Spider Mites

Spider mites are small arachnid pests that target cacti, often feeding on the plant's tender growing tips. While they are relatively easy to control on cacti compared to leafy plants, they can cause aesthetic damage and weaken the plant if left unchecked. Managing them effectively requires breaking their reproductive cycle and avoiding treatments that inadvertently destroy their natural predators.

Spider mites can be identified by their presence in the growing tips of the cactus. Over time, their feeding damage can lead to secondary issues, such as rust infections, which present as dark spots near the base or other areas of the plant.

When identifying mites, growers should observe their movement speed to distinguish pests from beneficial predatory mites:

• Pest Mites (Prey): Move slowly relative to their leg size and tend to settle in one spot to feed on plant sap.
• Predatory Mites: Move noticeably faster as they actively hunt for prey.

Spider mites are arachnids, not insects. They reproduce rapidly, and their populations can explode if their natural predators are eliminated. A common cause of population spikes is the improper use of systemic insect control granules (such as those designed for houseplants). Because these granules target insects rather than arachnids, they fail to kill the spider mites while successfully eliminating the beneficial predatory insects that keep mite populations in check.

*Note: Gee Bee did not participate in this community discussion. The following recommendations are based on consensus from experienced community members, including IPM specialist Chris Salvin.*

• Water Spray: Hosing the mites off the plant is a good initial step to reduce their numbers.
• Natra Soap / Insecticidal Soap: Apply every 5 to 7 days to break the reproductive cycle. If preserving the glaucous (waxy blue) coat of the cactus is a priority, use a highly diluted solution to avoid stripping it.
• Neem Oil: Apply as a spray to control infestations. *Note:* Some growers advise against using oil-based pesticides directly on the cactus body unless applied as a soil drench, suggesting alternatives like Spinosad instead.
• Isopropyl Alcohol (IPA): Spraying the plants with IPA on a warm day is used by some growers to treat active infestations.
• Drying Out: Allowing the soil and plants to dry out completely can help reduce pest pressure and associated fungal issues.

• Wettable Sulphur: Highly effective and easy to use for controlling mites on cacti.
• Spinosad (e.g., Captain Jack's Dead Bug): Recommended as a highly effective spray specifically designed to target and kill mites.
• Trifecta: Can be used as a soil drench combined with a light spray on the cacti (applied when there is no direct light) for 2 to 3 treatments every other day.
• Azamax: Recommended as an effective miticide option.
• Diatomaceous Earth (DE): Can be mixed heavily into the soil or mixed 50/50 with sulphur to dust the plants. *Caution:* DE is non-selective and will harm beneficial insects and pollinators. Additionally, growers must wear a mask when handling DE to avoid inhaling the dust, which is hazardous to the lungs.
• Avoid Systemic Insecticides: Do not use standard systemic insect granules (designed for insects) to treat spider mites, as this will worsen the infestation by killing predatory insects.

Introducing predatory mites is a highly effective natural control method:

• For Foliar/Red Spider Mites: Introduce *Amblyseius californicus* or *Phytoseiulus persimilis*, depending on your local climate.
• For Soil Pests: Soil-dwelling predatory mites like *Stratiolaelaps scimitus* (also known as *Hypoaspis miles*) are beneficial for soil health but will not target red spider mites on the upper plant body.

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

• Gee Bee's Participation: Gee Bee did not participate in this discussion thread.
• Diatomaceous Earth Disagreement: While Jesse Joseph Scrabonia advocates for heavy use of diatomaceous earth (DE) mixed into soil and dusted on plants to kill pests, Chris Salvin strongly cautions against it, noting that DE is “gnarly stuff” because it indiscriminately harms beneficial insects and pollinators. Furthermore, Kevin Earl Rasmuson and Julie Wolf emphasize that DE poses a severe inhalation hazard to humans and should never be handled without a mask.
• Insecticides vs. Miticides: Daryl Lee DeWeese Jr. initially attempted to use systemic insect granules to treat a mite issue. Lee Hatcher corrected this approach, explaining that because mites are arachnids, insect-specific systemics will not kill them and will instead exacerbate the infestation by eliminating the mites' natural predators.
• Soil Mites vs. Pest Mites: Nick VanWagner identified Jelle Buntinx's mites as harmless soil mites under a scope, but Jelle Buntinx noted that they had destroyed growth and required cutting, highlighting the difficulty in distinguishing beneficial soil mites from destructive pests without close observation.

* Topic Authority: Gee Bee did not participate in this discussion. * Contributors: Wilfy Fletcher, Pete Young, Isaac Taylor, Mandel Brot, Lee Hatcher, Daryl Lee DeWeese Jr., Jesse Joseph Scrabonia, Anton Kucharski, Mark Lyon, Chris Salvin, Chris Chu, Kevin Earl Rasmuson, Julie Wolf, Jasper Peeters, Darren B Spicer, Frank Rizzo, RC Figueroa, Jelle Buntinx, Nick VanWagner, Matt Heite, Chris Smoknofften, Jon Young, Maria Megalogeni, Jan Ratcliffe, Rex Hammack. * Photo Credits: Jelle Buntinx, Jon Young, Julie Wolf, RC Figueroa, Anton Kucharski, Daryl Lee DeWeese Jr., Pete Young.