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| ====== scale ====== | ====== Scale Insects ====== |
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| ===== Overview ===== | ===== Overview ===== |
| Scale is a destructive insect pest that affects cacti by attaching to the plant's epidermis and feeding on its sap. It presents a significant threat to growers because the insects can quickly multiply, scarring the plant's tissue and potentially destroying entire collections if left unchecked. While minor infestations can be treated manually, severe cases on highly textured plants often require systemic chemical intervention or culling. | Scale insects are small, sap-sucking pests that encrust themselves onto the flesh of cacti, appearing as small oval bumps. If left untreated, they can severely damage or ruin specimen plants. However, they are frequently misdiagnosed by growers, often being confused with fungal scarring, viral infections, or environmental damage. |
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| *Note: The community's recognized authority, Gee Bee, did not participate in this discussion. The following information is synthesized from other experienced community members.* | |
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| ===== Symptoms & Identification ===== | ===== Symptoms & Identification ===== |
| Scale is identified by the presence of small, raised, hardened circular or oval shell-like bumps on the surface of the cactus. | True scale presents as small, brownish, oval-shaped insects that physically encrust themselves to the epidermis of the cactus. They can be physically scraped or plucked off the plant. |
| * **Location:** They frequently settle in the hard-to-reach nooks, crannies, and ribs of the plant. | |
| * **Physical Characteristics:** Unlike fungal spots or physical scarring, these bumps can be physically "plucked" or scraped off the plant's skin using a fingernail, scalpel, or toothbrush. | Scale is commonly confused with: |
| * **Progression:** If untreated, the pests multiply rapidly, covering large surface areas of the cactus, halting growth, and causing severe aesthetic and structural damage. | * **Fungal or viral scarring:** Appears as dry, corky, or scab-like spots where the plant has healed itself. |
| | * **Pest debris:** Inchworm or cutworm droppings and insect eggs. |
| | * **Thrips damage:** Silvery or scarred patches on the epidermis. |
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| ===== Cause & Spread ===== | ===== Cause & Spread ===== |
| Scale infestations are caused by scale insects. They spread easily from plant to plant within a growing area, often capitalizing on a grower's "lack of attention" (Jeffery Waters) to establish a foothold. | Scale infestations are caused by parasitic scale insects. They typically colonize plants due to a lack of quarantine or grower attention, spreading slowly across the nooks and crannies of the host plant. |
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| Growers are strongly cautioned against using home-made tobacco preparations to treat scale. Chris Smoknofften warns that using tobacco can easily introduce and spread Tobacco Mosaic Virus (TMV), a pathogen capable of destroying entire plant collections. | Warning: Some growers attempt to use tobacco-based preparations as a natural insecticide; however, community members warn that using tobacco can easily introduce and spread Tobacco Mosaic Virus (TMV), which can destroy entire collections. |
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| ===== Treatment & Management ===== | ===== Treatment & Management ===== |
| Several treatment pathways exist depending on the severity of the infestation and whether the plant is intended for consumption. | Treatment depends on whether the plant is intended for human consumption and the severity of the infestation. |
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| ==== Physical Removal & Contact Sprays ==== | ==== Physical & Topical Treatments ==== |
| For localized or mild infestations, manual removal combined with contact sprays is highly effective: | * **Manual Removal:** Use a knife, scalpel, or toothbrush to scrape the hardened scale bodies off the plant. Chris Smoknofften recommends torching the removed scales to ensure they are destroyed. |
| * **Manual Scraping:** Use a scalpel, knife, or toothbrush to scrape the hardened scale bodies off the plant (Joshua Johaneman, Solas Black). Chris Smoknofften recommends plucking them off and torching the discarded scales to ensure they are destroyed. | * **Isopropyl Alcohol Spray:** Spraying with Isopropyl Alcohol (70% strength) dries out the pests. Ben Doolittle recommends spraying heavily on the plant and lightly on the soil for 4–5 consecutive nights. **Crucial Safety Note:** Use pure Isopropyl Alcohol rather than "Rubbing Alcohol," as some commercial rubbing alcohols contain oils that can cause severe chemical burns on the cactus epidermis under light. Always apply at night and ensure high airflow. |
| * **Isopropyl Alcohol Spray:** Spraying the plant with Isopropyl Alcohol is a highly regarded contact treatment. Ben Doolittle recommends using 70% Isopropyl Alcohol, noting that its water content allows the pest to absorb it and dry out from the inside, while it evaporates quickly enough to avoid foliar absorption. | * **Soap & Alcohol Mixture:** A topical spray consisting of 1 quart water, 1 tsp isopropyl alcohol, and 1 tsp Dawn dish soap can be applied repeatedly after manual scale removal. |
| * *Application Method:* Apply heavily on the plant and lightly on the soil for 4 to 5 consecutive nights. Always apply at night with good airflow to prevent the liquid beads from causing sunburn. | * **SNS 209:** Can be used post-treatment to make the plant unpalatable to future pests. |
| * **Soap and Alcohol Solution:** Chris Smoknofften recommends spraying the plant and soil with a mixture of 1 quart of water, 1 teaspoon of isopropyl alcohol, and 1 teaspoon of Dawn dish soap, repeating the process weekly until the pests do not return. | * **Bug Buster-O:** Mentioned as an organic topical option. |
| * **Other Contact Options:** "Bug Buster-O" has also been noted as a contact option (Lisa Mattson). | |
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| ==== Systemic Insecticides ==== | ==== Systemic Treatments (Non-Consumable Plants Only) ==== |
| For severe infestations, or plants with complex shapes where manual removal is impractical, systemic insecticides are the most reliable option. **Note: Systemics should only be used if the cactus will never be consumed.** | For heavy infestations or highly textured plants with many crevices, systemic insecticides are highly effective: |
| * **Dinotefuran:** A highly effective neonicotinoid. It is sold under the brand name *Safari 20sg* in the United States, and is available as *Seclira WSG* or *Starkle G* in Australia (Jay Bee, PsillyBilly). | * **Dinotefuran (Safari 20sg / Seclira WSG / Starkle G):** Highly effective systemic soil drench. Because dinotefuran is a powerful neonicotinoid, it is extremely toxic to pollinators. Treated plants must be quarantined, and blooms must be isolated from bees for at least a couple of months post-application. |
| * **Imidacloprid:** Imidacloprid-based soil drenches or sprays are also effective systemic options (PsillyBilly, Sam Redman). | * **Imidacloprid:** A widely available systemic insecticide alternative. |
| * **SNS 209:** Can be used as a systemic preventative to make the plant tissue unpalatable to future pests (Joshua Johaneman). | * **Nicotine / Neonicotinoids:** Used as systemic agents absorbed by the roots. |
| * **Pollinator Warning:** Neonicotinoids (such as dinotefuran and imidacloprid) are highly toxic to bees and other beneficial insects. If a treated cactus produces flowers, it must be quarantined and isolated from local pollinators for at least a couple of months, or through the next one to two bloom cycles (PsillyBilly, Jay Bee). | |
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| ==== Culling ==== | ==== Fungal Lookalikes Treatment ==== |
| For small or highly replaceable plants with severe infestations, PsillyBilly recommends discarding the plant entirely, far away from the greenhouse or home, rather than risking the infestation spreading to the rest of the collection. | If the issue is determined to be fungal rather than scale, the community recommends: |
| | * Spraying **Mancozeb** and applying a soil drench of **Phosphorous Acid** (Garden Phos) 8 days apart. |
| | * Improving soil drainage (aiming for 50% to 70% inorganic materials like pumice or perlite) and increasing airflow. |
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| ===== Reported Cases ===== | ===== Reported Cases ===== |
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| ^ Date ^ Reporter ^ Diagnosed by ^ Confidence ^ Key note / quote ^ | ^ Date ^ Reporter ^ Diagnosed by ^ Confidence ^ Key note / quote ^ |
| | 2026-06-22 | Curtis Williams | PsillyBilly | 8/10 | "I would say to throw the lottle one away far away from your house. Not worth treating in my opinion... If [not consuming], I would treat it with a systemic insecticide via soil drench." | | | 2026-06-22 | Curtis Williams | PsillyBilly / Jay Bee | 8/10 | "Given how many nooks and crannies that plant has I think that a systemic is likely the only practical treatment option." | |
| | 2026-06-22 | Tracy Lynn Stogner | Chris Smoknofften | 7/10 | "Remove all the visible scales. Use a knife to just 'pluck' em off... Then spray plant and soil with a solution of 1qt water, 1tsp iso alcohol... and 1tsp dawn dish soap!" | | | 2026-04-06 | Omar Lopez | Chris Cosby / Kevin Johnson | 8/10 | "Neither of these is scale. Both are fungal... Spray the mancozeb and soil drench the phos acid." | |
| | 2026-06-22 | Chris Cosby | Ben Doolittle | 7/10 | "Spray with 70% Isopropyl Rubbing Alcohol... Apply at night so the liquid beads don’t sunburn the cacti." | | |
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| ===== Notes & Contradictions ===== | ===== Notes & Contradictions ===== |
| * **Gee Bee's Participation:** The community authority Gee Bee did not participate in this discussion thread. | * **Gee Bee's Participation:** Gee Bee did not directly participate in this discussion thread. However, community members (Chad Harris and Chris Cosby) referenced Gee Bee's authoritative historical guidelines for treating fungal lookalikes using Mancozeb and Phosphorous acid. |
| * **Rubbing Alcohol vs. Pure Isopropyl Alcohol:** PsillyBilly noted an instance where spraying a cactus (a giant 'Mount Geronimo') at night in a well-ventilated greenhouse resulted in severe chemical burns. Ben Doolittle clarified that generic "rubbing alcohol" formulations sometimes contain added oils or denaturants that can damage the plant's cuticle. Growers should ensure they use pure Isopropyl Alcohol (diluted to 70% with water) rather than products labeled generically as "rubbing alcohol" containing additives. | * **Rubbing Alcohol vs. Isopropyl Alcohol:** PsillyBilly reported severe epidermal burning on a "Mount Geronimo" cactus after using rubbing alcohol. Ben Doolittle clarified that standard "rubbing alcohol" formulations may contain additives or oils that burn plants, whereas pure Isopropyl Alcohol (diluted to 70%) evaporates quickly without leaving damaging residues, provided it is applied at night. |
| * **Tobacco as a Systemic:** While Ryan TaskLabor noted that natural nicotine can act as a systemic pesticide, Chris Smoknofften strongly warned against using tobacco products due to the high risk of introducing Tobacco Mosaic Virus (TMV) to the collection. | * **Scale vs. Fungal Misdiagnosis:** There is a recurring disagreement on whether spots are scale or fungal. Chris Cosby and Chris Smoknoften pointed out that many suspected cases of scale are actually healing fungal lesions, which do not require insecticide treatments. |
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| ===== References ===== | ===== References ===== |
| * **Photo Contributors:** Curtis Williams, Tracy Lynn Stogner, Chris Cosby | Contributors to this topic include: Jeffery Waters, Chris Smoknofften, PsillyBilly, Lisa Mattson, Curtis Williams, Jay Bee, Sam Redman, Ben Doolittle, Ryan TaskLabor, Solas Black, Joshua Johaneman, Matthew Patterson, Jake Turner, Michael R. Hughes, Bobby Boykin, Cole Lightfoot, Ryan H. Fleming, Richard Goforth, Myco Heidar, Jason Klug, Phil Mack, Matt Beckinsale, Omar Lopez, Anthony Bosch, Kevin Johnson, Chris Cosby, Chad Harris, and Chris CactusLife. |
| * **Documented Contributors:** PsillyBilly, Jay Bee, Ben Doolittle, Chris Smoknofften, Joshua Johaneman, Ryan TaskLabor, Lisa Mattson, Sam Redman, Solas Black, Jeffery Waters | |
| | Photo contributions provided by: Omar Lopez, Jesse Bluebird Rye, Timothy Sutton, Curtis Williams, Tracy Lynn Stogner, and Chris Cosby. |
