In a landmark court decision, a judge has ruled against a West Australian organic farmer who was suing his neighbour for allegedly contaminating his farm with genetically modified canola.

Steve Marsh was suing former friend Michael Baxter in the WA Supreme Court, claiming he lost organic certification for more than half of his farm after GM canola drifted onto his land from Mr Baxter's property.

Organic farmer Steve Marsh has lost his court case against neighbour Michael Baxter over GM crop contamination. Credit:Robert Gunstone

In 2010, Mr Marsh's Kojonup oats, rye and sheep farming property, southeast of Perth, was certified organic by the National Association for Sustainable Agriculture Australia.

But he alleged GM canola blew 1.5 kilometres inside his fence, which caused him to lose his certification.