Patrick J Phelan: Herbicide resistance to inform weed control plan
The harvest is just about over and most of the winter oilseed rape has been sown. Pre- emergence weed control with either Katamaran or Butisan S to moist soil before the seed chits is the preferred option in many situations.
This year, some soils were considered too dry and it is now important to take the first opportunity after the cotyledons (seed leaves) are fully expanded and before weeds germinate to apply a post-emergence application.
Soil should be moist at application or get rain shortly after – but not heavy rain. If that opportunity is missed, weed control with Kerb is an option up to the end of January. Clopyralid may be used to control thistle, mayweed and marigold.
Salsa, introduced last winter by Dupont, will control charlock. Its label advises of the need not to rely on it to control chickweed or mayweed as, in common with the sulfonyl ureas, it is an ALS inhibitor.
This is a timely warning, before the season starts, of the urgency to plan weed control strategies so as to reduce the risk of building up herbicide resistance. Select herbicides with different modes of action and from different herbicide groups. Do not rely on the same herbicide year after year.
A combination of herbicide resistance, removal of approval from some existing herbicides and no new actives coming to the market will present a major problem for us in the not too distant future.
Sowing of winter cereals will commence from mid-September. Before sowing, check your most recent soil sample results so as to determine if the soil pH is suitable for the crop you intend to sow and the need for seedbed fertiliser – remember no nitrogen or phosphorus applications are allowed after mid-September.
Land should be sampled every 3-5 years. If you are fortunate to have second ley, be very wary of using this year's crop performance as an indicator of soil fertility. First ley will often produce an excellent crop of barley or even beet in spite of low pH, but the following crop will be hit severely. If renting grassland for tillage walk it carefully and take note of indicator species, such as sorrel, to give a preliminary assessment of the likely need for lime.