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Ministry of Agriculture, Food and Rural Affairs

Apple Rust Mite

Apple rust mite Bronzing on apple by mites
Click to enlarge.

Beginner

Scientific Name
Aculus schlechtendali (Nalepa)

Identification

  • Carrot or wedge-shaped,
  • Cream to light brown colouration.
  • Adults have two pairs of legs,
  • Small size (0.07 mm), easy to overlook.

Damage:

  • Variable and includes yellowed and distorted foliage,
  • Prolonged feeding by high populations damages the lower leaf surface and causes a leathery silver appearance, bronzing and curling of the leaf,
  • Feeding on developing fruit may damage the epidermis and cause russetting.

Often Confused With

  • European red mite and twospotted spider mite damage- European red mite and two spotted spider mites are much larger in size (0.3-0.4 mm) than apple rust mites (0.07 mm) and have four pairs of legs while adult apple rust mites have only two. Apple rust mite bronzing is more finely textured, and lacks the stippling of spider mite. Rust mite damage may cause leaves to roll lengthwise.  

Period of Activity
Female apple rust mites overwinter beneath bud scales, emerging to feed on foliage as buds open in spring. Overwintering adults (inseminated females) are produced as early as mid July to Fall. Monitor for rust mites from pink throughout the summer.

Scouting Notes
Monitor populations when examining leaf samples for other mites. Assess European red mite and twospotted spider mite populations first, then increase magnification to monitor for the presence of rust mites.

Thresholds
Do not use miticides unless apple rust mite populations are greater than 200-500 mites per leaf. Low populations of apple rust mites provide valuable prey for predatory mites

Advanced

Apple rust mites are commonly found in orchards, and generally are not a concern unless numbers are extremely high.

Scientific Name
Aculus schlechtendali (Nalepa)

Identification
Apple rust mites are carrot or wedge-shaped, with cream to light brown colouration. Adults have only two pairs of legs. A dissecting microscope with a 100X magnification is required for identification and counts. Their small size (0.07 mm) makes apple rust mites easy to overlook.  

Apple rust mite injury is variable and includes yellowed and distorted foliage. Low populations of apple rust mite are not a concern, but prolonged feeding by high populations (200 or more per leaf) damages the lower leaf surface and causes a leathery silver appearance, bronzing and characteristic curling of the leaf. Feeding on developing fruit may damage the epidermis and cause russetting.

Often Confused With

  • European red mite and twospotted spider mite damage- European red mite and two spotted spider mites are much larger in size (0.3-0.4 mm) than apple rust mites (0.07 mm) and have four pairs of legs while adult apple rust mites have only two. Apple rust mite bronzing is more finely textured, and lacks the stippling of spider mite. Rust mite damage may cause leaves to roll lengthwise.  

Biology
Female adult apple rust mites overwinter beneath bud scales, emerging to feed on foliage as buds open in spring. Eggs are deposited on the underside of leaves. There are numerous generations each year. These mites can be beneficial in low numbers because they are an important alternate food source for predatory mites when European red mite and twospotted spider mite numbers are low. The presence of apple rust mite encourages predatory mites and other natural enemies to remain in the tree canopy rather than migrate to other areas. 

Period of Activity
Female apple rust mites over winter beneath bud scales, emerging to feed on foliage as buds open in spring. Overwintering adults (inseminated females) are produced as early as mid July to fall. Monitor for rust mites from pink throughout the summer.

Scouting Notes
Monitor populations when examining leaf samples for other mites. Assess European red mite and twospotted spider mite populations first, and then increase magnification to monitor for the presence of rust mites.

Thresholds
Apple rust mites seldom cause a measurable loss in apple orchards. There are exceptions and miticides are sometimes needed for management of populations.

Do not use miticides unless apple rust mite populations are greater than 200-500 mites per leaf. Low populations of apple rust mites provide valuable prey for predatory mites. 

Management Notes

  • Some miticides are not effective against apple rust mites.
  • For a list of products with activity against apple rust mites, see OMAFRA Publication 360, Guide to Fruit Production - Chapter 3 Apples (PDF) or Apple Calendar only (PDF) :