Chilli Seeds NZ Close up photo of an Red Spider Mite

Red Spider Mites

Red spider mites are one of the most common pests on chillies in New Zealand, especially in greenhouses and on plants in hot, sheltered spots. They're tiny, they breed fast in dry heat, and by the time you notice webbing there are a lot of them. Caught early, they're very manageable.

What is a red spider mite?

The pest usually called red spider mite is the two-spotted spider mite (Tetranychus urticae). It isn't a spider, but it's related to one, and it's only about 0.5 mm long. For most of the year it's pale green-yellow with two dark spots. It turns orange-red in autumn, which is where the name comes from.

They feed on the undersides of leaves, piercing the cells and sucking out the contents. In NZ they're worst from mid-summer through autumn, roughly January to April, and can carry on all year in a heated greenhouse.

Tiny red specks running over paving, walls or outdoor furniture in spring? Those are usually other mites, not spider mites. They move quickly and in the open, and they don't web up your plants. Red spider mites stay on the plant, mostly under the leaves, and you'll rarely see one move without a magnifier.

Identification

Check the undersides of leaves with a magnifier, or your phone camera zoomed right in. Signs to look for:

  • Speckled leaves: fine pale dots on the upper side of the leaf, spreading until leaves look dull, bronzed or yellow.
  • Webbing: fine silk between leaves and stems, often at the growing tips, once numbers are high.
  • Moving dots: tiny mites under the leaves, often with pale eggs and shed skins.
  • Leaf drop: badly affected leaves dry out and fall, and flowering and fruiting slow down.

A quick test: hold a sheet of white paper under a leaf and tap it. If specks drop and start walking, you have mites.

Prevention

  • Check plants weekly from December, and every few days in a greenhouse during hot weather.
  • Keep plants watered. Dry, stressed plants get hit hardest.
  • Raise the humidity. Mites don't like it, so damp down greenhouse paths on hot days and keep air moving.
  • Where you can, avoid hot, sheltered corners against walls where the air sits still.
  • Look over new plants, including gifted seedlings, before they go next to the rest.
  • Leave ladybirds, lacewings and predatory mites to do their work. Broad-spectrum sprays kill them first.

Natural Treatments

  • Hose them off: a firm spray of water on the undersides of the leaves knocks numbers back. Repeat every few days, in the morning so the leaves dry by evening.
  • Remove the worst leaves: bin them rather than composting them.
  • Neem oil: this is what we use. Spray the undersides of the leaves in the evening, follow the bottle instructions, and repeat as directed, as one spray won't catch the eggs.
  • Predatory mites: Phytoseiulus persimilis eats spider mites and nothing else. It works best in a greenhouse and is sold in NZ by biological control suppliers. Release it early, before the webbing gets heavy.

Chemical Treatments

If a bad infestation doesn't respond, insecticidal soaps and horticultural oils are the next step. They work on contact, so coat the undersides of the leaves thoroughly.

Stronger miticides are sold at NZ garden centres. Choose one labelled for mites on edible crops, follow the label, and check the withholding period before you pick. Most will also kill beneficial insects, so keep them for last.

Red spider mites are easiest to deal with while numbers are small. A weekly look under a few leaves through summer does more than any spray. For the other pests you'll meet on chillies, see our chilli pests guide.

  • Chilli Seeds NZ Photo of a plant with Red Spider Mites
  • Chilli Seeds NZ Close up photo of an Red Spider Mites
  • Chilli Seeds NZ Close up photo of an Red Spider Mites

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