Pro Operator

Fine tuning helps beat blackgrass

spraying blackgrass

Leading spray application specialist, Tom Robinson, combines his own expert advice with guidance from BASF, Bayer, Monsanto and Syngenta to discover how to fine-tune autumn applications to get the best control from their herbicides.

Grass weed control in the autumn has become increasingly difficult in recent years, due in no small part to increased herbicide resistance, particularly post emergence selective products.

The challenge for the operator is to get the best out of each herbicide application, through a combination of sprayer set up, timing and application technique. Representatives from BASF, Bayer, Monsanto and Syngenta all agree fine tuning applications will help achieve the best autumn grass weed control and get the best from the products.

Pre-drilling sprays

Glyphosate is the active ingredient of choice for pre-drilling (stale seed bed) applications.

Spray off blackgrass with Roundup, once the largest plants have two leaves. Germination should take place in about ten days, provided there is enough moisture –          540g a.i./ha is sufficient for good control.

Modern Roundup sprays work best at reduced volumes 80-100 litres/ha. They are sensitive to cation lock up in hard water, so may need a water conditioner. Lower water volumes also reduce the chance of cation lock up.

Monsanto’s technical development manager, Barrie Hunt, recommends two or three sprays where possible. More blackgrass will be successfully removed by spraying each flush of weeds at the two-three leaf stage, than waiting for a single spray just before drilling. Ensure you cultivate between sprays to tackle any survivors.

Barrie also explains as Roundup is compatible with most pre-emergent herbicides, it can be usefully tank mixed as a post drilling pre-emergence spray combined with other pre-emergence products.

Monsanto recommends traditional fan jets at 1.5-2.5 bar pressure, and also supports the use of angled 3D nozzles. Monsanto emphasises the need to use the recommended dose for all herbicide applications, to reduce the onset of herbicide resistance.

Pre-emergence sprays

Shadows behind clods, where no spray lands, can be caused both by the prevailing wind, or the speed of the vehicle imparting a horizontal trajectory to the spray.

Improving coverage in three dimensions requires a spray that has a backward trajectory greater than the forward speed of the machine, as well as downwards and forwards. The nozzle developed specifically for this job in 2009 was the Defy nozzle from Syngenta.

The latest 3D nozzle gives even better three-dimensional coverage, and is Tom Robinson’s nozzle of choice for autumn applications. It also achieves 1 and 2 star LERAP status. The nozzles are alternated forward and backward along the boom, to achieve the 3D spray effect.

shadows behind clods stops the spray reaching the ground

Timing is key

Bayer CropScience emphasises the ideal timing of a pre-emergence application of Liberator (diflufenican+flufenacet) is within 48 hours of drilling. Later applications require pre-emergence herbicides to penetrate deeper into the soil profile to get within the rooting zone of the blackgrass.

Bayer recommends fan jets delivering a medium spray quality, and spray volumes of 100-200 litres/ha. It particularly emphasises the benefits of a smooth seed bed to ensure even soil coverage and to avoid the issue of clods causing shading or subsequent emergence as they break down.

BASF offers similar advice for its range of herbicides, stressing the need for a fine firm seed bed. BASF recommends spray volumes down to 100 litres/ha and forward speeds of 10-12km/hr. The preferred nozzle type is a traditional fan jet producing a fine spray for good soil coverage.

water volume affects spray efficacy
applying autumn herbicide

Latest thinking

The most up-to-date autumn herbicide application research work, in the past 2 years, has been carried out by James Thomas of Syngenta.

James has found with traditional fan jet sprays, that 50 litres/ha, 300 litres/ha and 400 litres/ha worked less well than 100 and 200 litres/ha. The 3D forward and backward at 100 litres/ha and 200 litres/ha outperformed all the fan jet treatments at the same water volumes.

Last season Syngenta trialled 90% drift reduction nozzles and achieved good results with these at the higher water volume of 200 litres/ha. The Syngenta recommendation is 12km/hr, 200 litres/ha using 3D nozzles forward and back when weather conditions are favourable, and 200 litres/ha using 90% drift reduction fan jets when conditions are unfavourable.

factors affecting drift, spray boom
spraying for black grass

Post-emergence foliar sprays

Winter wheat

The most widely used product is probably Atlantis WG (iodosulfuron+mesosulfuron). Bayer’s recommendations include: Water volume – 200 litres/ha down to 100 litres/ha. Timing – GS 11-13 (1 -3 leaves).

Avoid application if rain is forecast. Traditional fan jets are preferred but angled nozzles may do a good job too. Maximum speed 12km/hr. The adjuvant Biopower is a key component to the product’s performance.

Winter barley

The most widely used product is probably Axial (pinoxaden). Syngenta’s recommendations include: Water volume 100-200 litres/ha. Timing – GS 11-12 (1-2 leaves). Speed up to 12km/hr. The adjuvant Adigor should be added to the spray mix at a rate of 1%, at volumes less than 200 litres/ha – i.e. 1 litre in 100 litres/ha. Preferred nozzle is the 3D.

If access to the weeds is good, pointing the nozzles all forwards will apply the most product to the weed leaves. This can more than double the spray on the leaf compared with a fan jet. However if the weed leaves are likely to be shaded by clods, then it makes sense to alternate the nozzles forward and backward.

This article provides some of the pre-course reading for a CPD training course on keeping pre-ems on target.

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