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 invasion symptoms
Their 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.
Treatment against red spider mite
Red spider mite on indoor plants
On houseplants, getting rid of them is straightforward:
- Spray calcium-free water on the leaves to create a moist environment that will make them disappear. A simple hand-spray is enough for this. Calcium-free means soft water that doesn’t have many minerals. Rainwater is a good example, but demineralized water also works.
- Hosing down & showering also dislodges red spider mite. Best 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 are seen.
- 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.
- Build up moisture around houseplants to deter mites. A simple trick is to use hydroton clay beads to raise air humidity.
Red spider mite in greenhouses or in the open
Again, 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 mite – Beauveria bassiana is a type of fungus that greatly reduces red spider mite fertility and and egg hatching.
- Red spider mite natural predators – Phytoseiulus 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.
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:
- 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
- chili pepper
- wild tomato
Trees and shrubs that repel red spider mite
- malabar nut
- vitex (not a repellent per se, but a decoy plant)
Ornamental plants & flowers that repel red spider mite
- some varieties of croton
Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Red spider mite on a leaf by Lori Erickson ★ under © CC BY-NC 2.0
Two mites eating by Angelo Milioto ★ under © CC BY-NC-ND 2.0