Colorado state marijuana regulators Thursday announced a recall of a large amount of retail pot grown and allegedly treated with unapproved pesticides by MGI Inc. in Denver, whose cultivation facilities operate under the name Kindman.

The recall — which the state calls a public health and safety advisory — appears to extend to dozens of strains the company has grown as long ago as March 2014 and as recently as January 2016, according to an announcement by the Colorado Marijuana Enforcement Division.

Regulators said the recall is the result of an investigation by the state Department of Agriculture, which confirmed the presence of imidacloprid, one of the most widely used insecticides in the world but not approved for use on marijuana.

MGI owner Ryan Fox said his company “absolutely has not used this pesticide in production,” and is challenging the recall. [Read more at The Denver Post]