Management of Avena ludoviciana and Phalaris paradoxa with barley and lessherbicide in subtropical Australia

The competitive advantage of barley compared with wheat was quantified for suppressing seed production of Avena ludoviciana Durieu. (wild oats) and Ph alaris paradoxa L. (paradoxa grass), and for improving herbicide effectiven ess on these major winter grass weeds of the subtropical grain region of Au stralia. Eight field experiments were broadcast with weed seed before sowin g wheat or barley, in which the emerged weeds were then treated with 4 herb icide doses (0, 25, 50, 100% of recommended rates). Yield reduction from un treated weeds was on average 4 times greater in wheat than in barley, with greater losses from A. ludoviciana than P. paradoxa. Barley did not affect weed emergence, but suppressed weed tiller density and, to a lesser extent, the number of weed seeds per tiller. Seed production was, on average, 4340 and 5105 seeds/m(2) for A. ludoviciana and P. paradoxa, respectively, in u ntreated wheat compared with 555 and 50 seeds/m(2) in untreated barley. Wee d seed production following treatment with 25% herbicide rate in barley was similar or less than that after treatment with 100% herbicide rate in whea t. Overall, 25% herbicide rate was optimal for both conserving yield and mi nimising weed seed production in barley. For wheat, maximum yield was achie ved with 50% herbicide but weed seed production was lowest with 100% herbic ide rate. This indicates that weeds can be effectively controlled in barley with considerably less herbicide than required in wheat, highlighting the importance of including barley as a part of weed management strategies that aim to reduce herbicide inputs.