The high rainfall combined with high levels of blackgrass dormancy have reduced the effectiveness of stale seed-beds this autumn, putting pressure on residual herbicide programmes, warns an agronomist.

“Many farmers have been disappointed,” says Nick Myers, UK agronomy manager of ProCam. “Soils were either too dry or too wet and with weed dormancy the highest on record, very little blackgrass actually emerged to be treated with glyphosate.

“In effect this has lessened weed control options this season and places more focus on getting the best performance we can from residual herbicides. Better soil moisture should help, but the extended germination of blackgrass this year will be a problem.”

One positive aspect of delaying wheat drilling, either planned or imposed by the weather, is that this can lead to a 30% reduction in blackgrass population, he says.

“The selection and use of residual herbicides will be essential to ensure good grass weed control this year. Confidence in herbicide performance may have been shaken last year when control was generally well below expected levels, especially compared with the previous autumn.

“This was largely due to dry soil conditions, with soil moisture deficits lasting throughout the autumn. Soil and air temperatures were also well above the long-term average. None of these conditions was conducive to effective performance herbicides.”

However, conditions for herbicide applications this year are in complete contrast.

“The major challenge this year has been preparing a fine, firm seed-bed, which is needed for optimum herbicide performance. Ideal timing for pre-emergence herbicide application, providing soil and weather conditions are suitable, is within 48 hours of drilling.”

Growers should consider tank-mixing and/or sequencing pre-emergence residual products such as flufenacet + pendimethalin, flufenacet + DFF, prosulfocarb and pendimethalin to enhance the initial level of weed control.

Targeting the spray at the soil where it needs to be is also key, says Mr Myers.

“Work by Syngenta has shown that using angled nozzles alternating forward and backward along the boom gives a better and more even coverage of the soil.”

Read more

See our dedicated herbicide web page for weed control tips this autumn