Spider Mites
Spider mites are tiny sap-sucking arachnids (not insects) that pierce leaf cells and drain them.
Spider Mites at a glance
| Also known as | Red spider mite, two-spotted mite (Tetranychus) |
|---|---|
| Affected parts | Leaves / needles (undersides) |
| Most at risk | Conifers (junipers, spruce, pines) and many broadleaf trees in hot, dry, still air (esp. indoors) |
| Main cause | Sap-sucking mites multiplying fast in warm, dry conditions |
| Severity | Can be severe, heavy infestations defoliate and kill branches |
| Reversible? | Yes with prompt, repeated treatment |
What to look for
- Leaves: The first sign is fine pale/yellow stippling (tiny speckles) on the upper leaf surface; foliage fades to dull, silvery, or bronze, then yellows. On conifers, the inner/older needles dull and brown. Look on leaf undersides and mid-veins for mites like specks of moving pepper.
- Whole tree: Fine webbing strung across branch crotches and shoot tips in heavy infestations; a dusty, tired look overall. Test: tap a branch over white paper and watch for tiny crawling specks.
Overview
Spider mites are tiny sap-sucking arachnids (not insects) that pierce leaf cells and drain them. They breed explosively in warm, dry, stagnant air, a major reason they plague conifers and any tree kept indoors. Damage is easy to miss until the foliage looks dull and tired; by the time you see webbing, the infestation is advanced.
Causes
Hot, dry, still conditions (indoors, greenhouses, hot summers); dusty foliage; drought-stressed trees; and bringing in infested plants. Populations explode in heat.
Commonly confused with
Nutrient chlorosis yellows smoothly without stippling or webbing. Spider-web from actual spiders is coarse and catches insects; mite webbing is fine and coats the foliage. Drought bronzing lacks the speckled stippling. The paper-tap test confirms live mites.
Which species are affected
Very wide host range. Conifers are classic victims (junipers, spruce, pines, cypress, hemlock), as are many broadleaf and indoor trees; especially bad on anything kept warm, dry, and indoors.
Treatment
Hose/spray the foliage forcefully (especially undersides) to knock down mites and webbing; raise humidity. Apply insecticidal soap or horticultural oil thoroughly to all surfaces and repeat every 4 to 7 days for several weeks (mites breed fast and eggs survive single sprays); rotate a miticide for heavy cases. Predatory mites work well in greenhouses. Isolate infested trees.
Fix it
What the treatment above uses, from our shop:
Prevention
Keep foliage clean and humid; mist conifers in hot spells; avoid drought stress; quarantine new plants; inspect undersides regularly, especially in hot weather.