Roger Lawes1, Michael Moodie2, Penny Roberts3
1 CSIRO Agriculture and Food, Floreat, WA, 6014,email@example.com
2 Moodie Agronomy, Mildura, Victoria, 3500, firstname.lastname@example.org
3 1/7 Chandos Street, Clayton Bay, South Australia, 5256
Brome grass is becoming a greater problem than ryegrass in some parts the South Australian and Victorian grain belts. Brome grass has a larger seed than ryegrass and is slightly less fecund and at this stage it is not clear if these species differences influence the cost of weed seed management. It is not clear which weed seed bank is more difficult to manage. We accessed historical published information about plant-to-plant competition with wheat and seed bank dynamics and re-analysed these data using the hyperbolic equations in the LUSO model for this weed, thereby creating a LUSO brome grass model to accompany the LUSO ryegrass model. Overall, brome grass at low population densities was less competitive than ryegrass, but as the population density increase, it became more competitive than ryegrass. Weed species effected the profitability of the optimal rotation. Moderate ryegrass populations damaged wheat yields more than brome grass, resulting in approximately a $10/ha difference in annual returns over the 6-year crop sequence. Weed species altered the optimal rotation when the seedbank was low. When the seedbank exceeded 50 seeds/m2, weed species did not affect the optimal rotation, and the rotations were the same, regardless of weed species. When set rotations were evaluated, brome grass damaged crops less, and the overall profits with a brome grass infestation were higher, regardless of the rotation. In all cases, assuming control costs for the two weed species were similar, minimising and managing the weed seed bank generated the highest profits.