Influence of preseason weed management and in-crop treatments in two successive wheat crops 1. Weed seedling numbers and wheat grain yield

Abstract

The effect of 5 preseason management treatments on seed set reduction of annual weed grasses and their regeneration in the following autumn was evaluated in a 2-year field experiment commencing at Orange in spring 1986. Preseason (spring) treatments were paraquat, glyphosate (2 rates), unsprayed heavy grazing, and unsprayed control. In the first of 2 successive wheat crops (planted 1987), 3 in-crop weed control treatments [control, chlorsulfuron (both sod-seeded), and trifluralin plus cultivation] were imposed. In 1988, the second wheat crop was sown into a cultivated seedbed or direct-drilled. The preseason treatments reduced potential annual grass regeneration by 91-99% compared with the control, with heavy grazing being the best treatment. For each preseason treatment compared with the control, the pattern of actual seedling emergence within the crop during 1987 was similar to that of potential emergence for each grass species (except Lolium rigidum), but numbers were lower and more variable (7-86% of potential numbers). The proportion of Bromus spp. and Vulpia spp. emerging within the crop declined from the first to the second crop, while L. rigidum increased to an average of 93% of the annual grass population in 1988. Trifluralin plus cultivation increased the control of annual grasses in 1987. In 1988, the 1987 in-crop treatments had little carryover effect on annual grass control; however, wheat grain yield was increased by both chlorsulfuron and trifluralin. Preseason management reduced seed set of annual grass weeds, and this control was maintained under cropping for at least 2 years (except for L. rigidum). Wheat grain yield responded to this control. Long-term control of L. rigidum where soil is disturbed appears difficult because of apparent long-lived seed in the soil.