Producers in South Australia's Mid North and Flinders Ranges are reporting significant locust outbreaks.
One pastoralist said she was communicating with PIRSA for five weeks before the department conducted aerial spraying this week.
The department said it will continue to monitor locust numbers across the state and spray where possible.
Locust outbreaks are reaching new highs in parts of South Australia, as landholders raise concerns that the time for effective control has passed.
Outbreaks have occurred across SA, with producers reporting higher numbers this year than in previous years.
The Department of Primary Industries and Regions (PIRSA) began surveying the outbreaks in early September and has completed aerial spraying over 115,000 hectares for locusts around the Flinders and Mid North regions.
Peterborough livestock producer Bridget Woods said she filed a report with PIRSA after first noticing locusts at her property about five weeks ago.
"There were thousands of them everywhere that were about half a centimetre in size," she said.
"There's not much left there for them to eat now, but while we still had clover, they ate all the plants, just leaving half-formed seed pods behind."
Since then, the pests have grown, both in size and population.
"We had the rain, and they've hatched. The volume of them is like nothing I've seen. It's incredible," Ms Woods said.
