The department is currently surveying 45,000 hectares in the Great Southern and South Coast grain growing regions as part of an increased surveillance effort in the region.

About 200 plants have been found on a farming property near Wellstead, which had previously undergone a local eradication program.

More than 200 plants were found at another property near Jerdacuttup, approximately 10kms from a known infested site.

Skeleton weed project manager David Atkins said the finds demonstrated the importance of continued surveillance, particularly on paddocks where skeleton weed had previously been found.

"The property at Wellstead had skeleton weed in the past so it was considered a high priority for inclusion in the surveillance program," Mr Atkins said.

"The find was in canola stubble that previously had an infestation of skeleton weed in 2002. The infestation was thought to be have been eradicated and the property was released from the infested list in 2005, following two successive clear searches.

"The plants were well developed and were actively seeding. The plants will be treated to prevent further seed set."

The department will undertake further surveillance on the infested property and neighbouring properties over the next two weeks. Farmers in the district have been encouraged to conduct their own surveillance and report any suspect plants to their local department office.