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Sunday 19 November 2017

Patrick J Phelan: Herbicide resistance to inform weed control plan

Fine Tuning: Adrian Gallagher of A&A Contractors adjusts his plough while preparing a 50ac for winter barley for Michael Farrelly of Stackallen, Co Meath
Fine Tuning: Adrian Gallagher of A&A Contractors adjusts his plough while preparing a 50ac for winter barley for Michael Farrelly of Stackallen, Co Meath
Anna May McHugh (NPA managing director) with host family David, Shirley, Howard (left) and Clive Carter (right) at the official Media Launch of the 82nd National Ploughing Championships on the site in Ratheniska, Co Laois. The championships taker place from September 24 to 26

Patrick J Phelan

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.

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KWS Cassia, which performed very well in 2013, will be the principal winter barley variety as it comprises approximately 74pc of the certified seed availability. It is one of the top performers in both the fungicide treated and untreated in the HGCA trials.

Volume, which is a 6-row hybrid, has the highest yield potential at 114. However, it needs careful and different management to that of other varieties. In contrast to conventional varieties, which are normally sown at 325-350 seeds per square metre, Volume should be sown at 200 seeds per square metre.

This year, winter barley seed will be a bigger grain requiring a higher seeding rate. Seeding rate (kg/ha) for all varieties, and indeed different seed lots, will be determined by the 1,000 grain weight. JB Diego, Avatar and KWS Lumos make up 75pc of the winter wheat seed for sowing this autumn.

Avatar is high yielding at 107 but is the tallest variety and will need careful management for septoria. JB Diego and Avatar have performed well in early sowing. And while all three have performed well as first wheats, Avator lost some of its yield advantage when sown in continuous wheat.

While it is a little early yet to sow winter oats, variety choice is going to rest largely with Husky, while Barra fans will continue to sow it. In general, Husky and Barra will perform better when sown in the spring.

Finally, September is the month to dig trial pits to assess soil compaction and to decide on remedial action with ripping, deeper ploughing, sub-soiling or, indeed, no action at all. Do not allow anyone to sub-soil without careful assessment of the soil profile and measurement of the depth of compaction and the depth to free drainage underneath.

This year, with the dry soil conditions, there is a real opportunity to correct deep compaction with sub-soiling. That said, you must still remember that the purpose of sub-soiling is to break up a compacted structure which in effect means that the soil will have no structure. Therefore, it will have no strength and can be easily compacted again unless given careful management until such time as a new structure is established – that may take three to five years.

Patrick J Phelan is a member of ACA and ITCA and may be contacted at pj.phelan@itca.ie

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