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.

“We are contesting these findings and are attempting to have the hold released,” he said in a statement. “We believe the test process is faulty and that the Colorado Department of Agriculture has potentially cross-contaminated our samples during testing.”

The state said its lab is an “accredited facility” and that it adheres to “stringent samply and quality control standards,” according to Steve Bornmann, director of CDA’s Inspection and Consumer Services Division.

Fox said CDA tests showed traces of the pesticide as low as five parts per billion. He said he is having the plants retested.

Colorado attorney Rachel Gillette said the marijuana industry has concerns about the state’s pesticide tests.

“We’re getting conflicting results from this state-certified lab … and the licensee has no way to verify the results,” she said.

It is unclear just how large the recall is or how many actual plants and products are included since the state does not disclose that information. Fox said the strains are sold to cannabis stores across the state, which then sell to consumers.

The recall does not extend to the company’s retail store, which is known as Grass Station and operates from the same Elati Street address as one of the cultivation licenses impacted by the announcement.

The other grow location that is part of the recall is on Colorado Boulevard, records show.

The company has a third location on Smith Road that is not affected.

Regulators say consumers who have any of the recalled products — flower, trim, concentrates and infused-products such as edibles — should return them to the place of purchase so they are disposed of properly. Product labels will display the license numbers affected in the recall: 403R-00008 and 403R-00009.

Though widely used, some research has suggested imidacloprid is among pesticides thought to be contributing to the collapse of honey bee colonies.

Because marijuana is illegal under federal law, no pesticide is specifically approved for use on the crop. Colorado regulators have determined some pesticides can be used because they do not violate the prohibitions of the product’s label, a requirement of federal law.

Colorado began cracking down on the use of pesticides it says cannot be used to grow marijuana after Gov. John Hickenlooper issued an executive order in November declaring them a public safety risk that should be destroyed.

The governor’s actions followed months of stories last year by The Denver Post about the problem of pesticides and marijuana, an issue that arose despite existing regulations that should have prevented the practice.

David Migoya: 303-954-1506, dmigoya@denverpost.com or @davidmigoya