The management of annual ryegrass (Lolium rigidum Gaud.) in southern Australian broadacre farming systems is lacking in diversity

摘要

Australian winter broadacre crops have been planted on 19.4 million ha on average, over the five years 1999 to 2003. The cropped area is dominated by cereals and in particular wheat. Annual ryegrass (ARG), (Lolium rigidum Gaud.) is the most widespread, difficult to control and important weed of Australian winter broadacre farming systems, and is arguably the greatest threat to sustainability of these systems. Alemseged et al. (2001) calculated that it infests about 6 million ha. Syngenta's analyses of herbicide sales suggest that the area treated for annual ryegrass could be as high as 8 million ha. Herbicide sales have been used to estimate the area treated for ARG control. This analysis focuses on herbicides for which there is not yet widespread ARG resistance. Grain producers are heavily dependant on two groups of herbicides. Group M (glyphosate) is applied as a non-selective burn-down treatment prior to planting and is applied to as much as 25 million ha (applied up to 132% of the winter crop area). The Group D herbicides, especially trifluralin, are used for pre-emergent weed control on nearly 7 million ha, 36% of the cropped area, up from 25% in 2001. There is circumstantial evidence that Group D herbicides are mostly applied for the management of ARG, and there is a high risk of over-use. Minimum- and no-tillage are used on 76% of the cropped area, while burning as a weed control technique (hot burn) is used on just over 10% of the area. In view of the current willingness of grain growersto rely heavily upon herbicides for weed control, a greater burden is placed on ensuring herbicide rotational strategies are carefully thought through and implemented, This has resulted in extension of double-knockdown techniques with Spray. Seed~(R) toreduce the likelihood of glyphosate resistant ARG in reduced tillage environments. A similar education program needs to be directed towards Group D herbicides and alternatives promoted. Group K herbicides, including S-metolachlor (Dual~(R) Gold), are potential alternatives. Group K herbicides are generally well tolerated by barley, oats, legumes and canola and can be used at higher rates in these crops. Wheat is less tolerant at the rates required to manage ARG effectively. Rotating to Group K herbicides outside wheat is proposed. The grains industry could evaluate the model the Australian cotton industry has established for the very successful management of insecticide resistance. A better way to manage herbicide use and rotation needs to be found, particularly as fewer new active ingredients are expected to be developed than in the past.