Cherry-Prunus rust mite

Aculus fockeui

Pest description and crop damage The adult mite is a typical eriophyid mite with a cylindrical body, yellow in color early on but changing to brownish yellow or tan with age. The adults are minute and can barely be seen with the naked eye when placed against a black background. Immature mites are similar in structure to the adults but smaller and white. The mites feed on the surface of the leaf with piercing-sucking mouthparts, sucking fluids from the cells. Mature foliage may be curled upward or dwarfed. The lower surfaces of the leaves become brown or bronze. Feeding on younger leaves causes development of small yellow spots on the leaves, followed by shotholing. The impact of this feeding on vigor and yield is uncertain. Prunus rust mites are seldom a problem except on young, unsprayed trees.

Biology and life history The mite overwinters as an adult female under bud scales. As the buds expand, they leave the buds, scatter over the expanding foliage, and feed for several days before laying eggs. A complete generation requires 6 to 22 days, and generations are produced continuously in summer. As foliage hardens or degrades, overwintering females are produced for the following year.

Pest monitoring Observe the leaves for signs of feeding, and use a hand lens to check for the mites.

Management-biological control

Phytoseiid predator mites almost always keep mites under control if broad-spectrum insecticide applications are avoided. Rust mites are a significant food source for these predator mites, so damage from this mite can be tolerated.

Management-chemical control: HOME USE

Dormant-season spray

Apply sprays using enough water to cover the entire tree thoroughly, including small limbs. Apply only during dormant period.

  • horticultural mineral oil-Some formulations are OMRI-listed for organic use.

Growing-season spray

  • plant-derived essential oils-Some have shown efficacy against mites. Some formulations are OMRI-listed for organic use.

Management-chemical control: COMMERCIAL USE

  • fenbutatin-oxide (Vendex 50WP) at 1.5 to 3 lb/A. REI 2 days. PHI 14 days. Apply when mites first appear. Do not exceed two applications per season.
  • horticultural mineral oil-Rates vary; read product label. REI varies; check product label. Some formulations are OMRI-listed for organic use.
  • pyridaben (Nexter 75WSB) at 4.4 to 10.6 oz/A. REI 12 hr. PHI 300 days. Highly toxic to bees. Ground applications only. Do not exceed two applications per season.
  • spirodiclofen (Envidor 2SC) at 16 to 18 oz/A. REI 12 hr. PHI 7 days. Limited to one application per season.