Effect of pre-season management and in-crop herbicdes on weed seedling numbers and triticale grain yield

Abstract

Six pre-season treatments which aimed to reduce seed set of annual grasses were imposed at Orange, N.S.W., during spring 1985. Five in-crop treatments (cultivation plus trifluralin, trifluralin, oryzalin plus trifluralin, chlorsulfuron, nil - all direct-drilled) were superimposed over the pre-season treatments at sowing time. Triticale was sown 8 days after application of glyphosate (0.72 kg a.i. ha-1) in May 1986. All pre-season treatments reduced potential grass seedling numbers (89-94% reduction), with the grazing treatments being less effective then the herbicide treatments. Actual grass seedling numbers (those emerging within the crop) followed a similar pattern to potential seedling numbers, but at 10-20% of the potential level. Species not targeted for pre-season management (legume spp., Polygonum aviculare, Poa annua) tended to he present in larger numbers on those pre-season treatments where reduction of the topped grasses was greater. In-crop herbicides did not consistently reduce grass weed seedling numbers further. Grass weeds were more effectively controlled by the cultivation plus trifluralin treatment. Triticale crop yield was reduced as seedling numbers of topped grasses increased. In the direct-drilled situation, it was concluded that satisfactory crop yields will be obtained only after imposition of some form of pre-season management. For longer term grass control, these treatments would need to be imposed in at least two consecutive years.