Two men who used bat poop, or bat guano, as a cannabis fertilizer died from “a rare fungal lung infection” they caught from the bat guano, according to a Dec. 16 report on Live Science. The men, both from Rochester, N.Y., were cultivating cannabis for personal use and “developed a condition called histoplasmosis after breathing in spores of a harmful fungus known as Histoplasma capsulate” from the guano, Live Science reported.
One of the men, who was 59 years old, reportedly bought the guano online to use as a fertilizer in his home grow, though no specific information was given on the product name or company that produced and/or sold it. The other man, who was 64 years old, had found guano in his attic “following a ‘heavy’ bat infestation,” according to the report. It is unclear from the report whether he had begun using bat guano to fertilize his cannabis plants or if he got sick before he began.
“The doctors who treated them said that their deaths should serve as a warning about the potential dangers of using bat guano as a fertilizer for any plants,” Live Science reported. “This may be a particular issue for cannabis growers.”
Bat guano is used by many cannabis cultivators for its nutrient values, specifically the primary nutrients of nitrogen (N), phosphorous (P) and potassium (K), and it is permitted as a soil amendment (as is bird guano) “with restrictions” imposed by the U.S. Department of Agriculture, according to an article on the website for the University of Washington’s horticulture-focused Elizabeth C. Miller Library. “They must be decomposed and dried according to the USDA Organic Regulations requirements for raw manure.”
An internet search for bat guano fertilizers for cannabis turns up dozens and dozens of products.
“One of the best things about using bat guano is the nutritional value it contains,” according to the Humboldt Seed Organization blog. “Depending on where the guano has been sourced at the time it was harvested and treated, will determine the N- P-K value. Some brands will offer a powdered product that contains a value of 8-1-1 or 7-3-1, that are most suitable for the vegetative stage, and other brands will focus on a product that is more dominant in Phosphorus such as 0-10-0 and 0-12-0. These are better suited for the flowering phase and are often applied as cold-water extracts or aerated compost teas.”
The dangers of bat guano, however, have been highlighted over many years by media outlets and various health organizations. “Bats harbor diverse pathogens and are considered as a source of zoonotic diseases, in particular those caused by viruses. Large-scale epidemics that have occurred since the end of the 20th century have been associated with viruses of bat origin …,” according to the National Institutes of Health. “Histoplasmosis, caused by the fungus Histoplasma capsulatum, is one of the most frequently observed diseases associated with bat excreta ….”
The Miller Library article recommends that those interested in purchasing commercial guano fertilizer contact “the manufacturer of the products and asking them about where they obtain their bat guano, and whether they meet NOP (National Organic Program) and OMRI (Organic Materials Review Institute) standards.”
It also recommends wearing “a dust mask when opening bags of soil amendments, and when spreading them in the garden. A mask will help protect you from breathing in airborne fungal spores.”
