Witch's Broom

Witch's Broom is a highly feared condition in cactus cultivation characterized by abnormal, hyper-clustered growth. While some growers view it as a symptom triggered by environmental stress or pests, it is widely associated with infectious pathogens that can rapidly spread through a collection. Proper identification is critical, as benign genetic mutations and environmental stress can easily be mistaken for the disease.

Witch's Broom causes extreme, dense clustering of growth points. According to Thomas Lauritzen, true Witch's Broom will present growth that is “3X” more clustered than a normal active growth point.

It is frequently confused with: * Genetic mutations: Crested or monstrose growth forms. Matt Olson notes that hormonal changes in reverting plants can throw a bunch of pups that mimic the disease. * Cultivar quirks: Cultivars like “Olivia” are known for throwing funky growth in crosses. * Pest damage: Scarring or damage from insects can cause localized, abnormal growth clusters. * Caespitose forms: Naturally multi-headed growth habits.

The underlying cause of Witch's Broom is a subject of discussion among growers: * Pathogenic Cause: Kelly Beth Costello cites scientific literature identifying Witch's Broom as a disease caused by Mycoplasma-Like Organisms (MLO). * Environmental/Stress Cause: Cody Hinds suggests that Witch's Broom is a symptom rather than a single disease, potentially triggered by viral, fungal, bacterial, or insect infestations, as well as heat or sun stress. * Systemic Environmental Factors: Topic authority Gee Bee states that abnormal growth in certain cultivars (such as Olivia crosses) is actually “systemic environmental,” driven by factors like nutrients and lighting. * Transmission: The disease is highly contagious. Kelly Beth Costello warns that it “spreads via every means available” and spreads quickly. ScrapGoat Benjamin also notes that letting the disease go unchecked can result in it infecting an entire collection.

* Quarantine: Suspected plants should be immediately isolated far away from the main collection. * Culling (Recommended for true WB): Due to the high risk of transmission, Kelly Beth Costello advises to “burn it, pot and all” rather than risking the collection. * Surgical Removal & Disinfection: For localized damage or valuable plants, some growers attempt to salvage the plant. Johnathon Siwiec reported success by cutting off all affected parts using an isopropyl alcohol-sterilized knife, dusting the wounds with sulfur, removing feeder roots, dipping the main root in a diluted hydrogen peroxide solution, and repotting in fresh soil. * Environmental Adjustment: Before destroying a plant, evaluate if the growth is simply a reaction to lighting or nutrients, as advised by Gee Bee.

Community examples - the photos above belong to these reporters; credit them.

There is a ongoing division in the community regarding whether Witch's Broom is always an infectious disease or if it can be a general symptom of stress. While some contributors attribute the growth to pests or heat stress, Kelly Beth Costello provides scientific backing linking it to MLO (phytoplasmas).

Importantly, Gee Bee clarifies that funky, clustered growth on certain cultivars (specifically “Olivia” crosses) is often not a pathogen at all, but rather a “systemic environmental” response to nutrients and lighting. Growers should rule out genetic mutations and environmental factors before assuming a plant has infectious Witch's Broom.

* Topic Authority: Gee Bee * Contributors: Kelly Beth Costello, Thomas Lauritzen, Matt Olson, Cody Hinds, ScrapGoat Benjamin, Johnathon Siwiec * Photo Credits: Wes Byers, Gil Tsap, John Alan Steigenberger