Early in the 20th century, huge swathes of land in Queensland and New South Wales had been rendered unsuitable for farming due to an infestation of the prickly pear cactus.

Prickly pear plants were prized as a food source for cochineal insects, which produced a bright red dye when crushed. In the late 18th century, Sir Joseph Banks suggested that New South Wales might prove a suitable climate for establishing a cochineal dye industry. The insects soon died, but the prickly pear plants survived and thrived, particularly to the west of the Great Dividing Range. It overwhelmed native vegetation and farming land and it is estimated that by the early 20th century prickly pear had overrun more than 24 million hectares (60 million acres) across New South Wales and Queensland.

In 1886 the New South Wales Government passed the Prickly-pear Destruction Act. Landowners became responsible for the plant’s destruction, and government-appointed inspectors oversaw the law’s enforcement. However, the Act could not stop the prickly pear infestation.

T H B McGee, a forest ranger with the Forest Branch at Narrabri wrote a report in September 1887 requesting that further action be taken against the spread of prickly pear from Queensland to New South Wales. He states:

I have the honor to bring under your notice the fact that Prickly pear is growing in abundance in the Mungindi District in Queensland near to and along the boundaries dividing New South Wales from that Colony . . . Birds carry the seeds and floods wash the leaves and plants down the streams from the infested localities thereby imposing a heavy tax for their destruction upon land holders in New South Wales who would otherwise be free from the pest. As New South Wales has an Act enforcing upon occupants of land the eradication of the Prickly pear and in fairness to the people of New South Wales, Queensland should be in the same position.

The recommendations of McGee’s report prompted the Colonial Secretary’s Office Sydney to send a letter to the Colonial Secretary’s Office Brisbane in May 1888 which invites the Queensland Government to do something about the problem.

A further report submitted in June 1888 from the Under Secretary for Agriculture to the Secretary for Public Lands states that:

Legislative action should be taken that this noxious weed may be exterminated.

In Queensland, the government looked to innovation to solve the problem. A £5,000 reward was offered for an effective method of destroying the plants. Suggestions came from around the world and included salt, prairie cattle, steamrollers, arsenic, electricity and a machine that used mirrors to focus the sun’s rays to burn the prickly pear. None of these techniques worked and the bounty was never claimed.

Section 156B of the Local Authorities Amendment Act 1910 declared that prickly pear was a noxious weed. Local authorities were charged with certain responsibilities to assist with the eradication of prickly pear within their council areas.

Records in Queensland State Archives’ collection illustrate the issues surrounding the control and elimination of prickly pear in Queensland:

• A report from Goondiwindi in June 1889 highlights the spread of prickly pear to specific properties in the region and the cost involved with controlling the plant in existing areas of infestation;
• Suggestions for the eradication and prevention of prickly pear were made in 1899 and included a number of schemes for the clearing of plants on both leases and Crown land;
• By 1916, poisoning of prickly pear with an arsenic solution had been proposed to prevent its further spread;
• A report from the Warwick area in 1918 indicates that prickly pear, and other similar plants, were still a significant problem in agricultural and grazing areas.

Fortunately, as a result of the government’s research into the management of cacti in North and South America, a potential solution was found. The Cactoblastis cactorum moth was introduced in 1926 and by 1933 an estimated 80 per cent of the infested land in Queensland had been cleared of the pear. The release of the moths is regarded as one of the most impressive examples of biological weed control in the world.