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Sunday 4 December 2016

Consider cultivation change to cut sterile brome in your crops

Oak Park trials show wheat and barley benefiting from being planted at depths up to 150mm to kill-off spread of the weed

Ciaran Hickey

Published 30/08/2011 | 05:00

This year has been a much better season than that of last year for minimum tillage (min-till) crops in Oakpark. The wheat was sown in excellent conditions in 2009 but the month of rain afterwards in November had a very detrimental effect on the crop. That was a year when the ploughed ground was better suited to absorb that rainfall.

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There was a subsequent urge to change the cultivation depth away from 75-100mm (three to four inches) to something closer to 150-175mm to allow more permeability.

Because it is an ongoing trial-plot, it was decided to retain an unchanged system, and the crop looks none the worse for the decision. It demonstrates that the system is sound, even if it favours good weather at early establishment similar to what we achieved last autumn.

Ability

One of the emerging weaknesses of the min-till system for winter barley is its ability to cope with a weed called sterile brome. It became apparent early on this year that our winter barley min-till plots were suffering with a sterile brome problem. While there are good sprays available in wheat to tackle this problem, there is no chemical control available yet in winter barley.

To control a problem using cultural control instead of chemical requires a clear understanding of the weed itself.

Sterile brome, also known as barren brome, is a mainly winter grass, native in rough waste ground, hedgerows and roadsides. It normally spreads from the hedge bottoms and field margins into tillage fields where it may form dense patches. It is becoming more common due to the presence of more continuous winter cereals and the adoption of tillage systems that don't use a plough.

Sterile brome flowers from May to July. On average, more than 200 seeds are produced per plant and a high proportion of these are viable. Seeds start to become viable 3-7 days after flowering. The seed matures rapidly on the plant once ripening begins, and most seed is shed from late June to early August. Because the bulk of seed spreads before harvest, the aim should be to get this seed germinated so it can be sprayed off before the next crop is sown.

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To avoid dormancy and to get the majority of seeds to germinate, the seed needs contact with moist soil. This is achieved by cultivating the ground and a shallow burial of the seed. Dry conditions and sunlight will prevent germination. Autumn is the main period for emergence but if dormancy is enforced by drought, some seed may sit there until the following spring.

These seedlings require a period of cold for vernalisation in order to flower just like winter wheat. The spring-emerging seedlings may not become vernalised and can fail to flower before crop harvest.

The greatest emergence of brome is from depths of less than 50mm, with few seedlings emerging from deeper than 100mm. No seedlings emerge from 150mm.

In headlands and alongside ditches, the majority of seed is shed within 1m of the parent plant. Tillage actions are carrying the seed further into the field. In the open field, seeds can be dispersed up to 3.5m from the parent plant.

A combine harvester can carry sterile brome seed up to 50m in the forward direction and eject it up to 7m backwards and scatter it up to 1m on either side. Seed on plants near the headland would normally be moved parallel to it during combining rather than into the centre of the field.

Control options:

•Growing spring barley is likely to reduce the weed unless a dry autumn has prevented germination, leaving the weed to emerge in the spring-sown crop. In a moist autumn, there may be an opportunity to kill sterile brome seedlings if the winter cereal is not sown too early. In trials in Oak Park with early sown (mid-September) winter wheat, the sterile brome population was incredible. Therefore, delaying sowing, similar to the technique used to control all grass weeds, will reduce the population.

•While most farmers are looking for good, dry weather at the moment to progress the harvest, a spell of broken, showery weather is great for stale seedbeds as the moist conditions allow for excellent germination of the brome. A field with a bad brome problem here some years back underwent a programme of three cultivations and two applications of Glyphosate, which brought it right back under control.

•Seedlings are unable to emerge from below 130mm so ploughing can be effective if inversion is complete. Rotational ploughing, such as one year in three, will normally keep moderate infestations in check. You could also plough the headlands worst affected to limit the spread outward into the field.

Ciaran Hickey is a tillage enterprise adviser at Teagasc, Oak Park

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