Red spider mite, what is the best treatment ?

Tiny red spider mite on green leaf.

Red spider mite is a tiny mite of the Tetranychidae family. It attacks leaf and flower plants, indoors and outside.

Red spider mite facts

Name – Oligonychus ilicis, Panonychus ulmi, Tetranychus cinnabarinus & others
Family – Tetranychidae
Lifespan – 4-7 weeks (if not hibernating)
Size – 1/64th inch (0.5 mm)

Danger to plant – fatal if too many
Side effects – none. Rarely transmits viral diseases
Beneficial – no beneficial species

Appears in – spring & fall (year-round indoors)
Contagious – very (wind-carried on web strands)
Treatment – moisture & biocontrol

The term “spider” is a bit misleading, because in reality this is a mite. However, it does have 8 legs, spins webs, and is related to the same zoological class as spiders, Arachnida.

A few red spider mites will only cause little damage. If they are numerous, though, they might lead the plant to perish.

Here is how to eliminate red spider mites with organic treatments.

Conditions for red spider mite to appear

Red spider mites tend to multiply and attack plants when the weather is hot and dry.

That’s why they are found indoors all year round and in the garden in summer, when it doesn’t rain and that temperatures stay above 70°F (20°C).

Additionally, these spiders aren’t insects, and abusive use of pesticides actually contributes to their spread.

  • Since many other insects are their predators, killing insects blindly helps spider mites prosper.
  • Red spider mites quickly adapt to chemical threats. They build up immunity to many pesticides.

Red spider mite development cycle

Red spider mites feed on sap of plants, sucking it out of leaves to absorb leaf cells.

  • Since they reproduce very quickly, an invasion can be devastating if not caught early.

Moreover, they are perfectly capable of migrating from one plant to the next, which leads them to spread to multiple plants if one is infected.

  • If you locate an invasion on one plant, move other plants out of reach, especially if they’re touching.
  • For plants in pots, moving them is easy, but you might need to stake a few branches away from each other for shrubs planted in the ground.

Red spider mite symptoms

Red spider mite symptomsTheir tiny size makes them very difficult to see with the naked eye, but a small magnifying glass helps lift any doubt.

  • The first symptom is the appearance of small white or yellow dots and then leaves turn completely yellow.
  • Unlike thrips that produce larger white patches, red spider mite feeding is randomly spread around the area.

Also, the fact that they weave small webs around the leaves also helps one notice them more easily.

  • For that, spray or mist water on the plant and check whether small webs appear.
  • Shown just above, a red spider mite that specifically attacks gorse: Tetranychus lintearius

Treatment against red spider mite

As mentioned earlier, red spider mites love it when the air is very dry, it helps them spread.

Red spider mite on indoor plants

On houseplants, getting rid of them is straightforward:

  • Spray mineral-free water on the leaves to create a moist environment that will make them disappear. A simple hand-spray is enough for this. Rainwater is a good example, but demineralized water also works.
  • Hosing down & showering also dislodges red spider mite. Move the plant to the shower or bathtub first. Wrap the pot in a plastic bag tied with a knot around the trunk to avoid washing soil out.
  • For minor infestations, wipe a soft moist cloth on leaves (topside and underside). Repeat daily until no more red spider mites appear.
  • If that isn’t enough, purchase mite-killer that can be found in any garden shop.

Although red spider mites often only cause limited damage, keep an eye on your plants, especially in case of high temperatures and dry weather, because that is when they reproduce the fastest.

Red spider mite in greenhouses or in the open

A single red spider mite on a leafAgain, spraying soft water regularly for a few days is usually enough to dislodge small colonies.

There are other forms of biological control that don’t require daily work:

  • Fungus against red spider miteBeauveria bassiana is a type of fungus that greatly reduces red spider mite fertility and and egg hatching.
  • Red spider mite natural predatorsPhytoseiulus is also a type of red spider mite, but a beneficial one. It eats plant parasites, especially the damaging red spider mites much like a ladybug eats aphids. Ladybugs also eat red spider mites, too, not only aphids!
  • Bordeaux mixture is a valid organic mite killer.
  • Predatory thrips will also devour eggs, nymphs and adult red spider mites.
  • Spider eating red spider miteSpiders (real arachnids this time) will also devour red mites.

Different trials have shown that a range of natural pesticides can help get rid of the pest. Pyrethrum-based insecticides are a good example of this.

Red spider mite repellents

Certain plants will repel red spider mite near where they’re planted. Such protection usually extends about a yard (one meter) all around the healthy, mature plant. Sometimes a decoction, an extract or essential oils work better than simply growing the plant itself.

Spraying essential oils or extracts can both kill red spider mite and sterilize their eggs so they won’t hatch.

Herbs that fend off red spider mite

Many herbs naturally repel spider mites, among which you may find:

Garlic, rosemary, cinnamon, peppermint, lemongrass, chamomile, marjoram, horseheal (Inula helenium), thyme, caraway, certain curcuma varieties

  • Marjoram and thyme often stay small enough to be planted together with other plants in an indoor pot.
  • For rosemary, peppermint, chamomile and lemongrass, it’s the opposite. Give each a pot of its own and place it near houseplants you want to protect.

Vegetables that repel red spider mite

  • lettuce
  • chili pepper
  • wild tomato

Trees and shrubs that repel red spider mite

  • eucalyptus
  • neem
  • pongam
  • malabar nut
  • vitex (not a repellent per se, but a decoy plant)

Ornamental plants & flowers that repel red spider mite

  • santolina
  • some varieties of croton

Mites similar to red spider mites

Two red spider mites nibbling the same morcel.Not all small red bugs are red spider mites. Some are of a different species and family. For example, the two mites pictured here are velvet mites. They’re actually beneficial because they’re insectivores and will eat other pests.

  • Thanks Neil for the pointer in the comments!

If you see these soft-looking tiny spiders without any telling long hairs on their body, you don’t need to eliminate them. They’re among the many helpers you can have in the garden to help control pests!

Image credits (edits Gaspard Lorthiois):
CC BY-NC 2.0: Lori Erickson
CC BY-SA 4.0: Uwe Schneehagen
CC BY-SA 2.0: Franco Bianco
CC BY 4.0: Lek Khauv
CC BY-NC-ND 2.0: Angelo Milioto
CC BY 2.0: Thomas Shahan