Managerial practices to control wild oats in Queensland.

The repeated annual use of herbicides to control wild oats (Avena ludoviciana and A.fatua) was investigated. In the first trial the wild oat seed density in the soil after a wheat crop was less than the initial soil seed density only after treatment with tri-allate at 0.85 kg combined with barban 0.175 kg/ha. Seed numbers in the soil had declined 5 months after the crop, so that the number in the tri-allate plots was also less than one year previously. In a four-year trial, tri-allate and trifluralin (0.4 kg/ha) produced levels of wild oat control which resulted in grain yield increases between 55% and 120% in 3 of the years. There were still 5-12 wild oat plants/m2 in the maturing wheat crop in the third and fourth years of applying tri-allate and trifluralin. Barban was less effective on wild oats than the other herbicides, resulting in smaller yield increases. The incidence of wild oats in relation to crop rotations was surveyed over 4 years on 5 farms covering 2000 ha. Winter crops following 2 or 3 summer crops had low wild oat populations (1 on a scale 0 to 10). The wild oat density was rated at 2.5 and 5 in second and third winter crops respectively