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Grass control in pastures and implications for pasture yields, botanical composition, cereal root disease (take-all) and cereal grain yield

R.J. Inwood, D.K. Roget, A.D. Rovira and E.D. Carter

CSIRO Division of Soils, Waite Road, Urrbrae SA 5064

Traditionally, take-all caused by Gaeumannomyces graminis (sacc.) von Arx and Oliver var. tritici (Ggt), has been controlled by crop rotations using non-host crops. Control in the pasture phase has received less attention. The importance of grasses as hosts for Ggt has been reported by many authors, however, little is known about the effects of chemical removal of grasses and particularly the timing of herbicide application on the survival of Ggt from the pasture phase to the cropping phase. This poster reports on two trials which assess the importance of timing of chemical grass removal on the carry-over of Ggt and on pasture composition.


Two trials were established on a long-term pasture site at Kapunda, South Australia, on a red brown earth, Dr 2.3, with a pH (in water) of 6.0, and with a winter dominant annual rainfall of 500 mm. A randomised complete block design was used with four replicate plots for each of 11 treatments, each plot measured 2 m wide by 40 m long.

In 1989 the herbicides used were Gramoxoneor Fusiladeand were applied between 26 July and 3 September 1989 and in 1990 Gramoxone, Fusilade, Gramoxone/Simazine or Fusilade/ Simazine were applied between 3 August 1990 and 2 November 1990. Soil bioassays to assess Ggt carry-over were conducted during the summer following the herbicide applications.

Results and discussion

Herbicide applications from July to September significantly decreased grass density compared to the control plots which had 53-58% grass. Herbicide applications in July and August reduced grass density to 5% while the September application reduced it to 15-25%. Clover density increased as the grass population decreased.

Although the grass population was reduced with herbicide application until September, a significant decrease in Ggt carry-over only occurred at the first application dates of 26July 1989 and 3 August 1990 (33.3% and 30.5% incidence respectively) compared with the controls at 83.0% and 86.1% incidence.

This level of control although beneficial, is less than that achieved following a grass-free, break crop (typically 5-10% incidence of take-all) and suggests that either an earlier application and/ or more effective grass control may further reduce Ggt carry-over.

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