Farm Ireland

Wednesday 13 December 2017

Take action when slugs become evident

Dr Richard Hackett

This year's harvest has a long tail in the northeast, with a sizeable amount of spring wheat, spring oilseed rape and beans impatiently waiting for the cutter-bar. With short days and heavy dew, any opportunity to complete the harvest should be taken. It's still not time to panic, however, as it's relatively early and the huge harvesting capacity available will come to bear once the weather turns favourable to wrap up the harvest.

Oilseed rape crops have got off to a great start. Most crops were sown in good time, into perfect seedbeds and have a herbicide applied. Volunteer cereals are getting established in some fields, particularly along headlands. A low-rate graminicide should be applied sooner rather than later to avoid competition and a refuge for slugs. All crops should be monitored closely for slug activity and action taken as soon as activity is noticed.

Early sown wheat can be considered from now on in as non-take-all risk situations. The benefits of early sowing include potential for higher yield, spreading out the workload, an opportunity to reduce seed costs from low seed rates, higher soil nitrogen uptake which may reduce chemical nitrogen requirement and reduced potential for nitrogen leaching.

This can be especially important where soil nitrogen reserves are high, for example after a break crop. On the negative side, early sowing can increase fungicide and growth regulator costs, increase take-all risk and can result in rapid crop development which can come out of sync with the season.

For example, a crop may end up at growth stage 30 in January, or become infected with disease early on, requiring high levels of fungicide use for the remainder of the season.

The two most important management tools for early sowing of wheat are variety choice and seeding rate. Choose varieties that are slow to develop, but independent information from within Ireland is scant and grower experience is the main source of information. Current varieties that have been used for early sowing are Sahara, Alchemy or JB Diego, but seed availability is an issue.


Very low seed rates are required, the main purpose being that the crop can spend the autumn tillering and covering the available ground rather than racing through developmental stages to develop out of sync with the season. In this context st/ac is a useless parameter and seed should be sown to seeds/m2.

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For mid-September sowing into excellent conditions, the target seed rate would be about 200 seeds/m2, moving to 250/m2, and 300/m2 as the season progresses or conditions deteriorate.

To set such a low rate in the field, the thousand grain weight (TGW) of the seed must be known. Tools are available to measure the TGW of seed, which are effective and relatively cheap. Ideally this information should be on the bag or available to the merchant, but that's for another day. If nothing else is available, count out the target seeding rate/m2, for example 250 seeds, weigh them in grammes, and multiply by 10 to give target seeding rate in kg/ha, which can be readily set on most machines.

However, other factors can affect the 'flowability' of seed in the seeding unit, such as different seed dressings etc. These can impact severely at low seeding rates. Measure out a small amount of seed, for example 50kg, and sow it. When this is completed, measure the area sown and this will give the best indicator of actual seed rate. The alternative is to fill the seed hopper and discover at the end of 10ac that 15ac of seed has been used, which as well as wasting seed, can result in a costly headache during harvest.

Dr. Richard Hackett is an independent crop consultant and member of the ACA

Irish Independent