Walnut-Walnut blister mite

Aceria erineus

Pest description and crop damage Very small eriophyid mite causes blister like swelling on upper leaf surface and yellowish or brown concave pocket on underside of leaf. These insects usually do not cause enough damage to warrant control.

Biology and life history This mite overwinters beneath bud scales. When the weather warms up, the mites feed beneath the leaves amongst the leaf hairs. Several generations occur during the summer, which attack new foliage as soon as it unfurls.

Management-biological control

Phytoseiid predator mites almost always keep mites under control if broad-spectrum insecticide applications are avoided. Heavy rain and cold weather also suppress mite numbers.

Management-cultural control

Broadleaf weeds like mallow, bindweed, white clover, and knotweed enhance mite numbers. Avoid excessive nitrogen applications, as this encourages mites.

Management-chemical control: HOME USE

Control has not been necessary in the PNW for home orchards. This pest is held in check by natural enemies. If control is needed, use:

  • carbaryl
  • kaolin clay (Surround® at Home®)-Applied as a spray to leaves, stems, and fruit, it acts as a repellant to some insect pests. Some formulations are OMRI-listed for organic use.
  • horticultural oil-Some formulations are OMRI-listed for organic use.
  • sulfur-Some formulations are OMRI-listed for organic use.