Arable News

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Manage stale seedbeds to maximise black-grass kill

Hutchinsons’ technical manager Dick Neale.

Staleseedbeds will be a crucial weapon in the fight against black-grass this season,but they must be actively managed if growers are to maximise theireffectiveness, says leading agronomy firm Hutchinsons.

Three yearsof trials at the firms black-grass centre of excellence at Brampton inCambridgeshire show that appropriate management during the creation, growth anddestruction of stale seedbeds can significantly improve efficacy, the firmstechnical manager Dick Neale says.

Any growerwith high levels of black-grass should aim to get as many stale seedbeds in aspossible before drilling and Mr Neale strongly believes it is worth delayingdrilling until at least mid-October to create a wider window for such culturalcontrol. Our chemical options for black-grass control are disappearing, socultural control, including stale seedbeds, is essential.

Furthermore,with black-grass dormancy likely to be low this year given warm and dryconditions during the June maturation period, stale seedbeds could workextremely well if done correctly, says Gloucestershire-based agronomist PatrickLevinge.

Theoreticallywe should get a decent flush of black-grass early on, but it all depends on howwell you manage the stale seedbed.

In mostsituations, effective management centres on shallow cultivations and goodseedbed consolidation.

Seedbed creation

Whileblack-grass will naturally germinate in stubbles after harvest given adequatesoil moisture, emergence of the first and subsequent flushes can be greatlyimproved by shallow cultivations and good soil consolidation to improvesoil-to-seed contact, says Mr Neale.

But hewarns that cultivations should go no deeper than 50mm in order to create akill zone close to the surface where black-grass is exposed to light tostimulate germination and herbicides can work more effectively.

Moving thesoil in that kill zone with a quick cultivation at least twice in September andOctober should give good results as thats when 80% of black-grass wants togrow.

The CousinsSurface cultivator features a tine and ballastable roller design which is idealfor such operations, and can work at a consistent shallow depth on any soiltype, he notes.

Tightcontrol over cultivation depth followed by good seedbed consolidation is vital,whatever equipment is used and whatever the soil type, adds Norfolk tenantfarmer and Hutchinsons agronomist Alex Wilcox.

Moving thesoil within the black-grass kill zone not only encourages germination, but canhelp control slugs which look set to be another big issue this autumn, he says.

Moving soilfor subsequent stale seedbeds as soon as the first flush of black-grass hasbeen sprayed off, also prevents the build-up of root exudates that will stopfurther black-grass seeds germinating, he says.

Black-grassemergence is governed by a number of factors so you have to do all you can toget it to grow.

By minimisingcultivation depth throughout the autumn growers will create an undisturbeddepletion zone deeper in the soil profile where black-grass seed willnaturally decay at around 70% a year, says Mr Neale, who believes such a twotier approach to soil management is crucial on any bad black-grass land.

Spray timing is key

Once a goodflush of black-grass has germinated it must be controlled quickly with anaccurate timing of a non-selective glyphosate-based herbicide, says Hutchinsonstrials manager Bob Bulmer.

Black-grassshould be treated while it is at the seedling stage and before it gets to threeleaves. Robust rates should be used, which typically equates to around 1.5litres/ha by the time black-grass is at the two-leaf stage, increasing tonearer 2 litres/ha if the weed has started to tiller.

Smallblack-grass can be hard to spot in stubbles, so its important to monitorfields closely to make sure you catch the right timing.

Mr Nealesays black-grass flushes of more than 800/m2 must be destroyed with glyphosaterates of at least 600g of active ingredient per hectare before the three-leafstage otherwise root exudates build up in soil preventing the germination offurther black-grass seed. This should be followed by a repeat shallow cultivationto encourage further germination.

This yearwill be a game-changer for black-grass control, Mr Levinge concludes.Black-grass populations across the country have thrived in the conditions wehad throughout the winter and spring, and its clear that the answer tocontrolling the problem lies in cultural control options like stale seedbedsand spring cropping rather than chemicals.

Arablefarming has changed and growers cant afford to carry a poor crop. With lowsale prices, high input prices and only an average harvest on the cards, itsmore important than ever to make sure everything possible is done to giveyourself the best chance.

A case for ploughing

Whilerestricting soil disturbance to the top 50mm is generally the preferred approachfor black-grass control, Mr Wilcox acknowledges there can still be a strongcase for deeper ploughing on bad black-grass land.

Ploughingnot only buries the black-grass seed from the current season, allowing it todecay naturally, but the seeds that are brought back to the surface generallytend to produce weaker and less competitive plants, he says.

Mr Wilcox,who farms 300ha (750-acre) with two other growers near Downham Market inNorfolk, favours ploughing and power-harrowing his worst black-grass land aheadof drilling from mid-October onwards.

Wenormally try to establish at least two stale seedbeds prior to drilling, but itis vital we dont delay drilling so long that it impairs our ability to rollseedbeds. Consolidation is crucial.

Ploughingmust be done well to maximise weed control and he suggests this meansminimising furrow width to around 300mm (12), ensuring skim plates are setcorrectly, and not ploughing too fast or deep, typically to around 175-200mm(7-8).

As tenantfarmers we cant afford to fallow land for a year and switching to spring wheatcan be a big risk on some land. Ploughing in the autumn, especially on theheavier land, helps us to ensure we can get a crop established in good time.

 


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