Friday, July 8, 2022

Weeds feel the burn

A trial in Mid-Canterbury is controlling weeds without chemicals. Sandra Taylor reports. There are options for weed control beyond the use of chemicals. A project under way aims to raise awareness of the value of non-chemical routes to controlling grass weeds. Richard Chynoweth from the Foundation for Arable Research is heading a Sustainable Farming Fund project looking at alternative methods to controlling weeds, particularly Ripgut brome, and to generate economic values for various treatments.

Burning, ploughing and creating a stale seedbed were all found to be effective means of controlling Ripgut brome on a commercial trial paddock in Mid-Canterbury.

The paddock, later sown in Retriever winter barley, had a severe Ripgut brome infestation with 800seeds/m2 and 200 seedlings/m2 counted in mid-March.

On average, a stale seedbed dramatically reduced the infestation to 300 seeds/m2 by late in April. This was a reduction of 11 seeds/m2/day.

Burning also reduced the number of seeds a square metre, as long as the burn was hot enough to penetrate through trash and stubble.

Ploughing significantly reduced seed populations because it buried the seeds too deep to emerge assuming they germinated, whereas minimum tillage didn’t bury the seeds deep enough to reduce brome populations.

Ripgut brome in its various life stages.

Where burning occurred, either cultivation method (ploughing or top work) could be used with a similar result, but in unburned areas ploughing was needed to reduce the brome population and maintain similar grain yields in the subsequent cereal crop.

Increasing the sowing rate and therefore plant population of the cereal did increase grain yield, but the population was not enough to significantly reduce the numbers of brome seed heads at harvest.

The trial also received the farmer’s standard herbicide programme which included 300ml/ha of Firebird.

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