Impact of weeds on Australian grain production

Key results at a national level include the following.

• The overall cost of weeds (Figure 1) to Australian grain growers is estimated to be $3,300 million.
• Weeds are costing Australian grain growers $146/ha in expenditure and losses.
• Average expenditure on weed control, including herbicide and non-herbicide practices, was estimated to be $113/ha.
• Yield losses due to weeds amounted to 2.76 million tonnes of grain.
• Based on extent and cost, the most costly weeds nationally in terms of total yield loss remain ryegrass, wild radish and wild oats, with brome grass being the most notable major new weed.
• Barnyard grass, feathertop Rhodes grass, fleabane and sweet summer grass were found to be most costly in sorghum.
• Ryegrass remains the major weed in terms of the cost of herbicide resistance, with the cost being greater than the sum of all other forms of resistance.
• Herbicide resistance was estimated to cost $187 million in additional herbicide treatment costs, in addition to the costs of using extra integrated weed management practices.
• Most growers expect that a new selective or knockdown herbicide able to control weeds that are resistant to current herbicides will become available in the next decade.
• Nationally, the most costly weeds in fallow in terms of estimated yield loss were melons, heliotrope, fleabane, caltrop, barnyard grass and panic grass.
• The study estimates $487 million is spent on fallow weed control through herbicide application and cultivation.
• Despite this, weeds in fallows are still estimated to be costing more than $430 million through reduced crop yields.
• Overall, revenue loss due to weed populations reducing crop yields was $33/ha, which is similar to the cost of some herbicide applications.
• Yield losses due to weed competition from residual in-crop weeds were valued at $278 million.
• Using cultivation in crop seeding systems and as a weed control practice has declined dramatically since the 1998-99 study of Jones et al. 2000, but other practices including crop-topping, double knockdown and narrow windrow burning have increased.
• Weeds are typically the primary reason for Australian grain growers to use cultivation and burning.

Australian grain growers are investing heavily in weed management, mostly through herbicide-based methods.

Despite increasing levels of herbicide resistance, in-crop weed populations are being kept low and yield loss due to weed competition ($708 million) is much lower than total weed management costs ($2,573 million).

Reducing the cost of weed management is one of the grains industry’s largest challenges.

View on GRDC website.