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More than 90% of Calif. pot farms infected with ‘severe’ pathogen

Lester Black, SFGATE

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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 identified at a California pot farm in 2019, and 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.

FILE: Hop latent viroid is a pernicious pest for cannabis plants.Visoot Uthairam/Getty ImagesThese 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 detected 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.


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