This mite is one of the gall mites, also known as eriophyid mites. These minute animals are usually less than 0.2 mm long when fully grown. They have elongate bodies and two pairs of legs, unlike other mites which have four pairs. Their size means they can usually only be seen with the aid of a microscope. Their presence is readily detected by the distinctive abnormal plant growths induced by their feeding activities.

There are many species of eriophyid mite which are usually host specific this means that each species of mite will only feed on a single, or several closely related, plant species.

Eriophyid mites feed by sucking sap but while doing so secrete chemicals into the plant tissue that converts some of the normal (parenchyma) plant cells to meristem tissues which can give rise to a range of growth forms. These then grow to produce the gall. The mites can then suck sap from plant cells lining the gall structure, which are invariably more nutritious than unaffected tissue, but often do not cause serious damage to the plant. Raspberry leaf and bud mite is an exception as it can cause a lack of vigour when at high numbers. 

Raspberries with leaf and bud mite show a number of symptoms:

• From May onwards, pale yellow blotches develop on the upper leaf surface
• On the corresponding places on the underside of leaves, the colour is slightly darker than the usual whitish green
• Affected canes grow to their usual height and produce fruit but leaves at the tops of the canes may be malformed

Note: Some virus infections also cause yellow markings on the foliage, usually accompanied with stunting of the canes and poor fruit production. The mite is a more common problem than virus infections although it can transmit Raspberry leaf blotch virus.

• Raspberry leaf and bud mite can often be tolerated as it does not always affect cropping
• Heavily affected plants that no longer produce a worthwhile crop should be replaced
• Some raspberry cultivars are less susceptible to the mite. Observations on plants grown at Wisley indicate that these include ‘Glen Lyon’, ‘Glen Rosa’, ‘Glen Prosen’, ‘Glen Magna’, ‘Malahat’, ‘Gala’, ‘Tulameen’, ‘Julia’, ‘Rossana’, ‘Leo’, ‘Galante’, ‘Terrie Louise’ and ‘Lauren’
• More susceptible cultivars include ‘Glen Ample’, ‘Glen Shee’, ‘Malling Jewel’ and ‘Malling Enterprise’

The microscopic raspberry leaf and bud mites overwinter in and around the buds on raspberry canes.

They emerge in late spring and begin feeding by sucking sap from the underside of leaves. This results in yellow blotches developing on the upper surface and slightly darker patches on the lower leaf surface where the mites are active.

The mite population increases during the summer and leaves at the shoot tops may fail to expand to their usual size and shape if the population of mites is large.