During the 2006-07 financial year, farmers spent $1.57 billion controlling weeds, which is more than pests ($768 million) and land and soil problems ($649 million) combined.

The total cost of managing these problems was $2.99B , or an average of $21,094 per business, ABS reports.

Nationally, nearly two-thirds of farmers reported that they had improved their natural resource management practices.

Of these, 89pc reported doing so to increase productivity, 88pc for farm sustainability, and 75pc to improve environmental protection.

Other findings from the ABS include:

* farmers in Australia managed 425 million hectares of land, or just over half (55pc) of Australia's land mass;

* of all expenditure on weed management, nearly two-thirds ($982m) was spent on herbicides;

* of all expenditure on pest management, over half ($430m) was spent on pesticides; and

* erosion was the most common land and soil problem, reported by 48pc of the farmers, followed by soil compaction (43pc) and soil acidity (42pc).

The findings are based on the second Natural Resource Management survey conducted by the ABS.