Freshly shed blackgrass seed is reported to be of low dormancy this season, so hitting it early and hard will be key to optimising control, says technical manager Mark Hemmant.
Blackgrass that emerges with autumn-sown cereals is
10 X more competitive
than that which appears
later in the season.
There is likely to be a significant early flush this autumn,
so we need to employ all the tools in the armoury to achieve the best result.
Pre-drilling
With lots of low dormancy blackgrass near the surface, stale seedbeds should be particularly effective this year in getting a chit.
Spray off with a good formulation of glyphosate before drilling; in bad situations, an earlier application might also be beneficial.
Adding Companion Gold to minimise drift and condition hard water will optimise efficacy.
Pre-em product choice
Applying flufenacet at 240g/ha is crucial. Many years of Agrovista trials and field observations have shown it is best partnered with pendimethalin and diflufenican.
Pre-emergence herbicides formulated by the R&D manufacturers have consistently outclassed generic products.
Trooper (flufenacet + pendimethalin) at 2 litres/ha plus Herold (diflufencian + flufenacet) at 0.3 litres/ha with Avadex Excel) (tri-allate) at 15kg/ha have performed very well.
This was re-confirmed in a two-site trial carried out last season (see graph 1).
Application aids
A good application aid can improve the efficacy of pre-em herbicides.
We recommend Remix, a long chain paraffinic oil, in all cases.
It decreases the production of very fine and very coarse droplets, reducing spray drift and improving spray deposition.
Remix’s molecules are also positively charged, binding the herbicide active to clay and organic matter in the surface layer for longer, optimising weed control and reducing seedling damage.
Extensive trials over 10 years have shown Remix increases blackgrass control from a typical pre-em stack by 11%, for a few pounds per hectare.
Remix consistently outperforms competitor products.
In a pre-em only trial last season, for example, it gave an average 7% uplift in blackgrass control over a product that claims to be the same.
It also maintained a 2% lead overall under four different post-emergence follow-up treatments (see graph 2).
That could make the difference between achieving the 98% control we need to reduce the blackgrass burden, or not.
Application
Achieving an even coverage of the seedbed is vital. We need to paint the soil and, within reason, the more droplets we can apply, the better.
Using twin caps fitted to a single spray line doubles the number of nozzles, and therefore droplets, for the same water volume.
Using alternate forward-facing (30 degree) and vertical flat-fan nozzles optimises coverage of the soil.
This mimics a twin-line set up that gave excellent results in trials on heavily infested blackgrass land in Northamptonshire, producing a 10% uplift in control over a single line set-up when applying full-rate diflufenican and flufenacet.
Water volume also has a direct effect on droplet number.
We recommend a minimum of 200 litres/ha, increasing to 300 litres/ha for severe infestations.
Timing
To ensure pre-ems work as effectively as possible, the aim should be to drill, roll and spray within 48 hours, especially when using Avadex. This produces a gas, and rolling extends the time it remains in the soil.
Follow-up treatments
An early post-em is often required to control blackgrass that has emerged after the pre-em and to top up residual control.
Adding 250g/ha of ethofumesate (Xerton @ 0.6 litres/ha) to 240g/ha of flufenacet has proved very beneficial (see graph 3).
The combination has also outperformed other contact/residual mixtures.
It also means a top-up treatment of iodosulfuron + mesosulfuron can be applied in the spring – this is not permitted if these actives have been used in the autumn.
More information on blackgrass trials and management
Trials show the way
on blackgrass control
Cover crop beats fallow for
control of blackgrass
Persevere with spring cropping
to control blackgrass