planned spray sequences offer the best chance to control weed populations, he adds:

“Sequences give better, more robust weed control, and as soon as any second or subsequent application timing is delayed the whole programme risks falling apart”.

For September sown wheat crops the gap from cotyledon to first true leaf could be between five and seven days. Once you get into October sowing that gap may be a little wider – maybe seven to ten days.

“If that second timing is delayed then it is compromised. You must be confident you can get the applications nice and tight. “Otherwise you might be better off reverting to putting it all on in one application. That is better than doing nothing, but not as good as two applications both made at the right time”.

Farmers should not worry about the cost of installing drainage; they should be more concerned about the cost of not doing it, suggests Hutchinsons’ Will Foyle.

“Can you afford not to do it when poor drainage is damaging crop growth?

“Poor drainage leads to increase waterlogging, areas of poor, thin or stunted crops, and Black- grass thrives where there is no competition”.

It also reduces the farmers’ ability to make other management decisions and the ability to travel on affected fields.

His thoughts were echoed by Rob Burtonshaw, a third-generation drainage contractor.

He urges farmers to make sure they know where their drains are and keep them in good condition so they can continue working for years:

“Cleaning drainage outlets and ditches – that’s probably the best paid job on a per hour basis on the whole farm”.

They should also ensure that mole drains and any backfill among the main drains were working efficiently.

He accepts that mole ploughing is an awkward, slow operation.

It also needs careful timing to ensure that the mole itself is in plastic soil after the leg and expander pass through so the mole it makes holds, while the soil above it is fractured so water feeds down to it efficiently:

“Often the best conditions are in late spring, so you might benefit from moving the rotation around to open up working windows”.

Good moles can last several years- sometimes up to seven years -while main drains should survive for 25 years: “I still work on drains that my grandfather put in 60 years ago”.

The research at South Sea Farm includes a trial combining three different wheat varieties Dawsum, Typhoon and Mayflower with progressively deeper rooting characteristics to see whether they can deny Blackgrass rooting space.

“The blend of these three varieties means we have rooting structures at three slightly different depths, so the crop can access much more of the moisture and nutrients in the soil, and achieve excellent coverage of the soil surface as well.

“That enables the blend of wheats to out-compete the Blackgrass and reduce risks. The three varieties also produce different exudates, which helps feed different communities of microbes.

“Those differing exudates will also maintain a more diverse population of soil organisms as well”.

Maintaining healthy soil structure is key to reducing the threat of Blackgrass, suggests Jade Prince from Farmacy’s soil health team.

“Blackgrass tends to be more competitive where the ground is wet because your cash crop is normally weaker in those areas”.

Building organic matter levels should pay dividends, as every 1% increase will raise the soil’s moisture holding capacity by 125,000 to 225,000 litres/hectare:

“Not all organic matter is the same. It comes in different forms and sizes and helps increase the diversity of pore space and improves structure”.