A report from a farmer in southern Alberta led the RCMP to a marijuana crop worth more than $500,000, the second major marijuana bust this month.

A farmer was surprised to find a marijuana grow operation in his own wheat field and reported it to police, Brooks RCMP Const. Joel Culligan said on Wednesday.

Officers who went to investigate the field, about 200 kilometres southeast of Calgary, seized 452 plants with an estimated street value of $565,000.

"The farmer is not a person of interest. He had no idea how it got there," said Culligan. "It's on a secondary highway, so there's obviously limited avenues of investigation on that."

On July 4, Brooks RCMP executed a search warrant on a home and seized 449 marijuana plants worth an estimated $561,000.

In that case, five people have been charged with cultivation of a controlled substance, possession of a controlled substance for the purpose of trafficking and fraudulent use of electricity, Culligan said.

Alberta RCMP have been encouraging people in rural areas to report suspicious activity and unusual crops, pointing out that the dark green marijuana plants stand out among wheat or corn fields, and don't change colour like other crops before harvest.

With files from Andree Lau