Pathogen Infects 90% Of California’s Pot Farms

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California pot farm pathogen
Northern Californian cannabis farm Photo: Shutterstock

An infectious pathogen inside California’s pot farms is attacking cannabis plants and growing invisibly for months only to spoil a crop just as a farmer is ready to harvest. Scientists believe that it’s in nearly every pot farm in the state and could be causing billions of dollars in damages to the national weed economy.

Hop-latent viroid, or HLVd, shrivels pot plants and reduce how much weight they produce by as much as 30%. It also destroys the amount of THC, pot’s most common active compound, that a plant produces, greatly reducing the value of affected plants.

HLVd was first documented in cannabis in a pair of scientific studies published in 2019, including a study that confirmed the viroid’s presence in samples from a Santa Barbara pot farm. It’s now infected at least 90% of California’s cannabis grows, according to a 2021 estimate. It’s spreading globally, and a recent scientific paper declared the pathogen was the “biggest concern for cannabis” growers worldwide.

But one Bay Area startup has a new tool that they think will stop the pathogen’s spread in its tracks.

Oakland’s Purple City Labs released a new HLVd test earlier this year that can be conducted on site and deliver results to pot farmers in just a few hours. That’s much faster than the current methods for finding HLVd infections, which are predominantly done by farmers mailing samples to labs and waiting days or even weeks to get a result.

The company said this new at-farm testing could be pivotal in slowing the spread of this global pathogen, as it allows farmers to quickly identify infected plants.

“We didn’t just identify a great test that is accurate, but it’s [also] easy to use and it doesn’t require a high level of expertise,” said Luke Horst, director of business development for Purple City Genetics. “You can take microbiology to the public and put it in their hands. … It’s important for people to have this type of testing.”

A pernicious pest on cannabis farms
HLVd has likely been spreading in cannabis farms for more than a decade, but at first, growers didn’t know what was harming their harvest. It was commonly called “dudding,” and it would only show up at the end of the crop’s life cycle, distorting the plant’s shape and reducing the amount of active compounds produced, like THC, by as much as 50%. This effect can destroy the retail value of a crop.

HLVd’s late-acting symptoms make it a pernicious pest for modern cannabis farming. Farmers commonly grow cannabis by cutting small pieces off of one plant, frequently called the “mother,” which is then used to propagate hundreds of new baby plants.

These mother plants are artificially prevented from growing flowers, which allows them to keep producing offspring, but it also delays the symptoms of HLVd. That means a single mother plant infected with HLVd could silently spread the pathogen for months without showing any symptoms of the disease.

HLVd was first identified in hop plants, a close relative of cannabis, in the 1980s. It’s now commonly found in hop farms and can reduce the amount of aromatic compounds produced by hops, which are primarily used to flavor beer.

In 2019, HLVd was first identified in cannabis when scientists confirmed the viroid’s presence in samples from a Santa Barbara pot farm. But by 2021, the viral pathogen had spread to at least 90% of the state’s pot farms, according to a 2021 survey that sampled 200,000 California cannabis plants.

And now the viroid has spread to pot farms across the world, from Massachusetts to Europe.

Same-day results inspired by pandemic response
Ali Bektaş, the CEO of Purple City Labs, was the lead author on one of the 2019 papers that first identified HLVd in cannabis, but he didn’t start working on an HLVd test until he was hired in 2021 by Purple City Genetics, a well-known cannabis nursery in Oakland.

Bektaş was originally hired to help with breeding new pot strains, but he soon realized testing for HLVd was one of the nursery’s biggest problems. The nursery was sending hundreds of samples a week to labs to test for the viroid, but the results would often take weeks to come back. That allowed the pathogen to keep spreading exponentially.

“By the time you get the results back you may have cut that plant and sold it to your customers. So there is a real need for a high throughput onsite diagnostic test for hop-latent viroid,” Bektaş said.

Bektaş, who has a Ph.D. in microbial ecology from UC Berkeley, immediately thought of a testing method called LAMP that he worked on as a student and that had become hugely popular during the COVID-19 pandemic. Unlike PCR tests, which require specialized lab equipment and expert technicians, LAMP technology uses cheap equipment and can be accurately operated by almost anyone.

LAMP technology made COVID testing easier during the pandemic, so Bektaş thought it could also work on this new viral threat to cannabis. Working at the nearby Oakland Genomics Center, Bektaş developed a simple LAMP test for HLVd that allowed the nursery to quickly test thousands of plants and get results in just a few hours.

Bektaş said before long, other farms in the industry started asking if they could use the test.

“We didn’t develop a product to sell it. We made it to use in the nursery. But it was just perfect for this particular problem,” Bektaş said. “We weren’t even advertising it, but people would hear about it, and they would start asking us if they could also use it.”

The company is now selling the technology for $10 a test and is starting to sell it worldwide. Bektaş said he was recently on a business trip to Spain to demonstrate the new product. They found a plant with HLVd on their first test.

“They had something off the shelf, just a random [cannabis sample] from their fridge, so we tested it and it was positive. They assumed it was going to be clean because it was [in] Spain. But we tested it twice and both times it came back positive,” Bektaş said.