Weeds costing industry billions
The cost of Californian thistle alone has been assessed at about $700 million.
Weeds cost farming and forestry at least $1.7 billion a year - much more than previous estimates - but lack of research on the impact of many species means it is impossible to arrive at a definite figure.
AgResearch principal scientist Dr Graeme Bourdot said this most up-to-date estimate took account of only 10 of 187 pasture weeds, and was a gross underestimate.
The cost of Californian thistle alone has been assessed at about $700 million.
The $1.7b estimate, based on work carried out by AgResearch, Scion and Lincoln University’s agribusiness and economics research unit, did not include the cost of controlling weeds.
‘‘Nowhere is all the information on how much is spent collated and published. We can get figures on how much is spent on chemicals but not on how much it costs farmers to apply it.
‘‘I know of some big pastoral farms on the east coast of the North Island that spend $100,000 a year on aerial spraying of their thistles,’’ Bourdot said.
The latest Beef+Lamb NZ farm survey shows the average farm spent $14,585 a year on weed and pest control (not including animal health).
When multiplied by the 25,113 sheep and beef farms, the total onfarm spend is $363m a year.
One of the few weeds that had been looked at in depth was the Californian thistle. Scientists had estimated its $700m cost following a survey of pastoral farmers.
‘‘We arrived at that figure by asking them how much of their grazing land was not grazeable because of the thistle at the peak time of cover in February. We found that 94 per cent of farms had thistles, and the average amount of land that couldn’t be grazed was 12 per cent.’’
In the latest research, researchers had investigated the impact of broom, Californian thistle, Chilean needle grass, giant buttercup, gorse, hawkweeds, nassella tussock, sweet brier, and yellow bristle grass. Bourdot said many weeds such as Chilean needle grass or the giant buttercup were still only a local problem, but the researchers had developed a method of working out the costs of weeds that have not yet realised their potential range.
‘‘This dynamic approach applied to the giant buttercup weed in dairy pastures indicates that alone it would cost the dairy industry $592m per year in lost milk solids revenue if it were to spread across its entire range over the next 20 years.’’
One of the problems posed by the buttercup was that it was so off putting to stock that they avoided eating a large area surrounding the plant.
Bourdot said New Zealand had a ‘‘unique’’ opportunity to use biological agents against the nine thistles because there were no native thistles to worry about.
‘‘We are the only developed country in a temperate region that has no native thistles. That means we could bring in a range of insect predators.’’