Get black-grass growing for long-term control

Five years of research at its National Black-grass Centre of Excellence, near Brampton, Cambridgeshire, is beginning to dispel some common beliefs around how best to control it, which behaves differently depending on how it is managed, pointed out technical manager, Dick Neale.

"Trying to suppress black-grass is a short-term fix to a long-term problem. It is far more effective to manage it out of the upper part of the soil by encouraging growth in this area and controlling it before a crop is sown. Depth of cultivation is critical."

He acknowledged opinions are often divided as to whether shallow or deep cultivations are best for reducing black-grass, but insists the latter is not the quick fix it appears. Experience suggests seeds can survive in soil for up to 10-15 years, far longer than the five years it was once thought.

"No strategy is ever likely to manage black-grass out of soil completely, but whichever approach is taken, you have to buy into it fully. Don't take snippets of advice from different management regimes and expect it to fit around what you're doing," he argued.

Take action now

With black-grass heads well above crops now, it's a good time to walk fields, map black-grass patches, take samples for herbicide resistance testing and gauge likely seed return, advised Mr Neale.

"If you're on heavy, dry clay, some seed will fall down the cracks, but most will end up on the surface and stay within the top 50mm of soil."

Restricting cultivation depth and encouraging growth within this zone with stale seedbeds prior to drilling is therefore the best way to achieve a decent flush that can be sprayed off with a non-selective, glyphosate-based herbicide, he says.

"Stale seedbeds should be cultivated twice prior to drilling and well consolidated. Never go deeper than 50mm and that applies to following cultivations too."

Although black-grass grows for much of the year, September to mid-October is the best period for achieving a decent flush, he said. Emerging seedlings should be sprayed before the three-leaf stage where populations exceed 800 plants/m² to avoid a build-up of root exudates that inhibit further seed germination.

Careful cropping

Mr Neale believed black-grass populations and expected seed return should partly drive crop choice and urges growers to remain flexible by avoiding prescriptive rotations or block cropping on the worst-affected land.

Where weed numbers are at a relatively low level, there are more options than at higher levels, he says. "You could go into winter oilseed rape or a second wheat if you're prepared to drill late, but by the time you get to black-grass populations above 200 heads/m² the only winter crop that offers a reasonable chance of control is oilseed rape. In this case, the residual chemistry of propyzamide and carbetamide can do a good job, providing it is given the best possible chance of performing."

Spring crop breaks

At higher black-grass populations, spring cropping is the only way, he added.

Spring peas or linseed drilled late (typically end of April to early May) offer some opportunity to control black-grass in the autumn and again prior to drilling in the spring, however barley is proving an effective option, with spring wheat and beans offering little competition, he says.

"However, a disciplined approach to establishing spring wheat and beans can bring good results and this is an area of further investigation. But growers will need to throw away the rule book when growing spring barley for black-grass control and don't grow it in the traditional way that you might for malting crops on light soil," he said.

That means being prepared to use seed rates sufficient to achieve a target established plant population of 300-320 plants/m², to maximise crop competition over the black-grass, he argued. How that equates to seed rate varies depending on factors such as soil type, weather and drilling date,.

In one field at theBrampton site, spring barley seed rates were varied by 45%, from 350/m² on the best loam soil to 500/m² on an area of heavy clay in the same field.

However, with 90% establishment on the loam and just 65% on the cold, wet clay, the established plant populations were almost identical and both in the 300-320/m² range, Mr Neale said.

"Most growers spend £50-60/ha on seed, so a 50% increase in rate roughly costs an extra £25-30/ha. That's equivalent to an extra herbicide spend, which won't necessarily be as effective, particularly in the spring."

Black-grass control tips

— Manage black-grass in the top 50mm of soil only - keep all cultivations shallow

— Don't drill too early - allow time for control

— Pre-emergence residual herbicides are key to chemical control - flufenacet is most effective

— Use alternative chemistry in other crops, eg propyzamide/carbetamide in OSR

— Sequence active ingredients in close succession - be prepared to wait for best conditions

— Get black-grass tested for herbicide resistance - tailor chemistry accordingly

— Keep rotation and cultivations flexible on worst black-grass fields

— Spring barley and hybrid winter barley can dramatically reduce black-grass and seed return

— Mid-October-sown cover crops should be utilised after the initial Sept-Oct black-grass flush and kill. Covers such as spring oats or a spring oat/beans/peas mix, grown before a spring crop will dry and feed soil and improve soil structure. More expensive phacelia, clover or radish cover crops will not establish well in mid-October on heavy land

— Preventing black-grass seed return should drive everything you do.

— Quick weed knock-down from Kyleo —

A SURVEY OF leading agronomists has underlined key decision-making with stubble management and herbicide use to eliminate important weeds and prepare for following crops.

The independent poll asked what was wanted from a stubble treatment - 70% said they wanted to remove strategic weeds in the rotation (such as black-grass), with 63% saying that they were aiming to remove early weed competition to help the next crop establish.

One said that: "It's a hygiene thing. It is important to do it right at the time so that you get fewer issues rolling over into the next crop."

The survey also indicated that there were some challenges to effective stubble management. Nearly two-thirds (63%) of those interviewed said the main challenge they faced was getting effective control of weeds.

The second most important challenge cited was lack of time (42%).

The survey was carried out by chemical manufacturer, Nufarm, which has developed a new formulation of glyphosate boosted by the addition of 2,4-D, Kyleo. "It is not legal or indeed practical to tank-mix these two actives together as a stubble treatment, yet this unique coformulation, which has been made possible through the use of advanced adjuvant technology, delivers on several vital levels," said Jon Staton, of Nufarm.

"Firstly, it controls everything that glyphosate does and more. In addition, Kyleo controls volunteer oilseed rape, annual nettles, cranesbill, bindweed amongst other broad-leaved weeds. Secondly, this formulation is faster than straight glyphosate and rainfast after just one-hour."

When asked about Kyleo, 84%in the survey thought it was effective on weeds, 63% said it had good speed of activity and 42% said that it had the ability to control large weeds.