What is Dudding Disease and Why is it Stunting Cannabis's Growth?

Whether you’re growing thousands of plants in a professional greenhouse or growing a few plants for your own enjoyment, you’re always going to need to be on the lookout for specific pests and infections. Some of these diseases, such as powdery mildew and aphids, have blighted cannabis cultivators for decades, but there’s always new threats to watch out for. Perhaps the most pernicious and elusive at the moment is an often-latent condition, both inherited and acquired, called Dudding Disease. Caused by a deceptively simple pathogen called the hop latent viroid (HpLVd), this condition can, if left undetected, spread to entire crops and significantly stunt the harvest and the cannabinoid content of the plants it infects. Often, if detected, the only option left for professional cultivators is to destroy the plants, which has led to the elimination of entire crops. One micro-cultivator, Treez Botanicals in Canada, had to rid itself of ALL of his plants, including mothers and its entire genetic library.

Obviously, this is bad news for anybody who cares about cannabis. After all, if you’re eliminating genetics, you may be destroying a life-saving medicine or a brand-defining strain right along with it, forever. But how did we get to this point? How has it been able to start from the gardens of California to infect plants in Canada, Spain and Portugal? And what can be done to stop its spread? This is what we know so far.

The Viroid's Origins

While its spread may be likened to that of a virus’s, a viroid is a great degree simpler than one. Simply put, viroids are small infectious agents that consist of a single strand of circular RNA. They were first discovered in 1971 by plant pathologist Theodor Diener, who found that these agents were able to cause diseases in plants. Viroids can infect plants by entering the cells and hijacking the cellular machinery, namely stray remnants of RNA polymerase II, in the host cell, to produce more copies of themselves. This can lead to the death of the plant or the development of various symptoms, such as stunted growth or yellowing of the leaves. Viroids are able to spread through plants by being carried by insects or through mechanical means, such as when a farmer prunes a plant with a contaminated knife. While there are currently — and thankfully — no known human or animal diseases caused by viroids, they can have a significant impact on agriculture and food production.

Particularly upsetting is the ease of infection for cannabis plants. One stray aphid or a clip from an infected Fiskars can be enough to mark that plant, as well as any cuttings taken from that plant, for the rest of its life. In a random survey of 100 California cultivators, the Santa Cruz-based nursery Dark Heart Nursery found that 33% of the plants from 90% of those cultivators tested positive for HpLVd. Once infected, the plants undergo a “dudding” that encompasses changes in morphology, loss of vigor and alarming reductions in yield and potency, amongst other changes which directly impact the satisfaction of cannabis consumers.

The HpLVd has plagued the beer industry, which relies on cannabis’s cousin hops for flavoring and preservative purposes, since at least 1988, when the first paper on it was published. However, it first appeared in California crops around 2012, although it wouldn’t be recognized as a threat until Dark Heart began sounding the alarm in 2019. By then, it had spread throughout the country and the world. Estimates in terms of lost crops range from $44 million a year to $4 billion overall from Dudding Disease.

What Can be Done?

It’s not easy to determine which plants have HpLVd until they start dudding. The viroid can stay latent for quite some time in plants until the proper environmental factors kick in. And worst of all, there is no cure. As the University of Florida’s Emergency Pathogens Institute acknowledges, “Unlike humans, plants are rarely cured of disease. Instead, plant pathologists try to prevent plants from getting sick in the first place, and work to control the symptoms and spread of diseases.”

This requires testing any new plants before you bring them into a grow room or take cuttings from them. Unfortunately, the often confidential nature of starting up growrooms in newly legal US states, referred to in the industry as the “immaculate conception,” does not lend itself to being transparent about the provenance of one’s plants. Moreover, the federal government can’t come in to assist with funding and research into blight-resistant crops, as they do for cannabis’s federally legal counterparts.

This leads directly to tissue culture, a particularly advanced form of cultivation whose development may be expedited by this condition. Not all states are ready for it; Massachusetts, for instance, bans some of the hormones necessary to make it an industry standard. But the options are either to throw out one’s plants or grow substandard product. Or, of course, to press for federal legalization, which could bring the national government’s considerable resources off of the sidelines to help solve this problem, as it has pretty effectively for other businesses. HpLVd gives us one more reason to keep pushing for it.