Damage (Apple rust mite)

Adults and nymphs have needle-like mouthparts which they use to suck the sap from the surface cells of leaves and young developing fruitlets. Three types of damage can be distinguished.

Damage to rosette leaves caused at and shortly after bud burst
Young rosette leaves are inundated with mites emerging from behind buds which feed on the leaf tissue causing it to become dull, puckered and shrivelled.

• The outermost leaves are the worst affected, particularly around the base.

Damage to fruitlets
Mites feed on the receptacle of young developing fruitlets mainly round the calyx, swarming down the cheek when numbers are large.

• The feeding results in russeting which occurs in an irregular ring round the calyx and on the cheek of the fruit.
• The damage can be very severe if populations are high.
• The damage can be confused with ‘frost eye’ a ring of severe russeting round the calyx caused by frosts during or shortly after blossom. However, frost eye occurs as a clearly defined ring round the calyx.

Damage to leaves in extension shoots
Mites feed on the undersides of leaves, mainly in the younger leaves of extension shoots which are fresh and green.

• The undersides of leaves become brown (bronzed).
• As populations increase and the older leaves are less palatable to mites, so the infestation tends to move up the shoots with the growth.