Plum and prune-Rust mite

Includes

Big-beaked plum mite (Diptacus gigantorhynchus)
Plum rust mite (Aculus fockeui)

Pest description and crop damage The adult mites are four-legged and wedge-shaped and variable in color, being yellow or pinkish-white or purple in color. 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 plum foliage may be curled upward or dwarfed. The lower surfaces of the leaves become brown or bronze and scurfy. 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. Nevertheless, they are rarely a significant pest and seldom cause damage to prunes west of the Cascades.

Biology and life history These mites overwinter 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 of at least 20X power 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 form a significant food source for these predator mites, so damage from this mite can be tolerated. Hot, dry weather and the probable hardening off of leaves that this causes also reduce mite numbers.

Management-chemical control: HOME USE

Dormant-season spray

  • superior-type oil-Some formulations OMRI-listed for organic use.

Growing-season spray

  • sulfur-Some formulations are OMRI-listed for organic use.

Management-chemical control: COMMERCIAL USE

Dormant to delayed-dormant spray

  • horticultural mineral oil (rates vary; check product label)-Use oil at the highest concentration only in the dormant period. REI varies; check product label. Some formulations are OMRI-listed for organic use.

Spring and summer sprays

  • abamectin (Epi-Mek 0.15 EC) at 2.5 to 5 fl oz/100 gal (10 to 20 fl oz/a). REI 12 hr. PHI 21 days. Apply when mites first appear. Do not exceed two applications of abamectin products per season.
  • pyridaben (Nexter) at 10.67 oz/a. REI 12 hr. PHI 7 days. Do not exceed two applications per season.
  • spirodiclofen (Envidor 2SC) at 18 fl oz/a. REI 12 hr. PHI 7 days. Limited to one application per season.
  • wettable sulfur at 3 to 4 lb/100 gal water (12 to 16 lb/a). REI 24 hr. No PHI listed. Some formulations OMRI-listed for organic use.