What Are PGR’s and Why Are They In My Weed?


Health conscious smokers have recently made themselves aware of the dangers behind the use plant growth regulators, or PGR’s. Growers use these chemicals, sometimes unknowingly, to promote the short, stocky growth that’s favorable indoors. It’s time to take a closer look at what these compounds are, where they are found, what they do, and their history of agricultural use other than cannabis.

Despite healthier growth and increased resistance to fungus, pot grown using PGR’s often has an inferior flavor and visual appearance, and the harshest critics point out that exposure to these compounds put consumers at risk of liver damage, cancer and infertility. These damning claims warrant further investigation of the safety of these chemicals on cannabis.

Plant growth regulators, more aptly named “plant growth retardants,” are commercially available in a variety of brand names, and the most common active ingredients are: ancymidol, chlormequat chloride, daminozide, ethephon, flurprimidol, paclobutrazol and uniconazole. Ancymidol, flurprimidol, paclobutrazol and uniconazole are all structurally similar and suppress gibberellin, a natural growth hormone that lengthens cells in the stem. Daminozide and chlormequat chloride also suppress gibberellin at different stages in its biosynthesis. Ethephon is the only PGR that works in a different mode of action; plants uptake ethephon and convert it into ethylene, which in turn suppresses cell elongation and reduces apical dominance. Cannabis exposed to PGR’s grows shorter and more uniform with denser flower that have an abundance of orange hairs and poor flavor.

The two compounds of concern in the cannabis world are paclobutrazol and daminozide. These chemicals were found as unlisted, unregistered ingredients in the following cannabis fertilizers: Bushmaster, Gravity, Flower Dragon, TopLoad, PhosphoLoad and BushLoad. Most of these fertilizers have been banned in California mainly due to the fact that the PGR’s were not listed in the bottle, a requirement by law.

All of the additives listed above are approved for use plants not destined for consumption. Just look around, do you think those super markets poinsettia displayed during the holidays naturally grow all at the same height? What about trees growing under power lines, do you really think pruning is the only thing keeping them so manicured at the same height? Plant growth retardants keep synthetic ecosystems like parks and golf courses in check for the sake of reducing maintenance costs and improving aesthetic appearance.

In addition to their use in ornamental plants, some compounds like paclobutrazol are actually approved for use in apples, mangos, avocados, cabbage, cauliflower and broccoli. For tree crops, paclobutrazol makes shorter trees that are easier to trim and harvest while increasing resistance to harmful fungus. In the case of broccoli and cabbage, paclobutrazol is approved as a seed treatment only.

What about the safety profile of paclobutrazol? Studies done in lab mice show that paclobutrazol is toxic to the liver at high doses, but does not increase the risk of cancer, is not genotoxic and does not cause reproductive or developmental harm. In all instances, the studies performed on mice used exposures to paclobutrazol at concentrations far above those present in agricultural products when used correctly. Paclobutrazol is only indicated for use after the harvest of a crop so farmers don’t apply on the fruit. More potent than its competitors, paclobutrazol induces a response in plants at very low concentrations. Researchers have not been able to study the effects of small concentrations of paclobutrazol on the general population and may still present a danger to the public.

Daminozide, on the other, has a more colorful history. One of the first plant growth retardants/ pesticides available on the market, daminozide was approved for use in 1963. In 1989 the Environmental Protection Agency cancelled the use of daminozide on crops for food citing studies that found it probably causes cancer, putting consumers at a risk of 45 in one million. After Meryl Streep testified in Congress and a 60 Minutes special aired on CBS about the dangers of Alar, the nation went into a panic. The agri-business responded with a swift public relations campaign against alarmism, and reports say Walter Cronkite was paid $25,000 by an industry-sponsored organization to narrate a pro-pesticide, anti-“alarmist” documentary called Big Fears, Little Risks. Despite the backlash, daminozide remains banned for use on food crops to this day. Paclobutrazol sees more usage than daminozide because of its higher potency.

The cannabis world has seen a replay of the so-called “Alar scare” of 1989, but this time the truth is already out there. HIGH TIMES doesn’t approve the use of PGR’s on cannabis. These compounds are dangerous in high doses, and have untold effects at low, chronic amounts long-term. Growers should not have to fear that their nutrients could contain these chemicals, meaning the cannabis fertilizer industry needs a regulatory body to prevent the addition of unlisted, illegal and toxic ingredients.

Photo Credit: VortexFarmacy


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