Crop Rotation and Herbicides Key to Brome Grass Control
By Daenia Dundon
The 2026 GRDC Brome Grass Trial has now reached its final assessment stage, with crop head counts, brome grass head counts and seed samples collected for herbicide resistance testing. The trial is investigating how different crop rotations and herbicide management strategies influence brome grass populations and seed production over time.
Crop establishment and head counts
Crop establishment was excellent across the trial. The trial was sown into moisture, resulting in even crop establishment. Canola averaged 30 plants/m², compared with 177 plants/m² in barley and 151 plants/m² in wheat.
Average crop head counts reflected differences between crop types, with barley generally producing higher head counts than wheat. Barley AX and Barley CL recorded average crop head counts of 391–427 heads/m², compared with 234–248 heads/m² across the wheat treatments. No herbicide impacts were observed between the various Barley or Wheat treatments.
Brome grass density and head counts
Brome grass density was substantially higher in two of the seven treatments. Treatment 1 (continuous wheat) averaged approximately 111 brome grass plants/m², while treatment 5 (Barley AX) recorded the highest density at approximately 174 plants/m². In comparison, the remaining treatments recorded very low brome grass densities, averaging fewer than 3 plants/m².
Brome grass head counts showed a similar pattern, with treatment 5 standing out as the only treatment with a notably high number of brome grass heads, averaging approximately 40 heads/m². Treatment 1 averaged approximately 2 heads/m², while treatments 2, 4, 6 and 7 recorded no brome grass heads. Treatment 3 recorded fewer than one head/m² on average.
These results highlight a considerable difference in brome grass seedhead production between treatments, particularly the contrast between treatment 5 and the treatments with very low or zero head counts.
Herbicide management observations
Treatment 1 received Sakura + Avadex Xtra followed by Intervix during the 2026 season. With this herbicide program and high seed bank levels, brome grass density remained relatively high at the final assessment.
Treatment 5 received trifluralin + metribuzin followed by Aggressor AX. This treatment recorded both the highest brome grass density and the highest brome grass head count in 2026.
Interestingly, treatment 4 has the same crop and herbicide program this year as treatment 5, however it has an additional early post-emergent application of Jaguar at 1 L/ha. Treatment 4 achieved excellent brome grass control, with very low weed numbers recorded. Crop rotation may also have contributed to this difference, as treatments 4 is following a canola crop, while treatment 5 is following a wheat crop. This highlights the importance of both herbicide strategy and crop rotation in managing Brome Grass populations.
Once resistance testing and yield assessments are complete, the results can be considered alongside data from previous seasons to evaluate the longer-term effectiveness of the different crop rotation and herbicide strategies.
This trial is part of a GRDC investment into improved Brome Grass management, led by the University of Adelaide in collaboration with the Department of Primary Industries and Regional Development.
