Backyard Grapes Identify & treat grapevine problems
Insect / pest moderate severity

Spider mites

Tetranychus and Eotetranychus spp.

Tiny sap-sucking mites that stipple and bronze leaves in hot, dusty, dry conditions.

Spider mites (Tetranychus sp.) and their eggs on a leaf surface Photo: Ken Gray Insect Image Collection Pacific Northwest Pest Management Handbooks

Description

Spider mites are barely visible sap-feeders that live on the undersides of leaves and thrive in hot, dry, dusty conditions. Each bite empties a leaf cell, so heavy feeding turns leaves dull and stippled, then bronze or yellow, and finally scorched and dropping. In bad infestations you’ll see their fine webbing strung across the leaf underside.

A key point for control: spider mites are often a problem we create. Broad-spectrum insecticides sprayed for other pests kill the predatory mites and insects that normally keep spider mites in check, and a mild population then explodes. So the first line of defence is to conserve those natural enemies, cut the dust, and keep vines from drying out — reaching for a selective miticide only when damage genuinely warrants it.

What to look for

  • Fine pale stippling or speckling across the leaf, giving a dull, sandblasted look.
  • Leaves bronze (on red varieties) or yellow (on white) as feeding intensifies.
  • Fine webbing on the leaf underside in heavy infestations.
  • Scorched, curling, dropping leaves and reduced vigour, worst on dusty rows and water-stressed vines.

Treatment options

Cultural & prevention

Start here — habits that stop problems before they spread.

  • Reduce dust on and around the vines (dust flares mite outbreaks).
  • Keep vines adequately watered; drought stress makes damage worse.
  • Avoid unnecessary broad-spectrum insecticides that wipe out mite predators.

Organic / low-toxicity

Gentler sprays and biologicals for active outbreaks.

  • Conserve or release predatory mites, the main natural control.
  • Horticultural oil or insecticidal soap, and strong water sprays to the leaf underside.

Conventional fungicide / pesticide

For severe cases. Always follow the product label.

  • A selective miticide only if damage passes a threshold; avoid products that kill predators.

Sources

This entry is based on the references below. Read them for full detail and for spray timings and rates valid where you live.

  1. Webspinning Spider Mites / Grape / Agriculture: Pest Management Guidelines — UC IPM
  2. Grape-Spider mite — Pacific Northwest Pest Management Handbooks (OSU/WSU/UI)
  3. Grape: Spider mites — Washington State University Extension (Hortsense)
  4. Grape Year-Round IPM Program: Identifying Spider Mites — UC IPM